EPA

United States National Exposure EPA/600-R-98/161

Environmental Protection Research Laboratory September 1998

Agency Research Triangle Park, NC 27711

Research and Development

TECHNICAL ASSISTANCE

DOCUMENT FOR SAMPLING AND

ANALYSIS OF OZONE PRECURSORS
Technical Assistance Document for

Sampling and Analysis of Ozone

Precursors

September 30, 1998

U.S. Environmental Protection Agency

National Exposure Research Laboratory

Human Exposure and Atmospheric Sciences Division

Research Triangle Park, North Carolina, NC 27711
ii

DISCLAIMER

This document has been reviewed in accordance with U.S. Environmental Protection

Agency policy and approved for publication. Mention of trade names or commercial products

does not constitute endorsement or recommendation for use.
iii

TABLE OF CONTENTS

Page

Section 1 Introduction ...................................................... 1

1.1 Purpose .......................................................... 2

1.2 Organization ...................................................... 3

1.3 Summary of the Monitoring Regulations ................................ 4

1.4 References ....................................................... 8

Section 2 Methodology for Measuring Volatile Organic Compound Ozone Precursors in

Ambient Air ...................................................... 1

2.1 Network Monitoring Requirements .................................... 2

2.2 Target Volatile Organic Compound Ozone Precursors ..................... 4

2.2.1 Total Nonmethane Organic Compound (TNMOC) and PAMS

Hydrocarbons (PAMHC) ...................................... 6

2.3 Chromatography Discussion and Issues ................................. 9

2.3.1 Gas Chromatography with Flame Ionization Detection ............... 9

2.3.2 Identification and Quantification Issues .......................... 12

2.3.3 Sample Moisture Issues ...................................... 14

2.3.4 Calibration Standards ........................................ 17

2.3.4.1 Primary Calibration Standard ....................... 17

2.3.4.2 Retention Time Calibration Standard ................. 18

2.3.4.3 Calibration Standard Preparation .................... 19

2.3.4.3.1 Procedure for Humidification .............. 20

2.3.4.3.2 Calibration Standard Dilution Procedure ..... 30

2.3.5 Column Configurations ..................................... 36

2.3.6 Column Selection ......................................... 37

2.3.7 Pre-measurement Chromatographic System Verification ........... 46

2.3.7.1 Retention Times and Relative Retention Times ......... 46

2.3.7.2 Internal Standards ................................ 49

2.3.7.3 Identification of Co-Eluting Compounds and 

Matrix Effects ................................... 50

2.3.7.4 Detection Limits ................................. 51

2.4 Automated Method for Collecting and Analyzing Volatile Organic Compound

Ozone Precursor Samples .......................................... 51

2.4.1 Sample Collection ......................................... 52

2.4.1.1 Sample Probe and Manifold ........................ 53

2.4.1.2 Sample Introduction .............................. 55

2.4.1.3 Sample Conditioning ............................. 58

2.4.1.4 Sample Concentration ............................. 58
TABLE OF CONTENTS (Continued)

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2.4.2 Sample Analysis .......................................... 59

2.4.2.1 Sample Focusing or Cryofocusing ................... 59

2.4.2.2 Gas Chromatography ............................. 60

2.4.2.3 Analytical System Calibration ...................... 61

2.4.3 System Operation ......................................... 62

2.4.3.1 Initial System Set-up .............................. 63

2.4.3.2 Sampling Parameters ............................. 64

2.4.3.3 Field Operation .................................. 64

2.4.4 System Specifications ...................................... 65

2.5 Manual Method for Collecting and Analyzing Volatile Organic Compounds . . 66

2.5.1 Sample Collection ......................................... 67

2.5.1.1 Multiple-event Sample Collection Equipment .......... 68

2.5.1.2 Multiple-event Sample Collection Procedure ........... 71

2.5.1.3 Multiple-event System Specifications ................ 75

2.5.1.4 Single-event Collection Equipment .................. 77

2.5.1.5 Single-event Sample Collection Procedure ............. 80

2.5.1.6 Single-event System Specifications .................. 82

2.5.1.7 Canister Sampling System Certification ............... 83

2.5.1.7.1 Certification Equipment .................. 87

2.5.1.7.2 Certification Procedure ................... 88

2.5.2 Canister Cleaning ......................................... 90

2.5.2.1 Canister Cleaning Equipment ....................... 91

2.5.2.2 Canister Cleaning Procedure ........................ 94

2.5.2.3 Canister Blanking Procedure ....................... 96

2.5.2.4 Final Canister Evacuation Procedure ................. 97

2.5.3 Canister Sampling Issues ................................... 98

2.5.3.1 Precautions in the Use of Canisters .................. 99

2.5.3.2 Contamination ................................... 99

2.5.3.3 Sample Stability ................................ 101

2.5.3.4 Positive Pressure Samples ......................... 103

2.5.3.5 Diluted Samples ................................ 104

2.5.3.6 Canister Leakage ................................ 104

2.5.4 Sample Analysis ......................................... 106

2.5.4.1 Sample Introduction ............................. 106

2.5.4.2 Sample Conditioning ............................ 106

2.5.4.3 Sample Concentration ............................ 108

2.5.4.4 Sample Focusing or Cryofocusing .................. 109

2.5.4.5 Gas Chromatography ............................ 109

2.5.4.6 Analytical System Calibration ..................... 110
TABLE OF CONTENTS (Continued)

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2.5.5 System Operation ........................................ 111

2.5.5.1 Initial System Set-up ............................. 111

2.5.5.2 Sampling Parameters ............................ 112

2.5.5.3 Operation ...................................... 112

2.6 Data Processing Capabilities of Automated VOC Systems and Submittal of

VOC Data to the AIRS AQS Data Base .............................. 113

2.6.1 Data Processing Capabilities of Automated VOC Measurement 

Systems ................................................ 114

2.6.1.1 Data Acquisition and Processing ................... 116

2.6.2 AIRS AQS Data Submittal ................................. 120

2.6.2.1 Initial AIRS AQS Setup .......................... 123

2.6.2.2 Site and Monitor File Updates ..................... 125

2.6.2.3 Raw Data Transactions ........................... 131

2.6.2.4 Submitting Data ................................ 149

2.7 Validating Data from Automated VOC Systems ........................ 151

2.7.1 Data Validation Approach ................................. 153

2.7.1.1 Routine Procedures .............................. 154

2.7.1.2 Tests for Internal Consistency ...................... 161

2.7.1.3 Historical Data Comparisons ...................... 169

2.7.1.4 Parallel Consistency Checks to Identify Systematic Bias . 173

2.7.2 Treatment of Outliers ..................................... 173

2.8 Quality Control and Quality Assurance for VOC Measurements ........... 174

2.8.1 Data Quality Objectives ................................... 175

2.8.2 Quality Control .......................................... 183

2.8.2.1 Sample Collection ............................... 183

2.8.2.1.1 System Certification .................... 185

2.8.2.1.2 Calibration of Manual Sampling System

Components .......................... 185

2.8.2.1.3 Collection of Field Duplicate Samples ...... 187

2.8.2.1.4 Preventive Maintenance ................. 187

2.8.2.2 Sample Handling and Custody ..................... 188

2.8.2.3 Sample Analysis ................................ 190

2.8.2.4 Data Documentation and Archives .................. 194

2.8.3 Quality Assurance ........................................ 196

2.8.3.1 Development of Standard Operating Procedures ....... 197

2.8.3.2 QA Program Guidance ........................... 199

2.8.3.2.1 Audit Types ........................... 199

2.9 References ..................................................... 202
TABLE OF CONTENTS (Continued)

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Section 3 Determination of Total Nonmethane Organic Compounds Using 

Method TO-12 .................................................... 1

3.1 References ....................................................... 2

Section 4 Methodology for Measuring Oxides of Nitrogen and Total Reactive Oxides of

Nitrogen in Ambient Air ............................................ 1

4.1 Oxides of Nitrogen ................................................. 1

4.1.1 Measurement Principle ...................................... 2

4.1.2 Method and Equipment Description ............................ 4

4.2 Total Reactive Oxides of Nitrogen .................................... 6

4.3 Measurement of Total Reactive Oxides of Nitrogen in the Atmosphere

(Gas Phase Chemiluminescence)-Draft Instrumental Method ................ 7

4.3.1 Applicability .............................................. 8

4.3.2 Principle of Measurement .................................... 8

4.3.3 Measurement Apparatus ..................................... 9

4.3.3.1 Configuration .................................... 9

4.3.3.2 Reconfiguration .................................. 12

4.3.3.2.1 Shelter ................................ 12

4.3.3.2.2 Plumbing .............................. 13

4.3.3.2.3 Electronics ............................. 14

4.3.4 Calibration ............................................... 15

4.3.4.1 Apparatus ...................................... 16

4.3.4.1.1 Air Flow Controllers ..................... 16

4.3.4.1.2 NO Flow Controller ..................... 16

4.3.4.1.3 Air Flowmeters ......................... 16

4.3.4.1.4 NO Flowmeter ......................... 18

4.3.4.1.5 Pressure Regulator for Standard NO Cylinder . 18

4.3.4.1.6 Ozone Generator ........................ 18

4.3.4.1.7 Valve ................................. 18

4.3.4.1.8 Reaction Chamber ....................... 18

4.3.4.1.9 Mixing Chamber ........................ 19

4.3.4.1.10 Output Manifold ........................ 19

4.3.4.1.11 Valve ................................. 19

4.3.4.2 Reagents ....................................... 19

4.3.4.2.1 NO Concentration Standard ............... 19

4.3.4.2.2 Zero Air ............................... 20

4.3.4.3 Dynamic Parameter Specification .................... 20

4.3.4.4 Calibration Procedure ............................. 23
TABLE OF CONTENTS (Continued)

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4.3.4.5 Determination of Converter Efficiency ................ 29

4.3.4.6 Frequency of Calibration ........................... 29

4.3.4.7 Analyzer Challenge ............................... 30

4.4 Nitric Acid Measurement ................................... 30

4.5 References ............................................... 30

Section 5 Methodology for Determining Carbonyl Compounds in Ambient Air ......... 1

5.1 Ozone Scrubbers .................................................. 4

5.1.1 Denuder Ozone Scrubber .................................... 5

5.1.1.1 Denuder Ozone Scrubber Equipment .................. 6

5.1.1.2 Denuder Ozone Scrubber Operational Procedure ......... 8

5.1.2 Cartridge Ozone Scrubber .................................... 8

5.1.2.1 Cartridge Ozone Scrubber Equipment ................. 9

5.1.2.2 Cartridge Ozone Scrubber Operation Procedure .......... 9

5.2 Multiple-event Sample Collection Systems ............................. 11

5.2.1 Multiple-event Collection System Equipment ................... 11

5.2.2 Multiple-event Sampling Procedures .......................... 14

5.2.3 Sample Probe and Manifold ................................. 16

5.2.4 Multiple-event System Specifications ......................... 21

5.3 Process Blanks ................................................... 25

5.3.1 Blank Criteria ............................................ 25

5.3.2 Frequency of Collection .................................... 27

5.4 Breakthrough Analysis ............................................. 28

5.5 Collection of Collocated Samples .................................... 28

5.6 Quality Assurance and Quality Control ................................ 28

5.7 General Cartridge Handling Guidelines ................................ 29

5.8 References ...................................................... 31

Section 6 Guidance for PAMS Meteorological Monitoring ......................... 1

6.1 Background ...................................................... 1

6.2 PAMS Site Types .................................................. 3

6.3 Application of PAMS Meteorological Data .............................. 4

6.4 Surface Meteorological Monitoring .................................... 5

6.4.1 Siting and Exposure ........................................ 5

6.4.2 Specifications ............................................. 6

6.4.3 Wind Speed and Wind Direction .............................. 6

6.4.4 Temperature .............................................. 8

6.4.5 Atmospheric Humidity ...................................... 9
TABLE OF CONTENTS (Continued)

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6.4.6 Solar Radiation ........................................... 10

6.4.7 Ultraviolet Radiation ....................................... 11

6.4.8 Barometric Pressure ....................................... 12

6.4.9 Precipitation ............................................. 13

6.5 Upper-Air Meteorological Monitoring ................................ 13

6.5.1 Siting and Exposure ....................................... 16

6.5.2 Aircraft ................................................. 16

6.5.3 Tall Towers .............................................. 17

6.5.4 Balloon Systems .......................................... 17

6.5.5 Ground-Based Remote Sensors .............................. 19

6.5.6 Estimation of Mixing Height ................................ 22

6.6 References ...................................................... 23

APPENDICES

A Compendium Method TO-15. Determination of Volatile Organic Compounds

(VOCs) in Air Collected-Prepared Canisters and Analyzed by Gas

Chromatography/Mass Spectrometry (GC/MS).

B Humidity

C Method TO-12. Method for the Determination of Non-Methane Organic

Compounds (NMOC) in Ambient Air Using Cryogenic Preconcentration and

Direct Flame Ionization Detection (PDFID)

D Compendium Method TO-11A. Determination of Formaldehyde in Ambient Air

Using Adsorbent Cartridge Followed by High Performance Liquid 

Chromatography (HPLC) [Active Sampling Methodology]
ix

LIST OF FIGURES

Page

1-1 Isolated Area Network Design .............................................. 7

2-1 Water Content of Air at 75% and 100% Relative Humidity Over a Range of

Temperatures .......................................................... 24

2-2 Configuration of Materials to Perform Direct Injections of Water into the Canister

Before Filling with Dry Calibration Gas ..................................... 27

2-3 Configuration of Materials to Perform Injection of Water Through a Heated Tee While

Filling with Dry Calibration Gas ........................................... 28

2-4 Calibration Standard Dilution System ....................................... 31

2-5 Example Chromatogram for the PAMS Target Compounds from the PLOT Analytical

Column ............................................................... 39

2-6 Example Chromatogram for the PAMS Target Compounds from the BP1 Analytical

Column ............................................................... 40

2-7 Representative Ambient Air Sample Analyzed on a PLOT Column ................ 41

2-8 Representative Ambient Air Sample (Same as Figure 2-6) Analyzed on a 

BP-1 Column .......................................................... 42

2-9 Vertical Configuration ................................................... 56

2-10 Horizontal Configuration ................................................. 57

2-11 A Typical Multiple-Event Sample Collection System ........................... 69

2-12 A Typical Single-Event Sample Collection System ............................ 78

2-13 Dedicated Manifold for Zero Gas Certification ................................ 85

2-14 Dedicated Manifold for Challenge Gas Certification ........................... 86

2-15 Schematic of a Canister Cleanup System .................................... 92

2-16 Report Generating Process ............................................... 115
LIST OF FIGURES

Page

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2-17 Column Placement for a Type F1 Transaction ............................... 128

2-18 Column Placement for a Type A6 Transaction ............................... 132

 

2-19 Column Placement for an Hourly Data Transaction ........................... 140

2-20 Column Placement for a Daily Data Transaction ............................. 146

2-21 Flow of Data Validation Activities ........................................ 155

2-22 Appearance of Calibration Data at East Hartford, CT, in June 1995. Example scatter

plot showing calibration data of about 30 ppbC. Data are level 0, preliminary

data, CT DEP ......................................................... 160

2-23 Example PE Turbochrom Summary Report ................................ 163 ®

2-24 Time Series Plot ....................................................... 166

2-25 Time Series Plot of Several Species Groups at Stafford, CT, in 1994. Example of

misidentification of a paraffin for an unidentified peak ........................ 167

2-26 Time Series Example of System Contamination .............................. 168

2-27 Example of Peak Misidentification Using a Scatter Plot. Typically, data points would

be present in the region of the plot between the two extreme edges ............... 170

2-28 Example of a Typical “Fingerprint” Observed at a PAMS Site ................... 171

2-29 Example of Calibration Gas “Fingerprint” Observed in Data Submitted to AIRS .... 172

4-1 Flow Schematic of a Typical NO-NO2 Instrument .............................. 5

4-2 Flow Schematic of the Reconfigured NOy Instrument for PAMS Application ........ 11

4-3 Flow Schematic of a Typical Gas Phase Titration Calibration System .............. 17

5-1 Cross-Sectional View of the Denuder O3 Scrubber .............................. 7

5-2 Cross-Sectional View of the Cartridge O3 Scrubber ............................ 10
LIST OF FIGURES

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5-3 Schematic of a Typical Multiple-Event Carbonyl Cartridge Sampling System ....... 12

5-4 Vertical Configuration ................................................... 19

5-5 Horizontal Configuration ................................................. 20

5-6 Isolated Area Network Design ............................................. 23
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LIST OF TABLES

Page

1-1 PAMS Minimum Monitoring Network Requirements ............................ 5

2-1 Target Volatile Organic Compounds .......................................... 5

2-2 Target VOC Compound Classification ........................................ 7

2-3 Vapor Pressure of Water Below 100EC, mm HG ............................... 22

2-4 Peak Identifications, Ambient Air Sample .................................... 43

2-5 AIRS Transaction Types ................................................. 122

2-6 Current AIRS AQS Regional Coordinators ................................... 124

2-7 AIRS Sampling Frequency Codes .......................................... 127

2-8 Configuration Comments for Type A6 or A7 Transactions ....................... 130

2-9 Target Volatile Organic Compounds ........................................ 133

2-10 Carbonyl Target List .................................................... 134

2-11 AIRS Method Codes .................................................... 135

2-12 AIRS Interval Codes .................................................... 137

2-13 AIRS Unit Codes ....................................................... 138

2-14 Hourly Sample Valid Start Hour Based on the Interval .......................... 138

2-15 Null Values ........................................................... 139

2-16 QC Objectives for VOC Sample Collection .................................. 184

2-17 VOC QC Procedures .................................................... 191

2-18 Format for Standard Operating Procedures ................................... 198

5-1 PAMS Minimum Monitoring Network Requirements ............................ 2
LIST OF TABLES

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5-2 Example Schedule for the Collection of Blanks ................................ 27

5-3 Quality Assurance and Quality Control Criteria ................................ 30

6-1 Overview of PAMS Meteorological Monitoring Requirements ..................... 2

6-2 Application of the PAMS Meteorological Data .................................. 4

6-3 System Specifications for Surface Meteorological Measurement .................... 6

6-4 Principles of Humidity Measurement ........................................ 10

6-5 Classification of Pyranometers ............................................. 12

6-6 Capabilities and Limitations of Meteorological Measurement Systems for Vertical

Profiling of the Lower Atmosphere .......................................... 15

6-7 Manufacturers’ Specifications for Sensors Used in Rawinsondes ................... 17

6-8 Functional Precision of Rawinsonde Measurements ............................. 18
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Section 1.0

Introduction

Section 182 (c)(1) of the 1990 Clean Air Act Amendments (CAAA) required the

Administrator to promulgate rules for enhanced monitoring to obtain more comprehensive and

representative data on ozone air pollution. The Environmental Protection Agency (EPA) has

revised the ambient air quality surveillance regulations in Title 40 Part 58 of the Code of Federal

Regulations (40 CFR Part 58) to include provisions for enhanced monitoring of ozone (O ), 1

3

oxides of nitrogen (NO ), volatile organic compounds (VOCs), selected carbonyl compounds, x

and monitoring of meteorological parameters. The revisions require States to establish

Photochemical Assessment Monitoring Stations (PAMS) as part of their existing State

Implementation Plan (SIP) monitoring networks in ozone nonattainment areas classified as

serious, severe, or extreme.

The principal reasons for requiring the collection of additional ambient air pollutant and

meteorological data are the lack of successful attainment of the National Ambient Air Quality

Standard (NAAQS) for O , and the need to obtain a more comprehensive air quality data base for 3

O and its precursors. Analysis of the data will help the EPA understand the underlying causes of 3

ozone pollution, devise effective controls, and measure improvement. Data acquired from

enhanced ambient air monitoring networks will have a variety of uses, which may include:

C Developing, evaluating, and refining new O control strategies; 3

C Determining NAAQS attainment or non-attainment for O ;3

C Tracking VOCs and NO emissions inventory reductions; x

C Providing photochemical prediction model input;

C Evaluating photochemical prediction model performance; 
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C Analyzing ambient air quality trends; and

C Characterizing population exposure to VOCs and O .3

1.1 Purpose

The Technical Assistance Document (TAD) for Sampling and Analysis of Ozone

Precursors was initially published in October 1991. The document was intended to provide

guidance to those responsible for implementing PAMS. Since the initial publication, there has

been a draft revision in October 1994 to Sections 2.0, 4.0, and 5.0 and a revision to Section 6.0 in

June 1995, all of which were included in Appendix N of the PAMS Implementation Manual. 

Since these revisions, there have been significant advances in the methodology used to measure

the components and parameters of interest at PAMS. These advances have necessitated this

revision of the TAD.

The purpose of this document is to provide guidance in support to the enhanced ozone

monitoring revisions in 40 CFR Part 58. The document provides technical information and

guidance to Regional, State, and local Environmental Protection Agencies responsible for

measuring O precursor compounds in ambient air. Sampling and analytical methodology for 3

speciated VOCs, total nonmethane organic compounds (NMOC) and selected carbonyl

compounds (i.e., formaldehyde, acetaldehyde, and acetone) are specifically addressed. The

document also addresses methodology for measuring NO , as required by PAMS, and discusses X

issues associated with the collection of total reactive oxides of nitrogen (NOy) and

meteorological measurements.

The technical guidance provided for measuring O3 precursors is based on emerging and

developing technology. Guidance for automated applications, in particular, is based on

experience obtained from the application of this technology during the beginning years of PAMS

implementation. Because these methods are based on emerging technology and reflect state-of-
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the-art, they will be subject to continuing evaluation and improvements or clarifications in the

future. 

Users should consider this guidance a basic reference to assist in developing and

implementing their PAMS monitoring program. The technical assistance document is prepared

in a document control format to accommodate revisions that are anticipated as the emerging

technologies develop. 

1.2 Organization

The guidance provided in Section 2 of this document addresses the measurement of

volatile organic O3 precursors and includes method descriptions for manual and automated

sample collection and analysis. Detailed discussions are presented on selected topics such as

which volatile organic O3 precursors to measure, critical chromatography issues, moisture

control, data validation, Quality Control and Quality Assurance, AIRS data entry, and how

canister sampling should be approached.

Section 3 discusses the measurement of total NMOC using Method TO-12 from the

Compendium of Methods for Sampling and Analysis of Toxic Organic Compounds in Ambient

Air. Measurement of total NMOC by Method TO-12 has limited application to the 2

implementation of the 40 CFR Part 58 requirements, but Method TO-12 is included because of

its applications to canister cleanliness verification, application to alternative monitoring

strategies, and use in O prediction models. Alternative monitoring strategies involve the use of 3

canister and/or automated Method TO-12 complemented with an extensive canister sampling and

manual VOCs speciation analysis program.

Section 4 addresses the measurement of NOX and issues associated with NOy. Section 5

addresses the measurement of selected carbonyl compounds using Compendium Method

TO-11A from the Compendium of Methods for Sampling and Analysis of Toxic Organic

Compounds in Ambient Air and includes new information regarding the methodology and issues
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associated with the measurement of carbonyl compounds. Section 6 provides guidance for

PAMS meteorological monitoring, which is essential to the PAMS program. Note that all

sections of this Technical Assistance Document are intended to be independent. Figures, tables,

and text are therefore repeated as necessary.

1.3 Summary of the Monitoring Regulations

The 1990 CAAA required EPA to promulgate regulations to enhance existing ambient air

monitoring networks. Existing SIP stations are identified as State and Local Agency Monitoring

Stations (SLAMS) and National Air Monitoring Stations (NAMS). The enhanced O3 monitoring

stations are a subset to SLAMS and identified as Photochemical Assessment Monitoring Stations

(PAMS).

The monitoring revisions by EPA required changes to 15 separate Sections, Subparts, or

Appendices of 40 CFR Part 58, and varied in complexity and impact on State and local agencies.

The areas of the revised 40 CFR Part 58 regulations most relevant to enhanced ambient air

monitoring are operating schedules, PAMS methodology, and quality assurance. Section 58.13

of 40 CFR Part 58 contains the operating schedule for SLAMS, NAMS, and PAMS. This

section requires sampling for VOCs and carbonyl compounds according to the monitoring period

and minimum monitoring network requirements specified in Sections 4.3 and 4.4 of Appendix D

of the revised regulations.1

 Unlike the SLAMS and NAMS design criteria which are pollutant-specific, PAMS

design criteria are site specific. Design criteria for the PAMS network are based on selection of

an array of site locations relative to O3 precursor sources and predominant wind direction

associated with peak O3 events. Four PAMS site types are described in the regulations. The

number and type of monitoring sites and sampling requirements is dependent on the population

of the Metropolitan Statistical Area (MSA) or Consolidated Metropolitan Statistical Area

(CMSA). The specified minimum sampling requirements for VOCs and carbonyl compounds for

each site type are presented in Table 1-1. Monitoring for O and NO (including NO and NO ) 3 X 2
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Table 1-1 . PAMS Minimum Monitoring Network Requirements

Population Required Sampling Compounds Sampling

of MSA/CMSA Site Type Frequency Frequency 1

Minimum VOCs Minimum Carbonyl

2 2

Less than 500,000 (1) A or C -

500,000 to 1,000,000 (1) A or C -

1,000,000 to (1) A or C -

2,000,000 (2) B E

More than 2,000,000 (1) A or C -

 (2) A or C D or F

(2) B E

(3) A or C -

(2) B E

(3) A or C -

(2) B E

(2) B E

(3) A or C -

(4) A or C -

Whichever area is larger. 1

Frequency requirements are as follows: 2

A = Eight 3-hour samples every third day and one additional 24-hour sample every sixth day during

the monitoring period.

B = Eight 3-hour samples every day during the monitoring period and one additional 24-hour sample

every sixth day year-round.

C = Eight 3-hour samples on the 5 peak O3 days plus each previous day, eight 3-hour samples every

sixth day and one additional 24-hour sample every sixth day during the monitoring period.

D = Eight 3-hour samples every third day during the monitoring period.

E = Eight 3-hour samples on the 5 peak O days plus each previous day and eight 3-hour samples 3

every sixth day during the monitoring period.

F = Eight 3-hour samples on the 5 peak O3 days plus each previous day, eight 3-hour samples every

sixth day and one additional 24-hour sample every sixth day during the monitoring period.
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requires continuous measurements. The sampling schedule applicable to a specific area is

dependent on population and PAMS site types. Specific monitoring objectives are associated

with each sampling location. An example of an isolated area network design shown in

Figure-1-1 identifies the location of the four PAMS site types referred to in Table 1-1. 

The EPA has also prepared a guidance document on enhanced O3 monitoring network

design and siting criteria which provides assistance regarding the number of PAMS required, 3

station location, and probe siting criteria. The PAMS site types are described below. 

Type (1) PAMS characterize upwind background and transported O and precursor 3

concentrations entering the MSA or CMSA and are used to identify those areas subjected to

overwhelming transport. Type (2) PAMS monitor the magnitude and type of precursor emissions

in the area where maximum O precursor emissions are expected and are also suited for 3

monitoring urban air toxic pollutants. Type (3) PAMS characterize O precursor concentrations 3

occurring downwind from the area of maximum emissions. Type (4) PAMS characterize

extreme downwind transported O3 and its precursor concentrations exiting the area and identify

those areas which are potential contributors.

Appendix A of 40 CFR Part 58 references the Quality Assurance Handbook for Air

Pollution Measurement Systems, Volume IV (Revised March, 1995) - Ambient Air Specific

Methods for general quality assurance recommendations for PAMS. Quality assurance 4

procedures for VOC, NOX, O3 , and carbonyl and meteorological measurements must be

consistent with EPA guidance. This guidance, and other information from appropriate sources,

including Section 2.8 of this document, should be used by States in developing a Quality

Assurance program.
Isolated Area Network Design

Note: 

U1 and U2 represent the first and second most 

predominant high ozone day morning wind direction. 

U3 represents the high ozone day afternoon wind direction.

(4)

(3)

(1)

(2)

(2)

Central business district

Urbanized fringe

U1

U3

U2

o:s/g/morr/3797/pams/isolated.ppt

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(1), (2), (3), and (4) are different types of PAMS sites (See Table 1-1).

Figure 1-1. Isolated Area Network Design
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1. U.S. Environmental Protection Agency. Code of Federal Regulations. Title 40, Part 58. 

Ambient Air Quality Surveillance, Final Rule Federal Register, Vol. 58, No. 28,

February 12, 1993.

2. Compendium of Methods for the Determination of Toxic Organic Compounds in

Ambient Air. Compendium Method TO-12. Method for the Determination of NonMethane Organic Compounds (NMOC) in Ambient Air Using Cryogenic

Preconcentration and Direct Flame Ionization Detection (PDFID). EPA-600/4-89/017. 

Research Triangle Park, NC: U.S. Environmental Protection Agency, 1988.

3. Photochemical Assessment Monitoring Stations Implementation Manual. EPA-454/B93-051. Research Triangle Park, NC: U.S. Environmental Protection Agency, 1994.

4. Quality Assurance Handbook for Air Pollution Measurement Systems, Volume IV -

Ambient Air Specific Methods. EPA 600/4-77-27a. U.S. Environmental Protection

Agency, 1977. Revised March, 1995.

Appendix C of 40 CFR Part 58 requires that methods used for O3 and NOX be reference

or equivalent methods. Because there are no reference or equivalent methods promulgated for

VOC and carbonyl measurements, Appendix C of the revisions refers agencies to this guideline

document for direction. 

Appendix C of the revisions would also allow the use of approved alternative VOC

measurement methodology (including new or innovative technologies). This provision requires

States that pursue alternatives to the methodology described herein to provide details depicting

rationale and benefits of their alternative approach in their network description as required in

40 CFR Part 58, Section 58.40 - PAMS Network Establishment. 

1.4 References
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Section 2.0

Methodology for Measuring Volatile Organic Compound Ozone

Precursors in Ambient Air

In accordance with the provisions for the enhanced O3 ambient monitoring network

requirements specified in 40 CFR Part 58, Subpart E,1 this section provides guidance and method

descriptions for measuring volatile organic compounds (VOCs) that are considered to contribute to the

formation of ozone in the right atmospheric conditions. Information and guidance are provided to assist

in the development, implementation, and use of these methods for designing a VOC measurement

program consistent with the requirements of the enhanced O3 monitoring rule. Areas addressed

include:

C A review of the network monitoring requirements;

C A list of target VOCs to be measured;

C Chromatography issues associated with peak identification and quantification;

C Automated and manual methodology for collecting and analyzing samples;

C The minimum requirements of a Quality Assurance (QA) and Quality Control (QC)

program;

C Guidance for validating data from automated GC systems; and

C Submitting data into the AIRS AQS data base.

Measuring VOCs is a complex process involving the application of gas chromatographic

techniques for qualitative and quantitative determination of individual hydrocarbon compounds and an

estimation of total non-methane organic compound (TNMOC) content in ambient air. Two methods

are presented for collecting and analyzing VOC samples: an automated method (Section 2.4) and a

manual method (Section 2.5). Ideally, agencies responsible for designing, implementing, and operating
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their O3 monitoring networks will satisfy their monitoring requirements by using some combination of the

automated and manual gas chromatographic approaches. Even if agencies primarily choose the

automated methodology, manual sampling and analysis capability are needed to fulfill the 24-hour

sample requirement; verify the proper operation of the automated systems; characterize the quality of

the collected data; address the identification of unknown compounds; and enhance the

representativeness of the monitoring network.

Users are ultimately responsible for equipment selection, set-up, parameter optimization, and

preparation of Standard Operating Procedures (SOPs) for their specific network. Because of the

complexity of the measurement process and the numerous choices of instrumentation (e.g., sampling

equipment, gas chromatographs, data acquisition hardware and software, etc.), the method descriptions

presented are generic. Background information on the potential benefits and limitations of the methods

are also provided. 

2.1 Network Monitoring Requirements

The minimum sampling frequency requirements for speciated VOC monitoring are prescribed

in 40 CFR Part 58, Subpart E, Appendix D - Network Design for State and Local Air Monitoring

Stations (SLAMS), National Air Monitoring Stations (NAMS), and Photochemical Assessment

Monitoring Stations (PAMS). Section 4.3 - Monitoring Period requires, at a minimum, that O3

precursor monitoring be conducted annually throughout the months of June, July, and August when

peak O3 values are expected. Section 4.4 - Minimum Monitoring Network Requirements specifies the

minimum required number and type of monitoring sites and sampling frequency requirements based on

the population of the affected MSA/CMSA or nonattainment area, whichever is larger. These

monitoring requirements are outlined in Table 1-1. The minimum speciated VOC sampling frequency

requirements are summarized by site type below:
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C Site Type 1 - Eight 3-hour samples every third day and one additional 24-hour sample

every sixth day during the monitoring period; or eight 3-hour samples on the five peak

O3 days plus each previous day and eight 3-hour samples and one 24-hour sample

every sixth day, during the monitoring period.

C Site Type 2 - (population less than 500,000) - Same as Site Type 1.

C Site Type 2 - (population greater than 500,000) - Eight 3-hour samples every day

during the monitoring period and one additional 24-hour sample every sixth day year

around.

C Site Type 3 - (population greater than 500,000) - Same as Site Type 1.

C Site Type 4 - (population more than 2,000,000) - Same as Site Type 1.

Either of the two VOC methods (automated or manual) described in this section is capable of

satisfying the sampling frequency and sample integration requirements. Samples collected for either

method should represent a time-integrated average for the required sampling period. It is important to

understand that the 3-hour sample integration period is a maximum requirement in the sense that

samples can be collected more frequently at shorter sampling intervals (i.e., three 1-hour periods) but

not less frequently for longer sampling intervals. 

The manual methodology, where samples are collected in canisters, is primarily applicable to

the less frequent sampling required for site Types 1, 3, and 4 (i.e., eight 3-hour samples every third day

or during peak O3 events) and the 24-hour sample requirement. The automated method, which allows

for direct on-line sample collection, is primarily applicable to the more frequent sampling requirements

for Site Type 2 (eight 3-hour samples every day during the monitoring period). The automated method

provides a viable option for the continuous collection of hourly samples. Though not required,

continuous collection of hourly samples also offers a more definitive assessment of the temporal and

diurnal distribution of VOCs. Although it is possible to use the manual methodology for Site Type 2

sampling requirements, it is not practical due to the large number of SUMMA® canisters required. 
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2.2 Target Volatile Organic Compound Ozone Precursors

For the purposes of this document, the term VOCs refers to gaseous aliphatic and aromatic

nonmethane organic compounds that have a vapor pressure greater than 0.14 mm Hg at 25EC, and

generally have a carbon number in the range of C2 through C12. Many of these compounds play a

critical role in the photochemical formation of O3 in the atmosphere. Volatile organic compounds are

emitted from a variety of sources. In urban areas, the dominant source may be automobiles. Table 2-1

presents the target VOCs which could be measured and reported to satisfy the requirements of

40 CFR Part 58, Subpart E. Users should consider these target compounds in developing their

measurement systems and monitoring approach, and initially report and submit results for these

compounds into the Aerometric Information Retrieval System (AIRS) as described in Section 2.6.2 of

this document. The VOCs listed in Table 2-1 were selected primarily based on their abundance in

urban atmospheres and their potential role in the formation of O3. Polar compounds are not included

on the target list due to their surface adsorption characteristics and the difficulty in measuring these

compounds using the methodology designed for nonpolar hydrocarbons. The methodology described

in this document is designed to measure the more abundant non-polar hydrocarbons or VOCs.

The target list in Table 2-1 is not definitive or all-encompassing, but should be used as a

guideline for implementation that should evolve as the monitoring program matures. As experience is

gained in the collection of data regarding the abundance of specific VOCs at each site, target

compounds may be deleted from the list depending on the frequency of occurrence. If additional

compounds are identified and occur at high frequency, they should be added to the list of PAMS target

compounds.

The compounds listed in Table 2-1 are presented in the order of their expected

chromatographic elution from a J&W® DBTM-1 non-polar dimethylsiloxane capillary analytical column. 

The AIRS parameter code for each compound is also given in Table 2-1. Compounds
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Table 2-1. Target Volatile Organic Compounds

AIRS

Parameter

Code

43203

43206

43202

43205

43204

43214

43280

43212

43216

43217

43221

43224

43220

43243

43226

43227

43244

43242

43284

43285

43230

43245

43231

43262

43247

45201

43248

43263

43291

Target

Compound

Name

Ethylene

Acetylene

Ethane

Propylene

Propane

Isobutane

1-Butene

n-Butane

trans-2-Butene

cis-2-Butene

Isopentane

1-Pentene

n-Pentane

Isoprene (2-methyl-1,3-butadiene)

trans-2-Pentene

cis-2-Pentene

2,2-Dimethylbutane

Cyclopentane

2,3-Dimethylbutane

2-Methylpentane

3-Methylpentane

1-Hexene*

n-Hexane

Methylcyclopentane

2,4-Dimethylpentane

Benzene

Cyclohexane

2-Methylhexane

2,3-Dimethylpentane

AIRS

Parameter

Code

43249

43250

43232

43261

43252

45202

43960

43253

43233

45203

45109

45220

45204

43235

45210

45209

45212

45213

45207

45211

45208

43238

45225

45218

45219

43954

43141

43102

43000

Target

Compound

Name

3-Methylhexane

2,2,4-Trimethylpentane (isooctane)

n-Heptane

Methylcyclohexane

2,3,4-Trimethylpentane

Toluene

2-Methylheptane

3-Methylheptane

n-Octane

Ethylbenzene

m/p-Xylene

Styrene

o-Xylene

n-Nonane

Isopropylbenzene (cumene)

n-Propylbenzene

m-Ethyltoluene (1-ethyl-3-methylbenzene)

p-Ethyltoluene (1-ethyl-4-methylbenzene)

1,3,5-Trimethylbenzene

o-Ethyltoluene (1-ethyl-2-methylbenzene)

1,2,4-Trimethylbenzene

n-Decane

1,2,3-Trimethylbenzene

m-Diethylbenzene

p-Diethylbenzene

n-Undecane

n-Dodecane*

TNMOC**

PAMHC***

* These compounds have been added as calibration and retention time standards primarily for the purpose of retention

time verification. They can be quantitated at the discretion of the user.

** Total Nonmethane Organic Compounds

*** PAMS Hydrocarbons
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with lower boiling points typically elute first on this analytical column, followed by the heavier, higher

molecular weight components with higher boiling points. Concentrations of the target VOCs and

unknown compounds (unidentified peaks) are calculated in units of parts per billion Carbon (ppbC). 

The concentration in ppbC for a compound can be divided by the number of carbon atoms for that

compound to estimate the concentration in parts per billion volume (ppbv). The target compound list in

Table 2-2 has also been separated and classified into categories based on structure. The categories

include paraffins (alkanes and cycloalkanes), olefins (alkenes and cycloalkenes), aromatics (arenes),

and alkynes. Because the compound proved to be unstable and decomposed in the calibration gas

cylinder, 2-methyl-1-pentene was replaced on the list of PAMS target volatile organic compounds by

1-hexene. n-Dodecane was added as a late-eluting retention time marker.

2.2.1 Total Nonmethane Organic Compound (TNMOC) and PAMS Hydrocarbons

(PAMHC)

The TNMOC measurement is the unspeciated total concentration of VOCs (typically C2

through C12) in ambient air. This measurement supplements the O3 precursor compound measurements

and is used for O3 models that do not require speciated hydrocarbon measurement input. This estimate

can be made using either the automated or manual techniques described in Sections 2.4 and 2.5,

respectively. An estimate of the TNMOC in ppbC is determined as the sum of all identified and

unidentified gas chromatographic peaks in the C2 through C12 range as eluted from the analytical column

and detected by the flame ionization detector (FID). The concentration in ppbC of TNMOC is

calculated by taking the total area count measured and applying the response factor for propane, the

primary calibration compound. The C2 through C12 retention time window should be established and

periodically verified by analyzing ethylene or acetylene (C2) and dodecane (C12). These compounds

may be incorporated in the retention time or calibration standard.
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Table 2-2. Target VOC Compound Classification

Alkyne Paraffin

Acetylene Isopentane

3-Methylheptane

Aromatic 2-Methylheptane

Styrene n-Octane

m/p-Xylene 2,3,4-Trimethylpentane (isooctane)

o-Xylene Ethane

Toluene Propane

Ethylbenzene Isobutane

n-Propylbenzene n-Nonane

1,2,4-Trimethylbenzene n-Butane

1,3,5-Trimethylbenzene 2,2,4-Trimethylpentane

1,2,3-Trimethylbenzene n-Hexane

Benzene n-Pentane

Isopropylbenzene (cumene) 3-Methylpentane

m-Ethyltoluene (1-ethyl-3-methylbenzene) 2-Methylpentane

p-Diethylbenzene Cyclopentane

o-Ethyltoluene (1-ethyl-2-methylbenzene) 2,3-Dimethylbutane

p-Ethyltoluene (1-ethyl-4-methylbenzene) Methylcyclopentane

m-Diethylbenzene 2,4-Dimethylpentane

2,2-Dimethylbutane

Olefin n-Heptane

1-Hexene* 3-Methylhexane

1-Butene 2,3-Dimethylpentane

Isoprene (2-methyl-1,3-butadiene) Cyclohexane

1-Pentene 2-Methylhexane

trans-2-Butene Methylcyclohexane

cis-2-Butene n-Decane

trans-2-Pentene n-Undecane

cis-2-Pentene n-Dodecane*

Propylene

Ethylene

*These compounds have been added as calibration and retention time standards primarily for the purpose

of retention time verification. They can be quantitated at the discretion of the user.
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Percent Unidentified TNMOC - PAMHC

TNMOC

* 100

Compendium Method TO-12, preconcentration direct flame ionization detector (PDFID)

techniques described in Section 3.0 of this document and in Appendix C, may also be used to

determine TNMOC. Method TO-12 measures carbon-containing compounds from the sample as

concentrated by cryogenic trapping and thermal desorption directly into a FID. The FID response is

typically calibrated using propane to give a per-carbon response in area counts per ppbC. Compounds

with a carbon number greater than C12 may be transferred and detected using the Method TO-12

technique. Because of inherent differences between the “summation of peaks” and PDFID

approaches, the two approaches do not provide equivalent TNMOC results and are not directly

comparable. Since the vapor pressure of carbon-containing compounds decreases with increasing

molecular weight, compounds with a carbon number above C12 are not expected to contribute

significantly (more than a few percent) to the TNMOC value.

A subgroup of TNMOC, PAMHC is the sum of peak areas for only the PAMS target

compounds. Both TNMOC and PAMHC are valuable data components and the ratio

PAMHC/TNMOC may indicate the conversion of ozone precursors to carbon-containing products

resulting from atmospheric chemistry.

The PAMHC parameter itself is of limited value because the PAMS target list may change by

geographic area. Also, PAMHC provides a broad measure of compounds that is often not

substantially different from TNMOC. PAMHC could be used by a state or agency measuring only

listed compounds, and then calculating the percent of unidentified compounds as:

Alternatively, PAMHC can be used to determine the percentage of the total made up by the listed

compounds.
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Percent Identified PAMHC

TNMOC

* 100

This ratio for a given PAMS site usually stays within a range characteristic of the site, subject to

seasonal variation.

2.3 Chromatography Discussion and Issues

The following section discusses the basic operating principles of the gas chromatography with

flame ionization detection (GC/FID) methodology used to measure ambient VOCs either as an

independent analytical system or as part of an automated sampling/analytical system. Related

chromatography issues or concerns regarding peak identification and quantitation, sample moisture

removal, calibration, primary and retention time standard preparation and humidification, and analytical

column selection and configuration are also discussed.

2.3.1 Gas Chromatography with Flame Ionization Detection

Gas chromatography with flame ionization detection is the established analytical technique for

monitoring VOCs in ambient air. The sensitivity, stability, dynamic range, and versatility of GC/FID

systems make them extremely effective in measuring very low concentrations of VOCs. The gas

chromatograph may be an independent analytical system or a component of an automated

sampling/analytical system.

Typically, a sample taken from an urban environment contains more than 100 detectable

compounds that may reasonably be separated into quantifiable peaks. These compounds are generally

present at concentrations varying from less than 0.1 ppbC to greater than 500 ppbC with the typical

concentration ranging between 0.1 to 50 ppbC. Detection of typical urban concentration levels
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generally requires that samples be passed through a preconcentration trap to concentrate the

compounds of interest and separate them from components of the sample that are not of interest

(i.e., air, methane, water vapor, and carbon dioxide).

The GC/FID systems required for VOC measurement consist of the following principal

components: 

C Sample introduction;

C Sample conditioning for moisture removal (optional);

C Sample concentration;

C Sample focusing for optimal sample injection and improved chromatographic separation

(optional);

C Gas chromatography; and

C Flame ionization detection.

An air sample may be introduced to the measurement system directly from ambient air, an

integrated canister, or a calibration gas cylinder. The sample is optionally passed through a sample

conditioning system for moisture removal and then concentrated using an adsorbent or glass bead trap

that is cryogenically cooled using liquid nitrogen, liquid carbon dioxide, or thermoelectric closed-cycle

coolers. The concentrated sample is then thermally desorbed and introduced into the carrier gas prior

to being introduced to the analytical column. Sample refocusing is optional and may be performed

using a cryogenically or thermoelectrically cooled secondary trap. Sample refocusing may also occur at

the head of the cryogenically cooled analytical column. Sample focusing is used to concentrate the

desorbed sample into a narrow band for injection onto the capillary GC analytical column. The focused

sample is thermally desorbed rapidly and injected onto the analytical column of the gas chromatograph

as a “plug,” which maximizes GC column resolution and results in improved C2 and C3

chromatographic separation and peak shape. Sample focusing is effective when low carrier gas flow
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rates (1-2 mL/minute) are used. The analytical column separates the sample into individual components

based on the distribution equilibrium between the mobile (carrier gas) and stationary (liquid column

coating) phases. The separated components elute from the column and enter the FID, where a signal is

generated based on carbon response. The time of elution and detection (retention time) is the primary

basis for the identification of each compound. Retention time units are typically expressed in minutes

and are specific to the conditions of the GC system used. The identification of sample components is

determined by matching the known retention times of the components in a retention time standard with

those in the sample. It is desirable to confirm GC peak identification periodically using a mass

spectrometric detector, if available.

The FID is the most widely used, universal GC detector. As a general observation, the FID

provides good sensitivity and uniform response to n-alkanes based on the number of carbon atoms in

the compound. For unsaturated, cyclic, or aromatic hydrocarbons, the FID response is less

predictable. The FID is, therefore, well suited for ambient air analysis since a majority of VOCs in

ambient air are hydrocarbons. This uniformity of FID response to n-alkanes simplifies calibration in

that a single hydrocarbon compound (e.g., propane) can be used to calibrate the detector response for

all hydrocarbons.2,3 This FID response characteristic also provides for the unique capability of

estimating the concentrations of not only the target peaks (identified) but also the unidentified

components of the sample. Some automated GC systems require a two-component calibration mixture

(e.g., propane and benzene) due to the use of dual analytical columns. By summing all identified and

unidentified chromatographic peak areas, a useful estimate of the concentration of TNMOC is

provided. The FID also has a broad linear dynamic range of response, allowing for the analysis of

samples with concentrations ranging from picogram (using preconcentration) to microgram quantities of

hydrocarbons.

Modern GC technology, coupled with sophisticated data acquisition and processing software,

provides for reasonable estimates of both the identity and quantity of the target species to the extent that

the analytical column is capable of separating them and the system has been adequately characterized
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and calibrated. The retention characteristics of the analytical column must be determined for each

target compound using pure components or mixtures of pure components diluted with a humidified inert

gas.

2.3.2 Identification and Quantification Issues

Although the peak identification and quantification expected with GC/FID systems is

acceptable for meeting the objectives of PAMS, the GC/FID technique has some inherent limitations. 

Chromatographic systems using GC/FID rely primarily on the practical use of retention times to make

compound identifications for each chromatographic peak. Commercial GC/FID systems configured for

VOC analyses must be suitably designed to provide stability of system parameters to ensure consistent

retention times for confident peak identification.

Gas chromatographic peak misidentifications typically occur as a result of retention time

shifting and interferences due to co-eluting non-target compounds. Modern GC capillary columns are

generally capable of adequately separating the targeted compounds; however, co-elution of unidentified

species with the targeted species can and does occur. The identification and quantitative uncertainty

resulting from co-elution will depend on the type of unidentified compound and the abundance relative

to the affected target VOC. The target VOCs are exclusively hydrocarbons which are primarily

emitted into the atmosphere by mobile sources and generally dominate most urban samples. 

Concentration estimates for substituted hydrocarbon species such as oxygenated or halogenated

hydrocarbons using FID are uncertain since these compounds do not respond to the FID solely on a

per carbon basis. Generally, the identification and quantification of a targeted compound will not be

significantly affected unless a substituted species, at a significant concentration, co-elutes with the target

compound.
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The potential for target compound identification errors can be reduced or eliminated by:

C Ensuring that the measurement system is fully optimized and characterized as discussed

in Section 2.3.7, Pre-Measurement Chromatographic System Verification;

C Designating chromatographic reference peaks and using relative retention times for

peak identification (Section 2.7.1, Data Validations);

C Using dual-column configurations to provide improved resolution (Section 2.3.5,

Column Configuration);

C Having an experienced chromatographer conduct visual inspection of the

chromatograms at some practical frequency to verify proper system operation;

C Reviewing the chromatographic data using computer-based exploratory software

designed to improve and validate the GC data and determine outliers;

C Periodically re-analyzing samples on a different well-characterized GC system to

identify co-eluting compounds; and

C Periodically confirming peak identification using more definitive GC/MS techniques. 

Quantitative errors can be reduced by careful attention to quality control (calibration details

and system blanks), frequent response checks using canister samples containing target compound

mixtures of known concentration, and periodic performance audits or proficiency studies using

independent reference materials. Analytical system blank analysis of humidified, ultra zero air is

performed to characterize the background concentration of VOCs present in the measurement system. 

If unacceptable levels of background system contamination occur the data will be quantitatively

compromised. Sources of contamination can be related to the:

C Source of humidified, ultra zero air;

C Sample to trap transfer line;
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C Carrier gas and filters; and

C Analytical columns.

The effort devoted to peak identification, confirmation, and quantification is important to the quality of

the collected data. Users must determine the appropriate level of effort to devote to this activity based

on their specific needs and capabilities. 

2.3.3 Sample Moisture Issues

The accurate identification and quantitation of trace level VOCs in ambient air generally

require the use of sample concentration techniques for sample enrichment to enhance instrument

sensitivity. The effects of moisture must be considered in any measurement program where sample

concentration is required. Cryogenic concentration techniques are commonly used, especially for light

hydrocarbons. The vast difference in boiling points of the C2 and C12 hydrocarbons also may require

the use of sub-ambient chromatography to adequately separate the entire range of compounds. The

co-collection of moisture in the concentration trap and subsequent injection of water onto the analytical

column can cause a number of problems and adversely affect the overall quality of the data generated. 

These problems include:

C Cryogenic trap freezing which results in reduced sample flow or trap blockage;

C Chromatographic column plugging due to ice formation and subsequent retention time

shifting, peak splitting, and poor peak shape and resolution which result in incorrect

peak identification and peak naming;

C Chromatographic column deterioration (especially with Al2O3 columns);

C Baseline shifts due to elution of the water profile;

C FID flame extinction;

C Poor reproducibility and precision of the data generated;
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C Competition for active sites and adverse effects on adsorbent concentration traps; and

C Suppression of the FID signal.

In addition, if “cold spots” exist in the sample concentration or transfer system, water can collect and

cause sample carryover or “ghost” peaks in subsequent sample analyses. This carryover may affect the

data by causing chromatographic interferences which affect the resolution, identification, and

quantitation of the components of interest.

Moisture removal from the sample stream prior to sample concentration minimizes these

problems and also allows larger sample volumes to be concentrated, thus providing greater detection

sensitivity. Moisture related problems can be alleviated by various water management methods that

include Nafion® driers (Perma-Pure® Inc., Toms River, NJ), selected condensation at reduced

temperatures, selective temperature desorption, non-cryogenic hydrophobic adsorbent sample

concentration traps, dry gas purging, and selective multibed sorbent trapping. However, some methods

used to remove moisture from the sample may result in the loss of polar VOCs which affects the

TNMOC measurement. This effect is variable, based on drier efficiency and compound selectivity. A

drier that minimizes both polar VOC loss and the potential for introducing contaminants into the system

should be considered.

Nafion® driers are commonly used for ambient air sample drying, and are discussed in

Compendium Method TO-14.4 The Nafion® membrane consists of a hygroscopic copolymer of

tetrafluoroethylene and a perfluorosulfonic acid that is coaxially mounted within a larger Teflon® or

stainless steel tube. The humid sample stream is passed through the membrane tube, allowing water to

pass through the walls by a process called “perevaporation” into a dry nitrogen (N2) or air purge stream

that is counter-currently flowing through the annular space between the membrane and the outer tube. 

Variables that determine the drying efficiency include the surface area of the membrane used, sample

flow rate or sample residence time in the dryer, pressure or vacuum of the sample and purge flow rate,
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temperature, and sample humidity. Depending upon the variables affecting drying efficiency, Nafion®

drier water removal efficiency ranges of 80-95% have been reported.5,6,7

Nafion® drying devices have shown demonstrated losses of certain polar VOCs (amines,

ketones, alcohols, and some ethers).8,9 This reduction in recovery of polar VOCs significantly affects

TNMOC measurements made using a Nafion® drier. Reduction in recovery of polar VOCs by drying

can reduce the TNMOC measurement by 20-30% in typical ambient air samples. Nafion® driers have

also caused rearrangement of several monoterpenes (á-pinene and â-pinene) but have no effect on the

recovery of isoprene.6 Hydrocarbons, chlorinated or fluorinated hydrocarbons, esters, aldehydes, and

some ethers are unaffected by the drier.8,5,10

Recent information11 discusses issues reported when using Nafion® driers shortly after heating

to regenerate the drier by removing residual water vapor and organic compounds, in order to improve

drier efficiency. Heating can significantly affect the sample integrity of the C4- C6 alkenes and cause

compound losses and rearrangement. The degree of loss and rearrangement is dependent on length of

time and the temperature used for drier regeneration, as well as sample humidity. Isoprene may be lost

without reappearance of an equivalent amount of carbon. In the case of C6 alkenes, new, unidentified

peaks may emerge in the retention time area of the original peaks. Heating had no effect on C2-C3

alkenes, C2-C10 alkanes, cycloalkenes, and aromatics. The effects of heating are reversed if the drier is

immediately purged with clean, dry nitrogen or air at a flow rate of 50 cc/minute for at least three hours. 

Heating of Nafion® driers for regeneration should be avoided and is not recommended for PAMS. If

the drier shows a loss of efficiency as determined by recovery of the target compounds in the retention

time standard, the drier should be replaced. To improve efficiency and prevent memory effects, the

drier should be replaced at least seasonally or more frequently as needed. Information on the use of

Nafion® drying devices is presented in EPA Compendium Method TO-144 or EPA Compendium

Method TO-15, entitled Determination of Volatile Organic Compounds (VOCs) in Air CollectedPrepared Canisters and Analyzed by Gas Chromatography/Mass Spectrometry (GC/MS) (see

Appendix A).
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Sample drying using selective condensation at reduced temperatures is performed by

selectively condensing moisture at a reduced temperature from the sample stream during thermal

desorption from the sample concentration trap. This method of drying has been evaluated for

recoveries of compounds having a wide range of volatilities and was found to give good recovery,

reproducibility, and acceptable chromatography when operated at 15EC.12

Studies have been done incorporating the use of controlled vaporization of VOCs off glass

bead traps at ambient and reduced temperatures, non-cryogenic hydrophobic adsorbent sample

concentration traps, dry gas concentration trap purging at selected temperatures,13 and dual sorbent

trapping systems to selectively reduce sample moisture.14,15,16 Techniques for drying an ambient air

sample have been combined, including dry purging after collection on solid sorbent, loss of water by

breakthrough when collecting on solid sorbents, and sample splitting.17,18 These novel approaches to

mitigating the effects of moisture should be evaluated to determine any limitations or negative effects

prior to incorporating them into any VOC measurement system. EPA Method TO-15 (see Appendix

A) has recently been added to the EPA Compendium of Methods for the Determination of Toxic

Organics in Ambient Air and describes different techniques for drying ambient air samples. One of the

main goals of this method was to use drying methods that would not affect polar VOCs as drastically as

the Nafion® driers.

2.3.4 Calibration Standards

Calibrating a GC/FID system to measure VOCs requires two distinctly different types of

calibration mixtures: a primary standard to calibrate detector response for gas chromatographic peak

quantitation (primary calibration standard) and a qualitative mixture of known hydrocarbon compounds

to determine gas chromatographic peak retention times (retention time standard). 
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2.3.4.1 Primary Calibration Standard

The GC/FID response is calibrated in ppbC using a propane primary calibration standard

referenced to a National Institute of Standards and Technology (NIST) Standard. A propane and

benzene mixture is recommended for systems that utilize dual columns or column switching

configurations that use two FIDs. Standard Reference Materials (SRMs) from NIST and Certified

Reference Materials (CRM) from specialty gas suppliers are available for this purpose. NIST currently

has a fifteen component ambient non-methane organics in nitrogen SRM available (SRM 1800) for use

as a reference or primary calibration standard. SRM 1800 contains both propane and benzene. Less

expensive working standards needed for calibration verification over the range of expected

concentrations can be prepared by the user or purchased from a gas supplier, provided they are

periodically referenced to a primary SRM or CRM. The primary calibration standards must be

humidified to reflect the ambient air matrix being analyzed. A procedure for preparing humidified

standards is given in Section 2.3.4.3.1. A procedure for diluting standards is given in Section 2.3.4.3.2. 

Based on the uniform carbon response of the FID to hydrocarbons, the response factor determined

from the propane or benzene primary calibration standard is used to convert area counts into

concentration units (ppbC) for every peak in the chromatogram. 

It is also feasible to incorporate the primary calibration standard into the retention time

standard described below by confirming the concentration of propane and benzene in the retention time

mixture using a primary SRM or CRM.

2.3.4.2 Retention Time Calibration Standard

The retention time calibration standard is a multiple-component mixture containing all target

VOCs at varying concentration levels. The retention time calibration standard is a humidified working

standard used during the initial setup of the GC/FID system to optimize critical peak separation
Section: 2

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parameters and determine individual retention times for each of the target compounds. The retention

time calibration standard is also used during the routine operation of the GC/FID system as a QC

standard for verifying these retention times. 

The response of the GC/FID to selected hydrocarbons in this standard can be used to

monitor system performance and determine when system maintenance or recalibration of the FID using

the primary calibration standard is necessary. Proper operation of the FID according to the

manufacturer’s specifications produces a linear response across the chromatographic range. The

concentration of each compound in the retention time standard need not be directly referenced to the

SRM or CRM (as is the case for the primary calibration standard); rather, the concentration of each

compound can be determined with reasonable accuracy using the FID propane or benzene carbon

response factor from the calibrated GC system. If the propane and benzene in the retention time

mixture are used for primary calibration, then both must be directly referenced to an SRM or CRM. 

To reference a working standard to an SRM or CRM, the analytical system is calibrated with the SRM

or CRM, then the working standard is analyzed against the SRM or CRM calibration. If necessary, a

correction factor for the working standard is calculated.

A multiple-component high pressure mixture containing the target VOCs can be obtained

from a specialty gas supplier. Multiple-component mixtures can also be prepared by the user to

confirm the peak identifications using the retention time standard. The retention time standard must be

humidified for use as discussed in Section 2.3.4.3.

2.3.4.3 Calibration Standard Preparation

The primary propane and benzene calibration standards must be humidified to ensure integrity

and stability. Water vapor has been shown to improve the stability of low pressure VOC gas mixtures

in SUMMA® canisters.
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A stock multiple-component retention time calibration standard containing the compounds of

interest may be prepared at a concentration level approximately 100 times that of the anticipated

working standard concentration. The stock standard can be prepared by blending gravimetrically

weighed aliquots of neat liquids or by adding aliquots of gaseous standards with an inert diluent gas. 

The aliquot of each compound should be introduced through a heated injector assembly into an

evacuated SUMMA® passivated stainless steel canister or other inert container. For the neat liquid

aliquots, the pre-injection and post-injection syringe weights are recorded, and the difference used to

determine the amount of liquid actually transferred to the canister. Following injection of all neat liquid

and gaseous components, the canister is pressurized to at least 2 atmospheres above ambient pressure

with clean, dry N2. Concentrations are calculated based on the amount of compounds and diluent

injected and the final canister pressure, using ideal gas law relationships. 

The stock retention time calibration standard is used to prepare humidified retention time

working standards at the ppbC level. It is not necessary to determine exact component concentrations

in the multi-component mixture because the working retention time standard should not be used to

determine compound specific response factors. However, the approximate concentration of the stock

standard must be known in order to prepare the working retention time standards. Preparation of the

working standards is accomplished by syringe injection of a gaseous aliquot of the stock standard into a

SUMMA® passivated stainless steel canister or other inert canister, and subsequently humidifying for

use.

2.3.4.3.1 Procedure for Humidification

The relative humidity of the air in a canister is an important issue with respect to the storage

stability and recovery of VOCs. A study using SUMMA® passivated canisters under varying 

pressures, relative humidities (RHs) and different VOC residence times has shown that humidification of

canisters improves the recovery of higher molecular weight, less volatile components.19 The study

showed that RH levels above 18% were required for improved compound recovery. Another study
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using SUMMA® passivated canisters showed that a relative humidity of at least 15% was necessary to

ensure complete recovery of 41 chlorinated, brominated and aromatic compounds at concentrations of

2 to 4 ppbv.20 There is some evidence that canisters lined with fused silica (SilcoCanTM, Restek, Inc.

Bellefonte, PA) do not have a minimum requirement for humidity, as do the SUMMA® polished

canisters.21

The relative humidity of air taken from a humidified canister can vary over a significant

range. For example, as shown in Figures B-1 and B-2 of Appendix B (also see Reference 22),22 if

18L of air at 75% RH is sampled, the air subsequently released from the canister will vary from 33%

RH at 30 psig (first sample taken) to 100% RH at 0 psig. This knowledge is important since the

retention times of individual gas chromatographic peaks and the response factors of some types of gas

chromatographic detectors change appreciably with sample humidity. A second concern is the loss of

water-soluble VOCs either to condensed water or to water consolidated in drops on the canister

interior surface. For the example given above, after the canister is filled with 18L of ambient air at 75%

RH, 55% of the water in the fully pressurized canister (30 psig) will be condensed on the canister

interior surface and 45% will be in the gas phase. As sample is removed from the canister the water

adsorbed will be replenished by evaporation of the condensed water. The ratio of H2O in the gas

phase (maintained at the equilibrium vapor pressure by evaporation from the wall) to the amount of air

in the canister will increase and the RH will increase. If the RH of the ambient sample is high enough

(>70% RH) then there will still be condensed water inside the canister even when the canister pressure

is reduced to atmospheric pressure. The reader can gain a better appreciation for the variation in RH

of gas released from a canister by assuming various RH values for ambient air and using Figures B-1

and B-2 in Appendix B. 

In general, the amount of water in a given volume of air at a specified RH is calculated by

using the ideal gas law and a table of water vapor pressures (Table 2-3.)23 The ideal gas law applied

to calculating the amount of water required to humidify 6 liters of air to 100% RH at 21°C and one

atmosphere (zero psig) of pressure is:
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PV nRT (2-1)

n

PV

RT

18.65mm

760mm/atm

0.02454 atm

Where:

n = moles of H2O

V = canister volume, 6 L

 P = vapor pressure of H2O, atm

 T = temperature in K, 21EC + 273 = 294K

 R = ideal gas constant, 0.08205 L-atm/K mole

Converting the vapor pressure of H2O in mm at 21EC to atm:
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Table 2-3. Vapor Pressure of Water at Various Temperatures, mm Hg

Temp

EC 0.0 0.2 0.4 0.6 0.8

10

11

12

13

14

9.209

9.844

10.518

11.231

11.987

9.33

9.976

10.658

11.379

12.144

9.458

10.109

10.799

11.528

12.302

9.585

10.244

10.941

11.680

12.462

9.714

10.380

11.085

11.833

12.624

15

16

17

18

19

12.788

13.634

14.530

15.477

16.477

12.953

13.809

14.715

15.673

16.685

13.121

13.987

14.903

15.871

16.894

13.290

14.166

15.092

16.071

17.105

13.461

14.347

15.284

16.272

17.319

20

21

22

23

24

17.535

18.650

19.827

21.068

22.377

17.753

18.880

20.070

21.234

22.648

17.974

19.113

20.316

21.583

22.922

18.197

19.349

20.565

21.845

23.198

18.422

19.587

20.815

22.110

23.476

25

26

27

28

29

23.756

25.209

26.739

28.349

30.043

24.039

25.509

27.055

28.680

30.392

24.326

25.812

27.374

29.015

30.745

24.617

26.117

27.696

29.354

31.102

24.912

26.426

28.021

29.697

31.461

30

31

32

33

34

31.824

33.695

35.663

37.729

39.898

32.191

34.082

36.068

38.155

40.344

32.561

34.471

36.477

38.584

40.796

32.934

34.864

36.891

39.018

41.251

33.312

35.261

37.308

39.457

41.710

35

36

37

38

39

42.175

44.563

47.067

49.692

52.442

42.644

45.054

47.582

50.231

53.009

43.117

45.549

48.102

50.774

53.580

43.595

46.050

48.627

51.323

54.156

44.078

46.556

49.157

51.879

54.737
Section: 2

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(0.02454 atm)(6L)

(0.08205L atm/K mole)(294K)

n 0.00610 moles of H2O required for 100%RH inthe canister.

0.00610 moles x 0.2 x 18 gm

mole

x 1000 mg

gm

x

1.0 μL

1.0 mg

22.0 μL

Substituting values in the above equation:

To calculate the moles of H2O required for a given relative humidity multiply the value of n by the RH

expressed as a fraction (e.g., 20% = 0.2) and convert to the number of mg of H2O. Express the

number of mg as an equal number of μL since 1.0 mg of water occupies 1.0 μL. Thus:

The number of μL to be added for other sample volumes scales linearly with volume, e.g., for a sample

volume of 18L, multiply the number of μL to be added to 6L by the ratio 18/6 = 3. Hence, the number

of μL to be added to a canister in order to simulate the sampling of 18 L of sample air at 21°C and

20% RH is 66 μL. Figure 2-1 can be used to approximate the amount of water in 1 L of air at

temperatures from -30EC to 40EC at 75% and 100% RH. The values in the figure also scale linearly

with sample volume.

Based on the studies of SUMMA®-passivated canisters, low pressure (30 psig) calibration

standards prepared in canisters ideally should have at least a certain minimum amount of water vapor

($20% relative humidity) to ensure sample integrity but not enough water to cause condensation of

water vapor in the canister (#33% relative humidity). Using Equation 2-1, the amount of liquid water

that must be added to a 6L canister (pressurized to 18 L with dry air) to achieve these conditions at

21°C (70°F) is between 66 and 110 μL. This range will of course
Section:

2

Revision: 1Date: 09/30/98Page: 26 of 207

0

10

20

30

40

-30 -20 -10 0 10 20 30 40

Temperature, EC

100% R.H.

75% R.H.

50

60

Figure 2-1. Water Content of Air at 75% and 100% Relative Humidity Over a Range of Temperatures

Amount of water is expressed as mg/liter. The density of water under standard conditions is 1 g/mL. Thus 1 mg of water occupies a

volume of 1 μL. For a dry six-liter canister sample at 25EC, approximately (23 x 6) μL of water would be need to be added to

achieve 100% relative humidity. Pressure is measured at the exit of the canister.

Figure adapted from Tipler, A. “Water Management in Capillary Gas Chromatographic Air Monitoring Systems.” In Proceedings of

the 1994 U.S. EPA/A&WMA International Symposium: Measurement of Toxic and Related Air Pollutants, Research Triangle Park, NC,

1994.
Section: 2

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vary slightly with the sample temperature (and atmospheric pressure) and should be recalculated for

specific conditions. If excess water is added to the canister, water will condense inside the canister. 

However, the presence of condensed water is not observed to have any effect on the recovery of the

non-polar PAMS target compounds and an excess of water vapor has often been used in practice

when only non-polar compounds are of interest.

A detailed procedure for humidifying non-polar canister calibration standards prepared from

dry stock high-pressure cylinder gases is given below. Two simple methods can be used to humidify

calibration gas: 

C Direct injection of water into the canister before filling with dry calibration gas; and

C Injection of water into the canister through a stainless steel union tee, then filling with

dry calibration gas. 

Both procedures incorporate active temperature controlled heating of the gas transfer line to 90EC. 

Heating ensures that the higher molecular weight compounds are transferred quantitatively and not

adsorbed onto the stainless steel tubing during gas transfer. Heat also keeps the water injected through

the stainless steel tee from condensing on the surfaces.

The following materials are needed: 

Two-stage, non-corrosive, ultra high purity regulator - the regulator must have stainless

steel diaphragms and inert seats and seals to prevent air diffusion and adsorption of low

concentration trace level gases. 

1⁄4-Inch stainless steel tubing and union tee - chromatographic grade stainless steel, fused

silica-lined stainless steel, or nickel are all recommended tubing material choices. A stainless

steel union tee should be used. 

High purity water - HPLC or spectrophotometric-grade high purity water.
Section: 2

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Cord heater - 110 VAC rated for metal contact, with a 300-watt heat capacity minimum.

Temperature controller - active temperature controller operating on a thermocouple

feedback loop.

Figure 2-2 shows the configuration of the materials for direct injection and Figure 2-3 shows

the configuration of the materials for union tee injection.

Direct Injection of Water into the Canister—To humidify calibration standards by

direct injection, follow these steps:

1) Insert an inert 10-mm septum into the 1⁄4-inch nut on top of the canister valve and hand

tighten to seat the septum. 

2) Fill a glass syringe with the desired volume of high purity water for the canister size

used. Open the canister valve slightly while quickly injecting the water, allowing the

vacuum to draw the water into the canister. 

3) Close the valve and remove the cap. The canister is now ready to be filled with dry

calibration gas. Any remaining water droplets in the canister valve will be carried into

the canister by the flow of dry calibration gas.

4) Install the correct CGA type high purity regulator onto the calibration gas cylinder. 

Install a 1⁄4-inch stainless steel male connector to connect the female NPT thread on the

regulator to the 1⁄4-inch stainless steel tubing. Install a length of 1⁄4-inch stainless steel

tubing to connect the canister to the connector fitting on the regulator. 

5) Leak check the entire system by capping the 1⁄4-inch tube outlet and pressurizing the

system to the desired final canister pressure. Close the pressure regulator and monitor

pressure changes. If the pressure drops, check all fitting connections.

6) Loosely attach the canister so that a complete seal is not achieved. With the valve

closed, purge the entire system before use by opening and closing the pressure

regulator at least three times, allowing the excess gas to escape past the incomplete

seal. As an option, a stainless steel toggle shutoff valve may be installed between the

canister and gas transfer tube to vent the purge gas.
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7) Wrap the transfer tubing with a cord heater and plug it into the active temperature

controller. Activate the temperature controller and the system to equilibrate (for 5 to

10 minutes) at a setting of about 90EC.
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o\s\g\morris\3797\fig1-2.eps

Steps 4 through 7 Steps 1 through 3

Syringe filled with 

high purity water

1/4" nut

10 mm septum

1/4" nut

Canister valve

1/4" stainless steel tubing Two stage

high purity

regulator

High pressure

cylinder containing

dry calibration gas

Canister

Figure 2-2. Configuration of Materials to Perform Direct Injections of Water into

the Canister Before Filling with Dry Calibration Gas
Section: 2

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Heated zone

Two stage

high purity

regulator

Syringe filled with

high purity water

Tee with 10mm septum

in 1/4" nut on sideport

Canister valve

Thermocouple

Selectable

temperature

controller

Heater

power

(out)

High pressure

cylinder containing

dry calibration gas

Canister

Figure 2-3. Configuration of Materials to Perform Injection of Water Through a

Heated Tee While Filling with Dry Calibration Gas
Section: 2

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8) Tighten the canister nut and set the delivery pressure gauge on the regulator to the

desired final canister pressure. Fill the canister and allow it to sit overnight for static

equilibration.

Union Tee Injection of Water into the Canister—To humidify calibration standards

in canisters using a stainless steel union tee, follow these steps:

1) Install the correct CGA type high purity regulator onto the calibration gas cylinder. 

Install a 1⁄4-inch stainless steel male connector to connect the female NPT thread on the

regulator to the 1⁄4-inch stainless steel tubing.

2) Install a length of 1⁄4-inch stainless steel tubing to connect the canister to the connector

fitting on the regulator. Install a 1⁄4-inch stainless steel union tee at the end of the tubing

and place an inert 10-mm septum in the 1⁄4-inch nut on the side of the tee. Hand tighten

the nut to seat the septum.

3) Leak check the entire system by capping the 1⁄4-inch union tee outlet and pressurizing

the system to the desired final canister pressure. Close the pressure regulator and

monitor pressure changes. If the pressure drops, check all fitting connections.

4) Loosely attach the canister so that a complete seal is not achieved. With the valve

closed, purge the entire system before use three times by opening and closing the

pressure regulator at least three times, allowing the excess gas to escape past the

incomplete seal. As an option, a stainless steel toggle shutoff valve may be installed

between the canister and gas transfer tube to vent the purge gas.

5) Tighten the canister nut and wrap the transfer line and union tee with the cord heater

and plug it into the active temperature controller. Activate the temperature controller

and the system to equilibrate (for 5 to 10 minutes) at a setting of about 90EC.

6) Fill a glass syringe with the desired volume of high purity water for the canister size

used. Open the canister valve slightly, insert the syringe into the septum and quickly

inject the water. 

7) Set the delivery pressure gauge on the regulator to the desired final delivery pressure

and open the canister valve completely to allow the gas to fill the canister to the desired

pressure.
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8) When the final pressure is achieved, close the toggle valve, turn off the temperature

controller, and close the regulator. Allow the canister valve to cool before closing. 

The valve may become hot due to thermal conductivity. Note: Do not close the

canister valve when it is hot because the Viton® ring will be distorted and the

valve damaged.

9) Allow the canister to sit overnight for static equilibration.

10) Calculate the volume of water to be added using equation 2-1.

2.3.4.3.2 Calibration Standard Dilution Procedure

In order to prepare multiple concentration levels from the primary calibration standard for

system calibration, the calibration gas may be diluted according to the basic procedure. This dilution

procedure involves volumetric dilution based on pressure and is provided here as a simplified, proven

means of accurately preparing diluted calibration standards. Calibration gases may also be diluted by

dynamic flow dilution, or by using commercially available dilution systems.

The primary calibration standard is initially humidified as described in Section 2.3.4.3.1. The

standard is diluted with ultra high purity nitrogen. Stainless steel fittings and chromatographic grade

stainless steel tubing are used for all connecting lines and fittings. The primary calibration gas is

transferred into a canister for dilution. The calibration gas must be humidified as described in Section

2.3.4.3.1. The initial pressure of the canister is measured. The canister is then diluted to the desired

pressure and the final canister pressure is measured. Equilibration and static mixing are allowed to take

place for at least 18 hours prior to analysis. The calculated dilution factor is used to determine the final

concentration value for the calibration standard.

Dilution equipment is commercially available; a dilution apparatus can also be assembled in

the laboratory. The dilution apparatus shown in Figure 2-4 requires the materials described below for

assembly.
Section: 2

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Section: 2

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Pressure

regulator

N2

High

pressure

cylinder

N2

Source

shutoff

valve

Flow

control

valve

1/4” Stainless steel tubing

Bellows

vacuum

isolation

valve

High

vacuum

pump

High 

vacuum

pump 

power

Temperature controlled

1/8” stainless steel tubing

Canister

bellows

valve

Summa ®

canister

High

precision

absolute

pressure

gauge

Thermocouple

Temperature controller power out

High vacuum

pump power 

switch

Temperature

controller

power switch

Selectable

Temperature

controller

System

power

IN

Chassis

o:\s\g\morris\3797\pams\chassis.ppt

Figure 2-4. Calibration Standard Dilution System
Section: 2

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Ultra high purity grade nitrogen or air - 99.9999% purity or equivalent, hydrocarbon

free.

Hydrocarbon trap - available from chromatographic supply vendors to remove trace

impurities from high pressure cylinder gases.

1⁄4-inch and c -inch stainless steel tubing and union tees - chromatographic grade

stainless steel, fused silica-lined stainless steel, or nickel are all recommended tubing material

choices. 

Cord heater - 110 VAC rated for metal contact, with a 300-watt heat capacity minimum.

Temperature controller - active temperature controller operating on a thermocouple

feedback loop.

N2 source shutoff valve - a stainless steel bellows assembly designed valve. When the

shutoff valve is closed, the dilution gas cylinder and regulator are isolated during purge

evacuation of the system. When the shutoff valve is opened, the valve is used to apply

dilution gas to the system for controlled introduction.

Flow control valve - a stainless steel micro-metering needle designed valve, used to

introduce dilution gas into the system at a controlled flow rate.

Bellows vacuum isolation valve - a stainless steel bellows assembly designed valve. When

closed, the bellows vacuum valve isolates the high vacuum pump from the system. When

opened, the valve is used to apply vacuum, from the high vacuum pump, to the system.

High precision absolute pressure gauge - a compound pressure gauge used to measure

the pressure in the system and the calibration canister in both positive and negative pressure

modes. The pressure gauge must be able to measure pressure from 40 psig to 5 mm Hg

absolute.

High vacuum pump - An oil-less diaphragm pump used to apply vacuum to the system. 

The pump must be able to create vacuum to 5 mm Hg absolute.

Once a dilution system is available, the basic steps for standard dilution are described below:

1) Turn the temperature controller on and allow the system to equilibrate at 100E C. 

Open the main dilution gas cylinder valve. Set the delivery pressure using the second

gauge on the pressure regulator to approximately 10 pounds per square inch gauge
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(psig) pressure over the desired final canister pressure using the pressure control knob

on the regulator.

2) Zero the absolute pressure gauge by adjusting to zero. 

3) Connect the calibration gas canister to be diluted to the dilution apparatus.

4) Turn on the high vacuum pump and the active temperature controller.

5) With the canister bellows valve and the N2 source shut-off valve closed, open the

bellows vacuum isolation valve. Allow vacuum throughout the system to stabilize at the

lowest vacuum achievable by the pump to purge all residual gas from the system.

6) Once stabilized, close the bellows vacuum isolation valve. Open the canister bellows

valve and allow the pressure in the system to equilibrate to the initial canister pressure.

7) Measure the initial pressure of the canister from the absolute pressure gauge. Record

the initial canister pressure.

8) Close the flow control valve and open the N2 source shut-off valve. Slowly open the

flow control valve while monitoring the absolute pressure gauge. The slower the

canister is filled, the easier it is to meet the final target pressure.

9) Continue to fill the canister until the final set point is achieved. Allow the absolute

pressure gauge needle to equilibrate before reading the final pressure of the canister.

10) Once the canister has filled to the desired pressure, close the flow control valve, the N2

source shut-off valve, and lastly the canister bellows valve. Turn off the vacuum pump

and the active temperature controller.

11) Disconnect the canister, close the main valve on the dilution gas cylinder.

12) The canister should sit for at least 18 hours before analysis or further dilutions are

performed to allow for static mixing and equilibration.

Calculations—The following calculations are used to determine the target final pressure 

(Equation 2-2) and dilution factor (Equation 2-3). The calculations do not account for barometric

pressure and temperature changes, which are expected to be negligible. 
Section: 2

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Pfa

Ci(Pi+ 14.696)

Cf

(2-2)

Pfa

30 ppbC (5 psig + 14.696 psi)

15 ppbC

39.39 psia

DF

Pia

Pfa

(2-3)

where:

Pfa = Final Diluted Absolute Pressure, psia

Ci = Initial Concentration, ppbC

Pi = Initial Gauge Pressure, psig

Cf = Final or Target Diluted Concentration, ppbC

 14.696 = Atmospheric Pressure, psi

Example: 

To dilute a 30 ppbC calibration standard in a canister with an original pressure of 5 psig

(19.696 psia) to a final concentration of 15 ppbC, what is the target diluted pressure?

To convert psia to psig (the measured value), subtract 14.696:

39.39 psia - 14.696 = 24.70 psig

where:
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Pia Pi+ 14.696

5 psig + 14.696

19.696 psia

Pfa Pf+ 14.696

24.7 psig + 14.696

39.40 psia

DF

Pia

Pfa

19.696

39.40

0.499

Standard Concentration Ci* DF

0.499 * 30 ppbC

14.97 ppbC

Pi = Initial Gauge Pressure, psig

Pia = Initial Absolute Pressure, psia = Pi + 14.696

Pf = Final Gauge Pressure, psig

Pfa = Pf + 14.696

DF = Dilution Factor

Pfa = Final Absolute Pressure, psia

Example: 

Continuing with the example above, what is the dilution factor for the 30 ppbC standard

which was diluted to a final pressure of 24.70 psig? What is the final concentration of the standard?
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where:

Ci = Initial concentration, ppbC

2.3.5 Column Configurations

The chromatographic column configurations generally used for VOC monitoring programs

incorporate single-column, single-detector, or dual-column, dual-detector applications. The simplest

analytical column configuration involves the use of a single column with a single FID. However, this

configuration imposes limitations on the overall separation of the selected target VOCs. Analyzing the

full range of C2 through C12 target hydrocarbons using a single analytical column may result in less than

optimal separation for either the light or heavy hydrocarbons, depending on the analytical column

chosen. For example, to improve resolution of the C2 through C4 hydrocarbons, a thick liquid-phase

fused silica or Porous Layer Open Tubular (PLOT) column at sub-ambient column oven temperatures

may be desirable. However, PLOT columns generally result in less than optimal resolution of the C5

through C12 hydrocarbons. Likewise, PLOT columns increase retention times of the C10 through C12

hydrocarbons and require longer sample analysis time. If the heavier hydrocarbons are not eluted from

the thick phase or PLOT columns, the TNMOC measurement may be affected, and carryover and

ghost peaks may result.

In order to improve the separation characteristics for the light hydrocarbons (C2 through C4)

as well as the heavier hydrocarbons (C5 through C12), a dual-column, dual-detector configuration

should be considered. In this case, two columns can be judiciously selected to provide optimal

separation of both light and heavy hydrocarbons without sub-ambient column oven temperatures. 

Because both columns are generally contained in one gas chromatographic oven for automated

applications, columns must be selected that will provide the desired separation with a single GC oven

temperature program. Dual column systems may be configured with the analytical columns in parallel,
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operating either concurrently or sequentially. Pre-column and post-column switching valves and the

Deans®24 switch have been used to accommodate these dual-column configurations. 

2.3.6 Column Selection

Column selection for analysis of the target VOCs is dictated by the target compound

resolution requirements and other practical and cost considerations, such as the need to minimize

cryogen consumption and total sample analysis time. Selecting columns that will provide the desired

separation of the C2 through C4 hydrocarbons without cooling the column oven to sub-ambient

temperature decreases cryogen consumption significantly. 

Several columns suitable for either single- or dual-column applications are discussed below. 

The columns described have been used in either a single- or dual-column configuration in conjunction

with a single- or dual-FID for separation of the C2 through C12 hydrocarbons. The column conditions

described are recommendations provided from laboratory applications or conditions determined by the

manufacturer to provide adequate separation of the VOCs of interest. However, these conditions must

be evaluated and optimized to verify acceptable peak resolution prior to use.

The C4 through C12 hydrocarbons may be resolved using a 0.32 or 0.22 millimeter (mm)

inside diameter (I.D.), 50 meter (m) long SGE, Incorporated BP1 fused silica column with a

1-micrometer dimethyl polysiloxane coating. This column generally does not provide adequate

separation of the C2 and C3 hydrocarbons even at sub-ambient column oven temperatures. However,

the column can provide adequate separation of the C2 and C3 hydrocarbons if the coating is 3 μm thick

and Electronic Pressure Control is used along with sub-ambient column oven temperatures. Under

these conditions, a single column can be used for all of the target hydrocarbons. Other compatible

columns include the J&W DBTM-1, Hewlett-Packard HP-1, Chrompack CP-SIL 5 CB, Restek RTx1, and the Supelco SPB-1. The DBTM-1 column has been historically and extensively used in ambient

air applications. The SGE BP1 column can be used in conjunction with a 0.32 mm I.D., 50 m, Porous
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Layer Open Tubular (PLOT) fused silica analytical column with a 5-micrometer Hewlett-Packard

Al2O3/KCl or Al2O3/Na2SO4 coating. The Al2O3/Na2SO4 column is slightly more polar than the

Al2O3/KCl and provides optimal resolution of the C4 hydrocarbons. The PLOT column provides

acceptable light hydrocarbon separation under the same column oven temperature program conditions

used for the DBTM-1 column but does not provide complete separation and elution of C9 through C12

hydrocarbons. Other compatible columns include the J&W GS-AluminaTM Al2O3/KCl and

Al2O3/Na2SO4. However, alumina PLOT columns from different manufacturers may not be directly

interchangeable and may require some method modification due to the variation in column selectivity.

Because the alumina layer is active, PLOT Al2O3 analytical columns are very susceptible to

polar compounds such as water, which causes column deactivation and shifting of peak retention times. 

Moisture and other polar compounds must be removed from the sample stream using a membrane drier

or other drying device. If manual sample analysis using a single PLOT Al2O3 column is performed,

sequential analyses or the use of separate GC systems may be considered to optimize and obtain

complete C2 through C12 separation and elution. Figures 2-5 and 2-6 are example chromatograms of

retention time calibration standards containing the PAMS target compounds as eluted from the

0.32 mm I.D., 50 m, 5 micrometer, Al2O3/Na2SO4 PLOT and 0.22 mm I.D., 50 m, 1 micrometer,

SGE, Incorporated BP1 columns. Since these columns have been successfully used by others, users

should give primary consideration to these column types during their column selection process. Figure

2-7 shows a representative ambient air sample analyzed on a PLOT column; Figure 2-8 shows the

same sample analyzed on a BP1 column. Peaks are numbered on the chromatograms, identified peaks

are listed in Table 2-4.

Stationary phase selectivity is neither completely understood nor easily explained. Using a

simplification, selectivity can be considered the ability of the stationary phase to differentiate between

two compounds by virtue of a difference in their chemical and/or physical properties. Stationary phase

and solute factors such as polarizability, solubility, magnitude of dipoles and hydrogen bonding influence

selectivity. In many cases, more than one factor will be
Column: HP Al2O3

/Na2SO4

50m x 0.32mm x 5μm

Carrier: Helium, ~2.5ml/min

Initial Temp: 45oC, 15 minutes

Rate 1: 5oC/min

Temp 2: 170oC

Rate 2: 15oC/min

Final Temp: 200o C, 6 minutes

Peak # AIRS Code Compound Name

12 43221 Isopentane

13 43220 n-Pentane

14 43226 trans-2-Pentene

15 43224 1-Pentene

16 43227 cis-2-Pentene

17 43244 2, 2-Dimethylbutane

18 43284 2, 3-Dimethylbutane

19 43263 2-Methylpentane

20 43230 3-Methylpentane

21 43243 Isoprene

22 43246 2-Methyl-1-Pentene

Peak # AIRS Code Compound Name

1 43202 Ethane

2 43203 Ethylene

3 43204 Propane

4 43205 Propylene

5 43214 Isobutane

6 43212 n-Butane

7 43206 Acetylene

8 43216 trans-2-Butene

9 43280 1-Butene

10 43217 cis-2-Butene

11 43242 Cyclopentane

8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

Time (minutes)

o:s/g/morr/3797/pams/compoun1.ppt

Figure 2-5. Example Chromatogram for the PAMS Target Compounds from the PLOT Analytical Column

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2

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Column: SGE, Inc. BPI, 

50m x 0.22mm x 1μm

Carrier: Helium, ~2.5ml/min

Initial Temp: 45oC, 15 minutes

Rate 1: 5oC/min.

Temp 2: 170oC

Rate 2: 15oC/min.

Final Temp: 200oC, 6 minutes

Peak # AIRS Code Compound Name

18 45203 Ethylbenzene

19 45109 m/p-Xylene

20 45220 Styrene

21 45204 O-Xylene

22 43235 n-Nonane

23 45210 Isopropylbenzene

24 45209 n-Propylbenzene

25 45212 m-Ethyltoluene

26 45213 p-Ethyltoluene

27 45207 1, 3, 5-Trimethylbenzene

28 45211 o-Ethyltoluene

29 45208 1, 2, 4-Trimethylbenzene

30 43238 n - Decane

31 45225 1, 2, 3-Trimethylbenzene

32 45218 m-Diethylbenzene

33 45219 p-Diethylbenzene

34 43954 n-Undecane

Peak # AIRS Code Compound Name

1 43231 Hexane

2 N/A Unknown

3 43262 Methylcyclopentane

4 43247 2, 4-Dimethylpentane

5 45201 Benzene

6 43248 Cyclohexane

7 43263 2-Methylhexane

8 43291 2, 3-Dimethylpentane

9 43249 3-Methylhexane

10 43250 2, 2, 4-Trimethylpentane

11 43232 n-Heptane

12 43261 Methylcyclohexane

13 43252 2, 3, 4-Trimethylpentane

14 45202 Toluene

15 43960 2-Methylheptane

16 43253 3-Methylheptane

17 43233 n-Octane

14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46

2

1

3

4

5

6

7

8

9

1011

12

13

14

15

16 17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33 34

Time (minutes)

o:s/g/morr/3797/pams/compoun2.ppt

Figure 2-6. Example Chromatogram for the PAMS Target Compounds from the BP1 Analytical Column

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Figure 2-7. Representative Ambient Air Sample Analyzed on a PLOT Column
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Figure 2-8. Representative Ambient Air Sample (same as Figure 2-6) Analyzed on a BP-1 Column
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Table 2-4. Peak Identifications, Ambient Air Sample

PLOT Column BP1 Column

Peak Number Peak Identification Peak Number Peak Identification

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

ethane

unidentified

ethene

propane

propylene

isobutane

n-butane

acetylene

trans-2-butene

1-butene

unidentified

cis-2-butene

cyclopentane

isopentane

trans-2-pentene

1-pentene

cis-2-pentene

2,2-dimethylbutane

2,3-dimethylbutane

2-methylpentane

3-methylpentane

isoprene

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

hexane

methylcyclopentane

2,4-dimethylpentane

benzene

cyclohexane

2-methylhexane

2,3-dimethylpentane

3-methylhexane

2,2,4-trimethylpentane

n-heptane

methylcyclohexane

2,3,4-trimethylpentane

toluene

2-methylheptane

3-methylheptane

n-octane

ethylbenzene

m/p-xylene

styrene

o-xylene

n-nonane

isopropylbenzene

n-propylbenzene

m-ethyltoluene

p-ethyltoluene

1,3,5-trimethylbenzene

o-ethyltoluene

1,2,4-trimethylbenzene

n-decane

1,2,3-trimethylbenzene

m-diethylbenzene

p-diethylbenzene

n-undecane
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significant, so there will be multiple selectivity influences. Unfortunately, information about most

compound characteristics, such as the strength of hydrogen bonding or dipoles, is not readily available

or easy to determine. This lack of physical data makes it difficult to accurately predict and explain the

separation obtained for a particular column and set of compounds. Some generalizations, however, can

be made. The DB1 nonpolar phase (dimethyl polysiloxane) is the most nonpolar siloxane stationary

phase available. In most cases, compounds will elute from this column primarily in order of increasing

boiling point. However, both vapor pressure and solubility in the stationary phase influence the exact

elution order. 

PLOT chromatography is accomplished through the gas/solid adsorption interactions between

the solutes and the solid adsorbent coated on the column tubing wall. The aluminum oxide (Al2O3)

surface is deactivated using KCl or Na2SO4. Stationary phase polarity is based on the relative

retention of saturated and unsaturated hydrocarbons. The more polar column will result in unsaturated

compounds being more retained relative to the saturated hydrocarbons. The Na2SO4 deactivation of

the Al2O3 results in a slightly more polar column than the KCl deactivation. 

There are some alternative columns that can be used to separate C2 through C12

hydrocarbons for both single- or dual-column approaches. The column selection process should be

based on the capability of the column to separate the VOCs listed in Table 2-1 in conjunction with

desired overall sample analysis time and cryogen use. The manufacturer-recommended conditions and

carrier gas flow rates should be evaluated and optimized to verify acceptable peak resolution prior to

use. When choosing alternate columns, the user should consult directly with the analytical column

manufacturer for advice regarding column characteristics, optimum gas chromatographic oven

temperature programs, carrier gas flow rates, and other operational considerations.

The following columns are alternatives for single-column, C2 through C4 hydrocarbon

separation and may require sub-ambient temperature conditions to achieve adequate separation:
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1. J&W DBTM-1 with a 5-micron dimethyl siloxane phase thickness, an internal diameter

of 0.32 mm, and a length of 60 m. The recommended oven temperature program is -

60EC for 2 minutes then to 180EC at 8EC per minute. The final oven temperature is

maintained for 13 minutes for a total analytical run time of 45 minutes.

2. J&W GS-Q® fused silica PLOT capillary column with an internal diameter of 0.53 mm

and a length of 30 m. The recommended oven temperature program is 40EC for

4 minutes to 200EC at 10EC per minute. The final oven temperature is maintained for

5 minutes for a total analytical run time of 25 minutes. The GS-Q® column is not

affected by water.

The following columns are alternatives for single-column, C5 through C12 hydrocarbon

separation and may require sub-ambient oven temperature conditions to achieve adequate separation:

1. Restek® RTx-502.2 capillary fused silica column with a 3-micron phase thickness, an

internal diameter of 0.53 mm, and a length of 105 m. The recommended GC oven

temperature program is 35EC for 10 minutes to 200EC at 4EC per minute. The final

oven temperature is maintained for 7 minutes, which results in a total analytical run time

of 58 minutes. This column is capable of separating the C4 through C12 hydrocarbons

without the need for sub-ambient column oven temperatures.

2. J&W DBTM-624 capillary fused silica column with a 3-micron stationary phase

thickness, an internal diameter of 0.53 mm, and a length of 75 m. The recommended

oven temperature program is 35EC for 8 minutes to 200EC at 10EC per minute. The

final temperature of 200EC is maintained for 3 minutes, which results in a total analytical

run time of 27.5 minutes.

3. Restek® RTX-1 capillary fused silica column with a 3-micron dimethylsiloxane phase

thickness and an internal diameter of 0.32 mm and a length of 60 m. The

recommended oven temperature program is -25EC for 4 minutes then to 175EC at

4EC per minute, then to 220EC at 22EC per minute. The final oven temperature is

maintained for 5 minutes for a total run time of about 60 minutes. The Electronic

Pressure Control program is 18.3 psi for 5 minutes then to 37.5 psi at 0.35 psi/minute. 

Total program time is about 61 minutes.

A combination of these light and heavy hydrocarbon separation columns may be used to

accommodate dual-column approaches.
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2.3.7 Pre-measurement Chromatographic System Verification

Prior to making speciated VOC measurements using an automated GC system, the level of

system operation must be thoroughly documented. Information collected during this process is

important in characterizing the system operation and establishing a baseline for performance. The

information from the pre-measurement system verification is used to determine system specific target

analyte retention times, relative retention times, identification of co-eluting compounds and matrix

effects, internal standard retention times, interferences, and detection limits.

2.3.7.1 Retention Times and Relative Retention Times

The rigorous sampling frequency requirements and large data sets associated with PAMS

require the use of an automated GC system with FID, and presume the commercial availability of such

systems. These systems must rely on the practical use of retention times and relative retention times for

qualitative peak identification. Commercial GC/FID systems are designed to provide stable system

parameters that ensure adequate peak identification based on the use of retention times.

Retention time is the time at which the component elutes from the analytical column and

reaches the detection device. The retention of a compound will be determined by its distribution

equilibrium between the stationary and mobile phases, i.e., the distribution ratio. Retention time units

are typically expressed in minutes and this time is specific to the conditions of the GC system used.

When dealing with complex target analyte lists, as in the case of PAMS measurements,

preparing multiple retention time standards that contain 10-15 target analytes that are of known

retention order and well separated by retention time will simplify peak identification and retention time

assignment. These standards must be analyzed to determine specific retention times for the target

compounds and resolve chromatographic issues relative to the instrument conditions, analytical

column(s), and chromatographic conditions used. Retention time is widely applied in chromatography
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and based on the information gathered from standards. When the retention times for a GC system are

verified, it is important for the system to be operated for a period to allow equilibration and retention

time stabilization to occur. Several standards should be analyzed over a period of days to assess

retention time variability and system stability. The retention time variability is used to establish retention

time windows for each component. It is very important that standards be prepared in humidified air, at

a relative humidity similar to the samples being analyzed.

The identification of sample components is determined by matching the retention times of the

components in the standard with those in the sample. This procedure provides the chromatographer

with a certain degree of confidence that the correct peak has been accurately identified. Peak

identification by retention time is adequate for the PAMS network requirements. A compound’s

retention time is characteristic, though not unique. It is, therefore, possible for other compounds to

have the same retention time. The presence of co-eluting compounds or missed peak identifications

cannot be completely excluded. Periodic confirmation of peak identification and quantification using

more definitive techniques, such as GC/MS, is encouraged.

Retention times are typically stable and reproducible, but they are subject to system

variability. To account for any retention time variations, relative retention time (RRT) can be used to

aid in assigning peak identifications. Many commercial GC systems incorporate the use of relative

retention times for peak identification in their data acquisition and processing software. On most

commercial GC systems, the use of RRT for peak identification is easy to implement. An adjusted or

relative retention time can be determined by using both reference or internal standard peaks. Reference

peaks are those components of the sample that are typically present in the sample matrix (reference

peaks of opportunity). Internal standard peaks are components subsequently added to the sample that

are uncommon to the sample matrix. The relative retention time of a target compound (a), as compared

with a reference compound (b), may be calculated as:
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RRT

RTa

RTb

(2-4)

where:

RTa = retention time of the target compound

RTb = retention time of the reference peak

The relative retention time of a compound determined in this manner will vary with temperature and the

analytical column stationary phase, but should otherwise be independent of other analytical conditions. 

The relative retention time method of peak identification works well when the target compound elutes

relatively close to the reference peak used and retention time shifting is linear. The use of reference

peaks in several retention time windows is only recommended to compensate for retention time shifting

that is not linear. The use of too many reference peaks may actually compromise the ability of the data

system to adequately identify the target peaks consistently.

A retention time reference peak should be chosen that;

C Is always or typically present in the sample matrix;

C Is in the same general retention time area or carbon number range of the

chromatogram;

C Shows chromatographic behavior similar to target components (sharp peak shape); and

C Is well separated from other components in the sample matrix.

Suggested retention time reference peaks include propane, toluene, benzene, and butane, or other

compounds appropriate to the individual PAMS site.
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2.3.7.2 Internal Standards

When GC analysis is performed on a continuous basis at an often unattended or remote site,

fluctuations in ambient temperature and other factors can cause variations in instrument performance

and chromatographic retention times. Changes in ambient conditions can cause small changes or

variations in carrier gas flow rate, column temperature, detector response, sample injection volumes,

and sample moisture content. Use of internal standards can help to minimize the influence of GC

system variability. Internal standards are often also used as reference peaks for determining relative

retention times.

The internal standard should be added to the cryofocusing or adsorbent sample collection

system, concurrent with sample collection, to minimize the effects of the sample matrix. The chief

difficulty in using internal standards for VOC analysis lies in finding an internal standard that does not

interfere with the sample constituents. Characteristics that must be considered when choosing a suitable

internal standard include:

C Components that are uncommon in ambient air;

C Ease and reproducibility in handling and introducing into the GC system;

C Similar in chemical and physical properties to those compounds being analyzed;

C Moderate volatility and low vapor pressure comparable to the expected retention times

and concentrations of the sample hydrocarbons;

C Does not interfere with the measurement method;

C Complete resolution from all other components present in the sample;

C Stable under the conditions and method used; and

C Does not react with components of the measurement system.
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Perfluorotoluene (PFT) is a compound that meets these characteristics and has been used as an internal

standard for air monitoring programs.

Separation of the internal standard compound from other compounds normally found in the

sample must be accomplished using the measurement system and methods implemented by the user to

accomplish sample analyses. Typical ambient air samples are very complex and contain numerous

components. Verification of the internal standard performance and retention time characteristics using

the GC system chosen must be determined using actual ambient air samples. A suitable internal

standard can be analyzed concurrently with the sample to adjust for variations in retention time and

detector response.

2.3.7.3 Identification of Co-Eluting Compounds and Matrix Effects

Another important part of pre-measurement chromatographic system verification is the

determination and effect of possible co-eluting compounds and other sample matrix effects on the ability

to find reference peaks, make peak identification, and ultimately to quantitate target analytes.

Blank samples that contain humidified zero air should be analyzed to establish the GC system

background and determine the level of contamination or artifacts. Blank or zero air samples should not

contain the target VOCs at a concentration greater than the detection limit. Any significant levels of

contamination or artifacts that interfere with the retention times of target analytes must be addressed or

documented prior to sample analysis. Information from the analysis of standards containing target

analytes can then be used to determine where co-eluting compounds may occur. Co-elution issues can

be resolved by optimizing the chromatographic conditions of the system, such as carrier gas linear

velocity and column oven temperature.

Further information regarding co-eluting compounds in samples not identified by zero air

analyses may be obtained using GC/MS. When used under similar conditions (column type,
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temperature program, etc.), the GC/MS provides valuable information to aid the user in confirming

peak identification and determining the presence of co-eluting compounds and other unknowns. When

GC/MS is used for confirmation, it is important to ensure that the system sensitivity or detection limits

are equivalent to the O3 precursor GC/FID system being used.

2.3.7.4 Detection Limits

The development of methods to measure trace levels of organic compounds in ambient air

and the need for the ability to measure extremely low concentration levels for risk assessment purposes

requires that the analytical system detection limits for the target compounds be established for the

analytical system used. The analytical detection limit must meet the measurement quality objectives

given in Section 2.8. The detection limit is one of the most important performance characteristics of an

analytical system. The GC system detection limit should not be determined until a complete, specific,

and well defined analytical method has been developed. All sample processing steps used in the

analytical method must be included in the experimental determination of the detection limit. Refer to

Section 2.8 for guidance on the approach to establishing VOC detection limits for PAMS. If the

analytical method detection limit does not meet the quality objectives, the sensitivity of the GC system

and methodology used may not be adequate and should be re-evaluated and improved prior to use for

O3 precursor monitoring programs.

2.4 Automated Method for Collecting and Analyzing Volatile Organic

Compound Ozone Precursor Samples

The minimum monitoring network requirements for enhanced O3 monitoring are described in

Section 4.4 of 40 CFR Part 58, Subpart E, Appendix D, and are also discussed in Section 2.1 of this

document. The rigorous sampling frequency requirements of enhanced O3 monitoring (e.g., eight 3-

hour samples every day during the monitoring period) makes automated GC methodology a viable,

cost-effective approach for obtaining VOC measurements at all sites within a network. An automated
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GC system offers an additional advantage in its inherent capability to provide short-term (e.g., 1-hour)

measurements on a continuous basis for long time intervals. 

The following description of automated methodology is based on currently available

commercial automated GC systems and is described in general terms. The intent is to provide guidance

on the configuration and operation of automated GC systems, not to serve as a Standard Operating

Procedure (SOP). Alternative approaches using custom fabricated automated systems are acceptable. 

This guidance should be used to define equipment specifications and prepare system specific SOPs

consistent with the 40 CFR Part 58 enhanced O3 monitoring requirements. The users must recognize

that they are responsible for optimization and characterization of the critical parameters for their specific

GC system (consistent with the manufacturers’ instructions, if applicable). 

The GC system must be capable of automated sample collection, analysis, and data

acquisition on site and must be housed in a temperature-controlled shelter. The primary components of

an automated GC are a sample introduction system, sample conditioning system (for moisture removal),

sample concentration system (for sample enrichment), cryofocusing trap (as an option for improving

peak shape and resolution), gas chromatograph with FID(s), and a data acquisition and processing

system. Commercially available systems incorporate many variations of the primary components of an

automated GC system. 

The purpose of Section 2.4 is to describe the sample collection, sample analysis, system

operation, system calibration, and system specifications for an automated GC system. The sample

probe and manifold, sample introduction, sample conditioning, and sample concentration systems are

discussed in Sample Collection, Section 2.4.1. Sample cryofocusing, gas chromatography, and data

acquisition and processing are discussed in Sample Analysis, Section 2.4.2. This guidance should be

used to define automated GC specifications for procurement and to develop and implement a network

monitoring program consistent with the 40 CFR Part 58 enhanced O3 monitoring requirements.
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2.4.1 Sample Collection

Samples collected for automated analysis should represent a time-integrated average for the

required sampling period. In the case where an integrating canister is used to collect the sample, the

canister should be filled at a constant flow rate over the full integration period minus the time required to

transfer a sample to the primary trap and purge and evacuate the canister. In the case where the

sample is collected directly onto the primary concentration trap, the sample should be collected at a

constant flow rate for the full integration period minus the time required to desorb the sample onto a

secondary trap or onto the analytical column and perform system operations to accommodate the next

sample collection. The minimal sample integration time required to constitute a 1-hour sample is 40

minutes. Additional provisions must be made to meet the 24-hour sample requirement. A manual

approach to 24-hour sample collection and analysis is discussed in Section 2.5.

The O3 precursor compounds are collected from a sample manifold with a probe and

introduced into the automated GC system. Water may be removed from the sample stream as

discussed in Section 2.3.3 and then the VOCs concentrated onto a primary sample collection trap. 

The concentrated sample is thermally desorbed onto a secondary cryofocusing trap (optional) or onto

the head of the cooled GC column to focus the desorbed sample into a small volume or “plug.” The

sample volume is then desorbed for analysis by the GC/FID system.

2.4.1.1 Sample Probe and Manifold

A sample probe and manifold assembly should be used to provide a representative air sample

for collection and subsequent analysis. Sample probe and manifold assemblies are commercially

available or can be custom fabricated. Examples of typical sample probe and manifold assemblies are

presented below. If automated calibration techniques that periodically flood the manifold with

calibration standards are to be applied for the criteria pollutants, a separate manifold would be required

to support the VOC and carbonyl components of the PAMS program.
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The sample probe is constructed of glass that is approximately 1 inch in outside diameter

(O.D.). The inlet of the sample probe is configured with an inverted funnel, approximately 4 inches

O.D. The sample manifold is constructed of glass, approximately 1 and 1⁄2 inches O.D. The manifold

has ports used for sample distribution. The number of ports located on the manifold must be equal to

or greater than the total number of monitoring systems to which sample will be delivered. To reduce

the potential for bias, the port nearest to the inlet of the manifold should be reserved for VOC sampling.

Teflon® bushings are used to connect sample lines to the manifold. Because the manifold and

ports are constructed of glass, care must be taken to not place excessive stress on the assembly to

avoid breakage. For VOC sampling, the sample lines should be constructed of 1/8 inch O.D. stainless

steel tubing. The 1/8 inch tubing is flexible and will accommodate the flow rates typically associated

with VOC sample collection. The sample lines should be kept as short as possible to reduce sample

transfer time.

A blower and bleed adapter are located at the exit end of the sample manifold. The blower is

used to pull sample air through the probe and manifold and the bleed adapter is used to control the rate

at which the sample air is pulled through the manifold. An excess of sample air is pulled through the

sample probe and manifold to prevent back diffusion of room air into the manifold and to ensure that

the sample air is representative of outside ambient air. Sample air flow through the sample probe and

manifold should be at least two times greater than the total air flow being removed for collection and

analysis by all systems on the manifold.

The vertical placement of the sample probe and inlet funnel should be at a height of 3 to 15

meters above ground level. Because the O3 monitoring requirements involve multiple-pollutant

measurements, this range serves as a practical compromise for probe position. In addition, the probe

inlet should be positioned more than 1 meter, both vertically and horizontally, away from the housing

structure. The probe inlet should be positioned away from nearby obstructions such as a forest canopy

or building. The vertical distance between the probe inlet and any obstacle should be a least two times
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the height difference between the obstacle and the probe inlet. Unrestricted air flow across the probe

inlet should occur within an arc of at least 270 degrees. The predominant and second most

predominant wind direction must be included in this arc. If the probe inlet is positioned on the side of a

building, a 180 degree clearance is required. More specific details of probe positioning are presented

in the “PAMS Implementation Manual.”25 The glass probe should be reinforced or supported along the

straight vertical axis of the assembly. Typically this support is provided by routing the probe shaft

through a rigid section of metal or plastic tubing that is secured to the housing structure.

The manifold can be positioned in either a horizontal or vertical configuration. Figure 2-9

presents the manifold assembly in the vertical configuration. Figure 2-10 presents the manifold

assembly in the horizontal configuration. If the horizontal configuration is used, the sample ports must

point upward so that material that may be present in the manifold will not be transferred into the sample

lines.

With continuous use the sample probe and manifold can accumulate deposits of particulate

material and other potential contaminants. The sample probe and manifold should be cleaned to remove

these materials. The recommended frequency for cleaning is quarterly. To clean the assembly,

disconnect the sample lines and blower from the manifold. The sample lines and blower are not

cleaned. For safety, electric power to the blower should be terminated until the cleaning process is

completed. Disassemble the individual components by disconnecting the probe, manifold, collection

bottle, and coupling devices from each other. The individual components should then be cleaned using

heated high purity distilled water and a long handled bottle brush. The components should then be

rinsed with the distilled water and allowed to dry completely before reassembling. If required, mild

glass cleaner or detergent can be used to clean particularly dirty components. However, care should

be taken to select cleaners and detergents that are advertised to have low organic compound content

and the number of rinses performed should be increased to ensure that all associated residues are

removed.
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2.4.1.2 Sample Introduction 

The air sample can be introduced to the automated GC system directly from the air sample

manifold using a mass flow controller or other flow control device at a constant flow rate over the

prescribed sample integration time. As an alternative, the air sample may be collected into an

integrating canister at a constant flow rate over the prescribed sample integration time,
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Sampling cane

Sample

 in

Cane

support

Shelter roof

Shelter

wall

First port dedicated

to VOC sampling

Sample manifold

(with sufficient number of

ports to individually support

all monitoring conducted)

Bleed adapter

(flow control)

Blower

and mount

Exhaust

tube

Collection

bottle

To

atmosphere

Shelter

wall

o/s/g/morr/3797/pams/shelt1.ppt

Figure 2-9. Vertical Configuration
Sampling cane

Sample

 in

Cane

support

Shelter roof

Shelter

wall

First port dedicated

to VOC sampling

Sample manifold

(with sufficient number of

ports to individually support

all monitoring conducted)

Bleed adapter

(flow control)

Blower

and mount

Exhaust

tube

Collection

bottle

To

atmosphere

Shelter

wall

o/s/g/morr/3797/pams/shelt2.ppt

Figure 2-10. Horizontal Configuration

Section:

2

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and then supplied to the sample concentration trap at the end of the integrating period. For purposes of

calibration and proficiency studies, and to meet the 24-hour sampling requirements, samples may also

be introduced directly from pressurized SUMMA® canisters.

2.4.1.3 Sample Conditioning 

Moisture is removed from the sample stream for automated GC analysis to prevent or reduce

the detrimental effects of moisture on the primary concentration trap, analytical column(s), and

detector(s) as described in Section 2.3.3. Moisture removal also allows for analysis of larger sample

volumes, which provides lower detection limits, and is crucial to the measurement of very low

concentration VOCs.

Some commercially available automated GC systems incorporate the use of Nafion®

membrane sample drying devices. New developments in moisture removal include controlled

temperature vaporization, selective temperature condensation, hydrophobic concentration traps, and

micro-scale purge-and-trap. The loss of polar VOCs may result from moisture removal using some of

these techniques and this loss of polar VOCs may significantly affect the TNMOC measurement. The

user must characterize the effects of their particular sample conditioning method on the TNMOC

measurement and target VOCs of interest. 

2.4.1.4 Sample Concentration

Ambient air samples are primarily concentrated using multi-bed sorbent or

cryogenically-cooled deactivated glass bead traps. Sampling time and flow rate are typically used to

determine the total volume concentrated onto the primary trap. Multi-bed sorbent traps (Carbotrap®

and Carbosieve®) or cryogenically cooled glass bead traps are required to efficiently collect the

complete range (C2 through C12) of VOCs for O3 precursor monitoring. 
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Samples are collected onto sorbent traps at ambient temperature or the traps are cooled

using liquid cryogen (H2, CO2, Ar) or Peltier® electronic cooling devices to improve collection

efficiency. Ideally, sorbent traps selectively adsorb only the trace VOCs and do not interact with the

atmospheric constituents (i.e., CO2) or introduce any contaminants into the system. Sorbent traps may

also be designed to eliminate water vapor by using hydrophobic sorbent materials. 

Sample concentration using glass bead traps requires a trapping temperature of -185EC. 

Trapping at a temperature above -185EC will result in the loss of early-eluting C2 compounds such as

acetylene, ethane, and ethylene. Trapping at a temperature below -185EC can result in the collection

of methane and oxygen, and can have an adverse effect on chromatography. These traps are typically

cooled using liquid cryogen (N2 or Ar). This cooling process is commonly known as cryogenic

concentration or cryotrapping, and is the oldest and best known of the techniques for collecting C2

through C12 VOCs. The glass beads provide surface area for collection of the VOCs at the cryogenic

trapping temperature. 

2.4.2 Sample Analysis

Following sample collection and concentration, the sample is thermally desorbed directly onto

the analytical column(s). The analytical column may be cryogenically cooled to aid in focusing the

desorbed sample into a narrow band prior to chromatographic separation. The analytical column

chromatographically separates the sample into components for subsequent detection by the FID. The

signal from the FID is then acquired and processed using a PC-based data acquisition and processing

system.

2.4.2.1 Sample Focusing or Cryofocusing 

The sample cryofocusing step is optional and may not be employed in all commercially

available automated GC systems. The secondary cryofocusing trap is used to focus the desorbed
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sample from the concentration trap into a “plug” for injection onto the analytical column. Cryofocusing

improves the peak separation and in particular the resolution of C2 and C3 hydrocarbons. This

technique is especially helpful when the sample is desorbed from the concentration trap at low flow

rates. 

Cryofocusing traps incorporate the use of fused silica tubing that is cooled using liquid

cryogen. The fused silica tubing is wide-bore (0.32 mm I.D.) or megabore (0.53-mm I.D.) deactivated

fused silica tubing that is cooled to approximately -185EC. Cryofocusing traps may be packed to

increase the surface area and improve the focusing of the sample band. 

2.4.2.2 Gas Chromatography

The gas chromatograph contains the analytical column(s) of choice for PAMS VOC analysis. 

Refer to Sections 2.3.5 and 2.3.6 for guidance on column configuration and selection. Commercially

available GC systems are typically configured with the appropriate analytical column(s) to separate the

VOCs of interest. However, the user must determine if the system meets the enhanced O3 monitoring

requirements and specifications (Section 2.4.4) prior to procurement. The user must also characterize

the performance of the system operation prior to use. Commercial GC systems may incorporate the

use of single or dual-column configurations (in series or parallel) that may require sub-ambient oven

temperature programs. It is important to note that systems that eliminate the need for sub-ambient

column oven temperatures reduce the overall cryogen consumption of the system. New developments

in carrier gas electronic pressure programming and control have greatly improved peak resolution and

retention time stability for some automated GC systems. 

Automated GC systems employ the use of a PC-based data acquisition and processing

system for peak integration and quantitation. Data acquisition and processing systems are comprised of

hardware and software that perform data acquisition, peak detection and integration, peak identification

by retention time, post-run calculations and quantitation, calibration, peak reintegration, user program
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interfacing, and hard copy output. Data are automatically stored on magnetic media (e.g., hard disk or

floppy diskette).

The GC data acquisition and processing software is developed and supplied by the GC

manufacturer and should contain the necessary algorithms to acquire, integrate, and identify the

chromatographic peaks by retention time. The system should be capable of producing an electronic

and hard copy report file that contains the information needed to identify the sample and a listing of all

peaks detected in the chromatogram. This listing should contain the peak name if it is a target

compound. All detected peaks (both target and unidentified) should be reported with a concentration,

in ppbC, and a retention time. The listing should also contain the TNMOC estimate calculated by

summing the concentrations of all peaks (both target and unidentified) detected in the chromatogram. 

See Section 2.6.1 for a more detailed discussion on data processing capabilities of automated GC

systems.

2.4.2.3 Analytical System Calibration

The detector response of the analytical system should be calibrated with multiple level

propane primary standards over the expected sample concentration range. Benzene is suggested as a

second primary standard to calibrate dual-column systems. These dual-column systems employ a

Deans®24 switch or other column switching techniques. Benzene may also be used to quantitate the

target compounds when using a single-column approach. The primary calibration standard is used to

generate a response factor per carbon atom for determining the concentration of each target VOC, as

well as the TNMOC. It is impractical and unnecessary to determine compound specific response

factors for each of the target VOCs presented in Table 2-1 because the carbon response of the FID to

these compounds is approximately linear.

For a known, fixed sample volume, concentration is proportional to the area under the

chromatographic peak. The area is converted to ppbC using the following equation:
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CA RF(AC) (2-5)

RF

3(CB)

MAC

(2-6)

where:

CA = Concentration (ppbC)

RF = Response Factor, ppbC/area count

AC = Area Counts

The response factor (RF) is an experimentally determined calibration constant (ppbC/area count), and

is used for all compound concentration determinations. The response factor is determined by the

analysis of the primary standard using the following equation:

where:

3 = Carbon Atoms in Propane (6 when benzene is used as a second calibration

standard)

CB = Concentration of the NIST Propane Standard (ppbv)

MAC = Mean Area Count, determined from the analyses of multiple levels or multiple

injections of the primary standard

The retention time of target compounds is determined by analyzing the retention time

calibration standard as described in Section 2.3.4.2. This standard is analyzed in triplicate, at a

minimum, to establish the correct retention times and retention time windows for the peaks of interest.

The primary standard (Section 2.3.4.1) is used to perform a calibration check of the

analytical system in order to determine system variability and overall performance. The calibration and
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retention time checks may be performed concurrently using the retention time calibration standard. The

compound concentrations and retention times should compare within the limits of the data quality

objectives established for the monitoring program. If they do not, the analytical system should be

recalibrated.

2.4.3 System Operation

This section provides guidance and general operating considerations for initial system set-up,

optimization of sampling parameters, and field operation for automated GC systems.

2.4.3.1 Initial System Set-up

During the initial set-up of the automated system several parameters must be evaluated to

optimize the operating conditions. Critical parameters include, but are not limited to, the sample

collection flow rate and sample integration time, sample concentration and desorption conditions, oven

temperature program parameters, detector calibration, and the peak detection and integration methods

used by the data acquisition and processing system. These parameters are optimized by varying the

operating conditions to achieve the best resolution and detection of the target VOCs using primary

calibration and retention time calibration standards.

Prior to making VOC measurements using an automated GC system, the baseline

performance of the system must be thoroughly documented. The information from the system baseline

characterization is used to determine system specific target compound retention times, relative retention

times, identification of co-eluting compounds and matrix effects, internal standard retention times,

interferences, and detection limits. Subsequent calibrations and retention time QC checks should be

verified against the system baseline to identify trends or excursions from acceptable performance. See

Section 2.3.7 for a discussion of pre-measurement system characterization.
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Users should anticipate a minimum of six months for initial setup, configuration, familiarization,

and development of SOPs prior to the field implementation of an automated GC system. The system

should initially be set up by the manufacturer and demonstrate adequate system stability and

performance. Under terms of agreement for purchase, the manufacturer 

should be required to provide a detailed instruction manual for system operation and to meet the

specifications as defined by the user. For a set of primary system specification guidelines see Section

2.4.4.

2.4.3.2 Sampling Parameters 

Determination of optimum sampling parameters is dependent on field conditions

(i.e., expected compound concentration ranges, humidity, temperature, etc.), desired sensitivity,

cryogen consumption, and sample trapping efficiency. During the setup period, these sampling

parameters should be evaluated to determine the optimum conditions for each. Primary sampling

parameters are the sample collection frequency (1 sample each hour) and the minimum sample

collection or integration time (40 minutes).

For hourly sampling, the minimum sample collection or integration time is 40 minutes. A

sample collection volume of 200 to 600 mL is recommended. The sample volume used requires a

trade-off between the required detection limit and potential moisture interference problems. Longer

sample integration times may be implemented by using an intermediate sample collection or integration

device. This device usually consists of a sample integration vessel configured to provide integrated

collection of one sample while the previously collected sample is being analyzed. Advantages to using

an intermediate sample integration device include longer integration times and reduced cryogen use

during the concentration step of sample analysis.
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2.4.3.3 Field Operation 

The automated GC system should be installed in a temperature-controlled shelter at the field

location. Detailed SOPs for field operation of the automated GC system must be developed. The

SOPs should be based on information obtained during the set-up and familiarization period and the

requirements of the monitoring program. Refer to QA/QC Section 2.8.3.1 for a more detailed

discussion of SOP development. The system should be maintained by a qualified operator who should

perform the routine operational and quality control functions as specified in the SOPs. Critical

operational checks should be performed as frequently as practical. Operational parameters should be

adjusted, if necessary, so that the data quality objectives are met. It is recommended that all

adjustments to the operational parameters be documented in a laboratory notebook. Primary

calibration and retention time checks should be performed routinely according to the minimum QC

requirements given in Section 2.8. Retention time calibration checks are performed to provide retention

time reference information for validating compound identifications. The retention time calibration

standard can also be used to track the FID response to determine when recalibration is necessary.

2.4.4 System Specifications

A set of primary specifications is provided below to conduct the evaluation for procurement

of an automated GC/FID system. It is imperative that the enhanced O3 monitoring network

requirements for this type of system be compared against vendor offers to ensure that appropriate

systems are procured. Primary system specifications are presented below. Additional system

specifications may be added at the discretion of the user.

C The automated GC/FID system must be able to meet the sampling frequency

requirements as prescribed in 40 CFR Part 58, Subpart E, Appendix D, and the

sample integration requirements as discussed in Section 2.1 of this document (minimum

sample integration time of 40 minutes to comprise a 1-hour sample). The manual

methodology described in Section 2.5 is required for collection of the one 24-hour

sample every sixth day. 
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C Cryogen consumption is a primary consideration for system procurement. Transport

and delivery of liquid cryogen to the site may be impractical. The amount of liquid

cryogen consumed by the system will determine the frequency of site visits and impact

the cost for site operation and the level of data capture. Systems that utilize electronic

cooling devices should be strongly considered if all other user specified requirements

are satisfied.

C To avoid cross contamination, the system must demonstrate system background levels

that are below the 0.2 ppbC estimated detection level for each VOC target species and

3 ppbC for TNMOC.

C The system must demonstrate the ability to separate the target VOCs of interest (C2

through C12) and provide an adequate estimate of the TNMOC value. Refer to Section

2.2.1 for a discussion of TNMOC.

C To ensure adequate peak identification and quantitation by retention time, the system

must incorporate operating parameters that provide stable retention times. Observed

retention time drift must be less than 0.1 minutes.

C The sample conditioning device, used to remove moisture from the sample stream and

reduce the effects of moisture on the system, must minimize both polar VOC losses and

the potential for introducing contaminants into the analytical system.

C The minimum level of quantitation (LOQ) must be 3.0 ± 0.2 ppbC for propane and

correspond to an FID signal that is 3 to 5 times the baseline noise. 

C The system should incorporate microprocessor control and battery backup capability to

ensure that all programmed control activities for sample collection and analysis will be

retained should the system power be interrupted. The system should automatically

resume all operations once power is restored to the system to improve the level of data

capture. Although not a requirement, the capability to log and report system

interruptions (date, time, and type of failure) is advantageous. 

C The system operation should be flexible enough to allow sample collection and analysis

parameters to be easily modified to meet changes in network monitoring frequency and

sample integration times as required.

C Expedient and responsive vendor support is a key consideration. The user should

specify that the vendor maintain an adequate supply of replacement parts and a staff of

qualified service technicians to ensure that the minimum number of sampling events are

missed should a system failure occur. The user should specify that the vendor

guarantee that parts and components be delivered to the site within 2 working days
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from the placement of the order. The user should also specify that the response to

automated GC system service calls be received within 24 hours of placement and the

system be placed in acceptable working order within 7 days of the service request.

C The vendor must provide an in-depth, detailed manual covering all aspects of the

automated GC/FID system (i.e., operation, maintenance, etc.), initial system setup, user

training, and demonstrate adequate system performance.

2.5 Manual Method for Collecting and Analyzing Volatile Organic Compounds

The manual methodology for obtaining volatile organic compound (VOC) measurements

involves collecting time-integrated, whole air canister samples for subsequent analysis at a central

laboratory. Under the minimum network monitoring requirements in 40 CFR Part 58, Subpart E,

States must obtain 3-hour and 24-hour integrated measurements of VOCs at specified sample

collection frequencies based on individual PAMS site type requirements. The sample collection

frequencies range from one 24-hour sample every sixth day to eight 3-hour samples every day. 

Specific sample collection frequencies are discussed in Section 2.1. A discussion of sample collection

methodology is provided in EPA Compendium Method TO-15 (Appendix A).

Application of the manual methodology to the enhanced O3 monitoring regulations requires

the collection and analysis of a large number of canister samples. The magnitude and success of the

manual monitoring program depends on the quantity of canisters available, the capabilities of the sample

collection system used, the analytical capacity of the central laboratory, and the availability and skill of

staff to address the needs of the specific program design. An integrated, well planned sample collection

and analysis program is necessary to address the numerous aspects of a canister-based monitoring

operation, which include canister cleaning and transport, sample collection procedures and frequency,

analysis procedures, and data acquisition and reporting. These details must address the needs of the

specific program. Users of manual methodology are responsible for the selection, set-up, and

optimization of their specific system(s), and for the preparation of SOPs that delineate the details of all

operations.
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The intent of this section is to provide general guidance on manual methodology. The

following sections generally describe multiple-event and single-event canister sampling equipment,

procedures, and operation. Recommended system specifications applicable to the procurement of

canister sampling systems are also presented.

2.5.1 Sample Collection

This section describes the configuration and use of SUMMA® passivated canisters and

associated multiple- and single-event sample collection systems. These systems provide samples for

subsequent analysis at a central laboratory using a GC/FID analytical system with computerized data

reduction and reporting capabilities. 

Canister sample collection systems should be capable of unattended operation in order to

allow collection of samples in accordance with the network monitoring requirements presented in Table

1-1 (see Section 1). Procedures for collecting canister samples are described in Section 2.5.1.1 and

Section 2.5.1.4. Precautions pertaining to the use of canisters, canister cleaning procedures, and

sample collection system certification procedures are discussed in detail in Section 2.5.3.

Collecting time-integrated whole ambient air samples for subsequent analysis of target VOCs

is a widely accepted practice. Samples collected should represent a time-integrated average for the

required sampling period (i.e., collected at a constant flow rate over the full collection period). Sample

collection systems currently in use incorporate diverse operating approaches. The primary difference

among the various approaches is the technique and associated hardware used to perform timeintegration of canister sample collections and multiple- or single-event sample collection capabilities. 

Time-integration techniques generally involve the use of electronic and/or mechanical devices. Canister

sampling systems are available commercially or can be custom built by the user for a specific

application. 
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Multiple-event sample collection systems are needed to meet the 3-hour, around-the-clock

collection frequency. Back-to-back collection of the individual 3-hour samples may not be practical

using single-event systems due to the required attendance of an operator to change the sample canisters

between events.

2.5.1.1 Multiple-event Sample Collection Equipment 

A typical multiple-event sample collection system configuration is presented in Figure 2-11. 

The multiple-event canister sample collection system is comprised of the following primary components: 
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Microprocessor

Sample

Inlet

Manifold By-pass Pump

To Atmosphere

Pressure

Gauge

Metal

Bellows

Pump

Mass

Flow

Controller

Particulate

Filter

Mass Flow

Meter and

Variable

Orifice

3-hr

Samples

Mass

Flow

Controller

Mass Flow

Meter and

Variable

Orifice

3-hr Duplicate

or

24-hr Sample

Pressure Sensor

Pressure Sensor

Distribution

9 Solenoid

Valves

Rotary Valve

Sample Canisters

or

or

or

Figure 2-11. A Typical Multiple-event Sample Collection System
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Inlet probe and manifold assembly - Constructed of glass (see Figures 2-9 and 2-10) or

stainless steel. Used as a conduit to transport sample air from the atmosphere at the required

sampling height and distribute it for collection. 

By-pass pump - A single- or double-headed diaphragm pump, or a caged rotary blower. 

Used to continuously draw sample air through the inlet probe and manifold assembly at a rate

in excess of the sampling system total uptake. All excess sample air is exhausted back to the

atmosphere.

Sample pump - A stainless steel bellows pump, capable of 2 atmospheres above ambient

output pressure. Used to extract sample air from the manifold assembly and deliver it to the

sample canister during collection. 

Sample inlet line - Chromatographic-grade stainless steel tubing. Used to connect the

sampler to the manifold assembly.

Sample canisters - SUMMA® passivated stainless steel sample vessels of desired internal

volume with a bellows valve attached at the inlet of each unit. Used to contain the collected

sample air for transportation and analysis.

Electronic pressure sensor - A pressure measurement device capable of measuring

vacuum (0-30 in Hg) and pressure (0-30 pounds per square-inch gauge). Used to measure

initial and final sample canister pressures.

Adjustable orifice and mass flow meter assembly or electronic mass flow controller -

An indicating flow control device(s). Used to maintain a constant flow-rate (± 10%) over a

specific sampling period under conditions of changing temperature (20-40EC) and humidity

(0-100% relative).

Particulate filter - Two micron sintered stainless steel in-line filter. Used to remove

particulate material larger than 2 microns from the sample air being collected.

Microprocessor - An event control and data acquisition device. Used to allow unattended

operation (i.e., activation and deactivation of each sampling event) of the sampling system and

to record sampling event specific process data (i.e., start and end times, elapsed times, initial

and final sample pressures, etc.).

Solenoid valves or a multi-port rotary valve - Eight electric-pulse-operated or low

temperature coil, stainless steel body solenoid valves with Viton® plunger seat and o-rings or

one multi-port stainless steel body rotary valve with Viton® o-rings. Used to provide access

to or isolation of the sample canister(s). 
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F

P x V

T x 60 (2-7)

Stainless steel tubing and fittings - Isolation and interconnection hardware. Used to

complete system interconnections. All tubing in contact with the sample prior to analysis

should be chromatographic grade stainless steel and all fittings should be 316 grade stainless

steel.

2.5.1.2 Multiple-event Sample Collection Procedure 

Samples are collected in individual canisters using a single pump and one or more flow

control devices. A stainless steel metal bellows style pump draws in ambient air from the sampling

probe and manifold assembly at a constant flow rate to fill and pressurize each sample canister during

each specific sampling event.

A flow control device(s) is used to maintain a constant sample flow rate into each canister

over each specific sampling period. The flow rate used is a function of the final desired sample

pressure, the internal volume of the canister used, and the specified sampling period and assumes that

the canisters start at a pressure of 5 mm Mercury (Hg) absolute. The flow rate is calculated as follows:

Where:

F = flow rate (mL/min)

P = final canister pressure, atmospheres absolute

V = volume of the canister (mL) at one atmosphere pressure

T = sample period (hours)

60 = minutes in an hour
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F

1.5 atm x 6000 mL/atm

3 hr x 60 min/hr

50 mL/min

For example, if 6-L canisters are to be filled to 1.5 atmospheres absolute pressure each over individual

3-hour integration period (i.e., collection episode), the flow rate specific to each period is calculated as

follows:

During operation, the microprocessor control device is programmed to activate and

deactivate the components of the sample collection system, consistent with the beginning and end of

each individual sample collection period. 

The use of individual electric-pulse-operated or low temperature coil solenoid valves avoids

any substantial temperature rise that would occur with conventional coil solenoid valves. The

temperature rise associated with conventional coil solenoid valves could cause outgassing of organic

compounds from valve components into the samples.

Electric-pulse-operated solenoid valves require only a brief electrical pulse to open or close

at specified start and stop times. The valve, therefore, experiences no temperature increase. The

pulses may be obtained either from the microprocessor directly, if it can be programmed for short (5 to

60 seconds) actuation pulses, or by incorporating an attached electric pulse circuit.

Low temperature coil solenoid valves incorporate a low current draw circuit design to lift the

plunger and valve seat assembly (i.e., open the valve) when the coil is energized. A spring returns the

plunger and valve seat assembly (i.e., closes the valve) automatically when the coil is not energized. 

Because no electric-pulse circuit is required, the low temperature coil solenoid valves are much simpler

in design and considered more reliable.

Canister sampling systems can collect sample from a shared sample probe and manifold

assembly as described in Section 2.4.1.1 or from a dedicated stainless steel sample probe, manifold
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assembly, and by-pass pump. If a dedicated probe, manifold assembly, and by-pass pump are used,

provisions should be made (i.e., using a separate timer device, etc.) to start the by-pass pump several

hours prior to the first sampling event of a multiple-event collection period to flush and condition the

sample collection system components. The connecting lines between the sample inlet and each canister

should be kept as short as possible to minimize internal surface area and system residence time. 

The flow rate into each canister should remain relatively constant over the entire collection

period of each sampling event. If an adjustable orifice(s) is used as the flow control device(s), a drop in

the flow rate will occur near the end of the each sample collection period as pressure in the canister

increases. Typically this condition occurs when canister pressure exceeds one-half atmosphere above

ambient pressure. Consequently, care must be taken to select a sample flow rate that will yield a final

pressure that will not significantly exceed 22-24 psia (i.e., ~8-10 psig) at the end of the sample

collection interval.

Prior to any field use, each sample collection system should be certified as nonbiasing,

meaning that the sample collection system does not add to or subtract from the concentrations of the

samples collected using it. (Refer to Section 2.5.1.7 for details pertaining to canister sampling system

certification). The canisters should also be determined to be clean before each use. (Refer to Section

2.5.2 for details pertaining to canister cleaning.) Each adjustable orifice and mass flow meter assembly,

or mass flow controller, used as a flow control device should be calibrated against a primary flow

measurement standard (i.e., a bubble flow meter, etc.). The calibration qualifies the relationship

between indicated flow versus measured flow. Multiple calibration points of comparison, spanning the

entire range of the flow control device in increments of 10% of the device range, should be used. For

example, if a mass flow meter having a 0-100 mL measurement range is being calibrated, comparisons

would be made at 0, 10, 20, 30, 40, 50, 60, 70, 80, 90 and 100 mL. Calibration curves that

mathematically define the relationship between the flow rates indicated by the flow control device and

corresponding actual flow rates measured by primary flow measurement standard are generated from

these comparisons. The calibration curves are used to set actual desired flow rates, based on the flow
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rates indicated by the flow control devices. Pressure sensors should be calibrated against a primary

pressure measurement standard (i.e., manometer or absolute pressure gauge), and should also be

calibrated using the same process described above. Calibration of the flow control and pressure

measurement devices should be performed prior to any field deployment. A calibration check should

then be conducted periodically according to a program specific QA/QC schedule as developed by the

user. The calibration check should consist of performing a single point comparison at a representative

setting (e.g., a flow rate typically used for sample collection). The recommended frequency for

performing calibration checks is biannually (two calibration checks per year).

The following procedure provides generic steps for operating a typical multiple-event

sampling system:

1. Set the sample collection system to the desired sample collection flow rate(s)

(i.e., referencing the corresponding calibration curve(s) and considering the canister

volume and the desired final canister pressure). 

2. Program the microprocessor event control system to begin and stop sampling consistent

with user specific collection frequency requirements.

3. Attach all sample canisters to the sample collection system.

4. Open all the canister bellows valves.

5. After sampling, record the initial and final sample pressures in each canister

(i.e., referencing the corresponding calibration curve(s)), and the start and end time of

each collection event onto the sampling field data sheet. The microprocessor event

control and data acquisition system should automatically store these data for each

collection event. Final sample pressure should be close to the desired calculated final

pressure. 

6. Close all of the canister bellows valves. 

7. Attach an identification tag to each canister documenting the canister serial number,

sample event number, sample type, location, and collection date.

8. Disconnect and remove each canister from the sample collection system.
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An in-depth SOP, specific to the exact sample collection system utilized, must be developed.

2.5.1.3 Multiple-event System Specifications 

Multiple-event sample collection systems will be required if canisters are used to meet the

network monitoring requirements for VOC measurements in a practical, non-labor intensive manner.

A set of primary specifications is provided below to direct the evaluation and procurement of

multiple-event sample collection systems. It is imperative that the site requirements for this type of

system be compared against vendor offerings to ensure that appropriate systems are procured. 

Primary collection system specifications are presented below. However, additional collection system

specifications may be added at the discretion of the user.

C An in-depth, detailed manual describing all aspects of the sample collection system

(i.e., operation, maintenance, etc.) must be provided by the vendor.

C The overall size of the sample collection system, including canisters, should be kept as

compact as possible. The sample collection systems are usually installed into existing

sampling site shelters where many other parameters (i.e., criteria pollutant

concentrations, meteorological conditions, etc.) are also being measured. Each of the

other parameters requires separate instrumentation and consequently the shelters can

become very crowded.

C The sample collection system should meet all applicable electrical and safety codes,

operate on standard 110 Vac power, and incorporate a main power fuse or circuit

breaker. Specific potential electrical hazard and/or other safety considerations should

be detailed in a supplied users manual.

C The overall configuration, and components comprising that configuration, should allow

for simple operation, maintenance, and service of the sample collection system. 

Materials used in the construction of components of the sample collection system

should exhibit nonbiasing characteristics, i.e., the materials should neither contribute to

nor take away from the measured organic content. The components themselves should

generally conform to the descriptions presented in Section 2.5.1.1. All surfaces that
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come in direct contact with sampled air should be constructed of glass, stainless steel,

or Viton®. The use of Teflon® or other plastics or polymers should be avoided because

the absorption/ desorption characteristics of these materials increase the potential for

sample bias.

C The sample collection system should be able to be certified as nonbiasing. The user

should seek assurances and/or evidence that the sample collection system

design/configuration being considered will be, or has been certified according to the

recommended procedures presented in Section 2.5.1.7.

C Ideally, the sample collection system should be able to accommodate the sample

collection event frequency presented in Section 2.1 and simultaneously allow a

duplicate 3-hour sample collection as recommended for QC purposes. The sampling

system should have the capability to collect the following during any given 24-hour

period:

- Eight 3-hour time-integrated canister samples;

- One 3-hour time-integrated duplicate canister sample, collected concurrently

with one of the eight 3-hour canister samples; and

- One 24-hour time-integrated canister sample, collected concurrently with the

eight 3-hour samples, but not concurrently with the duplicate 3-hour canister

sample.

It is imperative that the sample system have the collection capabilities detailed above,

including the 24-hour sample collection. If not, a second sample collection system will

be required to address the 24-hour sample collection and, consequently, more overall

labor and space would be needed to fully address the network monitoring

requirements.

The ability of the sample collection system to perform sample collections as presented

above would allow the operator to visit the site only twice during the 24-hour period

being characterized; once to install cleaned evacuated canisters prior to sampling and

once to remove canisters containing the collected samples.

C The sample collection system must be able to perform time-integration of the canister

sample collections. The sample collection system should allow for variable collection

flow rates so that canisters of different internal volume may be used (refer to Section

2.5.1.2 for specifics on the relationship between canister volumes, collection duration,

and collection flow rate).
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C The sample collection system should incorporate a microprocessor event control and

data acquisition device. At a minimum this microprocessor should be programmable to

control the start and stop times of every collection event within a 24-hour sampling

period. The microprocessor should also be able to simultaneously collect and store all

the sample collection process data pertaining to each sampling event as follows:

- Start and stop times for each sample collection; and

- Beginning and ending sample canister pressures for each sample collection.

The microprocessor should incorporate a battery backup system to address power

failure situations. Battery backup is necessary to ensure fewer invalidated samples and

a higher collection completion rate. The battery backup system would ensure that all

programmed control activities and collection process data are retained for a

predetermined interval in the event that standard power to the system is interrupted. 

Retaining the programmed control activities would allow sample collection to resume

automatically at the next programmed event time when standard power is restored to

the sample collection system. Retaining the collection process data for samples

collected prior to the termination of standard power allows these samples to be

qualified as valid or invalid, based on sampling start and stop times and initial and final

pressures. Although not absolutely necessary, adding a miniature printer would allow

for the generation of a report listing all sample collection process data.

C Expedient and responsive vendor support should be a mandatory requirement and

primary consideration when procuring a multiple-event canister sample collection

system. The user should specify that the vendor maintain an adequate supply of

replacement parts and qualified service technicians to ensure that the absolute minimal

number of sampling events is missed should a sample collection system failure occur. 

The user should specify that the vendor guarantee that parts/ components be delivered

to the sampling site within two working days of order placement, and that a sample

collection system delivered to the vendor for repair or for other problems be serviced

and returned to the user within seven working days.

2.5.1.4 Single-event Sample Collection Equipment 

A typical single-event sample collection system configuration is presented in Figure 2-12. 

The single-event sample collection system consists of the following primary components: 
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Inlet probe and manifold assembly - Constructed of glass (see Figure 2-4) or stainless

steel. Used as a conduit to transport sample air from the atmosphere at the required sampling

height and distribute it for collection. 
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Metal

Bellows

Pump

Sample

Inlet

Manifold By-pass Pump

To Atmosphere

Particulate

Filter

3-Hr

or 24-Hr

Samples

Flow

Control

Solenoid

Valve

Duplicate

Sample

Canister

Primary

Sample

Canister

Pressure

Measurement

Pressure

Measurement

Microprocessor

(Optional)

Adjustable Orifice

and Rotameter

or Mass Flow Meter

Electronic Mass

Flow Controller

Mechanical

Pressure Gauge

Electronic 

Pressure Gauge

(Optional)

or

or

or

Figure 2-12. A Typical Single-event Sample Collection System
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By-pass pump - A single- or double-headed diaphragm pump, or a caged rotary blower. 

Used to continuously draw sample air through the inlet probe and manifold assembly at a rate

in excess of the sampling system total uptake. All excess sample air is exhausted back to the

atmosphere.

Sample pump - A stainless steel bellows pump, capable of 2 atmospheres above ambient

output pressure. Used to extract sample air from the manifold assembly and deliver it to the

sample canister during collection. 

Sample inlet line - Chromatographic-grade stainless steel tubing. Used to connect the

sampler to the manifold assembly.

Sample canisters - SUMMA® passivated stainless steel sample vessels of desired internal

volume with a bellows valve attached at the inlet of each unit. Used to contain the collected

sample air for transportation and analysis.

Stainless steel vacuum/pressure gauge or electronic pressure sensor (optional) - A

pressure measurement device capable of measuring vacuum (0-30 in Hg) and pressure

(0-30 pounds per square-inch gauge). Used to measure initial and final sample canister

pressures.

Adjustable orifice and rotameter, or mass flow meter assembly, or electronic mass

flow controller- An indicating flow control device (or devices). Used to maintain a constant

flow rate (± 10%) over a specific sampling period under conditions of changing temperature

(20-40EC) and humidity (0-100% relative).

Particulate filter - Two-micron sintered stainless steel in-line filter. Used to remove

particulate material larger than 2 microns from the sample air being collected.

Electronic timer or microprocessor (optional) - An event control device. Used to allow

unattended operation (activation and deactivation) of the collection system.

Solenoid valve - An electric-pulse-operated or low temperature coil, stainless steel body,

solenoid valve, with Viton® plunger seat and o-ring. Used to provide access to or isolation of

the sample canister(s).

Elapsed time indicator - A time measurement device used to measure the duration of the

sampling episode.

Stainless steel tubing and fittings - Isolation and interconnection hardware. Used to

complete system interconnections. All tubing in contact with the sample prior to analysis
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should be chromatographic grade stainless steel and all fittings should be 316 grade stainless

steel.

2.5.1.5 Single-event Sample Collection Procedure 

The sample is collected in a canister using a pump and flow control device. A stainless steel

metal bellows style pump draws in ambient air from the sampling probe and manifold assembly at a

constant flow rate to fill and pressurize the sample canister.

A flow control device is used to maintain a constant sample flow rate into the canister over a

specific sampling period. The flow rate used is a function of the final desired sample pressure, the

internal volume of the canister used, and the specified sampling period. A starting pressure of 5 mm

mercury (Hg) absolute for the canisters is assumed. The flow rate is calculated using the formula

presented in Section 2.5.1.2.

During operation, the timer is programmed to activate and deactivate the sample collection

system at specified times, consistent with the beginning and end of a sample collection period.

Single-event sample collection systems can collect sample from a shared sample probe and

manifold assembly as described in Section 2.4.1.1 or from a dedicated stainless steel sample probe,

manifold assembly, and by-pass pump. If a dedicated probe, manifold assembly, and by-pass pump

are used, a second electronic timer should be incorporated to start the by-pass pump several hours

prior to the sampling period to flush and condition the components. The connecting lines between the

sample inlet line and the canister should be as short as possible to minimize internal surface area and

system residence time. 

The flow rate into the canister should remain constant over the entire sampling period. If an

adjustable orifice is used as the flow control device, a drop in the flow rate will occur near the end of

the sample collection period because the orifice size is no longer critical as pressure in the canister
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increases. Typically this condition occurs when canister pressure exceeds one-half atmosphere above

ambient pressure. Consequently, care must be used to select a sample flow rate that will yield final

pressure that will not significantly exceed 22-24 psig (i.e., ~8-10 psig) at the end of the sample

collection interval.

Prior to field use, each sample collection system should be certified as nonbiasing. (Refer to

Section 2.5.1.7 for details pertaining to canister sample collection system certification.) The canisters

should also be demonstrated to be clean before each use. (Refer to Section 2.5.2 for details pertaining

to canister cleaning.)

The following generic steps are provided for the operation of a typical single-event sample

collection system:

1. Activate the sample collection system and verify the correct sample flow rate using a

calibrated mass flow meter or rotameter. The flow can be measured directly at the inlet

of the system. The calibrated mass flow meter or rotameter is attached to the sample

inlet line, before the particulate filter. The sample collection system is activated and the

indicated flow rate is compared to the desired collection flow rate. The values should

agree within ± 10%. If a mass flow controller is being used as the sample collection

system flow control device, allow the system to equilibrate for two minutes. After the

two-minute equilibration, the desired sample flow rate is attained by adjusting the

system mass flow controller until the calibrated mass flow meter or rotameter indicates

the correct flow rate. If the sample collection system uses a adjustable orifice assembly

as the flow control device, adjust the orifice size until the correct flow rate is achieved. 

If the sampling system uses a fixed orifice as the flow control device, ensure that the

orifice is the correct size to provide the desired flow rate.

2. Deactivate the sample collection system and reset the elapsed time indicator to show no

elapsed time.

3. Disconnect the calibrated mass flow meter or rotameter and attach a cleaned evacuated

canister to the sample collection system.

4. Open the canister bellows valve.
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5. Record the initial vacuum in the canister, as indicated by the sample collection system

vacuum gauge, on the canister sampling field data sheet.

6. Record the time of day and elapsed time indicator reading on the canister sampling field

data sheet.

7. Set the electronic timer to start and stop sampling at the appropriate times.

8. After sample collection, record the final sample pressure on the sampling field data

sheet. Final sample pressure should be close to the desired calculated final pressure. 

Time of day and elapsed time indicator readings should also be recorded.

9. Close the canister bellows valve. Disconnect and remove the canister from the sample

collection system.

10. Attach an identification tag to the canister documenting the canister serial number,

sample number, sample type, location, and collection date.

An in-depth SOP, specific to the exact sample collection system utilized, must be developed.

2.5.1.6 Single-event System Specifications 

Although different in complexity and general application, many of the collection system

specifications that apply to multiple-event collection systems also apply to single-event collection

systems. To ensure that a single-event collection system meets the user’s program needs, the following

system specifications should be presented to, and addressed by, the candidate vendor(s) prior to

procurement.

C An in-depth, detailed manual covering all aspects of the sample collection system

(i.e., operation, maintenance, etc.) must be provided by the vendor.

C Although fewer canisters are utilized at a time, as compared to the multiple-event

systems, the overall size of the sampling system should still be kept as compact as

possible.
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C The sampling system should meet all applicable electrical and safety codes, operate on

standard 110 Vac power, and incorporate a main power fuse or circuit breaker. 

Specific potential electrical hazards and/or other safety considerations should be

detailed in a supplied user’s manual.

C The overall configuration, and components comprising that configuration, should allow

for simple operation, maintenance, and service of the sample collection system. 

Materials used in the construction of components of the sample collection system

should exhibit nonbiasing characteristics. The components themselves should generally

conform to the descriptions presented in Section 2.5.1.4. All surfaces that will come in

direct contact with sampled air should be constructed of glass, stainless steel, or

Viton®. The use of Teflon® or other plastics or polymers should be avoided because

the absorption/desorption characteristics of these materials increase the potential for

sample bias.

C The sample collection system should be able to be certified as nonbiasing. The user

should seek assurances and/or evidence that the sample collection system

design/configuration being considered can or has been certified according to the

recommended procedures presented in Section 4.0 of Compendium Method TO-12

(Appendix C).

C The sample collection system should be able to perform time-integration of the canister

sample collections, and allow for variable collection flow rates so that different volume

canisters may be used.

C Expedient and responsive vendor support should be a mandatory requirement and

primary consideration when procuring a single-event canister sample collection system. 

The user should specify that the vendor maintain an adequate supply of replacement

parts and qualified service technicians to ensure that the absolute minimal number of

sampling events is missed should a sample collection system failure occur. The user

should specify that the vendor guarantee that parts/components be delivered to the

sampling site within two working days of order placement. The user should also specify

that a sample collection system delivered to the vendor for repair or for other problems

be serviced and returned to the user within seven working days.

An alternative procedure involves passive sampling into a SUMMA®-polished canister, with

subsequent pressurization of the canister to 30 psig at the central laboratory. This procedure reduces

the relative humidity in the canister but also dilutes the sample.
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2.5.1.7 Canister Sampling System Certification

Canister sampling systems should exhibit nonbiasing characteristics before being used to

collect samples. These sampling systems should be subjected to laboratory certification to quantify any

additive or subtractive biases that may be attributed directly to the sampling system. The following

procedure is recommended for certifying canister sampling systems. Alternative approaches are

acceptable provided they are properly described and documented. 

A challenge sample, consisting of a blend of organic compounds at a known concentration in

clean humidified zero air, is collected through the sampling system. A reference sample is concurrently

collected using a dedicated mass flow controller that has been characterized prior to each use. The

samples are then analyzed using a GC system that is equivalent to or better than the GC system that will

be used to analyze field volatile organic O3 precursor samples. The percent recoveries for target

challenge compounds are calculated, based on the concentrations determined for the reference sample. 

Recoveries of each of the challenge compounds should be in the range of 80-120% of the

concentrations determined for the reference sample. A system-specific overall recovery should also be

calculated. The overall recovery is the average of the individual compound recoveries. Each sampling

system should have an overall recovery of 85-115%. The challenge sample percent recoveries are

used to gauge potential additive and/or subtractive bias characteristics for each specific sampling

system.10

In addition to characterizing the sampling system with a blend of VOCs, the system should

also be characterized using humidified zero air. A humidified zero air blank sample is collected through

the sampling system to further gauge the potential for additive bias. The blank samples can be analyzed

for specific target analytes, TNMOC, or both, depending on individual program requirements. Two

criteria apply to the blank portion of the certification process: a determined concentration criterion of

0.2 ppbC or less for any individual target compound is required if speciation analysis of the blank

sample is performed, and a TNMOC concentration criterion of 10 ppbC or less is also required.
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Sampling is accomplished using dedicated manifolds for both the zero and challenge phases of

the certification procedure (Figures 2-13 and 2-14). Zero air supplied to the zero manifold should be

hydrocarbon-free and humidified to approximately 70% relative humidity. 

The zero air should be supplied from a canister cleaning system similar to the one described in

Section 2.5.2.
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Cleaned humidified

zero dilution gas (in)

Mass flow

controller

Sample

canisters

(5-8)

Sample

canisters

(1-4)

Canister sampling

systems (5-8)

Canister sampling

systems (1-4)

To atmosphere

Exit

rotameter

4 4

3 3

2 2

1 1

8 8

7 7

6 6

5 5

Zero manifold

(not temperature controlled)

Figure 2-13. Dedicated Manifold for Zero Gas Certification
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Certified challenge

stock gas (in)

Cleaned humidified

zero dilution gas (in)

Mass flow

controllers

Sample

canisters

(1-4)

Canister sampling

systems (1-4)

1 1

2 2

3 3

4 4

Mixing chamber

Controlled temperature challenge manifold

Power out

Thermocouple

Programmable

temperature

controller

Reference sample collection

(characterized mass flow controller)

Reference

sample

canister

Sample

canisters

(1-5)

Canister sampling

systems (5-8)

8 8

7 7

6 6

5 5

Exit

rotameter

To atmosphere

Figure 2-14. Dedicated Manifold for Challenge Gas Certification
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2.5.1.7.1 Certification Equipment

The equipment required to perform canister sampling system certification is described below. 

The equipment listed is consistent with the systems presented in Figures 2-13 and 2-14.

Mass flow controllers - Mass flow controllers located at the inlets to the manifolds. Mass

flow controllers are used to regulate the certification pollutant, diluent, and zero air flow rates. 

Also, a dedicated, characterized mass flow controller is used to collect reference samples.

Mixing chamber - A mixing chamber located between the outlets of the mass flow

controllers and the inlet of the challenge manifold. The mixing chamber is a stainless steel

vessel with opposed inlet and outlet ports that cause the blend of challenge gases and the

diluent gas to swirl and mix prior to entering the challenge manifold. The mixing chamber is

used to ensure that a homogeneous blend of challenge gas is delivered to the challenge

manifold. The zero manifold does not require a mixing chamber.

Challenge gas manifold - A challenge gas manifold constructed of 1/8-inch O.D.

chromatographic grade stainless steel tubing and 1/8-inch tee fittings. The challenge manifold

is used to distribute challenge gas to the individual sampling systems being certified. The

number of sample ports provided on the challenge gas manifold is determined by the number

of sampling systems to be certified simultaneously.

Zero air manifold - A zero air manifold constructed of 1/4-inch O.D. chromatographic

grade stainless steel tubing and 1/4-inch fittings. The zero manifold is used to distribute zero

air to the individual sampling systems being certified. The number of sample ports provided

on the zero air manifold is determined by the number of sampling systems to be certified

simultaneously.

Exit rotameter - An exit rotameter located at the outlet of both the challenge gas and zero

air manifolds. The exit rotameter is used to visually indicate that an excess of challenge gas or

zero air is present in the respective manifolds during certification sample collection.

Cord heater - A cord heater rated at 80 watts spiraled around the outside of the challenge

manifold. The cord heater is used to heat the challenge manifold to 80EC. Heating the

challenge manifold helps to reduce the potential for loss of challenge gas compounds to the

walls of the challenge manifold. The zero manifold is not heated.

Temperature controller- A temperature controller used in conjunction with the cord heater

to actively regulate the challenge manifold temperature at 80EC.
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Qt Qsx N1+ QRx N2x F1 (2-8)

2.5.1.7.2 Certification Procedure

The procedure to perform canister sampling system certification is presented below.

 1. Perform a positive pressure leak check of all sampling system fittings. Attach source of

pressurized air to the inlet of the system. Coat the fittings with indicating bubble solution

to locate leaks. Repair any leaks found. Perform a negative pressure leak check. 

Attach an evacuated canister to the exit of the sampling system. Open the canister

bellows valve and record the initial vacuum, indicated by the sample pressure gauge. 

Close the canister bellows valve and view the sample pressure gauge and determine

whether vacuum is maintained. The system is leak free if the vacuum is maintained. If

vacuum is not maintained, the system is not leak free. Repair leaks and retest the

system.

 2. Connect the sampling systems and the reference sample flow controller to the zero

manifold and purge them with humidified zero air for 48 hours. The purge air should

simultaneously be routed to the challenge manifold to clean and prepare it for challenge

sample collection. Terminate the humidified zero air flow at the end of the 48 hour

period.

 3. Purge the sampling systems, reference system, and manifold with dry zero air for 1 hour

to removed accumulated moisture. During the dry purge, determine the certification

flow requirements using the following equation:

where:

Qt = Total required flow rate (mL/min)

Qs = Individual sampling system collection flow rate (mL/min)

N1 = Number of sampling systems

QR = Reference system collection flow rate (mL/min)

N2 = Number of reference systems

F1 = Excess flow factor = 2.0
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F2

C1

C2

(2-9)

QpF2x QT (2-10)

QD QT- QP (2-11)

 4. Determine the pollutant and diluent flows required to generate the desired concentration

of challenge gas using the following equations:

Step 1

where:

F2 = Dilution factor (for use in next equation)

C1 = Desired challenge gas concentration (ppbv)

C2 = Concentration of the stock cylinder (ppbv)

Step 2

where:

QP = Pollutant flow rate (mL/min)

QT = Total required flow rate

Step 3

where:

QD = Diluent flow rate (mL/min)
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 5. Generate and deliver the challenge gas to the challenge manifold and sampling systems. 

Condition the challenge manifold with the challenge gas for 10 minutes, with the

sampling systems off. Condition the challenge manifold an additional 10 minutes with

the sampling systems on, and in the bypass mode. Connect a clean evacuated canister

to each sampling system.

 6. Collect the challenge and reference samples. Conduct challenge sample collection

according to the normal specified operation of the sampling system.

 7. Connect the sampling systems to the zero manifold and purge with zero air, humidified

to 100% relative humidity, for 48 hours. Dry the manifold and samplers with dry zero

air for 1 hour. Adjust the zero air stream to 70% relative humidity. Condition the zero

manifold for 10 minutes with the sampling systems off. Condition the zero manifold an

additional 10 minutes with the sampling systems on, and in the bypass mode. Connect

a clean evacuated canister to each sampling system.

8. Collect the humidified zero air blank samples. Conduct the blank sample collections

using the same sampling system operating procedures used during the challenge sample

collection.

9. Analyze the zero and challenge samples and calculate the percent recoveries.

The sampling system must be challenged with a known concentration of selected analytes

prior to deployment. Additional challenges at the middle and end of the sampling season are

recommended. Operator/analyst judgment is critical: a challenge should be performed whenever the

operation of the sampling system is questioned for any reason.

2.5.2 Canister Cleaning

The canister cleaning procedure and equipment described in this section are recommended

when obtaining integrated whole ambient air samples for subsequent analysis of VOCs. The cleaning

procedure involves purging the canisters with cleaned humidified air and then subjecting them to high

vacuum.
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The purpose of canister cleaning is to ensure that the canister interior surfaces are free of

contaminants and that the canister meets a predetermined cleanliness criterion (i.e., #10 ppbC

NMOC). This level of cleanliness minimizes the potential for carryover of organic pollutants from one

sample to the next, and helps ensure that the samples collected are representative.

2.5.2.1 Canister Cleaning Equipment

The equipment required to clean canisters includes a source of clean, humidified air to

pressurize the canisters to a pressure of 20 psig, and a vacuum system for evacuating the canisters to

5 mm Hg absolute pressure. Air from a standard oil-less air compressor will contain pollutants from the

ambient air. In addition, various VOCs will be found in the compressed air because of the lubricants

used in the air compressor. Hydrocarbon-free air may be purchased in cylinders and humidified before

being used in the cleaning process. However, this approach may be cost-prohibitive. Figure 2-

15 presents the schematic of a canister cleanup system that is suitable for cleaning up to 16 canisters

concurrently. This, and any alternative system, must include a vacuum pump capable of evacuating the

canisters to an absolute pressure of 5 mm Hg. The equipment is designed so that one manifold of eight

canisters is undergoing the pressurization portion of the cleaning cycle while the other manifold of eight

canisters is undergoing the vacuum portion of the cleaning cycle.

The following equipment is incorporated in a canister cleaning system.

Air compressor - A shop or laboratory oil-less air compressor used to provide the air

supply for the canister cleanup apparatus. 

Coalescing filter - A coalescing filter designed to remove condensed moisture or

hydrocarbon contaminants present in the air supplied from the air compressor.

Permeation driers - Permeation driers used to dry the air prior to introduction into the

catalytic oxidizers. Two permeation driers are installed in parallel.
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Moisture indicators - Visual moisture indicators installed in the transfer lines between the

permeation driers and the catalytic oxidizers to monitor the performance of the permeation

drier.

Catalytic oxidizers - Catalytic oxidizers installed in the clean-air system to oxidize any

hydrocarbon contaminants that may be present in the air supplied by the air compressor. For

best results and most efficient operation of the catalytic oxidizers, manufacturer's

specifications should be strictly followed.
o:/s/g/morr/3797/pams/hobson/graph5.ppt

Coalescing

Filter

Permapure Dryers Moisture

Indicators

Filter Assemblies

Catalytic

Oxidizers

Air Compressor

Air Flow

Rotameters

Pressure

Regulators

Air

Cryotrap

Absolute

Pressure

Gauge

Air

Humidifier

Air Bypass

To Certification System

Routing

Valve

Vacuum Source

Selector Valve

Vacuum

Cryotrap

8-Port

Manifold

Roughing

pump

Turbomolecular

Pump

A B

C

A B

C

A. Manifold Air Pressure Valve

B. Manifold Vacuum Valve

C. Manifold Pressure Release Valve

D. Manifold Port for Connecting Canisters to be Cleaned

D D D D D D D D D D D D D D D D

Figure 2-15. Schematic of a Canister Cleanup System

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2

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Filter assemblies - A 5-micron sintered stainless steel filter installed in the filter housing

assembly downstream of each catalytic oxidizer to trap any particulate material that may be

present in the air stream leaving the catalyst bed of the oxidizer.

Air cryotrap and purge valves - The air cryotrap allows the cleaned air supply lines to be

subjected to cryogenic temperatures to condense (1) water formed during the oxidation of

hydrocarbons, (2) any remaining unoxidized hydrocarbons, and (3) other condensables. Air

cryotrap purge valves are used to purge these condensed components from the air cryotrap,

as described in the operating procedure described below.

Pressure regulators - A high purity dual stage pressure regulator installed in each branch of

the air supply line so that the maximum pressure attained during the cleanup procedure is

controlled at 20 psig. 

Flow controllers - The flow control devices shown in the canister cleanup schematic (Figure

2-10) are metering valves. The flow rates are set not to exceed the maximum recommended

flow rate through the catalytic oxidizers.

Air flow rotameters - Rotameters installed in the air supply lines to allow monitoring of the

flow rates through the catalytic oxidizers.

Air humidifier- The air humidifier shown in Figure 2-15 is a SUMMA®-passivated,

double-valve stainless steel canister with an inlet dip tube that projects to the bottom of the

sphere. HPLC-grade water is placed in the canister prior to use. Two rotameters are

connected to control air flow so that about 80% of the flow rate can be directed to the

humidifier (to bubble through the water to become saturated), while the other 20% bypasses

the humidifier. This procedure allows the humidification apparatus to supply cleaned, dried

air that has been humidified to a relative humidity of ~80%.

Manifold air pressure valves - Manifold air pressure valves used to isolate the air supply

system from the manifold, or to make the pressurized air available to the manifold.

Eight-port manifolds - Eight-port manifolds designed to allow up to eight canisters at a time

to be connected. Fewer canisters may be connected to the manifold if the vacant ports are

sealed off with a plug fitting.

Roughing pump - The roughing pump shown in Figure 2-15 is a high-capacity diaphragm

vacuum pump used to remove the moist cleaning air from the canisters while evacuating the

canisters to about 100 mm Hg absolute. The high moisture content of the cleaning air

contained in the canisters will not impede the function of this diaphragm style pump, but will

impede the performance of the high-vacuum pump.
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High-vacuum pump - A high-vacuum pump capable of reducing the pressure in the canisters

to 5 mm Hg absolute. High moisture content will impede the performance of the high-vacuum

pump.

Vacuum cryotrap - A U-shaped trap located in the vacuum manifold that is sized to fit inside

a Dewar flask filled with cryogen. The purpose of this trap is to condense water vapor from

the air that is pulled from the canisters during the vacuum cycle and prevent back-diffusion of

organic vapors from the high-vacuum pump into the canisters during the vacuum cycle of the

cleaning procedure.

Vacuum source selector valve - The vacuum source selector valve is a multiposition valve

used to route either the roughing pump or the high vacuum pump to the eight-port manifold

assemblies or isolate both pumps from the manifold assemblies.

Compound absolute pressure gauge - An absolute pressure gauge used to measure the

pressure attained in the canisters during the vacuum and pressurization cycles of the cleaning

procedure. The absolute pressure gauge must be able to measure absolute pressures from 40

psig down to 0.5 mm Hg absolute.

Air bypass valve - The air bypass valve is used to allow for a 1.0 L/min flow of air to be

maintained through the catalytic oxidizers when the cleaning system is not in use. This flow

prevents the oxidizers from overheating when the clean up system is not in use.

Manifold valves - The manifold vacuum valve and the manifold pressure valve are used to

apply vacuum or pressure to the canisters, as required during the cleaning procedure. 

Manifold ports - The manifold ports permit connection of the canisters to the manifold. 

Fittings that mate directly with the canister valve fittings are used. These connections will not

leak during the pressurization portion or the vacuum portion of the cleaning procedure.

2.5.2.2 Canister Cleaning Procedure

The cleanup system is prepared for use by checking the position of all the valves. All valves

should be closed initially, with the exception of the air bypass valve. Fill both the air source and

vacuum pump vacuum flasks with cryogen and actuate the high-vacuum pump. Ensure that these

vacuum flasks remain filled with cryogen throughout all cleanup activities. The inlet bellows valve on the

humidifier is opened and the valve on the wet air rotameter is also opened. Close the valve on the dry
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air (bypass) rotameter to allow the air to become humidified. Allow the system to stabilize for 10

minutes. After preparing the cleanup system, canister cleaning is performed using the following

procedure.

 1. Connect the canisters to be cleaned to the cleaning manifolds. Record the canister

numbers and pre-cleanup concentrations, if available, as determined by the last

analysis, in the appropriate cleanup and canister history log book. Record data

pertinent to the vacuum and pressure cleanup cycles as they are completed.

 2. Remove collected moisture from the air cryotraps by opening and immediately closing

the air cryotrap purge valves. Removal of the collected moisture should be performed

at the beginning of each pressure cycle, so that the cryotraps do not plug with ice.

 3. Release pressure from the canisters by opening all the canister bellows valves and then

opening the manifold pressure release valve. When venting is complete, leave the

canister bellows valves open and close the manifold pressure release valve.

 4. Begin the first vacuum cycle by actuating the roughing pump, placing the vacuum source

selector valve in the roughing pump position, and opening the manifold vacuum valve.

 5. Evacuate the canisters to approximately 100 mm Hg, as indicated by the absolute

pressure gauge. 

 6. Position the vacuum source selector valve in the high-vacuum pump position.

 7. Evacuate the canisters to 5 mm Hg absolute pressure (or less) and maintain the vacuum

for 30 minutes.

 8. Close the manifold vacuum valve after the 30-minute high-vacuum period has been

completed.

 9. Begin the first pressure cycle by purging the air cryotraps (refer to Step 2) and then

closing the air bypass valve. Open the manifold air pressure valve. Using the air flow

control valves, adjust the air flow rate to the manufacturer's recommended optimum

flow rate for the oxidizers, as indicated by the air rotameters.

10. Check the pressure regulators to verify that they are set to deliver a final pressure of

20 psig. Fill the canisters to 20 psig. As the final pressure is attained, the flow rates

indicated on the air rotameters will drop to zero, regardless of the setting on the flow
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controllers because the pressure in the canisters and the pressure at the exit of the

regulators reach equilibrium.

11. Close the manifold air pressure valve when filling is complete. Open the air bypass

valve and adjust the air flowmeters to 1.0 L/min.

12. Release the pressure from the canisters after they have been under a 20 psig pressure

for 30 minutes by opening the manifold pressure release valve. 

13. Repeat steps 4, 5, 6, 7, and 8 for Vacuum Cycle 2.

14. Repeat steps 9, 10, 11, and 12 for Pressure Cycle 2.

15. Repeat steps 4, 5, 6, 7, and 8 for Vacuum Cycle 3.

16. Repeat steps 9, 10, and 11 for Pressure Cycle 3.

17. Close all of the bellows valves on the canisters.

2.5.2.3 Canister Blanking Procedure

Prior to initial use, the cleanliness of all canisters should be assessed. After the initial blanking

of 100% of the canisters, the blanking frequency can be reduced. One canister on a cleaning bank of

eight canisters is considered representative and should be blanked. The selection of the canister to be

blanked (from the bank of eight canisters) is determined by selecting the canister with the highest precleanup TNMOC concentration on the manifold. This canister is selected because the potential for

compound carryover is most likely to be the largest of any of the canisters on the manifold. The blank

sample is analyzed using the PDFID technique as described in Method TO-12 (Appendix C). If this

measurement meets the predetermined cleanliness criterion (i.e., #10 ppbC), then the other canisters on

the manifold are considered clean. Blanking is a part of the overall canister cleanup procedure, and is

described below.

 1. Select the canister to be blanked by referencing the cleanup history logbook to

determine the canister with the highest pre-cleanup TNMOC concentration.
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 2. Verify that all the canister bellows valves are closed. Disconnect the canister selected

to be blanked.

 3. Using the PDFID technique, if the canister analysis meets the predetermined

concentration criterion (i.e., #10 ppbC), then the blanked canister and all the other

canisters on the bank of eight canisters are considered clean.

 4. If the canister does not meet the cleanliness criterion (i.e., #10 ppbC), it is reconnected

to the manifold. The entire bank of canisters is given another vacuum and pressure

cycle. After the additional cycle, the same canister is blanked again.

 5. After the canister is blanked and has met the concentration acceptance criterion, it is

reconnected to the manifold.

2.5.2.4 Final Canister Evacuation Procedure

After cleaning and blanking, the canisters are ready for final evacuation in preparation for

sample collection. The procedure for final evacuation is described below.

 1. Release the pressure from the canisters by opening the manifold pressure release valve

and opening all of the canister bellows valves. When venting is complete, close the

manifold pressure release valve.

 2. Begin final evacuation of the canisters by actuating the roughing pump, placing the

vacuum source selector valve in the roughing pump position and opening the manifold

vacuum valve.

 3. Evacuate the canisters to approximately 100 mm Hg, as indicated by the absolute

pressure gauge.

 4. Activate the turbomolecular vacuum pump, checking to be sure there is liquid cryogen

in the vacuum cryotrap.

 5. Switch the vacuum source selector valve to the high-vacuum pump position. Allow the

canisters to evacuate to 5 mm Hg, as indicated by the absolute pressure gauge.

 6. Close the canister bellows valves on all of the canisters on the manifold. Close the

manifold vacuum valve.
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 7. Disconnect the canisters from the manifold and remove any old identification tags. 

Store the cleaned canisters in the designated storage area.

2.5.3 Canister Sampling Issues

The use of canister sampling for collecting and consequently determining concentrations of

VOCs in ambient air is an integral part of the sampling strategy and recommended monitoring

requirements specified in the proposed revisions to 40 CFR Part 58. The technology utilizes stainless

steel canisters with interior surfaces conditioned to minimize surface reactivity. Conditioning allows

stable storage for many of the compounds of interest. Currently, there are two processes used to

condition canister interior surfaces. They are the SUMMA® process and the Silcosteel® process. The

SUMMA® process is a proprietary electroplating treatment that passivates the internal steel surface of

the canister. The Silcosteel® process treats the internal surface by coating it with a thin layer of fused

silica. SUMMA® canisters have been used extensively for the collection of VOC samples since 1983,

and their use is well characterized. Silcosteel® canisters have been used since 1996 and although their

use is not as well characterized as the use of SUMMA® canisters, early evaluation suggests the

Silcosteel® canisters are suitable for use in ambient air sampling. Conditioned stainless steel canisters in

a variety of volumetric sizes are commercially available from several manufacturers. 

An important advantage of the canister based methodology is that the collected whole air

sample can be divided into portions for replicate analyses (permitting convenient assessment of

analytical precision) and reanalyses using different analytical systems for specific peak identification and

confirmation. General canister sampling procedures are described in Section 2.5.1.

The presence of high levels of particulate matter can also pose problems in sampling VOCs. 

If a filter is used to collect particulate matter, ozone can interact with the particulate material trapped on

the filter, resulting in the generation of artifacts. Also, use of a filter such as a 2 μ Teflon® filter on the

inlet to the manifold or on the inlet to the monitoring system means that the filter must be changed
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frequently (i.e., daily). However, if the monitoring station is near a source of particulate matter (such as

industrial emissions), it may be necessary to use a filter and accept the necessity of more frequent visits

to the monitoring site to change the filter.

2.5.3.1 Precautions in the Use of Canisters

The canister sampling technique is not without potential problems. Primary problem areas

associated with canister sampling include contamination and sample stability. If not controlled, these

problems can significantly reduce the quality and usefulness of the data obtained using the canister

sampling technique. The general discussion and guidance presented below are intended to provide

users with information that should minimize these problems.

2.5.3.2 Contamination

Contamination may cause additional compounds to appear in the sample or increase the

concentrations of compounds present in the ambient air. Contamination may also cause loss of

sampled compounds or may introduce compounds that interfere with gas chromatographic sample

analysis. Contamination can originate from the sample canisters, canister cleanup systems, components

in the sampling systems or analytical system, and improper canister storage practices. These problems

become more significant as analytical sensitivities (detection limits) are lowered.

To minimize collection system contamination, canisters should be purchased from a reputable

supplier who uses high-quality manufacturing and final cleaning procedures. Purchase requirements

should specify contamination-free valves and criteria for maximum residual concentrations of target

compounds. New canisters should be inspected carefully for proper welding and fittings and should

always be blank checked (filled with humidified zero air and analyzed) before use to check for

contamination. Canisters with excessive contamination should be returned to the supplier or cleaned
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repeatedly until acceptable. Some contaminated canisters may appear uncontaminated immediately

after cleaning but will outgas contaminants upon storage for several weeks. All canisters in routine use

should be blank checked frequently, and particularly after extended periods of storage, to ensure that

significant contamination does not appear.

Canisters used for ambient or low-level measurements should be segregated from those used

for higher-level concentrations or for higher-molecular-weight compounds. Higher-molecular-weight

compounds are more difficult to remove from the internal canister surface. Although the application of

heat during the cleaning process can facilitate the removal of the higher-molecular-weight compounds,

other potential problems may result. For example, if heat is repeatedly applied, it is difficult to maintain

valve integrity. Also, the effects of heat on the SUMMA® treated surfaces have not been clearly

established.

Canister cleanup systems should be constructed of clean, high-quality stainless steel

components, contain suitable cryogenic traps, and be operated systematically and meticulously to avoid

system contamination from vacuum pump oil, poor quality zero air, water used in humidification

systems, room air, or other sources. 

Sampling and analytical systems should be constructed of clean, high quality components,

with particular attention paid to pumps, valves, flow controllers, or components having any non-metallic

surface. Before installation and at periodic intervals, samplers should be carefully tested for

contamination or compound loss by analyzing collected samples of zero air and known concentrations

of target compounds. This procedure is termed “certification” and allows the potential contamination

characteristics of each specific sampling system to be assessed. A canister sampling system

certification protocol, as presented in Section 2.5.1.7, should be implemented to ensure that the status

of each sampler is known prior to use.
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Equipment found to be contaminated should be tested further to attempt to identify the source

of the contamination. Contaminated components should be replaced or cleaned, and the system

recertified. Minor contamination can often be reduced by purging the system extensively with

humidified zero air.

The entire measurement system (sampling and analytical) should be checked regularly for

additive and subtractive biases to ensure that measurements obtained are representative. Such

checking involves extensive and continual testing of the analytical systems, sampling systems, sample

canisters, and canister clean up systems. Program checks also involve using humidified zero air and

standards of known concentration, to perform canister blanks and system audits. Collection of samples

from collocated systems and other quality assurance techniques should also be performed.

2.5.3.3 Sample Stability

Sample stability refers to the representativeness of the ambient air sample contained in a

canister after sample collection and storage. For the sample to be stable, the compound matrix and

concentrations of the sample must not change significantly with time. Some of the ways that the

concentration of target compounds in an ambient air sample may change after sampling are: 

C Adsorption or desorption on the interior surfaces of the canister or on particulate matter

in the sample from the ambient air;

C Chemical reaction;

C Dilution of the sample with another gas after sampling; and

C Stratification of the sample in the canister.

A number of studies26,27,28,29 have shown that a wide range of VOCs are stable in canisters

for at least 30 days. Most of the reported studies were performed in SUMMA®-treated stainless steel

canisters at pressures above atmospheric pressure. SUMMA® passivation of the interior surfaces of
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the canisters is designed to passivate the surfaces to minimize catalytic activity on the surface and to

reduce the number and activity of adsorptive sites on the canister's interior walls.

While many compounds have been shown to be stable in canisters, it is not known how these

results extend to the variety of conditions that may be encountered during the use of canisters for

PAMS. These conditions include variable quality of the canisters and their passivation process,

variable moisture content or humidity in the sample air, previous history of use or residual contamination

of the canister, sample pressure in the canister above or below atmospheric pressure, storage

temperatures, and canister age. 

Current information indicates that hydrocarbon VOCs with vapor pressures above 0.5 mm

Hg at 25EC store well in canisters. Substituted hydrocarbons, particularly the halogenated

hydrocarbons with similar vapor pressure properties, also store well in canisters. Laboratory tests

indicate that many oxygenated hydrocarbons such as aldehydes, ketones, and alcohols have limited

storage stability in canisters. Recent studies in aluminum canisters have indicated that the presence of

water in the sample has a great effect on the stability of polar organic compounds.30 Results from

another study confirm that the presence of water is a key factor in ensuring the stability of polar organic

compounds in stainless steel canisters.31 Target analytes for which there is little stability information or

for which storage stability characterization is questionable should be specifically tested for storage

stability in the canisters. These tests should be performed under typical conditions of use. 

The potential for physical adsorption as a mechanism for loss of VOCs from the vapor phase

in canisters was evaluated using the Dubinin-Radushkevich isotherm, which provides a specific

relationship between the tendency for adsorption and compound or sample specific properties such as

polarizability, vapor concentration, temperature, and equilibrium vapor pressure.32 A computer-based

model has been developed for predicting adsorption behavior and vapor phase losses for

multicomponent systems. Solely on the basis of physicochemical properties of the compounds (i.e.,

independent of considerations of the properties of the surface), the model predicts displacement of the
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more volatile VOCs from a canister surface by water vapor at relative humidities in the range of 1 to

20%. This prediction is generally consistent with experimental observations, but in most cases,

experimental conditions (i.e., canister surface properties) are not sufficiently well characterized to permit

detailed quantitative comparison with the model. The model has contributed to the following guidelines

for canister sampling of VOCs:

C Relative humidity and temperature should be measured during the sampling process so

that water vapor can be added to the canister prior to analysis if the relative humidity is

low.

C Sample pressure in the canister should be as high as possible without causing

precipitation of liquid water within the canister.

C When considering the applicability of canister sampling to new compounds, the first

parameters to be evaluated should be chemical reactivity and vapor pressure of the

compound.

C Since all species present in the canister participate in the competitive adsorption

process, consideration of the quality of data obtained from multiple canisters at the

same site should include at least semi-quantitative specification (such as total FID

response) of non-target species present in the samples.

2.5.3.4 Positive Pressure Samples

Samples obtained so that the final sample pressure is above atmospheric pressure (typically 5

to 20 psig) are considered positive pressure samples. Positive pressure samples are the least likely to

be affected by the attainment of adsorption equilibrium in the canister after sampling. The only

precaution recommended in this regard is that after sampling, no sample be withdrawn until the sample

has been in the canister for at least 24 hours to allow the adsorption equilibria to stabilize.
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2.5.3.5 Diluted Samples

Samples may be diluted by adding pressurized, clean air, N2, or other gaseous diluent

(Section 2.3.4.3.2). It is recommended that at least 24 hours elapse between dilution of a sample and

removal of an aliquot for analysis.

2.5.3.6 Canister Leakage

There are three potential sources of canister leakage. These sources are:

C Faulty canister welds; 

C Leakage at the connection of the valve to the canister; and 

C Leakage through the valve.

A faulty weld is a manufacturing defect. Faulty welds are fairly rare and can be detected by conducting

leakage acceptance tests. Canisters may also sustain physical damage. Damaged canisters should be

repaired and retested for leaks.

Leaks at the connection of the valve to the canister are the most troublesome type of leak. 

Welding the valve to the canister virtually eliminates such leaks but makes subsequent valve

replacement impractical and expensive. Usually, the valve is connected to the canister using a standard

tubing compression fitting. Properly installed, these fittings are very reliable. However, these fittings

can loosen when an operator improperly opens and closes the valve. If the valve rotates with respect

to the canister during opening and closing, small leaks in this fitting can occur. Overtightening the fitting

in an attempt to prevent such movement exacerbates the problem, as does any other physical strain on
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the connection. Short of welding the valve to the canister, vulnerability to leakage in this connection can

be greatly reduced by:

C Using an oversize fitting (e.g., 5/16-inch or 3/8-inch rather than 1/4-inch);

C Equipping the canister with a valve guard to protect the valve from physical strain; and 

C Mechanically clamping or fastening the valve to the canister or valve guard to prevent

rotation during opening or closing.

These measures are offered by some canister manufacturers and should be specified. Even with these

precautions, periodic retesting of canisters is necessary to ensure that no significant leaks in the valve

connection develop with extended use.

Leaks through the valve can occur if the valve seat has become damaged through wear or

overtightening. The practice of installing a cap on the valve connection when the canister is not

connected to a sampling system effectively minimizes sample or vacuum loss during periods of storage.

A canister may quickly be tested for obvious leaks by pressurizing it with zero air and

submerging it in clean water to look for bubbles. To check for microleaks, the canister should be

evacuated and its pressure observed for several days with a sensitive absolute pressure gauge

connected. This test is performed with the canister valve open. To check the valve for leakage through

the bellows, evacuate the canister, check the absolute pressure, close the valve, disconnect the pressure

gauge, and do not cap the valve inlet fitting. Several days later, reconnect the pressure gauge and

check the pressure. The canister pressure should not increase more than a few mm Hg during that

period.

Canisters with excessive leaks must be repaired and repassivated or replaced, but those with

relatively minor microleaks can be used for many applications if precautions are taken. Canisters

determined to have microleaks can be prepared for use just prior to sample collection and analyzed
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promptly after sample collection. Reduction of the pre- and post-sampling time reduces the potential

for bias. Between evacuation and analysis, the canister connection should be tightly capped, and the

canister should be stored in a well ventilated, non-contaminated area. Avoid storing the canisters in

automobiles and laboratories where organic materials are used. Storage or shipping containers should

be of an all-metal construction, well ventilated, and should avoid the use of foam padding and other

organic materials.

2.5.4 Sample Analysis

The methodology in Section 2.5.1 describes the collection of whole air samples into

SUMMA® canisters. The canisters are then sent to a central laboratory location for sample analysis. 

When incorporating manual methods, the user must develop procedures to perform sample analysis. 

Those using manual methods for sample collection may also incorporate the use of automated GC/FID

systems as described in Section 2.4 for sample analysis. If a manual sample analysis system is used, it

should incorporate the same basic components as discussed in the automated method which include a

sample introduction system, sample conditioning system (for moisture removal), sample concentration

system for sample enrichment, an optional cryo-focusing trap, a gas chromatograph which houses the

appropriate analytical column(s) and FID(s), and a data acquisition and processing system. Capillary

GC/FID is the recommended analytical system for PAMS but individual sites may use GC/MS or a gas

chromatograph with multiple detectors (i.e., both FID and MS).

2.5.4.1 Sample Introduction

The air sample is introduced to the primary sample concentration trap of the GC system

directly from a SUMMA® canister using a mass flow controller or other flow control device at a

constant flow rate. Samples may also be introduced for purposes of calibration and proficiency studies

directly from pressurized canisters.
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2.5.4.2 Sample Conditioning

Sample moisture must be removed from the sample stream to prevent or reduce the effects of

moisture on the primary concentration trap, analytical column(s), and detector(s) as described in

Section 2.3.4. Moisture removal allows for analysis of larger sample volumes, which provides lower

detection limits, and is crucial to the measurement of very low concentration VOCs.

Moisture may be removed from the sample stream using a Nafion® membrane sample

conditioning device. Some commercially available concentration systems incorporate the use of

Nafion® sample drying devices. New developments in this area using controlled temperature

desorption, selective temperature condensation, hydrophobic concentration traps, etc., are currently

being studied (see Section 2.3.4). The loss of polar VOCs may result from sample conditioning and

significantly affect the TNMOC measurement. The user must characterize the effects of the sample

conditioning method chosen on the TNMOC measurement and the target VOCs of interest. 

Chromatographic retention times are changed by the presence of water vapor. Also, any MS analysis

is subject to response variability because of filament changes caused by the presence of water vapor. 

In order to characterize effects, primary calibration and/or retention time standards can be analyzed

with and without the conditioning device. If a commercially available analytical system with sample

conditioning is used, vendors should provide information regarding the effects of their conditioning or

drying device.

Preconcentration techniques in use for sampling of atmospheric VOCs are susceptible to

reactions occurring during sampling involving the organic compounds of interest and other reactive

constituents of the air. The most widely recognized and significant interference results from reactions

with ozone. Chemical reactions in or on the concentration media may alter the quantities of VOCs and

may also contribute to the formation of artifacts which may be interpreted as atmospheric constituents. 

If a solid sorbent is used for preconcentration, reactive constituents of the atmosphere may also react

with the solid sorbent bed to produce artifacts. In particular, unsaturated hydrocarbons such as
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isoprene and monoterpenes can be depleted during cryogenic concentration in the presence of ozone.33

In sampling trace organic gases onto solid sorbents such as Tenax® TA, unsaturated compounds such

as styrene, cyclohexene, and monoterpenes were found to react with ozone during ambient sampling

with loss of analyte34,35,36,37,38,39,40,41 and formation of oxidized products.41,42 Artifacts such as

benzaldehyde, phenol, and acetophenone have been found to result from direct reaction of ozone with

solid sorbents, especially Tenax® TA.34,42,43,44,45,46,47 Reactions with oxidants can be reduced or

eliminated by selectively removing the oxidant from the sample flow prior to concentration of the

organic trace gases of interest. Although numerous options are available for either chemically or

physically scrubbing ozone,48 none of these options for ozone scrubbing are sufficiently or thoroughly

characterized enough for VOC sampling applications to ensure that the concentrations of the trace

organic compounds are not affected by use of the ozone scrubber. There is, therefore, no generally

accepted ozone scrubber for VOC sampling presently in use. Ozone scrubbing options for carbonyl

sampling are discussed in Section 5 of this document.

2.5.4.3 Sample Concentration

Ambient air samples are primarily concentrated using multi-bed sorbent or deactivated glass

bead traps. Sampling time and flow rate are used to determine the total volume concentrated onto the

primary trap. Multi-bed sorbent traps (Carbotrap® and Carbosieve®) are required to efficiently collect

the complete range (C2 through C12) of VOCs for O3 precursor monitoring.13

Samples are collected onto sorbent traps at sub-ambient or ambient temperatures to improve

collection efficiency. Ideally, sorbent traps selectively adsorb only the trace VOCs and do not interact

with the atmospheric constituents or introduce any contaminants into the system. Sorbent traps may

also be designed to eliminate water vapor by using hydrophobic sorbent materials. 

Sample concentration using glass bead traps, which require concentrating temperatures

around -185EC, are cooled using liquid N2, CO2, or Ar. This process is commonly known as
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cryogenic concentration or cryotrapping, and is the oldest and best known of the techniques for

collecting C2 through C12 VOCs. The glass beads provide surface area for collection of the VOCs at

the cryogenic trapping temperature. The most prevalent system being used in the PAMS uses Peltier

cooling of the concentrator to eliminate the use of liquid cryogens and make unattended automated

monitoring feasible.49

2.5.4.4 Sample Focusing or Cryofocusing

Following sample collection and concentration, the sample is thermally desorbed either

directly onto the analytical column(s) or onto a secondary cryofocusing trap. For concentrated samples

that are desorbed directly onto the analytical column(s) to separate the VOCs, the analytical column is

cryogenically cooled to aid in re-focusing the desorbed sample into a narrower band prior to

chromatographic separation. 

Concentrated samples are optionally desorbed onto a cryofocusing trap to focus the

desorbed sample into a narrow “plug” for subsequent thermal desorption and injection onto the

analytical column. The sample cryofocusing step is optional. Cryofocusing improves the peak

separation and particularly the resolution of C2 and C3 hydrocarbons, and is especially helpful when the

sample is desorbed from the concentration trap at low flow rates. Cryofocusing traps incorporate the

use of fused silica tubing that is cooled using liquid cryogen. The fused silica tubing is wide-bore (0.32-

mm I.D.) or megabore (0.53-mm I.D.) deactivated fused silica tubing that is cooled to approximately -

185EC. These traps may be packed with glass beads to increase the surface area and improve the

focusing of the sample band. Closed cycle coolers are available and have been used in field tests.17,18

2.5.4.5 Gas Chromatography

The gas chromatograph contains the analytical column(s) of choice for PAMS VOC analysis. 

Refer to Sections 2.3.5 and 2.3.6 for guidance on column configuration and selection. The user must
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configure the GC system to meet the enhanced O3 monitoring requirements and specifications, and must

also characterize the system operation prior to use. Gas chromatographic systems may incorporate the

use of single or dual-column configurations (in series or parallel) and may require sub-ambient oven

temperature programs. It is important to note that implementing systems that eliminate the need for

sub-ambient column oven temperatures will reduce the overall cryogen consumption of the system.

Gas chromatographic systems employ the use of a PC-based data acquisition and processing

system for peak integration and quantitation. Data acquisition and processing systems are comprised of

hardware and software that perform data acquisition, peak detection and integration, peak identification

by retention time, post-run calculations and quantitation, calibration, peak reintegration, user program

interfacing, and hard copy output. Data are automatically stored on magnetic media (e.g., hard disk or

floppy diskette).

The GC acquisition and processing software is typically developed and supplied by the GC

manufacturer and should contain the necessary algorithms to acquire, integrate, and identify the

chromatographic peaks by retention time. The system should be capable of producing an electronic

and hard copy report file that contains the information needed to identify the sample, and a listing of all

peaks detected in the chromatogram. This listing should contain the peak name if the peak is a target

compound. All detected target and non-target peaks should be reported with the associated

concentration in ppbC, and a retention time. The listing should also contain the TNMOC and PAMHC

estimates as calculated by summing the concentrations of peaks as described in Section 2.2. See

Section 2.6.1 for a more detailed discussion on data processing capabilities of automated GC systems.

2.5.4.6 Analytical System Calibration

The detector response of the analytical system should initially be calibrated with multiple level

propane standards over the expected sample concentration range. Benzene is suggested as a second

primary standard to address the needs of dual-column systems that employ the use of column switching
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techniques. The primary calibration standard is used to generate a per Carbon response factor for

determining the concentration of each target VOC, as well as the TNMOC. It is unnecessary to

determine compound specific response factors for each of the target VOCs presented in Table 2-1,

because the Carbon response of the FID to these compounds is approximately linear. It is appropriate

to measure each compound concentration in terms of ppbC using the relative response factor

determined from the primary standard. Refer to Section 2.4.2.3 for a more detailed discussion of

analytical system calibration.

2.5.5 System Operation

This section provides guidance and general operating considerations for initial system set-up,

optimization of sampling parameters, and field operation for the GC system.

2.5.5.1 Initial System Set-up

During the initial set-up of the system, several parameters must be evaluated to optimize the

system operating conditions. Critical parameters include, but are not limited to, the sample collection

flow rate and sample integration time, sample concentration and desorption conditions, oven

temperature program parameters, detector calibration, and the peak detection and integration methods

used by the data acquisition and processing system. These parameters are optimized by varying the

operating conditions to achieve the best resolution and detection of the target VOCs using primary

calibration and retention time calibration standards.

Prior to making VOC measurements, the baseline performance of the system must be

thoroughly documented. The information from the system baseline characterization is used to determine

system specific target compound retention times, relative retention times, identification of co-eluting

compounds and matrix effects, internal standard retention times and interferences, and detection limits. 
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Baseline characterization is a very important step in determining the overall quality and validity of the

measurement data. See Section 2.3.7 for a discussion of pre-measurement system characterization.

The system should initially be set up and tested for conformance with the manufacturer's

operational specifications. Under terms of agreement for purchase, the manufacturer should be

required to provide a detailed instruction manual for system operation and be required to provide initial

system setup, user training, and demonstration of adequate system performance. See System

Specifications for automated GC systems in Section 2.4.5 as guidance for procurement.

2.5.5.2 Sampling Parameters 

Determination of optimum sampling conditions is dependent on field conditions (i.e., expected

compound concentration ranges, humidity, temperature, etc.), desired sensitivity (detection limit),

cryogen consumption, and sample trapping efficiency. During the setup period, these sampling

parameters should be evaluated to determine the optimum conditions. The primary sampling parameters

are the sample collection frequency and the sample collection or integration time.

2.5.5.3 Operation

The system should be operated in accordance with an SOP that is prepared by the user

based on the information obtained during the setup and familiarization period. The system should be

maintained by a qualified operator who should perform the routine operational and critical quality

control functions as specified in the SOPs. Operational parameters should be adjusted, if necessary, so

that the data quality objectives are met. Primary calibration checks should be performed at least once

each week or at an interval consistent with the individual site standard operating procedure. Retention

time calibration checks should be performed at least once per week or at an interval consistent with the

individual site standard operating procedure to provide retention time reference information for
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validating compound identifications. The retention time calibration standard can also be used to track

the FID response and compound recovery to determine when recalibration is necessary.

Detailed SOPs for operation of the system must be developed. The SOP should be based

on information obtained during the set-up and familiarization period and the requirements of the

monitoring program. Refer to QA/QC Section 2.8.3.1 for a more detailed discussion of SOP

development.

2.6 Data Processing Capabilities of Automated VOC Systems and Submittal of

VOC Data to the AIRS AQS Data Base

As prescribed in Section 58.45 of 40 CFR Part 58, PAMS Data Submittal, the data from

VOC measurement systems is required to be submitted to EPA's Aerometric Information Retrieval

System (AIRS) Air Quality Subsystem (AQS) within 6 months following the end of each quarterly

reporting period. The agencies may ultimately use the data to make attainment/ nonattainment

decisions, track VOC emission inventory reductions, provide input to photochemical models, prepare

air quality trends, and characterize population exposure to O3. The data that are ultimately submitted to

AIRS must be uniform across all networks and consistent with enhanced O3 monitoring requirements. 

The overall approach to generating data from automated GC systems involves the same basic

components (A/D converter, personal computer, acquisition and processing software, and data storage

module). These basic components comprise the automated GC data acquisition and processing

system. The VOC concentration data are ultimately generated in an electronic file and hard copy

format specific to the data acquisition and processing system used. The information generated must

finally be put in the required format for submittal to the AIRS data base. 
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This section discusses how data acquisition and processing occurs, the data acquisition and

processing capabilities of automated VOC systems and guidance on formatting and submitting the data

to the AIRS data base.

2.6.1 Data Processing Capabilities of Automated VOC Measurement Systems

Automated VOC systems employ a variety of hardware and software strategies to collect

and process chromatographic data. Despite these differences, their overall approach to processing

data involves the same basic system components and procedures. This section provides background

and important details on automated VOC data processing. 

The basic components of a typical data acquisition and processing system are an analog

signal generated by the chromatographic detector, an Analog/Digital (A/D) converter, a personal

computer for acquiring/processing data, and a data storage module, where data are stored on magnetic

media. After a sample is injected, the sample components are chromatographically separated and sent

to the detector. The detector electronics respond to the amount of the analyte passing through the

detector and generate an electronic signal which will be either analog or digital. Digital signals are sent

directly to the next step in processing; analog signals must first be digitally converted before further

processing can occur. Digitized signals are “filtered” by specified method acquisition parameters and

the resulting data stored to a file in the data acquisition system.

After the analysis is complete, the post-run method parameters further refine the raw data file

by applying integration algorithms and parameters, compound identification requirements, calibration

response factors and data reporting format to generate a processed data file. Processed data files

generally contain retention time data, peak height, peak area, and concentration data: all the elements

needed to compile a data report in a specified format. The entire process from signal generation is

repeated for each sample during automated operation. This report generating process is depicted in the

flowchart in Figure 2-16 and discussed in greater detail in Section 2.6.1.1. 
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Signal from 

Detector

A/D

Converter

Method 

Acquisition

Parameter

Applied

Raw Data

Generated

Raw Data

Stored

Post-run

Method 

Parameter

Applied

Processed

File Generated

Conversion

to ETF*

Is

Signal

“Digital”?

To Database

Application * Electronic Transfer Format

• Detect peaks

• Establish baseline

• Separate peaks

• Integrate peaks

• Identify 

• Calculate concentration

• Generate report

• Chromatogram

RT

RRT

RT window {

o/s/g/m/3797pams/jr-fig2.ppt

No

Yes

Figure 2-16. Report Generating Process
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2.6.1.1 Data Acquisition and Processing

This section presents a more detailed explanation of the steps involved in data acquisition and

processing.

Signal Output from Detector—An electronic signal, usually an analog voltage signal, is

produced by the detector during a chromatographic analysis and is measured by the detector

electrometer. The amplitude of the signal is related to the concentration of the sample. For the FID

response to hydrocarbon compounds, the relationship is a direct proportion. Depending on the type of

detector, the signal from the electrometer will be amplified before it is processed further. The

continuously varying analog signal must be converted to discrete bits for a computer data system to

process the data. These discrete bits are considered a “digital” signal. Digital signals can be

transmitted directly from the output terminal to the next step in the process. 

A/D Conversion—Computer systems handling data for chromatographic systems require

the data to be in digitized form prior to storage. Analog-to-Digital converters, also known as A/D

converters, take the continuously variable analog signal and “cut” it into discrete slices to make a digital

signal for computer-based storage. These slices represent the detector response during a specific slice

in time. The sum of these signals is proportional to the sample component concentration. These digital

slices are the fundamental data stored for subsequent data processing.

Signal Filtering - Method Acquisition Parameters—To acquire data, the analytical

system must be given a data acquisition method. This method tells the instrument how to collect the

data and which data are important. The method controls the instrument by starting and stopping data

collection and by controlling how frequently the data processor takes data slices, which is called the

sampling rate. The peak threshold for data collection, or the minimum signal amplitude above

background, is also specified. The signals collected using this set of conditions are referred to as raw

data. As raw data are acquired, the data are kept in the CPU memory until acquisition is complete. 
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Raw Data Storage—After sample collection is complete, the raw data are written to an

electronic storage module (e.g., computer disk) as a discrete data file. The raw data reside in memory

(CPU) until the PC controlling data acquisition is available to receive the data. Some systems have

capacity within memory to temporarily hold multiple raw data files and then to download the files to the

PC storage module at specified intervals. These systems must send data to the PC before memory is

exceeded or data may be lost. Once the data files are permanently stored to disk they can be backed

up and archived in long term storage.

Post-run Data Interpretation/Processed File Generation—Analytical methods contain

post-run instructions for interpreting raw data files. Accurate measurement of ozone precursors

depends heavily on accurate and consistent chromatographic data. Analytical methods should be

tailored to enhance the accuracy of output data. The term “peaks” will be used to describe the area

underneath the signal curve. In this section, the basic concepts and issues that the data system must

manage are presented. This information should be useful to operators setting initial conditions for postrun data processing for their particular equipment. Information presented here should also help direct

corrective action when problems are identified with processed chromatographic data. Post-run

routines accomplish the following tasks:

C Peak detection;

C Baseline determination;

C Peak separation and integration;

C Timed events application - controlling peak detection and integration parameters at

preset times;

C Peak identification;

C Concentration calculation;

C Report production; and
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C Chromatogram generation.

Peaks are detected by applying criteria for discriminating changes in signal associated with

compound detection from the background signal. Certain parameters, such as minimum peak width

and signal sampling rate, shape the chromatogram during acquisition by affecting the amount of detail. 

A higher sampling rate and smaller peak width will enhance the fine detail of the chromatogram. In

contrast, detail will be lost with smaller sampling rates and greater peak widths. Since detection

algorithms commonly monitor the rate of change of the signal -- looking at slope changes and the rate of

slope change -- to determine the start, apex and end of a peak, the number of points defining a peak is

very important for accurate detection. Some techniques, such as peak bunching, can be used to

“smooth” peaks by averaging adjacent signal slices and, therefore, screening unwanted noise. 

Excessive bunching will also cause loss of chromatographic detail, biasing quantitation high for some

compounds and completely eliminating others.

To integrate detected peaks, the data system determines how closely-eluting peaks are to be

separated and draws a baseline accordingly. Well-separated peaks require simple integration treatment

- either drawing a baseline from the start of one peak to the start of the next or separating peaks by

adding drop lines to the baseline. For overlapping peaks, most systems have criteria based on peak

proximity and size comparisons that allow reasonable quantitation. “Timed events” can be used to

tailor integration schemes to a particular chromatogram or set of chromatographic conditions by

changing integration parameters to be modified according to a user-defined timetable. A timed events

table queues changes in integration and detection factors to enhance data accuracy. These

modifications can help compensate for changes in peak characteristics, such as peak width, peak

shape, and incomplete separation, resulting in more accurate and consistent data treatment.

Peak identification is based on retention time (RT) windows or retention time relative to a

reference peak or internal standard.
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Concentration calculations for most automated VOC systems use external standard-based

quantitation. A calibration curve is generated for the primary calibration compounds and each response

factor from the curve used for quantitation of the C2 through C12 VOCs. For unidentified peaks, the

primary response factor for propane is used to estimate concentration in ppbC.

Report Production/Chromatogram Generation—Many data systems allow great

flexibility with reporting format, allowing the user to custom-build hardcopy reports. The hardcopy can

be generated directly by the data system software or through a third-party data package. The

information compiled in the report includes, but is not limited to, retention time, peak area, type of

integration, and limits of concentration. The user can automate post-run data handling to save the

processed data file in a specified electronic format to facilitate electronic data file transfer to a

spreadsheet or data base.

Reprocessing Capabilities—Chromatographic data systems generally allow the user to

change and re-apply data interpretation parameters to adapt them to a given set of chromatographic

conditions. Frequently, changes in peak width, bunching factors, integration approach, and

identification parameters are needed to compensate for changing sample conditions, flow rates, and

column degradation (over time), and to generate more consistent accurate data. The data can also be

reprocessed to apply different calibration response factors as needed.

Data Format Options—Data can be presented in two forms - hardcopy report or

electronic data file. While hardcopy reports facilitate review, electronic data files allow the user to

manipulate results to a desired format and to transfer information quickly. The electronic data formats

available as part of the data system package vary from vendor to vendor. Most systems are capable of

providing ASCII output files; others can produce comma-delimited files or AIA format (Analytical

Instrument Association's Chromatography Data standard format), as either a routine analysis file or a

result from a post-run program. This file then needs to be reformatted for submittal to AIRS as

discussed in Section 2.6.2.
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Telemetry—Telemetry is defined as remote interaction with the PAMS analytical system,

including communication, operation, and data transfer. Telemetric capabilities may be a part of the

analytical system as purchased, or these capabilities may be acquired by purchase of a commercial

software package and any required associated hardware. At the very least, telemetry can be used to

communicate directly with the analytical system to assess or modify the operation, as well as to transmit

data files to a centrally-located host computer for further processing. Other potential telemetric

capabilities may include remote operation of devices at the PAMS site, such as a standards injection

system, or to perform a system malfunction auto-call should the system recognize that it has a problem.

2.6.2 AIRS AQS Data Submittal

This section provides guidance for the submittal of O3 precursor monitoring data into the Air

Quality Data Storage Subsystem of AIRS, which is a computer-based system for handling the storage

and retrieval of information pertaining to airborne pollutants. AIRS AQS is administered by the U.S.

Environmental Protection Agency, Office of Air Quality Planning and Standards, Information Transfer

and Program Integration Division (ITPID), Information Management Group. The AIRS Air Quality

Subsystem (AQS) contains data submitted by state and local agencies, and EPA reporting

organizations. These data correspond to the data previously handled by the SAROAD system. AIRS

AQS includes descriptions of air monitoring sites and monitoring equipment, measured concentrations

of air pollutants and related parameters, and calculated summary and statistical information. AIRS

AQS is currently being re-engineered, but no information regarding operation of a re-engineered AIRS

AQS system is presently available.

All VOC and carbonyl data collected for the enhanced O3 monitoring network must be

submitted to AIRS AQS in the form of transactions. A transaction provides the monitoring information

for a particular parameter (compound) for a given day. Because the VOC target list includes over 50

compounds, over 50 line transactions are necessary to input the results from one VOC sample. 
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Because the carbonyl target list includes three compounds, three line transactions are necessary to input

the results from one carbonyl sample. Data can be input on-line one transaction at a time or in groups.

Transactions are used to provide data and control information for updating the AIRS data

base. Table 2-5 shows how the various transaction types are related.

Although transactions can be input into AIRS on-line, batch processing is recommended

considering the volume of data generated to meet the minimum network monitoring requirements. Prior

to submittal to AIRS, all data must be formatted to conform to the 80-character per line format as

required by AIRS and saved as an ASCII file. A group of transactions (e.g., data from one week) can

be saved as one file and loaded together into AIRS.

Within a transaction are fields corresponding to specific information. A field or “slot” is a

column or set of columns in the 80-character input line where a specific piece of data is placed. Four

general types of values are used to code the transactions: codes, dates, numeric data, and

alphanumeric data. Codes must be entered exactly as they are stored in the Geo-Common Subsystem

of AIRS. For example, a county code is three digits and all three digits of the code must be entered,

including any leading zeros. Dates are entered in the YYMMDD format, where YY is the last two

digits of the year, MM is the month number, and DD is the day of the month. Each part is two digits

and any leading zeros must be included. Numeric values must be entered right-justified and do not

have to include leading zeros. Alphanumeric values should be entered left-justified in the field.
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Table 2-5. AIRS Transaction Types

Transaction Type Related Transaction Records Have The Same......

Site (A1, A2, A3, A4, A5,

A6, A7)

Site-ID (state, county, site codes)

Monitor (F1, F2, F3, F4, F5) Monitor-ID (site-ID, parameter, and POC codes)

SLAMS (M, N, P, R, S, T, U,

V)

Monitor-ID, year, transaction type (any of codes M through V)

Raw Data:

Hourly (1) Monitor-ID, year, month, transaction type 1

AND type 4 transactions with the same monitor-ID

Daily (2) Monitor-ID, year, month, transaction type 2

AND type 4 transactions with the same monitor-ID

Composite (3) Monitor-ID, year, period, transaction type 3

Special:

Minimum Detectable Value

(Z) 

Monitor-ID, transaction type Z

Null Value (4) Monitor-ID, transaction type 4

Precision/Accuracy (8, 9) Monitor-ID, year, month, transaction type

Each field occupies a specific location in the 80-character per line format. For example, the

two digit code that identifies one of the 50 states, U.S. territories, or Washington, D.C., is called the

State Code and is placed in columns 2-3 of the 80-character per line format. There are also

international data, i.e., the code for Mexico is 80. The structure and placement of the fields in each

transaction is specific and must be carefully followed. 

All data collected must be entered into AIRS. Quantifiable data which are below the

detection limits should be entered as the quantified value. The raw data values will be retained within
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AIRS, but when any summary statistics are generated the system will automatically replace values

below the detection limits with a value that is one-half the detection limit prior to performing

calculations. Raw data listings will maintain the actual values. If the compound response is below the

detection limit and the data are not quantifiable, a sample value of zero is entered into AIRS. This value

will indicate to AIRS that the compound of interest was analyzed for but not present at a quantifiable

level. If a sample is missed or invalidated for any reason, appropriate null values or validity flags are

used.

Although sampling is conducted in accordance with 40 CFR Part 58 on local time, data are

reported to the AIRS in local standard time.

The following sections illustrate the specific formats required for the various types of

transactions.

2.6.2.1 Initial AIRS AQS Setup

A valid Time Sharing Option National Computing Center (TSO NCC) UserID and

Password must be established prior to the submittal of any monitoring data into AIRS. UserIDs can be

obtained by contacting the appropriate AIRS AQS Regional Coordinator. A list of the current

coordinators is provided in Table 2-6.

The Air Quality (AQS) data storage processes operate on the input data transactions while

they reside in a “screening file.” If data are resident on a PC, the file(s) must first be transferred to a

TSO dataset and then to an AIRS screening file. The screening file acts as a submittal buffer that

allows entry and review of data before inclusion into AIRS. Each data storage user group of AIRS has

a screening file for that organization's transactions. The records of an input transaction file are first

loaded into a screening file where they remain while the authorized users examine and modify them

through the AQS data storage processes. The transactions in the screening file are edited and
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corrected by the user and examined by the AIRS Data Base Administrator prior to inclusion in AIRS. 

Screening files should exist for state agencies. When the UserID is established, a request should be

made to the AIRS AQS Regional Coordinator for access to the appropriate screening file.
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Table 2-6. Current AIRS AQS Regional Coordinators

Region I

Ms. Wendy McDougall

U.S. EPA, Region I

60 Westview Street

Lexington, MA 4323

(617) 860-4323

Region VI

Ms. Ruth Tatom

U.S. EPA, Region VI

1445 Ross Avenue

Dallas, TX 75202-2733

(214) 655-8355

Region II

Mr. Ed Finfer

U.S. EPA, Region II

290 Broadway - 20th Floor

New York, NY 10007-1866

(212) 637-4244

Region VII

Ms. Joyce Sousley

U.S. EPA, Region VII

25 Funston Road

Kansas City, KS 66115

(913) 551-5050

Region III

Ms. Catherine Brown

U.S. EPA, Region III

841 Chestnut Street

Philadelphia, PA 19107

(215) 597-6149

Region VIII

Mr. Dale Wells

U.S. EPA, Region VIII (8ART-TO)

999 18th Street, Suite 500

Denver, CO 80202-2405

(303) 293-0967

Region IV

Mr. Darren Palmer

U.S. EPA, Region IV

345 Courtland St., NE

Atlanta, GA 30365

(404) 347-3555 x4184

Region IX

Mr. Jim Forrest

U.S. EPA, Region IX

75 Hawthorne Street

San Francisco, CA 94105

(415) 744-1291

Region V

Mr. William Damico

U.S. EPA, Region V (SQ-14J)

77 W. Jackson Boulevard

Chicago, IL 60604-3590

(312) 353-8207

Region X

Mr. Bill Puckett

U.S. EPA, Region X (ES-095)

1200 6th Street

Seattle, WA 98101

(206) 553-1702

Minimum detectable limit values in AIRS may be specified for each of the PAMS target

compounds by the reporting agency. If no specific value is enumerated by the reporting agency, AIRS

will utilize a default value defined in the Geo-Common File for the parameter, generally 0.1 ppbC.
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2.6.2.2 Site and Monitor File Updates

Before any VOC or carbonyl data are submitted to AIRS AQS, transactions must be

submitted to update the monitor information in AIRS. These transactions, called Type F transactions,

provide information concerning the compounds of interest, the organizations involved, and the relative

monitor dates. Column 1 is the transaction type code. For the Type F transactions, the entry in

Column 1 is “F.”

The monitor ID is placed in columns 2-16 and is comprised of the State, County, and Site

Code (columns 2-10) where the sample was collected, the parameter (columns 11-15), and Parameter

of Occurrence (POC) code (column 16). The POC code is used to distinguish between different

monitors at the same site that are measuring the same parameter. The first monitor at the site is

generally identified with POC = 1, with additional monitors at the same site measuring the same

compound identified with POC = 2, etc. If a new instrument were installed to replace the original

instrument used as the first monitor, that would be the same monitor and it would have POC = 1, even

if the sampling method or interval were changed. 

The monitor type is indicated in column 17. For PAMS Meteorological and VOC sites, the

monitor type is “3,” indicating other. Once the monitor information has been submitted to the AIRS

AQS, the Regional Coordinator should be contacted. The Regional Coordinator will then request that

the network be approved as a PAMS monitor.

The date when the monitor type became effective is recorded in columns 18-23. The date is

recorded in the YYMMDD format. The year, month, and day are each two digits and any leading

zeros must be included.

The next 9 columns indicate the organizations associated with analysis and collection of the

sample and reporting the subsequent data. Columns 24-26 are reserved for the code indicating the
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analysis laboratory. Columns 27-29 indicate the collection laboratory. The reporting organization code

is stored in columns 30-32. These codes can be found in the AIRS Geo-Common Subsystem and

must be entered exactly as they appear in that subsystem.

The date when the reporting organization became effective is recorded in columns 33-38. 

The date is recorded in the YYMMDD format. The year, month, and day are each two digits and any

leading zeros must be included.

The date when the sampling program began is recorded in columns 39-44. The date is

recorded in the YYMMDD format. The year, month, and day are each two digits and any leading

zeros must be included.

The 4-digit code indicating the urban area represented by the site is placed in columns 72-

75. The urban area codes can be found in the AIRS Geo-Common Subsystem and must be entered

exactly as in the subsystem.

The PAMS required sampling frequency code is placed in column 76. Table 2-7 presents

possible codes for the different sampling frequency requirements.

The transaction ID is placed in column 79. For a Type F1 transaction, the ID is “1.”

The action code placed in column 80 indicates the type of data base processing to be

performed by this transaction. In order to insert new values into the database, “I” is placed in column

80. Should modification to existing monitor information be necessary (e.g., a change in the reporting

organization, etc.), an “M” is placed in column 80. The deletion of existing monitor information is

indicated with a “D” in column 80.
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Table 2-7. AIRS Sampling Frequency Codes

Code Sampling Frequency

A Daily 24 1-Hr Samples - PAMS

B Daily 8 3-Hr Samples - PAMS

C Daily 1 3-Hr Sample - PAMS

D Daily 1 24-Hr Sample - PAMS

E Daily 4 6-Hr Samples - PAMS

G Every 3rd Day 24 1-Hr Samples - PAMS

H Every 3rd Day 8 3-Hr Samples - PAMS

I Every 3rd Day 1 3-Hr Sample - PAMS

J Every 3rd Day 1 24-Hr Sample - PAMS

K Every 3rd Day 4 6-Hr Samples - PAMS

L Every 3rd Day 4 3-Hr Samples - PAMS

M Every 6th Day 24 1-Hr Samples - PAMS

N Every 6th Day 8 3-Hr Samples - PAMS

O Every 6th Day 1 3-Hr Sample - PAMS

P Every 6th Day 1 24-Hr Sample - PAMS

One Type F1 transaction is necessary for each monitor. Unique Type F1 transactions need

to be submitted only once prior to the submittal of monitoring data. Should any of the information

change, the Type F1 transactions must be modified reflecting the changes. If Type F1 transactions

have already been submitted and no modifications are necessary, it is not necessary to submit Type F1

transactions again before the raw data are submitted.

Figure 2-17 shows the column placement of each of the fields for a Type F1 transaction. 

The “F” in column 1 (transaction type) and the “1” in column 79 (transaction ID) denote the Type F1
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transaction. Below the figure is an example Type F1 transaction. For this example, site 25-009-2006

(columns 2-10) began monitoring for isoprene (indicated by 43243 in
o:/s/g/morr/3797/pams/hobson/graph2.ppt Transaction Type State County Site Parameter

POCMonitor Type

Data Type Effective

Analysis Lab

Collect Lab

Report ORG.

Report ORG.Data Effective

Sampling Began

Sampling EndedLast EPA Audit

Project Class

Action TypeAction ReasonDominant SourceMeasurement ScaleMonitor Type Objective

Nonattainment AreaUrban Area Represented

PAMS Required Sampling FrequencyMonitor Open Data Number

Transaction ID

Action

Monitor ID

Dates

 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80

F

12345678901234567890123456789012345678901234567890123456789012345678901234567890

F2500920064324313900601001001001940601940601 1120P 1I

 1 2 3 4 5 6 7 8

Figure 2-17. Column Placement for a Type F1 Transaction

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columns 11-15) on June 1, 1994 (indicated by 940601 in columns 18-23). The state agency (001)

analyzed and collected the samples, and reported the results. This site was in the Boston urban area

(as indicated by 1120 in columns 72-75). The required sampling frequency was one 24-hour sample

every sixth day (indicated by P in column 76). Because isoprene previously had not been monitored at

this site, this transaction was inserted into AIRS (indicated by “I” in column 80). Had it been necessary

to modify information, a “M” would have been placed in column 80. It is important to note the column

placement of the codes in the transaction file. For example, because it is not required to input a

dominant source, column 64 is left blank. The second transaction indicates that the same site began

monitoring for formaldehyde (parameter 43502) on June 1, 1994, as well. Many of the necessary

codes are provided in subsequent sections of this document. These and other codes can also be found

in the Geo-Common Subsystem of AIRS. 

In addition to Type F1 transactions, comments need to be added to the site information to

identify the configuration of the sampling/analysis equipment used. Comments can be added to the site

cards by submitting Type A6 (or A7) cards. Type A6 transactions add a comment to the Line 1

comment line, whereas the Type A7 transactions add a comment to the Line 2 comment line. If a

comment does not appear on Line 1, submit a Type A6 transaction. If a comment currently appears on

Line 1 and no comment appears on Line 2, submit a Type A7 transaction. If comments appear on both

lines, submit either transaction where the comment includes the original comment plus the comment

concerning the configuration of the sampling/ analysis equipment. If additional comment space is

needed, the Line 2 comment may be used as a continuation of Line 1. A list of possible configuration

comments appears in Table 2-8. Because of the limited space within the comment lines, it is important

to make the comments concise yet as informative as possible. Choose the combinations of codes that

best reflect the configuration of the sampling/analysis equipment.
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Table 2-8. Configuration Comments for Type A6 or A7 Transactions

Monitoring Equipment Code Description

VOC GC 

(Choose one)

Single FID

Dual FID

GC configured with one FID

GC configured with two FIDs

Dryer 

(Choose one)

W/Dryer

W/O Dryer

Dryer is in line

No dryer is used

Concentrator

(Choose one)

Sorbent

Cryo

Sorbent sample concentrator

Cryogenic sample concentrator

Columns BP1

GS-Q

RTx

Al2O3/Na2SO

4

SGE, Inc. BP1 (0.22 mm diameter, 50 m

length)

J&W® GS-Q (0.53 mm diameter, 30 m length)

Restek® RTx-502.2 (0.53 mm diameter, 25 m

length)

Hewlett Packard® Al2O3/Na2SO4 (0.32 mm

diameter, 50 m length)

Carbonyl Ozone

Scrubber

(Choose one)

Denuder

Cartridge

KI Denuder

Sep-Pak® KI Cartridge

Column 1 is the transaction type and for Type A6 (or A7) the transaction type is “A.”

Columns 2-10 are the State, County, and Site Code where the sample is collected. The

comment will be added to the Site File for this site.

Columns 11-78 are reserved for the site comment. If a Type A6 transaction is inserted, the

comment will appear on Line 1. A Type A7 transaction will place a comment on Line 2. 
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Column 79 is the transaction ID. Type A6 transactions require a “6” in column 79, whereas

Type A7 transactions require a “7” in column 80. If a Type A6 transaction is submitted, a comment is

placed on Line 1. A comment is placed on Line 2 if a Type A7 transaction is submitted.

The action code placed in column 80 indicates the type of data base processing to be

performed by this transaction. In order to insert a new comment into the site files, an “I” is placed in

column 80. Should modifications to existing values in the site files be necessary, a “M” is placed in

column 80 to indicate a modify transaction. For a modify transaction, any alteration to the current site

comments will completely replace that comment. Therefore, any change will require that the entire field

be re-entered. Deletions are not valid for Type A6 (or A7) transactions. To delete existing site

comments, fill columns 11-78 with asterisks on a modify transaction. Be sure to fill all columns with

asterisks or only asterisks will be stored in the Site File as the Site Comments. 

Figure 2-18 illustrates the placement of information for a Type A6 transaction. Below the

figure is an example Type A6 transaction. The Type A6 is indicated with an “A” in column 1

(transaction type) and a “6” in column 79 (transaction ID). For this example, site 25-009-2006

(Columns 2-10) has the comment PAMS MONIT-CRYO-DUAL FID BP1/RTx W/Dryer -

DENUDER (Columns 11-78) inserted (column 80) as the Line 1 comment. Only one Type A6 (or

A7) transaction should be created for each site.

Type F1 and A6 (or A7) files should be saved as ASCII files (multiple lines can be saved as

one file). The files should then be transferred to the EPA mainframe for a subsequent loading into the

screening file. Once Type F1 and A6 (or A7) transactions have been loaded, they must be edited

(three edit levels). Any necessary corrections must be made and an update requested. This process is

described in Section 2.6.2.4.

2.6.2.3 Raw Data Transactions
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Following the update of AIRS AQS with the Type F1 and A6 (or A7) transactions, AIRS

AQS will accept raw data transactions. As with the Type F1 transactions, codes have been assigned

to the various fields required for the raw data transactions. Tables 2-9 and 2-10 present the AIRS

codes assigned to the target VOC and carbonyl O3 precursor compounds, respectively. Table 2-11

presents the various method codes associated with PAMS sampling and analysis. 
o:/s/g/morr/3797/pams/hobson/graph1.ppt Transaction Type State County Site

Site Comment

Transaction IDAction

 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80

A

12345678901234567890123456789012345678901234567890123456789012345678901234567890

A250092006PAMS MONIT-CRYO-DUAL FID DB-1/RTx W/DRYER -DENUDER 6I

 1 2 3 4 5 6 7 8

Figure 2-18. Column Placement for a Type A6 Transaction

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Table 2-9. Target Volatile Organic Compounds

AIRS

Parameter

Code

43203

43206

43202

43205

43204

43214

43280

43212

43216

43217

43221

43224

43220

43243

43226

43227

43244

43242

43284

43285

43230

43245

43231

43262

43247

45201

43248

43263

43291

Target

Compound

Name

Ethylene

Acetylene

Ethane

Propylene

Propane

Isobutane

1-Butene

n-Butane

trans-2-Butene

cis-2-Butene

Isopentane

1-Pentene

n-Pentane

Isoprene (2-methyl-1,3-butadiene)

trans-2-Pentene

cis-2-Pentene

2,2-Dimethylbutane

Cyclopentane

2,3-Dimethylbutane

2-Methylpentane

3-Methylpentane

1-Hexene*

n-Hexane

Methylcyclopentane

2,4-Dimethylpentane

Benzene

Cyclohexane

2-Methylhexane

2,3-Dimethylpentane

AIRS

Parameter

Code

43249

43250

43232

43261

43252

45202

43960

43253

43233

45203

45109

45220

45204

43235

45210

45209

45212

45213

45207

45211

45208

43238

45225

45218

45219

43954

43141

43102

43000

Target

Compound

Name

3-Methylhexane

2,2,4-Trimethylpentane (isooctane)

n-Heptane

Methylcyclohexane

2,3,4-Trimethylpentane

Toluene

2-Methylheptane

3-Methylheptane

n-Octane

Ethylbenzene

m/p-Xylene

Styrene

o-Xylene

n-Nonane

Isopropylbenzene (cumene)

n-Propylbenzene

m-Ethyltoluene (1-ethyl-3-methylbenzene)

p-Ethyltoluene (1-ethyl-4-methylbenzene)

1,3,5-Trimethylbenzene

o-Ethyltoluene (1-ethyl-2-methylbenzene)

1,2,4-Trimethylbenzene

n-Decane

1,2,3-Trimethylbenzene

m-Diethylbenzene

p-Diethylbenzene

n-Undecane

n-Dodecane*

TNMOC**

PAMHC***

* These compounds have been added as calibration and retention time standards primarily for the purpose of retention

time verification. They can be quantitated at the discretion of the user.

** Total Nonmethane Organic Compounds

*** PAMS Hydrocarbons
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Table 2-10. Carbonyl Target List

Compound AIRS Parameter Code

Reporting Requirement for

PAMS

Formaldehyde 43502 Required

Acetaldehyde 43503 Required

Acetone 43551 Required

2,5-Dimethylbenzaldehyde 45503 Optional

Acrolein 43505 Optional

Benzaldehyde 45501 Optional

Butyr/Isobutyraldehyde 43329 Optional

Crotonaldehyde 45316 Optional

Hexanaldehyde 43517 Optional

Isovaleraldehyde 43513 Optional

Propionaldehyde 43504 Optional

Tolualdehydes 45504 Optional

Valeraldehyde 43518 Optional

Methyl ethyl ketone 43552 Optional
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Table 2-11. AIRS Method Codes

Category Analysis Method AIRS Method Code

VOC - Automated Chrompack International Auto-TCT

Concentrator with Chrompack CP 9000 GC

124

Entech Laboratory Automation Model 2000

Concentrator with Hewlett-Packard 5890 Series

II GC

122

Nutech Model 3550A Concentrator with

Hewlett-Packard 5890 Series II GC

123

Perkin-Elmer Corporation Model ATD-400

with Perkin-Elmer Model 8700 GC

128

Varian Chromatography Systems Ozone

Precursor System with Varian Model 3600-CX

GC

129

 VOC - Manual Chrompack International GC 125

Hewlett Packard Company GC 126

Perkin-Elmer Corporation GC 127

Varian Chromatography Systems GC 130

Carbonyl Cartridges coated with DNPH on silica analysis

by HPLC with KI O3 scrubber

202
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Sample frequency codes and sample interval codes are listed in Table 2-7 and Table 2-12,

respectively. Units codes are listed in Table 2-13. Hourly data start hours are listed in Table 2-14. 

Null values are listed in Table 2-15. Other codes which may be necessary can be found in the

Geo-Common Subsystem of AIRS.

There are three types of raw data transactions: hourly, daily, and composite. The hourly

raw data transaction is used when the sample is collected for any period of time less than 24 hours. 

Hourly data are indicated with a “1” in the transaction type field (column 1). The daily raw data

transaction is used when the sample is collected for at least 24 hours. A transaction type code of “2” in

column 1 indicates daily data. If several samples obtained at different times are combined and analyzed

as one, the composite raw data transaction is used. 

Raw data transactions are generally inserted into AIRS, but modifications to or deletions of

previously inserted data can also be performed. An insertion is indicated with an “I” in the action field

(column 80), a “M” indicates a modification, and a “D” indicates a deletion.

Hourly Data—Hourly data are those which are collected for a period of time less than 24

hours. Because several hourly samples can be collected within a given day, AIRS allows for several

results for one parameter (compound) to be input with one transaction. Figure 2-19 illustrates the

format for hourly data. 

Composite data are indicated with a “3” in the transaction type field and will not be used for PAMS.

The transaction type, “1,” indicates hourly data and is placed in column 1. All the sample

values entered on a particular type 1 transaction line apply to the same day. 
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Table 2-12. AIRS Interval Codes

Code Interval

A 1 Week

B 3 Hours

C Composite Data

D Yearly

G Annual Geometric Mean

M Annual Arithmetic Mean

Q Quarterly Arithmetic Mean

X 24-Hr Block Average

Y 3-Hr Block Average

Z 8-Hr Run Average

1 1 Hour

2 2 Hour

3 4 Hour

4 6 Hour

5 8 Hour

6 12 Hour

7 24 Hours

8 1 Month

9 3 Months
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Table 2-13. AIRS Unit Codes

Code Unit Category

078 ppbC VOC Compounds

008 ppb Carbonyl Compounds

Table 2-14. Hourly Sample Valid Start Hour Based on the Interval

Sampling Interval Interval Code Start Hours

 1 hour 1 00, 08, 16

 2 hours 2 00, 01, 16, 17

 3 hours B 00, 01, 02

 4 hours 3 00, 01, 02, 03

 6 hours 4 00, 01, 02, 03, 04, 05

 8 hours 5 00, 01, 02, 03, 04, 05, 06, 07

12 hours 6 00, 01, 02, 03, 04, 05, 06, 07, 08, 09, 10, 11
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Table 2-15. Null Values

Value Reason

9967 Sample Pressure Out of Limits

9968 Technician Unavailable

9969 Construction/Repairs in Area

9970 Shelter Storm Damage

9971 Shelter Temperature Outside Limits

9972 Scheduled but NOT Collected

9973 Sample Time Out of Limits

9974 Sample Flow Rate Out of Limits

9975 Insufficient Data (Can't Calculate)

9976 Filter Damage

9977 Filter Leak

9978 Voided by Operator

9979 Miscellaneous Void

9980 Machine Malfunction

9981 Bad Weather

9982 Vandalism

9983 Collection Error

9984 Lab Error

9985 Poor Quality Assurance Results

9986 Calibration

9987 Monitoring Waived

9988 Power Failure (POWR)

9989 Wildlife Damage

9990 Precision Check (PREC)

9991 QC Control Points (Zero/Span)

9992 QC Audit (Audit)

9993 Maintenance/Routine Repairs

9994 Unable to Reach Site

9995 Multipoint Calibration

9996 Auto Calibration

9997 Building/Site Repair

9998 Precision/Zero/Span
o:/s/g/morr/3797/pams/hobson/graph3.ppt Transaction Type State County Site Parameter

POCInterval

Units

Method

Year

MonthDay

Start Hour

Decimal Position

Sample 1

Value

VFSample 2

Value

VF

Sample 3

Value

VF

Sample 4

Value

VFSample 5

Value

VF

Sample 6

Value

VF

Sample 7

Value

VF

Sample 8

Value

VF

Action

 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80

1

12345678901234567890123456789012345678901234567890123456789012345678901234567890

1250092006452011B078129940707002 398 462 521 983 1582 2345 761 416 I

1250092006435021B008102940707002 280 333 516 549 716 799 658 489 I

 1 2 3 4 5 6 7 8

Monitor ID

Figure 2-19. Column Placement for an Hourly Data Transaction

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The monitor ID is placed in columns 2-16 and is comprised of the State, County, and Site

Code (columns 2-10) where the sample was collected, the parameter (columns 11-15), and Parameter

of Occurrence (POC) code (column 16). The POC code is used to distinguish between different

monitors at the same site that measure the same parameter. The first monitor at the site is generally

identified with POC = 1, with additional monitors at the same site measuring the same compound

identified with POC = 2, etc. If a new instrument were installed to replace the original instrument used

as the first monitor, that would be the same monitor and it would have POC = 1, even if the sampling

method or interval were changed.

Column 17 is reserved for the sampling interval code. Table 2-12 gives several interval

codes which may be used. It should be noted that the interval codes must represent a non-composite

sampling interval of less than 24 hours. Because there can be as many as eight sample values per

transaction, the temporal scope of a given type 1 transaction varies considerably depending on the

sampling interval. With some intervals, a single transaction holds all the sample values for a day, while

multiple transactions are needed with other intervals. For example, only four slots of one transaction

are used to report the four 6-hour observations for a day, while all eight slots of three transactions are

needed to report the eight 1-hour observations for a day. 

The units code is placed in columns 18-20 and indicates the dimensional system in which the

parameter measurement is expressed. Table 2-13 presents several units codes. 

Columns 21-23 indicate the method used to sample and analyze the parameter. A method

code is valid if it exists in combination with parameter, interval, and units in the AIRS Geo-Common

File. Several method codes are summarized in Table 2-11. Choose the method code that describes

the analytical system used. Special notes describing the analytical system should be made using Type

A6 (or A7) transactions.
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Hour of a slot (start hour) + [(slot number 1) * (hours insampling interval)]

Sample Concentration 10DP Sample Value entered into AIRS as an Integer

The date of the sample is placed in columns 24-29 in the YYMMDD format. The year,

month, and day are each two digits and any leading zeros must be included. 

The start hour code is placed in columns 30-31. AIRS data base time is standard time. 

This code indicates the beginning hour of the sampling period for the first sample value “slot” on the

transaction, given in standard time at the location of the monitoring site. The first hour of a day, 00,

begins at midnight, and the last hour, 23, begins at 11:00 p.m. The hour of a sample value is

determined by its position on the transaction (which “slot” it occupies). The first slot is for the hour

specified in the start hour field (columns 30-31) of the transaction. The second slot is for the start hour

plus the sampling interval, the third slot is for the start hour plus twice the sampling interval, and so on. 

In general;

Table 2-14 presents valid start hours for hourly data based on the interval. 

Column 32 is the decimal point (DP) indicator. Because sample values are entered as

integers, this code is used to indicate the number of digits to the right of the decimal point in the sample

value fields. The following equation can be used to determine the correct DP for the data:

The DP applies to all sample value fields on the transaction. If the sample values require different DPs,

use multiple transactions to code the compatible DP and sample values. 

Columns 33-72 are reserved for eight sample values. These fields contain the actual

numeric values of the hourly data. There are eight “slots” for eight observations for the sample date. 

These slots are in columns 33-36, 38-41, 43-46, 48-51, 53-56, 58-61, 63-66, and 68-71. The slot

into which an observation is placed depends on the hour associated with the observation, the sampling
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SLOT# 1 +

(Hour StartHour)

NH

interval (in column 17), and start hour (in columns 30-31). For the day's observation, the following

relationship holds:

where:

Hour is the hour associated with the observation;

Start Hour is the start hour of the observations for that day (columns 30-31); and

NH is the number of hours between observations.

When inserting a transaction, there must not be a value in the data base for the date and hour

corresponding to the slot used. In the sample value “slot” enter a true observation of a parameter

value. Leave blank any occurrence of the sample value for an hour when you do not wish to report a

true observation. Numeric integer values (no decimal points) that represent true observations must be

entered right justified in the fields. Leading zeros are not required, but recommended. The sample

value and the decimal point indicator together indicate the compound concentration reported in the units

indicated by the unit code.

Following each sample value field is a field for the validity flag. The validity flag is used to

indicate the reason for an abnormal observation. The presence of a validity flag with an observation

indicates that the observation is due to an “exceptional event” or its abnormal value has been checked

and found to be valid. The use of any validity flag (except “V”) must be approved by state or EPA

regional personnel. If an observation results from an exceptional event (e.g., volcano, forest fire,

disaster clean-up, etc.), place a valid validity flag in column 37, 42, 47, 52, 57, 62, 67, and/or 72. A

valid validity flag is one that exists in the AIRS Geo-Common File for this parameter. If a validity flag is

not necessary, the validity flag field and/or fields should be left blank.
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The action code placed in column 80 indicates the type of data base processing to be

performed by this transaction. In order to insert new values into the raw data files, an “I” is placed in

column 80. Should modifications to existing values in the raw data files be necessary, a “M” is placed

in column 80. The deletion of existing values from the raw data files is indicated with a “D” in column

80.

A protocol has been established to explain “missing data” should there be an instance where

data have not been collected. If there is a instance where data should have been collected, but were

not, the DP indicator (column 32) should be left blank. This procedure indicates to AIRS that the value

entered in the sample value field is a code explaining why the data are missing. A list of approved null

value codes appears in Table 2-15. Always use the most appropriate null value code. When a reason

for a null value exists that is not listed, use the miscellaneous void code: Number 9979.

An example of an hourly transaction appears in Figure 2-16. In the first transaction line, site

25-009-2006 is submitting data for benzene (parameter 45201) for the primary sample (POC =1). 

The samples were collected for three hours (interval = B). The results are presented in ppbC (units =

078) for a Varian GC (method = 129). The sample was collected July 7, 1994 (columns 24-29). 

Because the start hour is 00 (columns 30-31), the three hour samples were collected beginning at

midnight, 3:00 a.m., 6:00 a.m., 9:00 a.m., noon, 3:00 p.m., 6:00 p.m., and 9:00 p.m. local standard

time. The results are presented so that a decimal point appears two places to the left of the indicated

value (column 32). The sample collected at midnight (columns 33-36) has a value of 3.98 ppbC

whereas the sample collected at 3:00 p.m. (columns 58-61) has a value of 23.45 ppbC. This

transaction summarizes the data collected for one compound (benzene) for one day. Similar

transactions would be necessary for each of the over 50 compounds on the VOC target list for this

date. 

The second line is the transaction for formaldehyde. Site 25-009-2006 is submitting data for

formaldehyde (parameter 43502) for the primary sample (POC=1). The samples were collected for
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three hours (interval = B). The results are presented in ppbv (units = 008) for cartridges coated with

DNPH on silica using a potassium iodide ozone scrubber (method = 202). The sample was collected

July 7, 1994 (columns 24-29). Because the start hour is 00 (columns 30-31), the three hour samples

were collected beginning at midnight, 3:00 a.m., 6:00 a.m., 9:00 a.m., noon, 3:00 p.m., 6:00 p.m., and

9:00 p.m. local standard time. The results are presented so that a decimal point appears two places to

the left of the indicated value. The sample collected at 3:00 a.m. (columns 38-41) has a value of 3.33

ppbv whereas the sample collected at 9:00 p.m. (columns 68-71) has a value of 4.89 ppbv. This

transaction summarizes the formaldehyde data collected for one day. Similar transactions would be

necessary for each of the three compounds on the carbonyl target list for this date.

Daily Data—Daily data are those which are collected for a period of at least 24 hours or

more. These data are called transaction Type 2 and are indicated with a “2” in column 1 of the

transaction. The column placement for daily data is presented in Figure 2-20.

The monitor ID is placed in columns 2-16 and is comprised of the State, County, and Site

Code (columns 2-10) where the sample was collected, the parameter (columns 11-15), and Parameter

of Occurrence (POC) code (column 16). The POC code is used to distinguish between different

monitors at the same site that are measuring the same parameter. The first monitor at the site is

generally identified with POC = 1, with additional monitors at the same site measuring the same

compound identified with POC = 2. If a new instrument were installed to replace the original

instrument used as the first monitor, that would be the same monitor and it would have POC = 1, even

if the sampling method or interval were changed.

Column 17 is reserved for the sampling interval code. Table 2-12 gives several interval

codes which may be used. It should be noted that the interval codes must represent a non-composite

sampling interval of at least 24 hours. 
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The units code is placed in columns 18-20 and indicates the dimensional system in which the

parameter measurement is expressed. Table 2-13 presents several units codes. 

Columns 21-23 indicate the method used to sample and analyze the parameter. A method

code is valid if it exists in combination with parameter, interval, and units in the AIRS Geo-Common

File. Several method codes are summarized in Table 2-11. Choose the method code that describes

the analytical system used. Special notes about the analytical system should be made using Type A6

(or A7) transactions.
o:/s/g/morr/3797/pams/hobson/graph4.ppt Transaction Type State County Site Parameter

POC

Interval

UnitsMethodYearMonthDay

Start Hour

Sample FrequencyDecimal Position

Sample Value

VF

Action

 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80

2

12345678901234567890123456789012345678901234567890123456789012345678901234567890

2250092006452011707812994070700P21864 I

2250092006435021700810294070700P2 280 I

 1 2 3 4 5 6 7 8

Monitor ID

Figure 2-20. Column Placement for a Daily Data Transaction

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Sample Concentration 10DP Sample Value entered into AIRS as an Integer

The date of the sample is placed in columns 24-29 in the YYMMDD format. The year,

month, and day are each two digits and any leading zeros must be included. 

The start hour code is placed in columns 30-31. This entry indicates the beginning hour of

the sampling period, given in standard time at the location of the monitoring site. The first hour of a day,

00, begins at midnight, and the last hour, 23, begins at 11:00 p.m. 

Sampling intervals of 24 hours or more should be reported on the day in which the majority

of the sampling occurred. Therefore, a 24-hour sample taken from midnight (00:00) to midnight

(24:00) local daylight time on June 5, would be reported with a start time of (00:00) on June 5 rather

than 23:00 on June 4.

The sample frequency code is placed in column 32 and indicates how much time elapses

between observations. This code is expressed in terms compatible with the associated Interval Code. 

Table 2-7 presents sample frequency codes.

Column 33 is the decimal point (DP) indicator. Because sample values are entered as

integers, this code is used to indicate the number of digits to the right of the decimal point in the sample

value fields. The following equation can be used to determine the correct DP for the data:

The sample value is placed in columns 34-37. The integer value represents the true

observation and is entered right justified. Leading zeros are optional. 

The validity flag is placed in column 38 and is used to give the reason for an abnormal

observation. The presence of a validity flag with an observation indicates that the observation is due to

an “exceptional event” or its abnormal value was checked and found to be valid. The use of any
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validity flag (except “V”) must be approved by state or EPA regional personnel. If a validity flag is not

necessary, the validity flag field should be left blank. 

The action code placed in column 80 indicates the type of data base processing to be

performed by this transaction. In order to insert new values into the raw data files, an “I” is placed in

column 80. Should modifications to existing values in the raw data files be needed, an “M” is placed in

column 80. The deletion of existing values from the raw data files is indicated with a “D” in column 80.

A protocol has been established to explain “missing data” should there be an instance where

data have not been collected. If there is a instance where data should have been collected, but were

not, the DP indicator (column 32) should be left blank. This blank column indicates to AIRS that the

value entered in the sample value field is a code explaining why the data are missing. A list of approved

null value codes appears in Table 2-14.

An example of a daily transaction appears in Figure 2-20. In the first transaction line, site

25-009-2006 is submitting data for benzene (parameter 45201) for the primary sample (POC =1). 

The sample was collected for 24 hours (Interval = 7). The results are presented in ppbC (units = 078)

for a Varian GC (method = 129). The sample was collected July 7, 1994 (columns 24-29). The

sample collection began at midnight (Start Hour = 00). The sample was collected on the PAMS

schedule of one 24-hour sample every 6 days (Sample Frequency = P). The results are presented such

that a decimal point appears two places to the left of the indicated value (column 33). The sample

value is 18.64 ppbC (columns 34-37). This transaction summarizes the data collected for one

compound (benzene) for one day. Similar transactions would be necessary for each of the over 50

compounds on the VOC list for this date. 

The second line is the example transaction for formaldehyde. In this transaction, site 25-

009-2006 is submitting data for formaldehyde (parameter 43502) for the primary sample (POC = 1). 

The sample was collected for 24 hours (interval = 7). The results are presented in ppbv (units = 008)
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for cartridges coated with DNPH on silica (method = 102). The sample was collected July 7, 1994

(columns 24-29). The sample collection began at midnight local standard time (Start Hour = 00). The

sample was collected on the schedule of one 24-hour sample every 6 days (Sample Frequency = P). 

The results are presented so that a decimal point appears two places to the left of the indicated value

(column 33). The sample value is 2.80 ppbv (columns 34-37). This transaction summarizes the data

collected for one compound (formaldehyde) for one day. Similar transactions would be necessary for

the three carbonyl compounds for this date.

2.6.2.4 Submitting Data

Once the raw data have been formatted in accordance with the required fixed block 80-

character per line formats, the process of submitting data to AIRS can begin. For batch processing,

groups of transactions should be saved as ASCII files which are then loaded onto the EPA mainframe. 

However, the transactions must still be placed in the screening file.

Once the raw data ASCII files have been loaded onto the EPA mainframe, work within the

AIRS system can begin. After accessing AIRS, entering AQS, and selecting the screening file, a four

step process begins to submit the data to AIRS AQS. The process begins by choosing Submit from

the AQS Menu. The submenu should then include, among others, choices for LOAD, EDIT,

CORRECT, and SUBMIT. 

The LOAD Process–Placing the Data in the Screening File—LOAD is a batch

process which is initiated from the Air Quality “Submit” menu. The transaction records are read from

the TSO dataset specified by the user and written into the user's screening file. A printed report is

generated that summarizes the processing performed in terms of the number of transaction records by

type or category. Suppression of the printed report can be achieved by selecting “N” for Print.
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The EDIT Process–Validating the Data—EDIT is a batch process which is initiated

from the Air Quality “Submit” menu. Transaction records in the user's screening file are examined and

edit/validation checks are applied. The purpose is to ensure that only “valid” data get into the data

base. A printed report is generated that lists each record that failed the edit checks and the reason(s)

why it failed. Suppression of the printed report can be achieved by selecting “N” for Print.

There are three (3) levels of edit/validation checks. Level 1 determines whether the

individual fields of a record have appropriate values (e.g., is the city code valid?). Level 2 checks the

relationship among the fields or records. Duplicate transaction records would result in a Level 2 error. 

Level 3 statistically tests for anomalies in the data and checks for relationships among the transaction

records and the AIRS Data Base. All transaction data must pass this 3-level editing system prior to

admittance into the AIRS Data Base.

The CORRECT Process–Correcting the Data—Air Quality transaction records in the

user's screening file may be modified in order to correct edit/validation errors identified by the EDIT

process or to correct some other problem known to the user. CORRECT does not generate a printed

report.

The CORRECT process allows one to “browse” in the screening file to view its contents,

and to modify, delete, or add transaction records. A particular record or group of records may be

selected for display on the user's terminal screen. As each record is displayed, the user may leave the

data fields intact, alter the contents of the data fields, or delete the record. The user may also set (or

clear) an indicator that causes the record to be excluded temporarily from EDIT and UPDATE

processing, while retaining it in the file. The same kinds of operations may also be applied to groups of

records using “global” commands that specify the identities (keys) of the records to be affected and the

actions to be applied. New transaction records may also be inserted into the screening file. Level-1

edit checks are applied to inserted and modified records and any errors are indicated on the user's

screen. Edit checks are not applied to each record modified by a global command, but to the
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command itself. Any records that have passed Level-2 or Level-3 edit checks and are interdependent

with a record affected by CORRECT processing will be reset to Level-1.

The NOTIFY Process–Requesting to Add Data to AIRS AQS—Once all records

have passed all three edit checks, the AIRS Data Base Administrator should be notified of the

impending AIRS AQS data by selecting NOTIFY from the submenu. NOTIFYing the AIRS Data

Base Administrator locks the screening file and prevents further use of it until the AIRS Data Base

Administrator releases it. The AIRS Data Base Administrator and the appropriate NAMS/PAMS

Coordinators review the data. The data are then added to the AIRS data base. 

Should there be any suspect data, the AIRS Data Base Administrator may elect not to add

the data to AIRS, but instead leave the data in the user's screening file and request the user to doublecheck the transaction. Upon inspection, should there be an error in the transaction, the user should

CORRECT the error, EDIT check/validate the data, and NOTIFY the AIRS Data Base Administrator

of the impending AIRS AQS data. If the data are valid, the user may want to indicate that the data

have been validated by placing a validity flag of “V” to indicate that the data are indeed valid. The

transaction should then proceed through the EDIT checks/validations and after successful completion of

the EDIT checks, the user should NOTIFY the AIRS Data Base Administrator of the data. 

2.7 Validating Data from Automated VOC Systems

Although manual sampling methods may be used, automated GC techniques are currently

the most practical and cost effective way to comply with the rigorous speciated VOC sampling

frequency required for PAMS. Measuring VOCs in the atmosphere on a daily and hourly basis using

these systems produces extremely large and complex data sets. Managing, processing, and validating

the data requires technical expertise and an intensive effort to obtain reliable and consistent data for the

timely input into the AIRS AQS data base. The AIRS data base is used as the national repository for

PAMS data and can be used to assist State and local agencies in determining if the program objectives
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and Data Quality Objectives (DQOs) described in the PAMS Implementation Manual25 are met. Data

submitted to AIRS by all agencies must be consistent with the PAMS monitoring DQOs and of

adequate quality to meet Clean Air Act Title I objectives. 

PAMS data use is discussed elsewhere in this document, but it is pertinent to the data

validation process to reiterate the discussion. The data will allow the state and local agencies to

develop, evaluate, and refine new O3 control strategies; determine NAAQS attainment or nonattainment for O3

; track VOCs and NOx emissions inventory reductions; provide photochemical

prediction model input; evaluate photochemical prediction model performance; analyze ambient air

quality trends; and characterize population exposure to VOCs and O3. Data from VOC measurement

systems must be submitted to AIRS within six months following the end of each quarterly reporting

period. 

Validating the measurement data can be as complex as the gas chromatographic techniques

and methods used to collect them. The evaluation of the quality and reliability of the data from GC

analyses is often referred to as the data validation process. The EPA defines data validation as a

systematic process consisting of data editing, screening, checking, auditing, verification, certification,

and review, for comparing a body of data to an established set of criteria to provide assurance that the

data are adequate for their intended use.50 Data validation is an element of quality assurance and

includes evaluation of the data quality and reliability and assurance that the data are consistent with

program data quality objectives.

 Data validation is the final and most critical part of the process used to generate PAMS

data. The data must be validated and reviewed to ensure the overall quality of the measurement prior

to inclusion in the AIRS AQS data base. Data validation is used in conjunction with program

objectives, DQOs, and QA/QC to remove inconsistencies in the data set and improve data quality. 

The key aspects of a complete data validation process are the pre-measurement chromatographic

system verification, development of QC procedures and measurement quality objectives; and validation
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of the data prior to AIRS AQS data base entry. Although the data validation process is embodied in

the last of these aspects, all are of critical importance to the overall process. Prior to the development

of systematic data validation procedures, pre-measurement system validation and QA/QC

measurements for establishing the DQOs must be completed. QA/QC procedures pertain to the

techniques applied prior to obtaining data, such as calibration checks, system blanks and external

audits. Guidance for pre-measurement validation and QA/QC is given in Sections 2.3.7 and 2.8. This

process is necessary to set the stage for ensuring the overall quality of the monitoring network data. 

2.7.1 Data Validation Approach

This guidance provides procedures for implementing a systematic data validation process for

those responsible for validating PAMS VOC data. Data validation in the context of this guidance refers

to the procedures performed after the data are collected. Pre-measurement chromatographic system

verification, QA/QC procedures and measurement quality objectives are established prior to collection

of the data to minimize the amount of faulty data generated.

Data validation is performed as a last step before the data are submitted to AIRS and is a

screening process to prevent additional unacceptable or questionable data from being submitted to

AIRS. Timely data validation is required to more easily resolve data issues and unusual events and take

the necessary corrective actions to minimize the generation of additional faulty data. 

This data validation approach has been selected with respect to the PAMS DQOs and data

use; volume and type of data generated; anticipated computational and graphical capabilities of the state

and local agencies; and nature of the expected errors. Four categories have previously been

identified51 for validating air monitoring data: 

C Routine checks made during the initial processing and generation of the data, including

proper data result file identification, review of unusual events, review of 
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chromatography result reports, performance checks of the data processing system, and

deterministic relationships.

C Tests for internal consistency to identify values in the data set which appear atypical

when compared to values of the whole data set.

C Comparing the current data set with historical data to verify consistency over time.

C Tests for parallel consistency with data sets from the same population (region, period of

time, air mass, etc.) to identify systematic bias.

The data validation guidance presented here for VOC encompasses mainly routine checks,

tests for internal consistency, and historical data comparisons. Additional checks for parallel

consistency, which incorporate statistical evaluations, may be considered for data validation and are

only briefly discussed in this document. A flow chart of data validation activities is given in Figure 2-21.

2.7.1.1 Routine Procedures

Routine validation checks during the processing of the data include verification of proper

data file identification information, chromatography result report file review, identification of unusual

events, deterministic relationship checks, and performance checks of the automated data processing

systems. These routine checks should be done frequently (i.e., daily or weekly) to parcel the data into

manageable segments. The checks must be timely in order to address issues before the amount of

faulty or unusable data generated becomes too large, thereby significantly affecting the data

completeness.

Computerized data acquisition systems are used to collect the chromatographic information

from the analog output of the GC systems as discussed in Section 2.6. The resulting chromatographic

data files must be clearly and correctly identified, including the correct acquisition time and date,

sampling location, sample name or type, processing and calibration methods, and file naming

conventions. Examples of errors that may occur include: incorrect sampling locations, especially if

methods are copied from one site location to another; incorrect date and time stamp due to daylight
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savings time change; or a sample name that indicates a normal sample when in fact a calibration or

blank check sample has been analyzed. Since these errors are mostly due to human error, an individual

other than the person originally generating the data should review the information.
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Data Collection

Review Result File

Information

Review Sample

Chromatogram

Review

Instrument QC

Information

Update

Acquisition

Method

Take Necessary

Corrective Action

Routine

Checks

Review and Update

Site Log Book

Deterministic

Relationships

Data Processing

Performance Review

Figure 2-21. Flow of Data Validation Activities
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Summary Report

Review

Internal

Consistency

Checks

Time Series, Scatter

Plot, Finger Print,

Review for Outlier

Control

Charts

Gross Limit Checks

Historical

Consistency

Checks

Data Average, Mean,

and Range Checks

Sign, Wilcoxon

Signed-Rank,

Wilcoxon Rank Sum,

and Intersite

Correlations Tests

Parallel

Consistency

Checks

Treatment of Outlier

Figure 2-21. Continued
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Due to the large volume of data generated from PAMS monitoring, close scrutiny of all

chromatograms and result reports is not practical. For example, a system making continuous, hourly

measurements of 56 target compounds can produce over 1,300 measurements per day. However, all

chromatograms should go through a cursory review by the station operator to determine if the quality of

the chromatography (i.e., appearance of the chromatogram, the peak shape, peak resolution, peak

integration, retention times, and baseline) is acceptable. This level of review can be done quickly by an

experienced chromatographer and will also determine if the chromatographic system is performing

properly. Comparison of the chromatogram to reference or historical information, such as calibration

and typical sample chromatograms, can simplify this process. Chromatograms are also reviewed to

determine if there are any gross errors present and whether chromatographic abnormalities, such as

electronic spikes, contamination, or levels of target analytes above the electrometer or calibration

ranges, exist. If the chromatography is acceptable, the chromatogram can then be further processed by

the data reduction and/or peak identification software as chosen by the user.

The cursory review of chromatograms may include the following determinations: 

C The signal from the FID or baseline is normal and the signal output is positive (onscale);

C Chromatographic peaks are present, integrated correctly, and the peak-shape is sharp;

C The peak resolution or separation is acceptable based on historical instrument

performance;

C All components have been eluted from the analytical column as indicated by a flat or

normal baseline at the end of a run; and

C No chromatographic abnormalities exist, such as large contamination or non-target coeluting compounds, and electronic spikes.

The result reports must also go through a more in depth review, in conjunction with the

chromatogram, to ensure that the key reference or internal standard compounds are identified correctly
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and the resulting target peak retention times have not shifted. The results reports generated by the

automated GC system are subsequently reviewed and compared to calibration or standard analyses

information from the pre-measurement system verification discussed in Section 2.3.7. This review is

used to ensure that correct peak assignments or identifications are made and that the resulting

concentrations are correct. The information is also reviewed to determine whether the information used

to make the peak identifications (i.e., retention times, relative retention times, retention indices, etc.)

requires updating. The need for updating peak identification information in the acquisition method is

indicated by the frequency of missed or inaccurate peak identifications automatically made by the GC

system. Typically, a minimum of 10% of the data are processed through this level of review. The

minimum percentage of the chromatograms generated daily are selected by the station operator for

review. Chromatograms generated at the beginning and the end of an analysis day to bracket sample

analyses are selected. It can then be presumed that the data generated between bracketed result files

and chromatograms are acceptable and also accurate. 

Routine review of the analytical instrument calibration is imperative for the ultimate quality and

usefulness of the data generated. As a QC function, the station operator must review this calibration

information on a regular basis to ensure that quality objectives are met and the system is operating

properly during the measurement process. If the GC system calibration has gone awry and QC sample

results do not agree with the specified quality objectives, the data should be appropriately qualified to

indicate any impact on the analytical results. If “real-time” (same day) calibration review is

implemented, quality issues can be identified and corrective actions, such as repeat analyses and

instrument maintenance, can be performed prior to continuing data collection. If post analysis

calibration information review is performed, the previously generated sample data should be flagged to

clearly qualify any uncertainty in the results. 

An on-site logbook should be maintained to record information relative to instrument repair

and maintenance (replacing the cold trap) and unusual events (mowing the lawn, power outages, or

repairing the sampling shelter roof) that could explain variations or excursions in the data. This
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information could be critical in the explanation of missing data files, high sample concentrations, or used

to reject outliers.

Deterministic relationships where two or more related parameters can be routinely checked

ensure that measured values of an individual parameter do not exceed that of an aggregate parameter.

The aggregate parameter must include the individual parameter. Also, relationships or ratios between

two source-related compounds can be compared in order to identify errors. For example, if the total

unidentified VOCs measured are greater than an established empirical percentage of the total NMOC

measurement at that site, a large number of target peaks were misidentified. A total unidentified VOC

value that comprises more than 30% of the total NMOC may indicate that retention times have shifted

and target peak identifications are incorrect. The concentration of benzene can be compared to

acetylene or toluene (all present in automobile exhaust) by developing scatter plots or calculating the

ratios and comparing this information to empirical relationships determined at a specific site. The

example in Figure 2-2252 shows a scatter plot of benzene and toluene that incorrectly includes

calibration information in the data set, as demonstrated by the data points around the concentration of

30 ppbC at the top part of the graph. Most of the ambient air data points in this scatter plot fall below

8 ppbC for benzene. Again, these relationships are site specific and empirical relationships must be

established.

Performance checks of the automated data processing system and supplemental procedures

developed to handle the data, including telemetry, should be implemented. All agencies should develop

data flow diagrams to indicate the steps taken to process the data following collection, including data

formatting, transmission, and processing or formatting for AIRS. The data are reviewed for

inconsistencies, missing data files, or nonsensical information. Any computerized programs put in place

to manipulate data should be validated at a minimum using methods for checking errors such as

developing a standard set of test output parameters, processing the test data set, and comparing the

results to the reference. Information regarding complex procedures required for testing and validating

computer systems can also be obtained from NIST. 
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Figure 2-22. Appearance of Calibration Data at East Hartford, CT, in June 1995. 

Example scatter plot showing calibration data of about 30 ppbC. Data are level 0,

preliminary data, CT DEP.

Main, H.H., P.T. Roberts, and M.E. Korc. Analysis of PAMS and NARSTO-Northeast Data -

Supporting Evaluation and Design of Ozone Control Strategies: A Workshop. Report and

presentation prepared for U.S. Environmental Protection Agency, Research Triangle Park, NC. 

Presented at U.S. Environmental Protection Agency, Research Triangle Park, NC. 

STI-94551/94581-1551-WD1, EPA WA-5-95 and WA-8-95, December 1995.
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Any software or calculation spreadsheet programs (Excel® or QuattroPro®) implemented by

the user must also be verified for accuracy. Errors in spreadsheets can occur during spreadsheet or

program development in the continued course of the program. Implementing a verification check of the

calculations in these spreadsheets and programs can help to avoid errors in the data generated. 

Verification checks are accomplished by using the spreadsheet or program to calculate results for a

previously known data set. A more complete test of the user developed program would include testing

at the minimum and maximum expected input values. If the expected result is not obtained the program

may be in error and the appropriate corrective action should be taken.

2.7.1.2 Tests for Internal Consistency

Data review for internal consistency identifies values in the data set which appear atypical

when compared to values of the whole data set. Tests for internal consistency include the identification

of outliers and extreme differences in adjacent values that require further investigation. A number of

statistical tests can be used for internal consistency checks and determining outliers. Graphical and

visual presentation of the data, such as review of summary report file information, scatter plots, timeseries, or fingerprints can also be used for consistency checks. 

Manual data review for internal consistency is impractical for the volume of continuous gas

chromatographic data generated by PAMS. The user should consider implementing a commercially

available peak processing or identification software package as an alternative to manual review. 

Software packages, such as MetaChromTM (Meta Four Software, Inc.) and VOCDat (developed by

Sonoma Technology, Inc., under sponsorship by EPRI53) have been designed to review large and

complex data sets for consistency.

Summary report file information, scatter plots, time-series, fingerprints, and control charts can

be generated using the Perkin-Elmer Turbochrom® Summary Report option, spreadsheet software

(Excel®, QuattroPro®, or Lotus®), or the VOCDat software developed for NARSTO-NE by Sonoma
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Technology, Inc. VOCDat provides a useful graphical interface for generating time-series plots,

fingerprint plots, and control charts for VOC data generated by Perkin-Elmer Turbochrom® data

systems. 

Qualitative comparison review for internal consistency may by done by generating a data

base or summary report file or “flat-file” of the concentration and peak identification results generated

over time. A typical summary file can contain a large number of measurements for the target PAMS

compounds: a system making continuous, hourly measurements of 56 target compounds can produce

over 1,300 measurements per day. The summary files can be reduced into manageable segments for

visual review. This information can assist the user in identifying system problems, target compound

misidentifications, system contamination, outliers, or missed information. Qualitative comparison review

of the final concentration results and peak identifications is valuable in checking for outliers or

inconsistencies in peak identification, retention times, calculations, and results. The information can also

be globally reviewed for clear changes in trends. 

For example, the Peak Summary Option of the Perkin-Elmer Turbochrom® software can

easily be used to summarize the concentration and retention time results as shown in Figure 2-23. This

file can be generated weekly and the information reviewed to identify abrupt changes in concentration

or retention time, and the presence of ubiquitous compounds measured at the site. A criterion for

retention time shifts may also be established based on the percent relative standard deviation (%RSD)

information obtained for the site to pinpoint misidentification of target peaks. 

When data are reviewed for internal consistency, dealing with values that fall below the

established detection limits for the system is at the discretion of the reviewer. For example,

concentration values below the detection limit may not be subject to data validation due to the inherent

uncertainty of these data. An action limit of 3 times the detection limit or a concentration value (i.e., 5

ppbC) may be used.
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*******SUMMARY REPORT********

ETHANE ETHYLENE PROPANE HEXANE

File Time of Ret. Area Conc. Ret. Area Conc. Ret. Area Conc. Ret. Area Conc.

b152001 01:42 ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- 14.26 4336 2.50b152002 02:42 ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- 14.25 4873 2.81b152003 03:42 ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- 14.27 4789 2.76b152004 04:42 ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- 14.26 5232 3.02b152005 05:42 ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- 14.26 5977 3.45b152006 06:42 ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- 14.26 6774 3.91b152007 07:42 ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- 14.25 9423 5.44b152008 08:42 ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- 14.25 13032 7.52b152009 09:42 ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- 14.27 6930 4.00b152010 10:42 ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- 14.27 2423 1.40b152011 11:42 ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- 14.28 2655 1.53b152012 12:42 ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- 14.28 2440 1.41b152013 01:42 ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- 14.27 930 0.54b152014 02:42 ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- 1429 624 0.36b152015 03:42 ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- 14.28 620 0.36b152016 04:42 ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- 14.28 535 0.31b152017 05:42 ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- 14.27 991 0.57b152018 06:42 ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- 14.28 994 0.57b152019 07:42 ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- 14.28 2154 1.24b152020 08:42 ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- 14.29 1736 1.00b152021 09:42 ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- 14.29 1174 0.68b152022 10:42 ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- 14.31 970 0.56b152023 11:42 ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- 14.30 844 0.49b152024 12:42 ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- 14.30 906 0.52p152001 01:42 8.37 12417 7.25 9.22 11100 6.48 11.60 18984 11.08 ---------- ---------- ---------- p152002 02:42 8.37 13944 8.14 9.22 11113 6.48 11.60 23687 13.82 ---------- ---------- ---------- p152003 03:42 8.37 14162 8.26 9.22 10356 6.04 11.60 22974 13.41 ---------- ---------- ---------- p152004 04:42 8.37 15815 9.23 9.22 12174 7.10 11.60 26559 15.50 ---------- ---------- ---------- p152005 05:42 8.38 17284 10.09 9.22 13219 7.71 11.60 28519 16.64 ---------- ---------- ---------- p152006 06: 8.38 21046 12.28 9.22 17568 10.25 11.60 32186 18.78 ---------- ---------- ---------- p152007 07:42 8.37 25884 15.10 9.23 20883 12.19 11.60 40227 23.47 ---------- ---------- ---------- p152008 08:42 8.37 42656 24.89 9.22 28060 16.37 11.59 65558 38.25 ---------- ---------- ---------- p152009 09:42 8.38 23186 13.53 9.25 14600 8.52 11.61 32459 18.94 ---------- ---------- ---------- Figure 2-23. Example PE Turbochrom® Summary Report
Section:

2

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*******SUMMARY REPORT (Continued)********

ETHANE ETHYLENE PROPANE HEXANE

File Time of Ret. Area Conc. Ret. Area Conc. Ret. Area Conc. Ret. Area Conc.

p152010 10:42 8.38 11453 6.68 9.26 6846 3.99 11.61 15163 8.85 ---------- ---------- ---------- p152011 11:42 8.38 10410 6.07 9.24 5129 2.99 11.62 12338 7.20 ---------- ---------- ---------- p152012 12:42 8.38 12713 7.42 9.24 4591 2.68 11.60 23293 13.59 ---------- ---------- ---------- p152013 01:42 8.39 7639 4.46 9.25 1636 0.95 11.60 8271 4.83 ---------- ---------- ---------- p152014 02:42 8.38 5728 3.34 9.26 796 0.46 11.60 3063 1.79 ---------- ---------- ---------- p152015 03:42 8.39 5820 3.40 9.24 1269 0.74 11.61 3161 1.84 ---------- ---------- ---------- p152016 04:42 8.38 5877 3.43 9.24 1417 0.83 11.61 3919 2.29 ---------- ---------- ---------- p152017 05:42 8.38 5551 3.24 9.24 1417 0.83 11.61 7688 4.49 ---------- ---------- ---------- p152018 06:42 8.38 5811 3.39 9.21 1242 0.72 11.60 4021 2.35 ---------- ---------- ---------- p152019 07:42 8.38 6652 3.88 9.22 4785 2.79 11.59 5855 3.42 ---------- ---------- ---------- p152020 08:42 8.39 7521 4.39 9.26 3769 2.20 11.62 5476 3.20 ---------- ---------- ---------- p152021 09:42 8.39 8675 5.06 9.23 1806 1.05 11.61 4968 2.90 ---------- ---------- ---------- p152022 10:42 8.38 9052 5.28 9.23 2324 1.36 11.60 4917 2.87 ---------- ---------- ---------- p152023 11:42 8.38 8392 4.90 9.24 2735 1.60 11.61 7198 4.20 ---------- ---------- ---------- b152024 12:42 8.37 8699 5.08 9.23 2950 1.72 11.60 6452 3.76 ---------- ---------- ---------- Avgs

%RSD

8.380.08

12766

67

7.45

67.07

9.230.14

7574

 96

4.42 

95.83

11.60

0.06

16956

90

9.89

90.23

14.28

0.11

3390

95

1.96

95.20

Figure 2-23. Continued
Section: 2

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The Turbochrom® Peak Summary Report may also be generated as an ASCII file for import

into Excel® or other spreadsheet software. The ASCII summary data base file can be loaded or

imported directly into spreadsheet software for further data processing or manipulation. Once the data

base file is loaded into the spreadsheet software, graphical representations of the continuous

measurements can easily be generated. Generation of diurnal graphs of hourly site measurement

information can be very useful in clearly identifying trends and determining if the potential for outliers

exists in the data base. 

The VOCDat software53 can generate graphical presentations of the data in the form of time

series plots, scatter plots, and fingerprint plots for internal consistency determinations. Time series plots

as shown in Figure 2-2453 can be used to inspect each target compound, groups of target compounds,

and total NMOC. This information allows the identification of outliers, increased single-hour

concentrations, possible missed peak identifications, and extended periods of unusually high or low

concentrations. Experienced PAMS personnel frequently look for unusual “jumps” in the time series

plot between successive hourly data or departures from expected diurnal or seasonal patterns. Figure

2-2453 shows two items that warrant further investigation: first, the unusually high concentration of 62

ppbC for propane compared to the other data points for the period which are all below 20 ppbC; and

second, missing data for two periods (8/24 and 8/28). Review of the site log would be important in this

case to determine if downtime occurred or instrument maintenance was performed.

The time series plot in Figure 2-2554 shows an example of misidentification of a paraffin for an

unidentified VOC, indicated on the plot by the abrupt decrease in paraffin concentration with

concurrent increase in the unidentified VOC concentration. The time series plot in Figure 2-2654 shows

system contamination of the selected components that decreased in concentration, or were cleared out

of the system over a period of five days.
Section: 2

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Figure 2-24. Time Series Plot

Main, H.H., P.T. Roberts, J.D. Prouty, and M.E. Korc. Software for Display, Quality Control, and Analysis of Continuo

VOC Data. Report prepared for Electric Power Research Institute, Palo Alto, CA by Sonoma Technology, Inc., Sant

Rosa, CA. STI-996142-1594, EPRI Research Project No. WO9108-01, June 1996.
Section: 2

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Figure 2-25. Time Series Plot of Several Species Groups at Stafford, CT, in 1994. Example of

misidentification of a paraffin for an unidentified peak.

Main, H.H., P.T. Roberts, and L.R. Chinkin. PAMS Data Analysis Workshop: Illustrating the Use of PAMS Data to Su

Ozone Control Programs. Report and presentation prepared for U.S. Environmental Protection Agency, Research

Triangle Park, NC. Presented at California Air Resources Board and EPA Region IX, Sacramento, CA. STI-997100-1

WD7. May 1997.
Section: 2

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Figure 2-26. Time Series Example of System Contamination

Main, H.H., Roberts, P.T., and Chinkin, L.R. PAMS Data Analysis Workshop: Illustrating the Use of PAMS Data to Su

Ozone Control Programs. Report and presentation prepared for U.S. Environmental Protection Agency, Research

Triangle Park, NC. Presented at California Air Resources Board and EPA Region IX, Sacramento, CA. STI-997100-1

WD7. May 1997.
Section: 2

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Date: 09/30/98

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A scatter plot (shown in Figure 2-2754) can be used to compare pairs of target compounds or

target groups to identify outliers and excursions in the data such as the improper inclusion of calibration

data in the data set (discussed previously). The figure shows a comparison of 2-methylheptane to

toluene. The relationships between two species show a “cone” of data rather than the two distinct lines

observed in the figure. In this example, the toluene peak was misidentified as 2-methylheptane over a

period of several days.

A fingerprint plot shown in Figure 2-2852 allows further inspection of samples previously

flagged for more detailed review. The fingerprint plot shows the compound concentration for each

compound for a single hour. The fingerprints can quickly be scanned, hour-by-hour to allow the

observation of diurnal changes and inspection of hours surrounding suspect data to identify additional

effects. The time series plot in Figure 2-2952 clearly illustrates calibration data mistakenly included in

the data set. In this case, the calibration gas contained about 25 ppbC of the PAMS target

compounds.

Whatever methodology is used, the qualitative comparison review of summarized

measurement data can be a useful tool in verifying the internal consistency and overall accuracy of the

data generated from automated GC systems.

2.7.1.3 Historical Data Comparisons 

Testing or comparing data for historical consistency uses many of the graphical techniques

discussed in Section 2.7.1.2 to compare the data set with previous data compiled from the monitoring

location. Pattern and successive value tests, parameter relationship tests, and control charts may also

be used.51 Gross limit checks are used to detect data that are unlikely and considered impossible. 

Upper and lower limits are established based on historical data from the site. These limits are specific

to the monitoring site and should consider parameters and instrument characteristics. Values

representing pollutant behavior outside the specified limits are flagged for further investigation. Limits
Section: 2

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on the individual concentration, difference in adjacent concentration or retention time values, difference

or percent difference between both adjacent
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Example of Species Misidentification

0

5

10

15

20

25

30

35

0 5 10 15 20 25 30

2-Methylheptane (ppbC)

Toluene (ppbC)

Figure 2-27. Example of Misidentification Using a Scatter Plot. Typically, data

points would be present in the region of the plot between the two extreme edges.

Main, H.H., Roberts, P.T., and Chinkin, L.R. PAMS Data Analysis Workshop: Illustrating the Use of

PAMS Data to Support Ozone Control Programs. Report and presentation prepared for U.S.

Environmental Protection Agency, Research Triangle Park, NC. Presented at California Air

Resources Board and EPA Region IX, Sacramento, CA. STI-997100-1719-WD7. May 1997.
Section: 2

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Example Typical Fingerprint

acety

ethyl

ethan

prpyl

propa

isbta

1butenbuta

t2bte

c2bte

3mlbe

ispna1pntenpnta

ispre

t2pne

c2pne

2m2be

22dmb

cypne4mlpecypna

23dmb2mpna3mpna

nhexa

t2hex

c2hex

mcpna24dmp

benz

cyhxa

2mhxa

23dmp

3mhxa

224tmp

nhept

mcyhx

234tmp

tolu

2mhep3mhep

noct

ebenzm/pxy

styr

oxyl

nnon

ispbz

npbz

apine

135tmb124tmb

bpine

0

5

10

15

20

25

30

Concentration (ppbC)

Figure 2-28. Example of a Typical “Fingerprint” Observed at a PAMS Site
Section: 2

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Example Calibration Gas

acety

ethyl

ethan

prpyl

propa

isbta

1butenbuta

t2bte

c2bte

3mlbe

ispna

1pntenpnta

ispre

t2pne

c2pne

2m2be

22dmb

cypne4mlpecypna

23dmb2mpna3mpna

2m1pe

nhexa

t2hex

c2hex

mcpna24dmp

benz

cyhxa

2mhxa

23dmp

3mhxa

224tmp

nhept

mcyhx

234tmp

tolu

2mhep3mhep

noct

ebenz

m/pxy

styr

oxyl

nnon

ispbz

npbz

apine

135tmb124tmb

bpine

0

10

20

30

40

50

Concentration (ppbC)

Figure 2-29. Example of Calibration Gas “Fingerprint” Observed in Data

Submitted to AIRS

Main, H.H., P.T. Roberts, and M.E. Korc. Analysis of PAMS and NARSTO-Northeast Data -

Supporting Evaluation and Design of Ozone Control Strategies: A Workshop. Report and

presentation prepared for U.S. Environmental Protection Agency, Research Triangle Park, NC. 

Presented at U.S. Environmental Protection Agency, Research Triangle Park, NC. 

STI-94551/94581-1551-WD1, EPA WA-5-95 and WA-8-95, December 1995.
Section: 2

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values, and the average of four consecutive values are comparisons that may be considered. 

Supplemental statistical tests can be used to identify data sets which have mean or range values that are

inconsistent with previous data sets.

2.7.1.4 Parallel Consistency Checks to Identify Systematic Bias

Tests to check for consistency with parallel data sets from the same population (region,

period of time, air mass, etc.) are used to identify systematic bias. Systematic bias is determined by

checking for the difference in average value or overall distribution values. The sign test, Wilcoxon

signed-rank test, Wilcoxon rank sum test, and intersite correlation test are recommended for testing

two parallel data sets.49 The first three tests are nonparametric and consequently can be used for

nonnormal data sets which frequently occur in air quality data.

2.7.2 Treatment of Outliers

Outliers may result from errors in the processing of a data set, instrument problems, and 

calibration errors. Once an outlier has been identified using any of the approaches identified above,

treatment of the outlier must be decided. The outlier should not be arbitrarily dropped from the data

set. Outliers that are found to be errors should be corrected, if possible. If the correct value cannot be

obtained, the value may be appropriately flagged and excluded from the data set. Alternatively, if the

suspect data are retained in the data set the necessary qualifying information in the form of a “flag” must

be included with the value. There should be an explanation that warrants the exclusion or replacement

of data along with documentation reflecting the action taken. If no explanation is available, the outlier

should not be excluded.

The data point may be real. Data should only be excluded by the reporting agency when the values are

verified as not representative of ambient data, such as calibration runs, instrument malfunction,
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contamination, etc. Verification should include site or operator log book, laboratory notes, etc. Later

data analysts may then choose to use the outlier or not, depending upon their analyses.

2.8 Quality Control and Quality Assurance for VOC Measurements

 Data submitted to AIRS by all agencies will ultimately be used by the agencies to develop,

evaluate, and refine new O3 control strategies; determine NAAQS attainment or non-attainment for O3;

track VOCs and NOx emissions inventory reductions; provide photochemical prediction model input;

evaluate photochemical prediction model performance; analyze ambient air quality trends; and

characterize population exposure to VOCs and O3. Data from VOC measurement systems must be

submitted to the Aerometric Information Retrieval System (AIRS) within six months following the end

of each quarterly reporting period, and the data must be consistent with enhanced O3 monitoring

regulations and of sufficient quality to meet Clean Air Act Title I objectives.

The quality of the data submitted to the AIRS data base must be consistent across all

agencies. Because a significant investment of time and assets is expended to generate measurement

data, a quality control/quality assurance (QC/QA) program should be developed to ensure that the data

collection is consistent and that data quality objectives (DQOs) for the measurement program are met. 

The quality program for VOC measurements, similar to programs for other air monitoring efforts,

incorporates quality control and quality assurance. These two systems work together to achieve the

goal of continuing quality in measurement efforts. 

Quality assurance and quality control have been defined and interpreted in different ways. 

Some sources differentiate between the two terms by stating that quality control is “the operational

techniques and the activities which sustain a quality of product or service (in this case, good quality

data) that meets the needs; also the use of such techniques and activities,” whereas quality assurance is

“all those planned or systematic actions necessary to provide adequate confidence that a product or

service will satisfy given needs.”55
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Quality control may also be considered “internal quality control;” mainly, routine checks

included in normal internal procedures; for example, periodic calibrations and system blanks, duplicate

checks, and split samples. Quality assurance may also be viewed as “external quality control,” those

activities that are performed on a more occasional basis, usually by a person outside of the normal

routine operations; for example, on-site system surveys, independent performance audits,

interlaboratory comparisons, and periodic evaluation of internal quality control data.56

EPA’s Quality Assurance Handbook56 uses the term quality assurance collectively to include

both quality assurance and quality control. A description of the elements necessary for a PAMS QA

program are found in 40 CFR Part 58, Appendix A “Quality Assurance Requirements for State and

Local Air Monitoring Stations (SLAMS).” Existing SIP stations are SLAMS; National Air Monitoring

Stations (NAMS) and PAMS are considered a subset of SLAMS. Appendix A specifies the minimum

QA requirements applicable to SLAMS air monitoring data submitted to EPA. States are encouraged

to develop and maintain QA programs more extensive than the required minimum. The references

found at the end of this document are also found in the 40 CFR Part 58, Appendix A for reference

purposes in preparing quality assurance program documents.

This section is divided into three parts: DQOs, QC, and QA. Section 2.8.1 discusses the

development of data quality objectives. Section 2.8.2 deals with the systematic activities of a QC

program and Section 2.8.3 presents those assessment activities that are part of a QA system. The

QC/QA procedures discussed in the following sections are the minimum and must be tailored and

expanded for each PAMS monitoring network as appropriate. A clearly written QC/QA plan and

associated SOPs must be developed for each network.

2.8.1 Data Quality Objectives

Data quality objectives are defined in the PAMS Implementation Manual25 as “statements

that relate the quality of environmental measurements to the level of uncertainty that decision-makers
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are willing to accept for results derived from the data.” The development of DQOs starts with the

monitoring program objectives and goals. In order to develop DQOs for each program objective, it is

first necessary to narrow each program objective to one or more specific monitoring or data objectives.

Specific and often different program objectives are associated with each specific PAMS

network. The overall network should supply information sufficient to develop, evaluate, and refine new

O3 control strategies; determine NAAQS attainment or non-attainment for O3; track VOCs and NOx

emissions inventory reductions; provide photochemical prediction model input; evaluate photochemical

prediction model performance; analyze ambient air quality trends; and characterize population exposure

to VOCs and O3. The program objectives are discussed in detail in the PAMS Implementation

Manual25 and are classified into six general categories given below:

Category 1 Responsible and cost-effective control strategies;

Category 2 Photochemical modeling support;

Category 3 Reconciliation of emissions inventories;

Category 4 Ozone and precursor trends;

Category 5 Attainment and non-attainment decisions; and

Category 6 Population exposure analyses.

The DQOs must quantify the measurement variability in order for the risk in decision-making

to be adequately assessed. This quantification of variability can only occur if there exists a base level of

experience in use of the technologies and /or methods outlined for the program. In the case of PAMS,

until its implementation in 1993 there had never been a program of this scope, with these goals and

program objectives. Data compiled from the 1990 Atlanta Study57 and other studies of this type

provided the information for initial development of the PAMS DQOs.

It is important to note that all possible uses of the PAMS data are not known; therefore,

every practical attempt should be made to improve data quality beyond that necessary to satisfy the
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DQOs specified for PAMS. The DQOs are considered preliminary and are expected to be revised as

improvements are made to the monitoring and statistical methods; as changes and/or additions are

made in the program objectives or in the data use; and/or as results of the monitoring indicate a need. 

The PAMS DQOs are discussed in detail in the PAMS Implementation Manual25 and highlighted

below in relationship to each monitoring program objective category :

DQO 1.1 The data for any given pollutant measured at a PAMS site must be able to show

the presence of a diurnal pattern, if a pattern exists, with an 80% confidence level.

DQO 1.2 The data for any given pollutant measured at a PAMS site must be able to show

a change in the diurnal pattern, if a change exists, with an 80% confidence level.

DQO 2.1 The speciated VOC, ozone, NOx and meteorological data must satisfy the

regulations, including monitor siting, operation, and data quality criteria.

DQO 3.1 The monitoring data for total VOC concentrations collected at a Type 2 site must

be able to demonstrate a 3% annual trend (upward or downward) over a 5-year

monitoring period, if a trend exists, with an 80% confidence level.

DQO 3.2 The speciated VOC monitoring data collected at a Type 2 site, when composited

into categories, must be able to demonstrate a 20% change (upward or

downward) in the seasonal average between two consecutive years, if it exists,

with an 80% confidence level.

DQO 3.3 The speciated VOC data collected at a Type 2 site must be able to detect ratios

between key species that are indicative of specific sources. If the ratio between

the emissions of two species is N:1, the compounds must be measured so that

this ratio can be estimated to within ±50% with an 80% confidence level.

DQO 4.1 The composite monitoring data for a given MSA, CMSA for ozone, NOx, and

speciated VOC must be able to demonstrate a yearly downward trend with an

80% confidence level until an area achieves attainment.

DQO 5.1 The ozone (and NO2 where appropriate) monitoring data must satisfy the criteria

specified in the NAMS and SLAMS monitoring regulations, including monitor

siting, operation, and data quality criteria.

DQO 6.1 The speciated VOC monitoring data must be able to provide annual average

concentration data at Type 2 sites within ±50%, with a confidence level of 80%.
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DQO 7.1 Meteorological data should be of sufficiently high quality that the relationship

between ozone and wind speed, direction, and solar radiation can be determined. 

This level of quality can be shown if a functional relationship of ozone to

meteorology explains a definite percentage of the ozone variation. Wind direction

measurements must be of sufficient quality to develop a wind field for use in

trajectory analysis.

The set of DQOs presented above assumes that the physical location of the site remains the

same for the entire five-year period under consideration and that the area external to the site does not

change in such a way that the appropriateness as a Type 2 site is impacted. Should either of these

conditions occur, the DQOs must be modified to reflect the change in site conditions.

To meet the overall PAMS monitoring program DQOs above, specific quality objectives for

VOC measurements are expressed in terms of sensitivity (detection limit), accuracy, precision, and

completeness. The measurement quality objectives should not require more than the sampling and

analytical procedures can provide, nor should they be based solely on the performance capability of the

measurement system and methodology. The procedures used to assess the DQOs should be specified

so that QC and QA procedures can be assembled to determine DQO attainment. If DQOs are not

routinely met, a rapid resolution of the problem is required. Possible resolutions include redefinition of

the DQO, repair/replacement of instrumentation, and/or modification of the methodology and

procedures.

Detection limits reflect the smallest measured concentration of a compound that can be

measured with a known degree of certainty and should be based on empirical data from the sampling

and analytical system used for VOC measurements. The limit of detection is defined in the Federal

Register58 as the minimum concentration of a substance that can be measured and reported with 99%

confidence that the analyte concentration is greater than zero and is determined from analysis of a

sample in a given matrix containing the analyte. Definitions for the detection limit should be related to

the standard deviation of the measured values at or near zero concentration of the analyte.59 Detection

limit information should not be used to screen air measurement results. All results, even at
Section: 2

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% Bias Measured Value - True Value

True Value

x 100 (2-12)

concentrations below the estimated detection limit, should be reported. More information is gained

when a result is reported even if the data are somewhat imprecise.

Method detection limits (MDLs) for PAMS are estimated using 40 CFR, Part 136,

Appendix B.60 Replicate analyses are performed at least seven times at very low ppbC concentrations

(within a factor of five times the estimated method detection limit). The standard deviation of the

concentration for the replicate samples is related to the Student's t-value at the 99% confidence level

with a standard deviation estimate having n-1 degrees of freedom. The detection limit is calculated by

multiplying the standard deviation by the appropriate Student's t-value. (Appropriate values for six,

seven, and eight replicates are 3.365, 3.143, and 2.998, respectively.) Specific MDLs are developed

for each measurement method at the start of a season by performing a detection limit study. The

estimated detection limit for specific target VOCs is 3 ppbC or better.

Accuracy is the relative closeness of a measurement to a known reference value. The

assessment of accuracy includes both accuracy and precision and is usually expressed as bias or

percent bias:

Bias is thus a signed value: i.e., the bias may be positive or negative. 

Accuracy can also be expressed as percent difference, relative percent difference, percent

recovery, and percentage deviation. Estimates of bias require the analysis of a reference material or

standard of known or established concentration. Reference standards are submitted in canisters as

“blind” audits by an internal or external laboratory. A “blind” audit usually refers to a sample that has

been submitted to the audited laboratory and identified as an audit sample of unknown concentration. 

The reference value for an accuracy standard should be a certified reference material (CRM) or

traceable to a standard reference material such as a NIST Standard Reference Material (SRM). 
Section: 2

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s

ji

(Yi- Y)

2

n- 1

RPD

V2- V1

V1

x 100

Accuracy should be determined for as many target VOCs as practical based on individual testing needs

consistent with the standard operating procedure at the individual PAMS site. Federal regulations

require State and Local air monitoring agencies to perform annual accuracy checks. In the absence of

specified objectives, the absolute accuracy should be within ±25% of the reference value.

Precision refers to the agreement among a group of experimental measurements made under

identical conditions. The most commonly used estimate of precision for environmental measurements is

standard deviation, or the square root of the variance. The sample standard deviation (typically used

for less than 30 observations) is calculated as follows:

where:

GY = means of all observations

Yi = i

th value of observations

n = degrees of freedom

To make a comparison of two values (i.e., duplicates or replicates), Relative Percent

Difference (PRD) is a more meaningful statistic than RSD, since the number of values is only two.

Where:

V2 = second determination
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V1 = first determination

Other measures of precision include relative standard deviation, coefficient of variation, percent

difference, range, and relative range. Precision is an inverse relationship, i.e., the smaller the measure of

precision, the better the agreement among measurements. For manual canister sampling approaches,

two different evaluations of precision can be made: the repeated analyses of duplicate canister samples,

which provide an assessment of the total method precision including elements of imprecision in both the

sampling and analytical procedures; and/or replicate analysis of a single canister sample, which provides

only analytical precision. Use of these two precision estimates is valuable in determining the source of

imprecision in the measurement effort. 

Since automated GC systems employ “real-time” sample collection and measurement

techniques, estimates of precision require repeat measurements of single or collocated SUMMA®

canister samples that have been collected using an external sampling device. A replicate sample is a

sample that has been divided into two or more portions, at some step in the measurement process. 

Collocated samples are individual samples collected so they are equally representative of the variable(s)

of interest at a given point in space and time. Information gathered from collocated sample results

allows for estimation of sampling precision. Repeated analyses of collocated, or duplicate, samples

permits estimation of the sampling and analytical precision. Precision estimates should therefore

represent the variability of the entire measurement system. Collocated samples are recommended,

when possible, for assessing sampling and analytical precision.

Another measure of precision involves intra-laboratory and inter-laboratory precision. 

Collocated samples that are processed and analyzed by the same organization provide intra-laboratory

precision information for the entire measurement process. Collocated samples that are processed and

analyzed by different organizations provide inter-laboratory precision information for the measurement

process. A sample exchange program that involves both inter-laboratory or intra-laboratory precision

gives important information concerning inconsistencies that may exist. Interpretation of these data must
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be based on clear understanding and knowledge of how the data were obtained. Differences in the

methodologies (i.e., detection limits, analytical column, calibration procedures, etc.) used to analyze the

exchange sample must be clarified in order to interpret and resolve any inconsistencies in the results. 

Precision for inter- and intra-laboratory exchange samples is calculated in the same manner as precision

for replicate analyses. In the absence of specified DQOs, objectives for precision should be

determined from the QA program, pre-measurement system verification, and historical information for

the target compounds of interest. In the absence of specified objectives, values for precision are

considered acceptable if they fall within ±25% RPD. This 25% target applies to both automated

methodology and manual sampling (duplicate prepared canisters or replicate analysis of a single

canister).

When evaluating the precision of VOC measurements, states or agencies must consider each

individual target compound because precision will be compound-dependent with an influence of

physical and chemical properties (such as vapor pressure and reactivity). In reviewing species data

pairs (primary and duplicate samples), the number of non-detects in both samples will probably be

significant. In these “non-detect pairs,” the RPD will not be useful. Instead these pairs can be said to

have a qualitative precision. Data pairs where the compound is detected in both samples can be

evaluated for relative percent difference, with a goal of ±25%. In the evaluation of the data, it should

be noted that there will be a large range of concentrations and that compounds with an average

concentration near the method detection limit will probably exceed the goal of 25%.

Specific requirements for precision and accuracy of automated and manual methods are

contained in Sections 3.1 through 3.4 of Appendix A, 40 CFR 58. The calculations used for precision

and accuracy data quality assessments are given in Section 5 of 40 CFR 58, Appendix A.

Completeness is the percentage of valid data reported compared to the total number of

attempted field samples, minus blanks, standards, and scheduled audit analyses. Completeness is

determined after the data validation process is complete, and after precision and accuracy are
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determined and evaluated against the quality objectives. The objective for completeness is 85% and is

determined on an annual basis.

2.8.2 Quality Control

General QC guidance can be found in the EPA QA Handbook.56 Quality control for

measurement programs covers topics from preventive maintenance to corrective actions. Four areas of

particular importance to VOC measurements described in this section are sample collection, sample

handling and custody, sample analysis, and data documentation and archiving. 

2.8.2.1 Sample Collection

Quality Control for sample collection should address: certification of the sample collection

system, calibration of the system components, field acquisition of duplicate samples, and preventive

maintenance efforts. A table of QC objectives for sample collection is given in Table 2-16. Technical

information pertaining to manual multiple-event and single-event VOC sample collection systems is

presented in Section 2.5. Similar information pertaining to automated GC systems is presented in

Section 2.4.
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Table 2-16. QC Objectives for VOC Sample Collection

Assessment QC Procedure Frequency Acceptance Criteria Corrective Action

Sampling System

Carry-over

Challenge with target

compounds

Annual 80-120% recovery for target

compounds, overall

compound recovery of 85-

115%

1) Additional system purge

with humid zero air

2) Repeat challenge

Sampling System

Background or

Contamination

Humid zero air blank Annual 2 ppbC or the MDL,

whichever is less for target

species or # 10 ppbC

TNMOC

1) Additional system purge

with humid zero air

2) Repeat zero air

collection

Accuracy of

Collection Period

Elapsed time meter

or timing device

check

On/off timer check

6 Months

Quarterly

Gain or loss in time

# 2 minutes per 24-hour

period

Adjust or replace the timing

device

Adjust or replace timer

Sampling Integration

Period

Flow control check Weekly Measured transfer standard

flow within 10% of indicated

flow

Adjust or replace flow control

device

Sampling System

Pressure/Vacuum

Measuring Device

Accuracy

Pressure/vacuum

gauge or electronic

sensor check

Annual # 10% difference between

field and lab measured

canister pressure

1) Adjust for differences in

pressure/vacuum

measurement technology

2) Repeat check

Duplicate Sample

Correction Precision

Comparison of

duplicate canister

sample results

10% of field

samples

Agreement within ±25%

RPD.

1) Perform sampling

system PM

2) Repeat duplicate sample

collection

3) Check analytical system

precision

4) Check canisters for

leaks.
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2.8.2.1.1 System Certification

Canister sampling systems should exhibit non-biasing characteristics before being used to

collect samples. These sampling systems should be subjected to laboratory certification to quantify any

additive or subtractive biases that may be attributed directly to the sampling system. The procedure is

described in Section 2.5.1.7, Canister Sampling System Certification. Collection system certification

should be conducted prior to and after each PAMS season or at the start and end of each calendar

year. The percent recoveries for target challenge compounds are calculated, based on the determined

reference sample concentrations. Recoveries of each of the challenge compounds should be in the

range of 80-120% of the concentrations determined for the reference sample. A system-specific

overall recovery should also be calculated. The overall recovery is the average of the individual

compound recoveries. Each sampling system should have an overall recovery of 85-115%.

In addition to characterizing the sampling system with a blend of VOCs, the system should

also be characterized using humidified zero air. A humidified zero air blank sample is collected through

the sampling system to further gauge the potential for additive bias. The blank samples can be analyzed

for specific target analytes, total NMOC, or both, depending on individual program requirements. Two

criteria apply to the blank portion of the certification process: a determined concentration criterion of

3 ppbC or less for any individual target compound is required if speciation analysis of the blank sample

is performed, and a total NMOC concentration criterion of 10 ppbC or less is also required.

2.8.2.1.2 Calibration of Manual Sampling System Components

A QC check for the timing device in most manual sample collection systems is described in

the Quality Assurance Handbook.56 Every six months the elapsed-time meter should be checked

against a timepiece of known accuracy. If the meter shows any signs of temperature-dependence, it

should be checked on site during each season of the year. A gain or loss greater than 2 min/24-hour

period warrants adjustment or replacement of the indicator. 
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The on/off timer should be calibrated and adjusted quarterly by using a calibrated

elapsed-time meter as the reference. Specific procedures for QC of the elapsed-time meter and on-off

timer calibration checks are provided in Section 2.2.2 of the Quality Assurance Handbook.56

The accurate and consistent control of flow into the sample canister is required to ensure that

the sample collected is time-integrated. To check the sample collection flow rate, a flow meter

(e.g., calibrated transfer standard) is installed at the inlet to the manual collection system and the system

activated. The flow rate measured by the transfer standard should agree within ±10% of the flow rate

indicated by the flow control device housed in the sample collection system. This check should be

performed annually or as needed based on performance. The ability of the collection system to

consistently perform an accurate time-integration can be assessed indirectly by making a control chart

of the sample pressure collected over each sampling event. If the collection flow rate and sample

collection period are not varied, the total pressure of samples collected should not differ by more than

±10%, assuming that the canisters all start with the same initial vacuum.

The vacuum/pressure measuring devices (e.g., gauges or electronic sensors) used in the

manual sample collection systems must be checked for accuracy. To perform this check, a series of

comparisons between a primary pressure measuring standard and the sample collection system device

should be conducted prior to installation and then annually. The comparisons should cover the range of

the device operation at increments representing 10% of the total range. Ensuring the accuracy of the

pressure measuring device also allows the sample canister to be assessed for leaks. The final sample

pressure in a canister as measured in the field should be within 10% of that measured when the canister

is received for analysis at the laboratory. Note that differences in pressure may occur due to

temperature and barometric pressure changes, and differences in the accuracy of the pressure

measurement technology used. 
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2.8.2.1.3 Collection of Field Duplicate Samples

Field duplicate samples should be collected at a scheduled frequency of at least 10% (or at

the frequency specified by the site standard operating procedure) and are used to estimate the precision

of the manual sample collection method. Most commercially available manual sample collection

systems allow for collection of duplicate samples. Care should be taken to ensure that the duplicate

samples represent the same parcel of air over the same sample integration period.

Automated sample collection and analysis configurations have the same general QC

requirements for sample collection as manual systems. All of the QC checks for automated systems

should be done at the field station. Because true duplicates cannot be collected and analyzed with an

automated GC system, precision is estimated using repeated analyses of the target VOCs at ambient

concentrations. A humidified canister standard or sample is typically used as the source instead of the

sample manifold. This check is actually a measure of analytical precision (replicate analysis of a single

canister rather than duplicate analysis of multiple canisters). Replicate results should agree within 25%

RPD.

2.8.2.1.4 Preventive Maintenance

Preventive maintenance is an important part of the overall QC program for both manual and

automated sample collection systems. Maintenance items are generally specified by each sample

collection system manufacturer in the operating manual. These items may include any moving parts such

as valves or pumps. Most manual sample collection systems have an in-line particulate filter which

needs to be replaced on a regular basis. The location and physical conditions of the sample collection

system may dictate other maintenance activities that are necessary to reduce the effects of heat, dust,

corrosion or other concerns. 
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Any maintenance activity that involves the disassembly of hardware and replacement of parts

should be viewed as a potential change to the performance of the system. Replacement of major

sample collection system components (e.g., a flow control device) may warrant recertification of the

sample collection system. Duplicate analysis of multiple component calibration standard samples can

be used to assess whether changing a major component has affected the performance of the collection

system. If the duplicate analysis results compare within the quality objectives for the program, the

sample collection system does not require recertification. If duplicates do not meet the quality

objectives, then the sample collection system should undergo full challenge and blank recertification. 

Repeated analyses of a multiple component calibration standard for the automated GC should also be

conducted and reviewed to check for shifts in retention time or changes in response factors that may be

caused by a maintenance activity.

Quality Control activities should be thoroughly documented in a log book dedicated to the

monitoring site. In addition to the technical details of the site maintenance activity, the time, date,

sample collection system or instrument ID, and monitoring site ID should be recorded.

2.8.2.2 Sample Handling and Custody

The QC procedures for canister preparation are vital to manual sample collection and

calibration standard preparation because all of these activities rely on leak-free uncontaminated

canisters. All canisters prepared for field use should initially be checked for leaks by pressurizing the

canister with zero air to a known measured pressure. Gross leaks are located by coating critical

canister surfaces considered to have leak potential (e.g.,valves and fittings) with a leak detection

solution. More subtle leaks are indicated by pressure changes in the canister over time. All canisters

should be cleaned and checked for contamination and certified clean to 10 ppbC TNMOC. Canister

cleaning procedures are described Section 2.5.2. 
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Sample documentation includes chain-of-custody for canister samples and proper sample

identification and labeling. A chain-of-custody protocol should be developed so that at any point

between the canister's initial cleaning and its disposition after analysis the sample custodian can identify

and track the status of the canister. A unique identification is required for each canister at each point in

the sampling event. The canister should have a permanently assigned serial number and, after the

sample is collected, a unique sample identification number. A tag or label should be attached to the

canister so that it can easily be identified. The chain-of-custody form should always accompany the

canister and provide the means for each person responsible for custody to relinquish the canister to the

next person handling that canister. For example, the laboratory technician who provides the cleaned

canister to the field technician should initiate the chain-of-custody form and sign the canister over to the

field technician. After the sample is taken, the field technician returns the canister to the laboratory, with

the appropriate custody forms indicating the shipper and destination. The final completed form, upon

receipt at the laboratory, is signed by the sample custodian. This record allows the history of each

sample to be reconstructed if a problem arises with the analytical results.

A communication protocol should be established between the field sampling personnel and

the analytical laboratory personnel to ensure that sample canisters arrive at the monitoring locations

ahead of the scheduled sampling date. Sufficient numbers of canisters should be available to collect all

required samples, including any blank or duplicate samples that may be scheduled. The communication

protocol should include how to return the sample canister to the laboratory after collection.

For automated GCs, sample documentation can be accomplished using instrument specific

data collection software. Each chromatogram should have a header that uniquely identifies the sample

(e.g., filename and sample ID) as well as notation of the analysis conditions and column(s) used. Good

maintenance records are very important for automated GCs due to the large volume of data produced. 

An injection or sample collection logbook should be maintained to provide a history for each analysis

so that any questions about results can be resolved.
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A standardized approach should be followed for identifying samples, blanks, calibration runs,

audits, and other analyses. All samples collected and analyzed with an automated GC should have a

unique file name designated to identify the site, instrument used to collect the sample, and the sampling

date and time. A data system should automatically append a character(s) to the end of the electronic

storage file which corresponds to the order in which the sample was analyzed. The user is typically

limited to eight characters. 

Electronic copies of all original and reprocessed files should be maintained to provide a

record of any and all changes made to the data. The original raw data files should never be changed

and should contain, if possible, a file name extension (such as .RAW) to differentiate them from other

files. The .RAW files should be archived with any processed data files. Data processing can be

checked at a later date. 

2.8.2.3 Sample Analysis

Several steps are taken to ensure that the analytical system is in control, and these steps apply

to GC operations whether the sample is collected using an automated or a manual method. A summary

of these quality objectives is shown in Table 2-17. These objectives are the minimum QC procedures

pertaining to VOC analyses. States are strongly encouraged to develop more detailed, site-specific

SOPs.

During the initial analytical system set-up a multiple point calibration check using propane

and/or benzene is performed, and retention time windows are determined using the retention time

standard for each target compound. Calibration is the single most important operation in the

measurement process. Calibration is the process of establishing the relationship between the output of

a measurement process and a known input. For routine operation, the retention time calibration check

samples are analyzed to demonstrate that the retention times for each target VOC are within the

established window, to monitor the detector response drift, and verify the target compound recoveries. 
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Results outside of the expected retention time window or detector response range may indicate the

need for maintenance, adjustment or recalibration of the analytical system before further sample

analysis. A humidified zero air blank should be analyzed after the highest level calibration standard to

assess analytical system carry-over of any target analytes.
Table 2-17. Continued

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Table 2-17. VOC QC Procedures

Assessment QC Procedure Frequency

Acceptance

Criteria Corrective Action

System

Background and

Carry-over

System Blank

Analysis, Humidified

Zero Air

Weekly, following

retention time/calibration

check and after multiplepoint calibration curve

20 ppbC total, both

analytical columns,

or 10 ppbC per

column

1) Repeat analysis

2) Check system for leaks

3) Clean system with wet

air

4) Condition sample trap

Calibration Multiple Point

Calibration (3 points

minimum). 

Propane/benzene

bracketing the

expected sample

concentration

Prior to analysis at start

of season and when

system maintenance is

performed

Correlation

Coefficient $ 0.995

1) Repeat individual

sample analysis

2) Repeat linearity check

3) Prepare new

calibration standards

and repeat

Quantitative and

Qualitative

Performance

Retention

Time/Calibration

check using

mid-point of

calibration curve

Weekly RF within 10% RPD

of calibration curve

average RF

RT within ± 0.1

minutes of target

% recovery for

targets 80-120%

1) Repeat check

2) Repeat calibration

curve

Qualitative

Performance

Canister cleaning

certification

All canisters prior to use # 10 ppbC total Reclean canister and

reanalyze

Detection Limit 40 CFR 136 Part B Prior to analysis at start

of season

2 ppbC or better,

specific target peaks

selected

N/A
Table 2-17. Continued

Assessment QC Procedure Frequency

Acceptance

Criteria Corrective Action

Precision Replicate sample

analysis, manual or

automated

10% of samples Within ± 25% RPD

for target

concentrations > 5

times the MDL

Repeat sample analysis

Accuracy Performance

evaluation or NPAP

sample analysis

Prior to start of season,

and monthly during

monitoring season

20% absolute bias Repeat sample analysis
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After the system is optimized as described in Section 2.4.3.1, analytical system blanks are

analyzed to verify that the analytical system contributes no more than the maximum specified

background level of a total 20 ppbC (10 ppbC per analytical column) to the analytical results. System

blanks are typically run with each analysis batch (or at a specific time of day for continuous GCs but not

the same time every day to avoid loss of data for the same time period for the entire season), and

usually in a predetermined order, such as the first or last analyses in a batch, after a calibration check

standard, etc. The hour chosen for system blank analysis on automated systems should be varied so

the data from the same hour are not consistently lost. Each blank must be humidified to ensure that the

analytical system responds similarly to ambient samples. 

A calibration control standard or calibration curve should be analyzed to assess qualitative

and quantitative performance of the sampling system. Sample analyses should not be attempted until

the results demonstrate performance within the program's acceptance criteria. This type of control

sample should also be analyzed with each batch (or at various times of day for automated GC) and in a

predetermined order, usually before the analytical system blank. Again, the analysis hour should be

varied for automated GC systems. A calibration check sample is analyzed at least weekly to verify

calibration control. 

An additional QC check of retention time windows for all target analytes should be

performed on both manual and automated GC systems using a retention time standard. This standard

should be used at program start up and weekly or as needed thereafter to provide a comprehensive

check of retention time windows and peak identifications for all target VOCs. The retention times

should not vary by more than 0.1 minutes. The results from repetitive analysis of this standard can

indicate trends in quantitative performance of the GC. If independent verification of the vendor

supplied cylinder can be performed, then the cylinder can also be used as the quantitative QC check

discussed in the preceding paragraph. 
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The QC check standard may also be used to measure percent recovery for the target

compounds. Compound recovery can be used to verify sample trapping and transfer efficiency. At a

minimum, one target compound representing each carbon group should be checked for recovery

between 80 and 120%.

Replicate analyses are valuable in providing a means to estimate analytical precision. From

these data, control charts may be generated and simple statistical analyses performed on the analytical

results for each compound to estimate precision. The calculations are typically made in units of relative

percent difference or relative standard deviation (percent coefficient of variation). Variability in the

measurement data will be higher at low concentrations, which is also the range in which most ambient

VOC data are measured. For these reasons, precision measurements are made at ambient

concentrations, even though variability (imprecision) increases as the detection limit is approached. 

Manual sampling systems provide sufficient sample in each canister to perform replicate analyses. 

Repeated analysis should be performed on 10% of the samples to determine if the analytical precision is

within ±25% RPD for compounds greater than 5 times the MDL.

To determine precision for automated GC systems, analysis of a humidified gas standard or

typical field sample is required. The sample is composed of target compounds at ambient

concentrations in humid air. A control check sample from a gas cylinder or a diluted aliquot in a

SUMMA® canister can be used for this purpose. 

2.8.2.4 Data Documentation and Archives

Data documentation protocols are vital for reporting results in a consistent manner and for

providing an audit trail. Identification of samples must be consistent throughout the documentation

process. Logbooks should be maintained for each system in the laboratory, including logs for

calibration standard, instrument run logs, and maintenance logs. Good laboratory practices should be

followed for logbook entries, including the use of indelible ink, corrections made only by single line
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strikeout (initialed and dated), and identification of authorship for each entry. These logbooks should

be periodically peer reviewed by one person and evidence of the review should be written in the

logbooks. 

Electronic logbooks may be used if certain precautions are taken. A prime concern for QC

of data documentation files is the ability to recover data in the event of equipment failure. Logbooks

may be kept in electronic format if desired, but a protocol specific to the use and backup of electronic

log entries must be established. All software and data files used in recording and archiving raw data

should be backed up so that an equipment hardware failure or tampering does not destroy the logbook

information. Once entered, electronic logbook files should have file attributes set to “Read Only.” 

Bound hard copy indices of each electronic notebook should also be maintained. Index entries should

include file name, date of entry, author's name and subject.

Logbooks can be kept in electronic form for calibrations, computer access (recording logins),

computer boot logs, etc. Among the advantages of using electronic logs is the capability for remote

access to the information contained in the logbook. An automated GC system can be designed to allow

personnel remote access to all monitoring data, including all supporting documentation.

As part of a QC program, the data should periodically be reviewed to look for anomalies in

the data. Examples of items that should be examined in the periodic QC or validation of data include

the following:

C Missing data;

C Consistency of identification of target compound between standards and samples;

C Concentrations of compounds within expected ranges and variances according to

weather conditions, traffic patterns, etc.;

C Identification of target compounds in the retention time check standard;
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C Response factors from the primary calibration check standard within acceptable limits;

and

C Compounds detected in the blank within acceptable levels.

A complete discussion on data validation is found in Section 2.7.

Data validation cannot practically be performed on 100% of the compound identifications

and concentrations. The analyst should be responsible for cursory review of all chromatograms,

primarily for anomalies. The analyst should also review a small percentage of the files in depth to

confirm peak identifications and look for changes in methods that could affect automated data

processing. The key element to this activity is consistency to ensure that the same peak is identified the

same way to the extent allowable by the automated software in a batch reprocess mode. Exploratory

data processing software packages like MetaChrom® and VOCDat® may be used to validate the data

in more depth.

The processed results from raw data should be stored in a different directory on the

computer system. Reprocessed files should be compressed into storage files and given a unique file

name. The compressed file name may be used to designate that the automated software files have been

reprocessed and the level of reprocessing.

2.8.3 Quality Assurance

The procedures and activities associated with QC need periodic independent review and

assessment to ensure that the data meet the quality expectations of the program. This independent

review or auditing function should be done by an independent source with no daily involvement in the

operation of the sampling or analysis systems. In addition, independent review should be done on

DQOs and SOPs to ensure that the quality goals of the agency are reflected by the QC program. After
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SOPs and the QC program are put into place, the QA function provides review of their adequacy and

implementation in meeting the DQOs of the monitoring program.

2.8.3.1 Development of Standard Operating Procedures

An SOP is written so that procedures may be performed consistently by everyone involved in

the monitoring program. The decision of whether an SOP is needed for a particular procedure is made

by answering two questions:

C Does the procedure significantly affect data quality?

C Is the procedure repetitive or routine?

If the answer to both questions is yes, an SOP is needed.

Few routine laboratory or field projects can be described completely in just one SOP;

several may be needed. In general, an SOP for each of several smaller segments should be written

instead of one large SOP for an entire operation.

At a minimum, written SOPs to support the VOC monitoring effort should be prepared for

the following activities:

C Sample collection;

C Sample analysis;

C Sample canister handling;

C SUMMA® canister preparation and blanking;

C Data handling; 

C Sample identification and labeling requirements; and
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C Automated or manual data reporting.

Table 2-18 shows the suggested format for an SOP, including examples of items that should

be included in each section. The examples shown are only a few of the many that may be
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Table 2-18. Format for Standard Operating Procedures

A. Technical Sections

Section Typical Examples

1. Scope and Application Overview outlining purpose, range, sensitivity, acceptance

criteria

2. Summary of Method Overview describing sampling criteria and analytical methods,

method and instrumentation detection limits, reasons for

deviations from Federal Register methods

3. Definitions All acronyms, abbreviations, specialized terms

4. Interferences Sources of contamination

5. Personnel Requirements Educational level and training of intended SOP users, number

of operators required

6. Facilities Requirements Mobile analytical laboratory, air conditioning, type of

electricity

7. Safety Precautions Special handling procedures; i.e., handling compressed gases,

hazard warnings, placed immediately before relevant part of

text

8. Apparatus Larger items such as a meteorological tower, audit device, gas

chromatograph

9. Reagents/Materials All chemicals used, including distilled or deionized water;

grades of reagents and materials

10. Samples/Sampling Procedures Sample preparation, collection, storage, transport, and data

sheets

11. Calibration/Standardization Preparation of standards and calibration curves, frequency,

and schedule

12. Analysis Procedures Standard and custom-tailored methods for all target analytes 

13. Calculations Data reduction, validation, and statistical treatment, including

confidence levels and outliers

14. Data Reporting Selection criteria, format, equations, units

15. Corrective Action Criteria for initiation; individuals responsible

16. Method Precision and Accuracy Tabular or narrative summary of DQOs

B. Quality Control/Quality Assurance Sections

Section Typical Examples

1. QC Checks Precision, accuracy, reproducibility, blanks, replicates, criteria,

and frequency summarized in tables

2. QC/QA Controls Audits, notebook checks, control charts and graphs; actions

to be taken when QC data approaches or exceeds QC limits

C. Reference Section

Standard reference methods, reports, SOPs, journal articles; avoid citing unpublished documents
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covered. The SOP must be comprehensive and cover every step of the procedure in detail. The

author of a SOP tends to be extremely familiar with the material and may omit “obvious” information. 

The written SOP should be reviewed extensively and executed by persons not intimately familiar with

the procedure to evaluate the completeness of the instructions presented in the SOP. Once the DQOs

have been established and SOPs are in place, QA measures can be planned and implemented to ensure

that DQOs are met. In the remainder of this section, program audits are described that guide QA for

sample collection, analysis, and reporting. Additional guidance for development of a VOC monitoring

QA program are discussed in the EPA QA Handbook,56 and this information should be used in

conjunction with the guidance presented here.

2.8.3.2 QA Program Guidance

The QA program plan and activities should be developed to catalog and assess the data

quality requirements of the program. The QA plan ensures that procedures are being implemented

correctly and that all of the QC and SOP requirements are being followed to collect, analyze, and

report samples that meet agency DQOs. The QA plan also provides guidance for regular assessment

of the quality program for the monitoring network. An integral part of the QA program is a regular

series of audits. The QA plan should provide guidance for audits, performed by an independent

person or group to formally evaluate if systems are in place and being followed in order to meet the

DQOs. The QA program should be a cooperative effort between independent auditors and program

auditees so that quality issues can be identified and, if necessary, appropriate corrective actions

implemented. 

2.8.3.2.1 Audit Types

Three audit types are described in the following sections: technical systems audits,

performance audits, and data quality audits. These audits are used to determine whether data quality
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objectives are being met. An audit may also uncover additional findings useful in improving the

monitoring program.

As defined in the QA Handbook (Volume II)61 the Technical Systems Audit is a

systematic, qualitative on-site review of the adequacy of the facilities, equipment, training, record

keeping, validation, reporting, sampling, analysis, and QC/QA procedures. This type of audit should

be used throughout the VOC monitoring program to ensure that the QA/QC program elements are in

place and being followed. Systems audits are normally done immediately before, or shortly after,

measurement systems are operational and should be repeated on a regularly scheduled basis, at least

annually.

Technical systems audits should cover areas specific to VOC monitoring networks, including

sampling system certification, QC check procedures, and record keeping. Sampling system

certification critical to the success of a VOC monitoring program is often overlooked. Sampling system

QC checks should be reviewed to determine if proper blank and challenge gas tests have been

performed on the sampling systems before they are used to collect samples. Checks for leaks in

sampling systems and canisters, vacuum/pressure gauge calibration, and flow meter testing should be

reviewed to confirm that the QC procedures were implemented and systems are ready for use. 

Vacuum and pressure measurement checks should be audited with a NIST-traceable high resolution

gauge. Changes in canister pressure can then be corrected for barometric pressure differences and final

corrected canister pressures can be reviewed to identify leaking canisters. 

The technical systems audit investigates the specific elements of the measurement system to

ensure that established procedures are followed. With an emphasis on improving the program, the

technical systems audit evaluates the documentation and paper trail of a particular site to show that the

VOC monitoring is conducted according to the QA/QC program elements. An audit of this type is

conducted by an auditor familiar with VOC monitoring and the required types of record keeping used

in a VOC program. The auditor uses QA/QC guidance documents such as this document as well as
Section: 2

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the site-specific SOPs to evaluate the site’s measurement system. A specific checklist of required

elements is prepared and used as a guide for the auditor’s review. Significant deficiencies are noted

and discussed at the time of the audit and any additional deficiencies are noted and resolved by the

generation of a list of corrective actions to be taken by the site. Additional suggestions for improvement

are made by the audit team and delivered as part of their systems audit report. 

A Performance Evaluation Audit is a quantitative evaluation of the measurement system

and includes all associated data collection and analysis procedures. A Performance Evaluation Audit

involves the analysis of a reference material of known value. For both manual and automated VOC

sampling systems, the audit sample is usually a canister or compressed gas cylinder containing

humidified air with VOC target analytes at known concentrations. Performance evaluation audits

should be conducted on a regular basis specific to the program, at least once per season.

The EPA initiated a national performance audit program (NPAP) which applies to the VOC,

carbonyl, O3, and NO2 measurement systems used at PAMS monitoring stations. This program

mirrors the present EPA national performance audit program for SLAMS criteria pollutants. Agencies

collecting data in the PAMS monitoring network are required to participate in the national audit

program. The audit program uses performance evaluation samples which were field tested by the EPA

in 1993-1994. The EPA has established limits for acceptable performance on each type of

Performance Evaluation sample based on a statistical analysis of the results obtained from pilot tests.

The VOC and Performance Evaluation samples were pilot tested through a series of

proficiency tests. The VOC samples consist of 1.5 L compressed gas cylinders containing 10 to 50 of

the target VOC compounds. Participants in the audit program receive the Performance Evaluation

samples, determine the concentrations and report the results to the EPA. The EPA compares the

reported results to the expected results and issues a report to all participants.
Section: 2

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1. U.S. Environmental Protection Agency. Code of Federal Regulations. Title 40, Part 58. 

Ambient Air Quality Surveillance, Final Rule Federal Register, Vol. 58, No. 28, February 12,

1993.

2. David, D.J. Gas Chromatographic Detectors. John Wiley and Sons, New York, NY,

1974.

3. Dietz, W.A. Response Factors for Gas Chromatographic Analyses. J. Gas Chromatogr.,

1967.

A Data Quality Audit exhaustively evaluates the information generated from data collection

through reporting. Procedures that are evaluated include raw data recording and transfer, calculations

and equations, documentation of data handling, reporting and completeness, comparability, and

discussion of QC indicators such as precision, accuracy, and representativeness. A Data Quality Audit

for PAMS should include an audit of the data entered into the AIRS. Data Quality Audits should be

conducted routinely on various components of the data generation system, and a comprehensive Data

Quality Audit should be combined with Technical Systems Audits once the program is generating data

on a regular basis.

The QA/QC Procedures outlined in the above sections serve as a guide to the process of

ensuring that the VOC measurements are conducted properly. Collection of data and the subsequent

submission of the data to the AIRS data base must be consistent across all agencies. The defined

sections of DQOs: Sample collection, certification, calibration, duplicates, maintenance, sample

handling and custody, and sample analysis are a necessary framework and starting point for sitespecific SOPs. Coupled with the documentation of the data, the technical and system audit program

provides a regular evaluation of the system, data collection, and analysis process. The QA/QC

program in this document establishes the program elements which are necessary for the successful

operation of a VOC measurements analytical program. 

2.9 References
Section: 2

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4. Compendium of Methods for the Determination of Toxic Organic Compounds in Ambient Air. 

Compendium Method TO-14. The Determination of Volatile Organic Compounds (VOCs)

in Ambient Air Using SUMMA® Passivated Canister Sampling and Gas

Chromatographic Analysis. EPA-600/4-89/017, Research Triangle Park, NC: U.S.

Environmental Protection Agency, 1988.

5. Foulger, B. E. and P. G. Simmonds. Drier for Field Use in Determination of Trace

Atmospheric Gases. Anal. Chem., 51: 1089-1090 (1979).

6. Burns, W. F., D. T. Tingey, R. C. Evans, and E. H. Bates. Problems with a Nafion®

Membrane Dryer for Drying Chromatographic Samples. J. Chromatogr. 269: 1-9 (1983).

7. Pleil , J. D., K. D. Oliver, and W. A. McClenny. Enhanced Performance of Nafion® Dryers in

Removing Water from Air Samples Prior to Gas Chromatographic Analysis. J. Air Pollut.

Control Assoc. 37: 244-248 (1987).

8. Baker, B. B. Measuring Trace Impurities in Air by Infrared Spectroscopy at 20 Meters Path

and 10 Atmospheres Pressure. Amer. Ind. Hyg. Assoc. J. 35: 735-747 (1974).

9. Campbell, N. T., G. A. Bere, T. J. Blasko, and R. H. Groth. Effect of Water and Carbon

Dioxide in Chemiluminescent Measurement of Oxides of Nitrogen. J. Air Pollut. Control

Assoc. 32: 533-535 (1982). 

10. Rasmussen, R. A. and A. K. Khalil. Atmospheric Methane (CH4): Trends and Seasonal

Cycles. J. Geophys. Res. 86: 9826-9832 (1981).

11. Gong, Qing, and K. L. Demerjian. Hydrocarbon Losses on a Regenerated Nafion®

Drier. J. Air Waste Manage. Assoc. 45: 490-493 (1995).

12. Ogle, L.D., D. A. Brymer, C. J. Jones, and R. L. Carlson. “Moisture Management Techniques

Applicable to Whole Air Samples Analyzed by Method TO-14, II; GC/MS Considerations.”

In Proceedings of the 1993 U.S. EPA/A&WMA International Symposium: Measurement

of Toxic and Related Air Pollutants, Research Triangle Park, NC, 1993.

13. McClenny, W.A., K.D. Oliver, and E.H. Daughtry, Jr. Analysis of VOCs in Ambient Air

Using Multisorbent Packings for VOC Accumulation and Sample Drying. J. Air Waste

Manage. Assoc. 45: 792-800 (1995).

14. Cardin, D. B. and J. T. Deschenes. “A Cryogenless AutoGC System for Enhanced Ozone

Monitoring Using a Simplified Single Detector Approach.” In Proceedings of the 1993 U.S.

EPA/A&WMA International Symposium: Measurement of Toxic and Related Air

Pollutants, Research Triangle Park, NC, 1993.
Section: 2

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15. Soroka, J. M., R. Isaacs, G. Ball, R. Singhvi, and T. Pritchett. “The Effect of Water on

Recoveries in Sorbent Tube and SUMMA® Canister Analysis.” In Proceedings of the 1992

U.S. EPA/A&WMA International Symposium: Measurement of Toxic and Related Air

Pollutants, Research Triangle Park, NC, 1992.

16. Levaggi, D. A., W. Oyung, and R. V. Zerrudo. “Noncryogenic Concentration of Ambient

Hydrocarbons for Subsequent Nonmethane and Volatile Organic Compound Analysis.” In

Proceedings of the 1992 U.S. EPA/A&WMA International Symposium: Measurement of

Toxic and Related Air Pollutants, Research Triangle Park, NC, 1992.

17. Oliver, K.D., J.R. Adams, E.H. Daughtry, Jr., W.A. McClenny, M.J. Yoong, M.A. Pardee,

E.B. Almasi, and N.A. Kirshen. Technique for Monitoring Toxic VOCs in Air: Sorbent

Preconcentration, Closed Cycle Cooler Cryofocusing, and GC/MS Analysis. Environ. Sci.

Technol. 30: 1939-1945 (1996).

18. Oliver, K.D., J.R. Adams, E.H. Daughtry, Jr., W.A. McClenny, M.J. Yoong, and M.A.

Pardee. Techniques for Monitoring Ozone Precursor Hydrocarbons in Air at Photochemical

Assessment Monitoring Stations: Sorbent Preconcentration, Closed-cycle Cooler

Cryofocusing, and GC-FID Analysis. Atmos. Environ. 30, 15: 2751-2757 (1995).

19. Miguel, M.G. “A Comparison Study to Determine the Effects of Pressure, Relative Humidity,

and Canister Residence Time on NMHC Recovery Rates from Stainless Steel Canisters.” In

Proceedings of the 1995 U.S. EPA/A&WMA International Symposium: Measurement of

Toxic and Related Air Pollutants, Research Triangle Park, NC, 1995.

20. Holdren, M.W., and D.L. Smith. Development of Procedures for Performance Evaluation

of Ambient Air Samplers for Volatile Organic Compounds. Final Report, EPA Contract

68-02-4127. Research Triangle Park, NC: U.S. Environmental Protection Agency, 1987.

21. Ochiai, N., S. Daishima, M. Morikawa, and C. Watanabe. “Stablility of Polar Volatile Organic

Compounds in Stainless Steel Canisters with Multi-Layer Pretreatment.” Poster presented at

the 1997 U.S. EPA/A&WMA International Symposium: Measurement of Toxic and

Related Air Pollutants, Research Triangle Park, NC, 1997.

22. McClenny, W.A., S.M. Schmidt, and K.G. Kronmiller. “The Variation of the Relative

Humidity of Air Released from Canisters after Ambient Sampling.” In Proceedings of the

1997 U.S. EPA/A&WMA International Symposium: Measurement of Toxic and Related

Air Pollutants, Research Triangle Park, NC, 1997.

23. Handbook of Chemistry and Physics. CRC Press: Boca Raton, FL (1974).

24. Deans, D. A New Technique for Heart Cutting in Gas Chromatography. Chromatographia,

1: 18-22 (1968).
Section: 2

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Page: 222 of 225

25. Photochemical Assessment Monitoring Stations Implementation Manual. EPA-454/B93-051. Research Triangle Park, NC: U.S. Environmental Protection Agency, 1994.

26. Oliver, K.D., J.D. Pleil, and W.A. McClenny. Sample Integrity of Trace Level Volatile

Organic Compounds in Ambient Air Stored in SUMMA®-Polished Canisters. Atmos.

Environ. 20: 1403-1411 (1986).

27. Holdren, M., D. Smith, and W. McClenny. Storage Stability of Volatile Organic

Compounds in SUMMA®-Polished Stainless Steel Canisters. Final Report, EPA Contract

No. 68-02-4127. Research Triangle Park, NC: U.S. Environmental Protection Agency,

1986.

28. McAllister R., D-P. Dayton, J. Rice, P. O'Hara, D. Wagoner, and R. Jongleux. Stability

Study - Final Report. Report to Scientific Instrument Specialists, Moscow, ID, 1988.

29. Kelly, T.J. and M.W. Holdren. Applicability of Canisters for Sample Storage in the

Determination of Hazardous Air Pollutants. Atmos. Environ. 29: 2595-2608 (1986).

30. Gohlson, A.R., R.K.M. Jayanty, and J.F. Storm. Evaluation of Aluminum Canisters for the

Collection and Storage of Air Toxics. Anal. Chem. 62: 1899-1902 (1990).

31. Pate, Bruce, R.K.M. Jayanty, and M.R. Peterson. Temporal Stability of Polar Organic

Compounds in Stainless Steel Canisters. J. Air Waste Manage. Assoc. 42 (4): 460-462 

(1992). 

32. Coutant, R.W. and W.A. McClenny. “Competitive Adsorption Effects and the Stability of

VOC and PVOC in Sampling Canisters.” In Proceedings of the 1991 U.S. EPA/A&WMA

International Symposium: Measurement of Toxic and Related Air Pollutants, Research

Triangle Park, NC, 1991.

33. Goldan, P.D., W.C. Kuster, F.C. Fehsenfeld, and S.A. Montzka. Hydrocarbon

Measurements in the Southeastern United States: The Rural Oxidants in the Southern

Environment (ROSE) Program 1990. J. Geophys. Res. 100:25, 945-25, 963 (1995).

34. Roberts, J.M., F.C. Fehsenfeld, D.L. Albritton, and R.E. Sievers. “Sampling and Analysis of

Monoterpene Hydrocarbons in the Atmosphere with Tenax Gas Chromatographic Porous

Polymer.” In Identification and Analysis of Organic Pollutants in Air, Butterworth, Boston,

1984, 371-387. 

35. Pellizzari, E.D., and K.J. Krost. Chemical Transformations During Ambient Air Sampling for

Organic Vapors. Anal. Chem., 56: 1813-1819 (1984).

36. Pellizzari, E., B. Demian, and K. Krost. Sampling of Organic Compounds in the Presence of

Reactive Inorganic Gases with Tenax GC. Anal. Chem., 56: 793-798 (1984).
Section: 2

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37. Jüttner, F. A Cryotrap Technique for the Quantitation of Monoterpenes in Humid and

Ozone-Rich Forest Air. J. Chromatogr. 442: 157-163 (1988).

38. Bufler, U. and K. Wegmann. Diurnal Variation of Monoterpene Concentrations in Open-Top

Chambers and in the Welzheim Forest Air, F.R.G. Atmos. Environ. 25A: 251-256 (1991).

39. Janson, R., and J. Kristensson. Sampling and Analysis of Atmospheric Monoterpenes. 

Report CM-79, Department of Meteorology, Stockholm University, International

Meteorological Institute of Stockholm. Distribution by Library, Department of Meteorology,

Stockholm University, Arrhenium Laboratory, S-10691, Stockholm, Sweden.

40. Hoffmann, T. Adsorptive Preconcentration Technique Including Oxidant Scavenging for the

Measurement of Reactive Natural Hydrocarbons in Ambient Air. Fesenius Journal of

Analytical Chemistry, 351: 41-47 (1995).

41. Calogirou, A., B.R. Larson, C. Brussol, M. Duane, and D. Kotzias. Decomposition of

Terpenes by Ozone During Sampling on Tenax. Anal. Chem., 68: 1499-1506 (1996).

42. Helmig, D., and J. Arey. Organic Chemicals in the Air at Whitaker’s Forest/Sierra Nevada

Mountains, California. Sci. Total Environ. 112: 233-250 (1992).

43. Mattsson, M. and G. Petersson. Trace Analysis of Hydrocarbons in Air Using Standard Gas

Chromatographic and Personal Sampling Equipment. Int. J. Environ. Anal. Chem. 11: 211-

219 (1982).

44. Ciccioli, P., E. Brancaleoni, M. Possanzini, A. Brachetti, and C. DiPalo. Sampling,

Identification and Quantitative Determination of Biogenic and Anthropogenic Hydrocarbons in

Forestal Areas. In Physico-Chemical Behaviour of Atmospheric Pollutants, Proceedings

of 3rd European Symposium, Varese, Italy. 10-12 April 1984. Reidel, Dordrecht, pp 62-73

(1984).

45. Walling, J.F., J.E. Bumgarner, D.J. Driscoll, C.M. Morris, A.E. Riley, and L.H. Wright. 

Apparent Reaction Products Desorbed from Tenax Used to Sample Ambient Air. Atmos.

Environ. 20: 51-57 (1986).

46. Cao, X.-L., and C.N. Hewitt. Study of the Degradation by Ozone of Adsorbents and of

Hydrocarbons Adsorbed During the Passive Sampling of Air. Environ. Sci. Technol. 28:

757-762 (1994).

47. Bowyer, J.R. and J.D. Pleil. Supercritical Fluid Extraction as a Means of Cleaning and

Desorbing Common Air Sampling Sorbents. Chemosphere 31: 2905-2918 (1995).

48. Helmig, D. Ozone Removal Techniques in the Sampling of Atmospheric Volatile Organic

Trace Gases. Atmos. Environ. 31: 3635-3651 (1997).
Section: 2

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49. McClenny, W.A. “Future Monitoring Techniques for VOCs.” In Chemistry and Analysis of

Volatile Organic Compounds in the Environment. H.J. Th. Bloemen and J. Burn, Editors,

Blackie Academic and Professional, London, UK 1993, 237-267.

50. Interim Guidelines and Specifications for Preparing Quality Assurance Project Plans.

QAMS-005/80. Washington, D.C.: U.S. Environmental Protection Agency, 1980. 

51. Validation of Air Monitoring Data. EPA-600/4-80-030. U.S. Environmental Protection

Agency, Research Triangle Park, NC, 1996.

52. Main, H.H., P.T. Roberts, and M.E. Korc. “Analysis of PAMS and NARSTO-Northeast

Data - Supporting Evaluation and Design of Ozone Control Strategies: A Workshop.” Paper

presented at U.S. Environmental Protection Agency, Research Triangle Park, NC, December

1995.

53. Main, H.H., P.T. Roberts, J.D. Prouty, and M.E. Korc. Software for Display, Quality

Control, and Analysis of Continuous VOC Data. Report prepared for Electric Power

Research Institute, Palo Alto, CA, EPRI Research Project No. WO9108-01, June 1996.

54. Main, H.H., P.T. Roberts, and L.R. Chinkin. “PAMS Data Analysis Workshop: Illustrating the

Use of PAMS Data to Support Ozone Control Programs.” Paper presented at California Air

Resources Board and EPA Region IX, Sacramento, CA, May 1997.

55. Juran, J. M. Quality Control Handbook. Third Edition, McGraw-Hill, New York, 1974. 

Section 2.

56. Quality Assurance Handbook for Air Pollution Measurement Systems Volume I - A Field

Guide to Environmental Quality Assurance. EPA/600/R-94/038a, U.S. Environmental

Protection Agency, 1994.

57. Holdren, M.W. and D. L. Smith. “Performance of Automated Gas Chromatographs Used in

the 1990 Atlanta Ozone Study.” In Proceedings of the 1991 U.S. EPA/A&WMA

International Symposium: Measurement of Toxic and Related Air Pollutants, Research

Triangle Park, NC, 1991.

58. U.S. Environmental Protection Agency. Federal Register, Vol. 49, No. 209, October 26,

1984.

59. Parsons, M. L. The Definition of Detection Limits. J. Chem. Ed. 46: 290-292 (1969).

60. U.S. Environmental Protection Agency. Code of Federal Regulations. Title 40, Chapter 1,

Part 136, Appendix B. Office of the Federal Register, July 1, 1987.
Section: 2

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61. Quality Assurance Handbook for Air Pollution Measurement Systems. Volume II -

Ambient Air Specific Methods (Interim Edition). EPA/600/R-94/038a. U.S. Environmental

Protection Agency, 1994.
Section: 3.0

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Section 3.0

Determination Of Total Nonmethane Organic

Compounds Using Method TO-12 

Qualitative and quantitative determinations of individual VOCs and measurement of total

NMOC using the GC based methodology described in Section 2.0 requires instrumentation that

is expensive, complex, and difficult to operate and maintain. Method TO-12 provides a similar 1

measurement of total NMOC, but does not provide information on the individual VOCs

comprising the total. Method TO-12 is part of the “Compendium of Methods for the

Determination of Toxic Organic Compounds in Ambient Air,” and is presented in Appendix C. 

Method TO-12 involves a simple preconcentration procedure with subsequent direct flame

ionization detection and provides accurate and sensitive measurements of total NMOC

concentrations. The instrumentation for this method can be configured for either automated

in situ measurements or for analyzing integrated samples collected in canisters.

Although Method TO-12 is not directly applicable to PAMS, the method is included here

because:

C Method TO-12 is a viable, practical, and effective method of post clean-up

determinations of canister cleanliness; 

C Method TO-12 can be used for ambient total NMOC measurements as input into

O predictive models that do not require speciated VOC information; and 3

C Used in combination with the manual (canister) methodology described in

Section 2.5 or in an automated form, Method TO-12 can be applied (i.e., with the

approval of the EPA Administrator) as a viable alternative monitoring approach to

the automated methodology described in Section 2.4.

Total NMOC data, resulting from measurements made using Method TO-12, should be

entered into the AIRS data base. These NMOC data are entered under Parameter Code 43102. 

The abbreviation for parameter code 43102 is “TNMOC.” The Method Code is 012. Method
Section: 3.0

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1. Compendium of Methods for the Determination of Toxic Organic Compounds in

Ambient Air. Compendium Method TO-12. Method for the Determination of

Non-Methane Organic Compounds (NMOC) in Ambient Air Using Cryogenic

Preconcentration and Direct Flame Ionization Detection (PDFID). EPA-600/4-89/017. 

Research Triangle Park, NC: U.S. Environmental Protection Agency. 1988.

Code 012 describes the sum of data gathered by preconcentrated direct flame ionization detection

PDFID). PDFID is the TO-12 EPA-approved method which includes not only the sum of C2-C12

data, but also any compounds larger than C that are detected. 12

3.1 References
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Section 4.0

Methodology for Measuring Oxides of Nitrogen 

And Total Reactive Oxides of Nitrogen in Ambient Air

Measurement of ambient concentrations of nitric oxide (NO) and nitrogen dioxide

(NO2) is a requirement of the 40 CFR Part 58, Subpart E, enhanced O3 network monitoring 1

program. The NO and NO measurements are used to better characterize the nature and extent of 2

the O problem, track oxides of nitrogen emission inventory reductions, assess air quality trends, 3

and make attainment/nonattainment decisions. Information on measuring NO and NO ,2

including method and equipment descriptions, is presented in Section 4.1.

Although not specifically required under 40 CFR Part 58, Subpart E, measurement of

total reactive oxides of nitrogen (NO ) is strongly encouraged by the EPA. Measurements of y

NO constitute a valuable adjunct to current NO and NO monitoring because the individual y 2

species comprising NO include not only NO and NO but also other organic nitroxyl compounds y 2

that have recently been shown to play a significant role in the photochemical O3 formation

process. Information on measuring NOy, including measurement principle and procedures and

equipment descriptions, is presented in Section 4.2.

4.1 Oxides of Nitrogen

Oxides of nitrogen, defined here as the sum of the concentrations of NO and NO2 at the

same point in time, are principal precursors to the formation of O . The Urban Airshed Model 3

(UAM), another type of mathematical O prediction model, requires NO and NO , total NMOC, 3 2

and speciated VOC concentrations as inputs.
(NO % O3

) 6 (NO2% O2% h<)

(NO2% Mo) 6 (NO % MoO3)

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(4-1)

(4-2)

4.1.1 Measurement Principle

NO and NO2 are typically measured using a chemiluminescence instrument. The

principle of operation of this instrumentation is based on the gas-phase reaction of NO and O . 3

This reaction produces a characteristic near infrared luminescence with an intensity that is

linearly proportional to the concentration of NO present. Specifically,

where:

h< = emitted photon energy (function of Planck’s constant and the

frequency of radiation)

Prior to measurement, nitrogen dioxide is converted into NO using a molybdenum (Mo) reducing

surface heated to 325EC. Specifically,

where:

Mo = molybdenum chemical reductant

The reaction results in electronically excited NO molecules which revert to their ground state, 2

resulting in an emission of light or chemiluminescence.

To determine the concentration of NO, the sample gas is blended with O3 in a reaction

chamber causing the reaction to occur. The chemiluminescence that results from the reaction is

monitored by an optically filtered high-sensitivity photomultiplier. The optical filter and

photomultiplier respond to light in a narrow-wavelength band unique to the NO and O reaction. 3

The electronic signal produced in the photomultiplier is proportional to the NO concentration.

To determine the concentration of NOx (i.e., NO + NO2), the sample gas is routed

through an NO2-to-NO chemical reductant converter and the NO2 converted to NO+O2. The
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NO+O2 is blended with O3. The chemiluminescent response is proportional to the concentration

of NO entering the converter. The NO determinations are not the result of direct measurement. x 2

The concentration of NO2 is calculated as the difference between a measured NOx value and a

measured NO value representing the same point in time. There are basically two types of

NO2-to-NO converters; the chemical reductant converter and the photolytic converter. The

chemical reductant converter uses a reducing agent such as molybdenum or gold/carbon

monoxide to convert NO2 to NO. The photolytic converter uses high energy light to perform the

conversion.

Instruments using chemical reductant conversion permit accurate measurement of NO,

NO2, and NOx as long as there are no other nitroxyl compounds present in the sampled

atmosphere. Peroxyacetyl nitrate (PAN) and nitric acid (HNO3) are primary interferents to the

accurate measurement of NO when a chemical reductant converter is used. Chemical reductant 2

converters may partially or completely convert PAN, HNO3, and/or other nitroxyl compounds to

NO. The conversion of compounds other than NO2 causes artificially high values for NO2. The

least biased measurements are typically early morning measurements in urban areas where NO

and/or NO concentrations are high and concentrations of PAN, HNO , and/or other nitroxyl 2 3

compounds are low. The potential for biasing the NO measurement due to the chemical 2

reductant conversion of PAN, HNO , and/or other nitroxyl compounds is greatest in urban areas 3

during late afternoon because the ambient concentration of NO is negligible (i.e., at or below the

detection limit of most conventional instruments) and PAN and HNO and/or nitroxyl 3

compounds other than NO and NO2 comprise a significant percentage of the total airborne

nitroxyl compounds. Therefore, the conversion of the interfering compounds has a greater

biasing effect yielding values that are more closely related to NO (i.e., organic nitroxyl y

compounds including NO and NO ) than to NO . Although the potential for measurement bias 2 x

exists, measurements of NO and NO2 are required under 40 CFR Part 58, Subpart E using EPA

approved instrumentation.

The photolytic converter uses high energy light (i.e., wavelengths from 300 to

430 nanometers) to specifically convert NO2 to NO+O2. The NO+O2 are then mixed with O3 and
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measured by a chemiluminescence detector. Although the photolytic converter specifically

converts NO2 to NO, it is not 100% efficient and must be calibrated regularly to determine and

quantify conversion efficiency. Because the photolytic converter converts only NO to NO, bias 2

caused by the partial or complete conversion of other nitroxyl compounds is not experienced. 

The photolytic converter is not as well developed as the chemical reductant converter and is

therefore more expensive to purchase, operate, and maintain.

4.1.2 Method and Equipment Description

Instrumentation approved or designated as reference or equivalent methods for

measuring ambient concentrations of NO2 are listed in 40 CFR Part 53. Subject to any 2

limitations specified in the applicable designation, each instrument is acceptable for use in

enhanced O monitoring networks, unless the applicable designation is subsequently canceled. 3

Instruments designated as reference methods for NO2 are also approved for measuring NO. The

detailed procedure for measuring ambient concentrations of NO2 using approved instrumentation

is contained in 40 CFR Part 50, Subpart C, Appendix F.3

Figure 4-1 presents the flow schematic of a typical NO-NO2 instrument (i.e., the

Thermo Environmental Instruments, Inc., Model 42, Designated Reference Method Number

RFNA-1289-074). Sample enters the instrument through a flow control capillary. A solenoid

valve routes the sample either through the converter (i.e., NO2 measurement mode) or around the

converter (i.e., NO measurement mode). When the sample flow is routed through the converter,

the chemiluminescence measured in the reaction chamber represents the concentration of NO +

NO and any other oxides of nitrogen compounds that are converted. When the sample flow is 2

routed around the converter, only NO is measured. The concentration of NO2 is calculated

automatically by a microprocessor in the instrument as the difference between a measured NOx

value and a measured NO value for the sample point in time.
Air Dryer

Dry Air

Ozone

Generator

Ozone

Cleanser Capillary

T.E.

Cooler

RX

Chamber

Ozone

Scrubber

Exhaust

Chamber Pump

Pressure

Gauge NO2

Converter

NO

NC

C

Capillary

Filter

Sample 

In

Sample

NC Valve

NO

C

NC

NO

C

Span/Zero

Valve

Zero

Span

o:/s/g/morris/3797/pams/fig4-1.ppt

Figure 4-1. Flow Schematic of a Typical NO-NO2 Instrument

Section:

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4.2 Total Reactive Oxides of Nitrogen

The nitroxyl compounds in ambient air included in the group of specific compounds

referred to as NO have not been specifically defined. This group contains all of the nitroxyl y

compounds that react in the troposphere to any significant extent and, therefore, contribute to the

photochemical formation of O . 3

Identified NO constituents include: y

C NO; 

C NO ; 2

C nitrogen trioxide, N O ; 2 3

C nitrogen pentoxide, N O ; 2 5

C nitrous acid, HNO ; 2

C HNO ; 3

C peroxynitrate; 

C PAN; 

C other organic nitrates; and 

C other aerosol nitrates.

In typical urban environments the principal NO compounds are NO, NO , PAN, and HNO . y 2 3

Measurements of NO are a valuable metric serving multiple purposes. Speciated measurements y

of NO compounds provide valuable information relevant to understanding photochemical cycles y

and evaluating the behavior of chemical mechanisms applied in O3 prediction models. Because

NOy is a conservative determination of all nitrogen emissions releases, excluding losses due to

deposited nitrogen, NO should be an excellent indicator of NO and NO emissions trends. y 2

However, speciated NOy measurements (i.e., analyzing separately for each NOy compound) on a
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routine basis are presently impractical because they require that the user know the identity of all

the compounds to be measured and that appropriate individual methods can be applied.

One of the more important uses of NOy data is predicting tropospheric O3 and assessing

the importance of NO and NO and VOC levels to O production and control. Observational 2 3

based models (OBMs) assess the age of air masses to evaluate control strategies. Generally, air

masses that contain predominantly “fresh” NO emissions are more likely to be

hydrocarbon-deficient and require VOCs to produce O . Air masses that contain nitroxyl 3

compounds are aged and are NO deficient, requiring NO for maximum O production. In either x x 3

case, it is critical to know NO, NO and NO levels to decide the best regional control strategy for 2 y

O .3

Since the measurement of individual reactive nitroxyl compounds is technically

difficult, time consuming, and expensive, it is currently impractical to require routine monitors of

these species at PAMS stations. However, a practical instrument based total NO measurement y

procedure has been developed. This total NOy measurement principle and procedure is presented

in Section 4.3. Measuring total NO is not required by 40 CFR, Part 58, Subpart E. However, y

1

for the reasons discussed above, it is strongly encouraged by the EPA as part of enhanced O3

monitoring programs. 

4.3 Measurement of Total Reactive Oxides of Nitrogen in the Atmosphere

(Gas Phase Chemiluminescence) - Measurement principle and

Procedures

The measurement principle and procedures addresses the need to measure total NOy in

a practical, standardized manner. The total NOy measurement principle and procedures is based

on reconfiguration and operation of a commercially available NOy instrument (i.e., the Thermo

Environmental Instruments, Inc., Model 42s)—the only NOy instrument commercially available

at the time of preparation of this guidance. Although the total NOy measurement principle and

procedures are based on this specific instrument, the approach is sufficiently generic to be used
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with other similar equipment. Any instruments used to measure NOy must have the sensitivity to

measure the low concentrations typically encountered during late afternoon periods and also be

able to measure the high concentrations encountered during early morning periods. Automatic 

range change capabilities will probably be required to accommodate the wide range of NOy

concentrations experienced in a typical urban atmosphere. The total NOy measurement principle

and procedures are structured according to Federal Register format and includes the same topics

and level of detail as the EPA NO2 instrumental method. The EPA recognizes that NOy

measurement is an emerging technology. As advances in the technology are made, the NOy

instrumental method will be updated.

Applicability of the measurement of total NOy is presented in Section 4.3.1 and the

operational principle of measurement is presented in Section 4.3.2. Information on modification

and final configuration of the NOy instrument is presented in Section 4.3.3. Calibration

procedures, including generation of calibration curves and determination of converter efficiency,

are found in Section 4.3.4.

4.3.1 Applicability

The total NOy measurement principle and procedures are applicable to the

measurement of ambient concentrations of NO and NOy as part of PAMS networks. The data

obtained using these procedures are intended for use in mathematical models that predict

tropospheric O trends. 3

4.3.2 Principle of Measurement

Ambient NO and NOy concentrations are determined by photometrically measuring the

light intensity at wavelengths greater than 600 nanometers from the chemiluminescent reaction of

NO with O . This principle is identical to that used for the measurement of NO and NO . 3 2

4,5,6
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To measure NO , sample air is passed through a probe-mounted chemical reductant y

converter and the nitroxyl compounds present are reduced to NO. NO, which commonly 7,8,9,10,11

exists in ambient air, passes through the converter unchanged. The NO resulting from the

reduction of these nitroxyl compounds, plus any native NO, is reacted with O3 and the resulting

chemiluminescent light is measured as the total NO concentration. y

To measure NO separately and specifically, sample air is by-passed around the

chemical reductant converter so that no reduction of the other nitroxyl compounds to NO 10

occurs. The NO (i.e., native NO only) is reacted with O and the resulting chemiluminescent 3

light is measured as the NO concentration.

It should be noted that field and laboratory studies have been conducted to compare

various NOy measurement techniques. Application of the total NOy measurement principle 11,12

and procedures using a heated chemical reductant surface is supported by these studies. 

However, qualifiers do apply.

4.3.3 Measurement Apparatus

The NOy instrument presented in these procedures is based on the design of an

approved NO2 instrument. Details on the differences between the configuration of the NOy

instrument and the EPA-approved NO instrument are presented below. 2

4.3.3.1 Configuration

The configuration of the NOy instrument is very similar to that of the EPA-approved

NO2 instrument. The primary differences between the configurations are the locations of the

converter, particulate filter(s), flow control capillary, and the 3-way solenoid valve used for mode

control. Differences between the NOy instrument configuration and the EPA-approved NO2

instrument configuration can be better understood by comparing the NOy instrument flow
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schematic presented in Figure 4-2 to the flow schematic of the approved NO instrument 2

presented in Figure 4-1. 

The NOy instrument uses a heated molybdenum chemical reductant converter that also

serves as the sample probe inlet to the instrument. The converter is positioned at a program

specific height above ground level within the range of 3 to 15 meters as required for enhanced O3

monitoring programs. Because the converter serves as the sample probe inlet, conversion of

PAN, HNO3, and other nitroxyl compounds to NO is maximized because the surface area, and

consequently surface adsorption of these compounds that typically occurs prior to reaching the

converter, is minimized. It is critical to the performance and longevity of the reductant material

that it not be overheated. The converter operating temperature is actively controlled at 325EC

(±20EC). Separate sample transfer lines are used for the NO and NO channels, and another y

separate transfer line is used to deliver calibration and converter efficiency assessment standards

to the sample inlet.

The EPA-approved NO instrument incorporates a particulate filter that is located prior 2

to the flow control capillary and the chemical reductant converter. In the NO instrument y

configuration, the particulate filter is located after the chemical reductant converter in the NOy

sample transfer line to further minimize surface area and consequently surface adsorption of

nitroxyl compounds in the sample air. Because the NO channel uses a separate sample transfer

line, a second separate particulate filter is installed.

The EPA-approved NO instrument uses a 3-way solenoid valve (i.e., mode control 2

valve), located prior to the chemical reductant converter, to route sample gas through or around

the chemical reductant converter depending on whether the instrument is in the NO or NO2

mode. In the NOy instrument configuration, the mode control valve performs the same function

but is located after the chemical reductant converter to reduce surface area and surface effects.
Sample

In

o:/s/g/morris/3797/pams/fig4-2.ppt

Weatherproof

Enclosure

(Positioned at

Probe Inlet Height)

Molybdenum

Converter

(Calibration)

(NOY)

(NO Only)

Filter

Filter

Gas Phase

Titration

Calibration

System

NO C

NC

Capillary

Capillary Prereactor

Ozone

Generator Dry Air

Air

Dryer

NC

C NO

RX

T.E.

Cooler

Exhaust

Pump

Chamber

Pressure

Gauge

Figure 4-2. Flow Schematic of the Reconfigured NOy Instrument for PAMS Application

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The EPA approved NO2 instrument incorporates a glass capillary to control the sample

air flow rate through the instrument. The capillary is located prior to the mode control valve and

chemical reductant converter. In the NO instrument configuration, the flow control capillary is y

located after the chemical reductant converter and mode control valve. Positioning the capillary

after the mode control valve allows the flow rate through the separate NO and NOy sample

transfer lines to be controlled equally using only one flow control device.

4.3.3.2 Reconfiguration

The reconfiguration of the commercially available NOx instrument into the NOy

instrument applicable to PAMS requires modification of elements of the plumbing (i.e., the flow

pattern) and electronics (i.e., the converter temperature control system) of the instrument. 

Modifications to the sampling station must also be made to accommodate the PAMS NOy

instrument configuration. General information on these modifications is presented below. 

Specific details on modifications must be obtained from individual manufacturers.

Note: Refer as needed to Figure 4-2 and the instrument manual supplied by the

manufacturer while performing the modifications. All modifications should be made in

strict accordance with applicable ordinances (e.g., OSHA Regulations, electrical codes,

zoning requirements, etc.).

4.3.3.2.1 Shelter

Attach an open-bottomed weatherproof enclosure (i.e., unpainted aluminum or stainless

steel), sized (i.e., approximately 12 in. high, 6 in. wide, and 7 in. deep) to accommodate the

converter assembly to a 4 ft. long sampling tower mast. Attach the mast with enclosure to the

sampling tower at the sample probe inlet height specified in the monitoring program

requirements. Attach one end of a length of 1-1/2 in. O.D. flexible conduit to the weatherproof

enclosure. Route the flexible conduit along the mast, down the tower, and into the shelter,

securing as required to provide adequate support.
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4.3.3.2.2 Plumbing 

The following modifications are performed outside the instrument chassis:

(a) Remove the converter assembly from the chassis of the instrument and mount it in

the weatherproof enclosure so that the inlet of the converter faces down toward the open bottom

of the enclosure. Connect a 3/8 in. “Cross” fitting to the inlet of the converter using ancillary

fittings as required to insure proper mating.

(b) Extend a length of uniquely identified 1/4 in. O.D. thick wall Teflon tubing ®

through the flexible conduit from the shelter into the weatherproof enclosure. Connect this

uniquely identified Teflon tube to the outlet of the converter to serve as the NO sample transfer ®

y

line.

(c) Extend a length of uniquely identified 1/4 in. O.D. thick wall Teflon tubing ®

through the flexible conduit from the shelter into the weatherproof enclosure. Connect this

uniquely identified Teflon tube to one of the side ports of the 3/8 in. “Cross” fitting using ®

ancillary fittings as required to insure proper mating to serve as the NO sample transfer line.

(d) Extend a length of uniquely identified 3/8 in. O.D. thick wall Teflon tubing ®

through the flexible conduit from the shelter into the weatherproof enclosure. Connect this

uniquely identified Teflon tube to the remaining side port of the “Cross” fitting to serve as the ®

calibration and converter efficiency assessment standards transfer line. Connect the end of the

Teflon tube located in the shelter to the outlet of the calibration system (refer to ®

Section 4.3.4.1).

Note: The bottom port of the “Cross” fitting is left open. This open port serves

as the sample air inlet during monitoring and as the excess calibration standard gas vent

during calibration.
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The following modifications are performed inside of the instrument chassis:

(a) Remove and replumb the flow rate control capillary so that it is connected to the

common port (C) of the mode control solenoid valve.

(b) Remove and replumb the particulate filter assembly so that the outlet of the

particulate filter assembly is connected to the normally closed port (NC) of the mode control

solenoid valve. Attach the appropriate Teflon tube leading from the sampling probe to the inlet ®

of the particulate filter assembly.

(c) Plumb a second particulate filter assembly so that the outlet of the particulate

filter assembly is connected to the normally open port (NO) of the mode control solenoid valve. 

Attach the appropriate Teflon tube leading from the sampling probe to the inlet of the ®

particulate filter assembly.

4.3.3.2.3 Electronics 

The following modifications are performed outside of the instrument chassis:

(a) Extend a length of thermocouple wire (i.e., type K - Chromel/Alumel, 16 gauge

solid core, twisted pair with stainless steel overbraiding) through the flexible conduit from the

shelter into the weatherproof enclosure. Connect the thermocouple wire to the thermocouple

located in the converter. Ensure that the chromel wires are mated and that the alumel wires are

mated.

(b) Extend a length of power wire (i.e., two conductors with ground, 14 gauge solid

core copper, rated for outdoor use) through the flexible conduit from the shelter into the

weatherproof enclosure. Connect the two conductors of the power wire to the heater located in

the converter. Connect the ground wire directly to the weatherproof enclosure using a screw and

nut.
(NO % O3

) 6 (NO2% O2)

Section: 4

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(4-3)

The following modifications are performed inside of the instrument chassis:

(a) Connect the thermocouple wire (i.e., end located in the shelter) to the converter

temperature control board. Ensure that the chromel and alumel wires are attached to the correct

terminals (refer to the manufacturer's instrument manual).

(b) Connect the power wire (i.e., end located in the shelter) to the converter

temperature control board. Ensure that the two conductors of the power wire are attached to the

correct terminals (refer to the manufacturer's instrument manual). Connect the ground wire

directly to the chassis ground of the instrument.

4.3.4 Calibration

Calibration of NOy instruments is accomplished by gas phase titration (GPT) of an NO

standard with O3. Major equipment/components required are a stable O3 generator, a

chemiluminescence NOy instrument with strip chart recorder(s), and an NO concentration

standard. The principle of this calibration technique is based upon the rapid gas phase reaction

between NO and O3 to produce stoichiometric quantities of NO2 in accordance with the

following equation:13

When the NO concentration is known, the concentration of NO can be determined. Ozone is 2

added to excess NO in a dynamic calibration system, and the NO channel of the

chemiluminescence NO instrument is used as an indicator of changes in NO concentration. y

Upon the addition of O3, the decrease in NO concentration observed on the calibrated NO

channel is equivalent to the concentration of NO2 produced. The amount of NO2 generated may

be varied by adding variable amounts of O from a stable uncalibrated O generator. 3 3

14
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Note: Because the principle, apparatus, and procedures used to calibrate the NOy

instrument are consistent with calibration of NOx and NOy instruments, it should be

possible to calibrate both types of instruments simultaneously. However, the large quantity

of calibration gas required may render simultaneous calibration of NOx and NOy

instruments impractical.

4.3.4.1 Apparatus

Figure 4-3 presents a schematic of a typical GPT calibration system and shows the

suggested configuration of the components listed below. All connections between components

in the calibration system downstream from the O generator should be constructed of glass, 3

Teflon , or other nonreactive material. ®

4.3.4.1.1 Air Flow Controllers

Devices capable of maintaining constant air flows within ±2% of the required flow rate.

4.3.4.1.2 NO Flow Controller 

A device capable of maintaining constant NO flows within ±2% of the required flow

rate. Component parts in contact with the NO should be made of a nonreactive material.

4.3.4.1.3 Air Flowmeters 

Calibrated flowmeters capable of measuring and monitoring air flow rates with an

accuracy of ±2% of the measured flow rate.
o:/s/g/morris/3797/pams/fig4-3.ppt

NO

Standard

To Instrument (NO)

To 

Instrument

(NOY)

Vent to Atmosphere

Valve

Molybdenum

Converter

Sample

Inlet

From 

Calibration

System

To Inlet of NOX

Instrument

Being Calibrated

Extra Outlets Capped

When Not in Use

Output Manifold F

T

Vent to Atmosphere

Reaction

Chamber

F

NO

Valve

Flowmeter

Flowmeter

Flowmeter

Flow

Controller

Flow

Controller

Flow

Controller

O3

Generator V

AC

Mixing

Chamber

F

D

F

O

Zero

Air

FD = flow of diluent gas FNO = flow of NO

FO = flow of ozonated gas FT = total flow 

Figure 4-3. Flow Schematic of a Typical Gas Phase Titration Calibration System

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4.3.4.1.4 NO Flowmeter 

A calibrated flowmeter capable of measuring and monitoring NO flow rates with an

accuracy of ±2% of the measured flow rate. Rotameters have been reported to operate unreliably

when measuring low NO flows and are not recommended.

4.3.4.1.5 Pressure Regulator For Standard NO Cylinder 

The regulator must have a stainless steel diaphragm and internal parts and a suitable

delivery pressure.

4.3.4.1.6 Ozone Generator 

The generator must be capable of generating sufficient and stable levels of O for 3

reaction with NO to generate NO2 concentrations in the range required. Ozone generators of the

electric discharge type may produce NO and NO2 and are not recommended. Photolytic O3

generators are recommended.

4.3.4.1.7 Valve 

A valve used to divert the NO flow when zero air is required at the manifold. The

valve should be constructed of glass, Teflon , or other nonreactive material. ®

4.3.4.1.8 Reaction Chamber 

A chamber, constructed of glass, Teflon , or other nonreactive material, for the ®

quantitative reaction of O3 with excess NO. The chamber should be of sufficient volume such

that the residence time meets the requirements specified in Section 4.3.4.3. For practical reasons,

residence time should be less than 2 minutes.
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4.3.4.1.9 Mixing Chamber 

A chamber constructed of glass, Teflon , or other nonreactive material and designed to ®

provide thorough mixing of reaction products and diluent air. The residence time is not critical

when the dynamic parameter specification given in Section 4.3.4.3 is met.

4.3.4.1.10 Output Manifold 

The output manifold should be constructed of glass, Teflon , or other non-reactive ®

material and should be of sufficient diameter to ensure an insignificant pressure drop at the

analyzer connection. The system must have a vent designed to ensure atmospheric pressure at

the manifold and to prevent ambient air from entering the manifold.

4.3.4.1.11 Valve 

A valve used to isolate the calibration line (i.e., Teflon line used to deliver standard ®

gases to the NO instrument sample inlet during calibration) when the instrument is monitoring. y

The valve must be sized to ensure atmospheric pressure at the manifold and should be

constructed of glass, Teflon , or other nonreactive material. ®

4.3.4.2 Reagents

4.3.4.2.1 NO Concentration Standard 

Gas cylinder standard containing 50 to 100 ppm NO in N with less than 1 ppm NO . 2 2

This standard must be traceable to a National Institute of Standards and Testing (NIST) NO in N2

Standard Reference Material (SRM 1683 or SRM 1684), an NBS NO2 Standard Reference

Material (SRM 1629), or an NBS/ EPA-approved commercially available Certified Reference

Material (CRM). A recommended protocol for certifying NO gas cylinders against either a 15 16

NO SRM or CRM is given in Section 2.0.7 of the reference. Procedures for certifying a NO gas 17
PR

' [NO]RC x tR' 2.75 ppm&minutes

[NO]RC ' [NO]

STD

FNO

Fo% FNO

tR'

VRC

Fo% FNO

ó 2 minutes

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(4-4)

(4-5)

(4-6)

cylinder against a NIST NO2 SRM and for determining the amount of NO2 impurity in a NO

cylinder are presented in the reference.

4.3.4.2.2 Zero Air 

Zero air is free of contaminants that are detectable on the NO/NO analyzer or that react y

with either NO, O , or NO in the gas phase titration. A procedure for generating zero air is 3 2

given in the reference.14

4.3.4.3 Dynamic Parameter Specification

1. The O generator air flow rate (F ) and NO flow rate (F ) (see Figure 4-3) must 3 0 NO

be adjusted such that the following relationship holds:

where:

PR = dynamic parameter specification, determined empirically, to ensure

complete reaction of the available O3, ppm-minute

[NO]RC = NO concentration in the reaction chamber, ppm

tR = residence time of the reactant gases in the reaction chamber, minute

[NO]STD = concentration of the undiluted NO standard, ppm

FNO = NO flow rate, scm /min 3
FNO '

[NO]OUT x Ft

[NO]

STD

FO'

[NO]

STD x FNO x VRC

2.75

& FNO

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(4-7)

(4-8)

FO = O3 generator air flow rate, scm /min 3

VRC = volume of the reaction chamber, scm3

2. The flow conditions to be used in the GPT system are determined by the

following procedure:

(a) Determine the total flow required at the output manifold (F =analyzer T

demand plus 50% excess). If a conventional NOx instrument is being

calibrated simultaneously with the NOy instrument, FT must reflect the

demand of both.

(b) Establish [NO]OUT as the highest NO concentration (ppm) which will be

required at the output manifold. [NO]OUT should be approximately

equivalent to 90% of the upper range limit (URL) of the NO2 concentration

range to be covered.

 (c) Determine F as follows: NO

 (d) Select a convenient or available reaction chamber volume. Initially, a trial

V may be selected to be in the range of approximately 200 to 500 scm . RC

3

 (e) Compute F as follows: O
tR

'

VRC

FO% FNO

FD' FT& FO& FNO

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(4-9)

(4-10)

(f) Compute t as follows: R

Verify that t < 2 minutes. If not, select a reaction chamber with a smaller V . R RC

(g) Compute the diluent air flow rate as follows:

where:

FNO = NO flow rate, scm /min 3

[NO] = the highest NO concentration (ppm) that will be required at the output OUT

manifold

F = analyzer demand plus 50% excess T

[NO]STD = concentration of the undiluted NO standard, ppm

FO = O3 generator air flow rate, scm /min 3

VRC = volume of the reaction chamber, scm3

tR = residence time of the reactant gases in the reaction chamber, minute

FD = diluent air flow rate, scm /min 3

(h) If FO turns out to be impractical for the desired system, select a reaction

chamber having a different V and recompute F and F . RC O D

Note: A dynamic parameter lower than 2.75 ppm-minutes may be used if it

can be determined empirically that quantitative reaction of O3 with NO occurs. A

procedure for making this determination as well as a more detailed discussion of
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the above requirements and other related considerations is included in the

reference.14

4.3.4.4 Calibration Procedure

The calibration procedure is presented below.

1. Assemble a dynamic calibration system configured like the one shown in

Figure 4-3.

2. Ensure that all flowmeters are calibrated under the conditions of use against a

primary standard (i.e., bubble flow meter or wet-test meter). All volumetric flow

rates should be corrected to 25EC and 760 mm Hg.

3. Precautions must be taken to remove O2 and other contaminants from the NO

pressure regulator and delivery system prior to the start of calibration to avoid any

conversion of the standard NO to NO . Failure to do so can cause significant 2

errors in calibration. This problem may be minimized by (1) carefully evacuating

the regulator after the regulator has been connected to the cylinder and before

opening the cylinder valve; (2) thoroughly flushing the regulator and delivery

system with NO after opening the cylinder valve; and (3) not removing the

regulator from the cylinder between calibrations. If the regulator is removed,

steps 1 and 2 should be repeated.

4. Select the operating range of the NO/NOy instrument to be calibrated. In order to

obtain maximum precision and accuracy, the NO and NOy channels of the

instrument should be set to the same range.

5. Connect the recorder output cable(s) of the NO/NO instrument to the input y

terminals of the strip chart recorder(s). All adjustments to the instrument should
[NO]OUT '

FNO x [NO]

STD

FNO % FO% FD

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(4-11)

be performed based on the appropriate strip chart readings. References to

instrument responses in the procedures given below refer to recorder

responses.

6. Determine the GPT flow conditions required to meet the dynamic parameter

specification as indicated in Section 4.3.4.3.

7. Adjust the diluent air and O3 generator air flows to obtain the flows determined in

Section 4.3.4.3, step 2. The total air flow must exceed the total demand of the

instrument(s) connected to the output manifold to ensure that no back diffusion of

ambient air occurs. Allow the instrument to sample zero air until stable NO and

NOy responses are obtained. After the responses have stabilized, adjust the

instrument zero control(s). Record the stable zero air responses as ZNO and

ZNO .y

 

Note: Some instruments may have separate zero controls for NO and

NOy, while still others may have only one zero control common to both

channels. Offsetting the instrument zero adjustments to +5% of scale is

recommended to facilitate observing negative zero drift.

8. Prepare the NO and NO calibration curves as follows: y

(a) Adjustment of NO span control. Adjust the NO flow from the standard NO

cylinder to generate a NO concentration of approximately 80% of the URL

of the NO range. The exact NO concentration is calculated from:
Recorder Response '

[NO]OUT

URL

x 100 % ZNO

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(4-12)

where:

[NO] = the highest NO concentration (ppm) that will be required at the output OUT

manifold

FNO = NO flow rate, scm /min 3

[NO]STD = concentration of the undiluted NO standard, ppm

FO = O3 generator air flow rate, scm /min 3

FD = diluent air flow rate, scm /min 3

 

Sample this NO concentration until the NO and NO responses have stabilized. Adjust y

the NO span control to obtain a recorder response (percent scale) as indicated below:

where:

 [NO]OUT = diluted NO concentration at the output manifold, ppm

URL = nominal upper range limit of the NO channel, ppm

ZNO = stable zero air response for NO, percent scale

 

Note: Some instruments may have separate span controls for NO and

NOy, while still others may have only one span control common to both

channels. When only one span control is available, the span adjustment is

made on the NO channel of the instrument.

 

If substantial adjustment of the NO span control is required, it may be necessary

to recheck the zero and span adjustments by repeating Section 4.3.4.4, step 7 and

step 8(a). Record the NO concentration and the instrument's NO response. 
[NO

y

]OUT '

FNO ([NO]

STD % [NO2

]

IMP)

FNO % FO% FD

[NO

y

]OUT

URL

x 100 % ZNOx

Section: 4

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(4-13)

(4-14)

(b) Adjustment of NOy span control. When adjusting the instrument’s NOy span

control, the presence of any NO impurity in the standard NO cylinder must 2

be taken into account. The exact NO concentration is calculated from: y

where:

[NOy]OUT = diluted NOy concentration at the output manifold, ppm

FNO = NO flow rate, scm /min 3

[NO]STD = concentration of the undiluted NO standard, ppm

[NO2]IMP = concentration of NO2 impurity in the standard NO cylinder, ppm

FO = O3 generator air flow rate, scm /min 3

FD = diluent air flow rate, scm /min 3

Adjust the NO span control to obtain a recorder response (percent scale) as indicated below: y

where:

[NOy]OUT = diluted NOy concentration at the output manifold, ppm

URL = nominal upper range limit of the NO channel, ppm

ZNOy = stable zero air response for NOy, percent scale

Note: If the instrument has only one span control, the span adjustment

is made on the NO channel and no further adjustment is made for NO . If y
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substantial adjustment of the NOy span control is required, it may be

necessary to recheck the zero and span adjustments by repeating

Section 4.3.4.4, step 7 and step 8(a). Record the NOy concentration and the

instrument’s NO response. y

(c) Generate several additional concentrations (at least five evenly spaced points

across the remaining scale are suggested to verify linearity) by decreasing

F or increasing F . For each concentration generated, calculate the exact NO D

NO and NO concentrations using Equations 4-11 and 4-13, respectively. y

Record the instrument’s NO and NO responses for each concentration. Plot y

the instrument responses versus the respective calculated NO and NOy

concentrations and plot the NO and NOy calibration curves and calculate the

linear regression. For subsequent calibrations where linearity can be

assumed, these curves may be checked with a two-point calibration

consisting of a zero air point and NO and NO concentrations of y

approximately 80% of the URL.

9. Preparation of NO Converter Efficiency Assessment Standards. 2

(a) Assuming the NO zero has been properly adjusted while sampling zero air y

as described in Section 4.3.4.4, step 7, adjust FO and FD as determined in

Section 4.3.4.3, step 2. Adjust FNO to generate a NO concentration near 90%

of the URL of the NO range. Sample this NO concentration until the NO

and NOy responses have stabilized. Using the NO calibration curve obtained

in Section 4.3.4.4, step 8, measure and record the NO concentration as

[NO] . Using the NO calibration curve obtained in Section 4.3.4.4, step 8, orig y

measure and record the NO concentration as [NO ] . y y orig

(b) Adjust the O3 generator to generate sufficient O3 to produce a decrease in the

NO concentration equivalent to approximately 80% of the URL of the NO2
[NO2

]OUT ' [NO]

orig & [NO]rem

%

FNO ([NO2]

IMP)

FNO % FO% FD

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(4-15)

range. The decrease must not exceed 90% of the NO concentration

determined in Section 4.3.4.4, step 9(a). After the instrument responses

have stabilized, record the resultant NO and NO concentrations as [NO] y rem

and [NO ] . y rem

(c) Calculate the resulting NO concentration from: 2

where:

[NO2]OUT = diluted NO2 concentration at the output manifold, ppm

[NO]orig = original NO concentration, prior to addition of O3, ppm

[NO]rem = NO concentration remaining after addition of O3, ppm

FNO = NO flow rate, scm /min 3

[NO2]IMP = concentration of NO2 impurity in the standard NO cylinder, ppm

FO = O3 generator air flow rate, scm /min 3

FD = diluent air flow rate, scm /min 3

(d) Maintaining the same F , F , and F as in Section 4.3.4.4, step 9(a), adjust NO O D

the ozone generator to obtain several other concentrations of NO2 over the

NOy range (at least five evenly spaced points across the remaining scale are

suggested). Calculate each NO2 concentration using Equation 4-15 and

record the corresponding instrument NO responses. y
[NO2

]CONV ' [NO2]OUT & ([NO

y

]

orig& [NOy

]

rem

)

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(4-16)

4.3.4.5 Determination of Converter Efficiency

For each NO2 concentration generated (see Section 4.3.4.4, step 9), calculate the

concentration of NO converted from: 2

where:

[NO2]CONV = concentration of NO2 converted, ppm

[NO2]OUT = diluted NO2 concentration at the output manifold, ppm

[NOy]orig = original NOy concentration prior to addition of O3, ppm

[NOy]rem = NOx concentration remaining after addition of O3, ppm

 

Plot [NO2]CONV (y-axis) versus [NO2]OUT (x-axis) and plot the converter efficiency curve

and calculate the linear regression. The slope of the curve times 100 is the average converter

efficiency (EC). The EC must be greater than 96%; if it is less than 96%, replace or service the

converter.

4.3.4.6 Frequency of Calibration

The frequency of calibration, as well as the number of points necessary to establish the

calibration curve and the frequency of other performance checks, will vary from one instrument

to another. The user's quality control program should provide guidelines for initial establishment

of these variables and for subsequent verification and alteration as operational experience is

accumulated. Manufacturers of instruments should include in their instruction/operation manuals

information and guidance as to these variables and on other matters of operation, calibration, and

quality control.
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1. U.S. Environmental Protection Agency. Code of Federal Regulations. Title 40, Part 58,

Subpart E. Enhanced O Monitoring Regulations. Office of the Federal Register, 3

February 12, 1993.

2. U.S. Environmental Protection Agency. Code of Federal Regulations. Title 40, Part 53,

Office of the Federal Register, July 1, 1987.

3. U.S. Environmental Protection Agency. Code of Federal Regulations. Title 40, Part 50,

Subpart C, Appendix F. Measurement Principle and Calibration Procedure for the

Measurement of NO2 in the Atmosphere (Gas Phase Chemiluminescence). Office of the

4.3.4.7 Analyzer Challenge

The instrument must be challenged annually, at the start of the sampling season. 

Additional challenges, at the beginning, middle, and end of the sampling season, are suggested. 

The optimum challenge would consist of a mixture of representative NOy compounds, but there

is presently no comprehensive commercial mixture covering a broad range of the compounds of

potential interest available to be used as a challenge gas. To assess general instrument

performance, the instrument should be challenged with NO, since this is the gas used for

calibration. Additionally, the system should be assessed for its ability to measure other NOy

constituents by challenging the instrument with other candidate analytes such as 50 ppm n-propyl

nitrite or nitric acid.

4.4 Nitric Acid Measurement

The NOy measurement instrument described above can be obtained from the vendor in

a modified configuration that allows for the separate measurement of total NO and nitric acid. y

This configuration is called the Model 42CW. The Model 42CW cycles between two separate

converters. One of the converters has a nylon filter located at the inlet. Ambient nitric acid is

absorbed by the nylon filter. The nitric acid concentration is determined as the difference

between unfiltered total NO value and the value determined for the filtered channel. y

 

4.5 References
Section: 4

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Federal Register, December 1, 1976.

4. Fontijn, A., A.J. Sabadell, and R.J. Ronco. Homogeneous Chemiluminescent

Measurement of Nitric Oxide with Ozone. Anal. Chem. 42: 575 (1970).

5. Stedman, D.H., E.E. Daby, F. Stuhl, and H. Niki. Analysis of Ozone and Nitric Oxide by

a Chemiluminiscent Method in Laboratory and Atmospheric Studies of Photochemical

Smog. J. Air Poll. Control Assoc. 22: 260 (1972). 

6. Martin, B.E., J.A. Hodgeson, and R.K. Stevens. “Detection of Nitric Oxide

Chemiluminescence at Atmospheric Pressure.” Paper presented at 164th National ACS

Meeting, New York City, August 1972.

7. Hodgeson, J.A., K.A. Rehme, B.E. Martin, and R.K. Stevens. “Measurements for

Atmospheric Oxides of Nitrogen and Ammonia by Chemiluminescence.” Paper

presented at 1972 APCA Meeting, Miami, FL, June 1972.

8. Stevens, R.K. and J.A. Hodgeson. Applications of Chemiluminescence Reactions to the

Measurement of Air Pollutants. Anal. Chem. 45: 443A (1973).

9. Breitenbach, L.P and M. Shelef. Development of a Method for the Analysis of NO2 and

NH by NO-Measuring Instruments. J. Air Poll. Control Assoc. 23: 128 (1973). 3

10. Winer, A.M., J.W. Peters, J.P. Smith, and J.N. Pitts, Jr. Response of Commercial

Chemiluminescent NO-NO Analyzers to Other Nitrogen-Containing Compounds. 2

Environ. Sci. Technol. 8: 1118 (1974).

11. Williams, E.J., K. Baumann, J.M. Roberts, S.B. Bertman, R.B. Norton, F.C. Fehsenfeld,

S.R. Springston, L.J. Nunnermaker, L. Newman, K. Olszyna, J. Meagher, B. Hartsell,

E. Edgerton, J. Pearson, and M.O. Rodgers. Intercomparison of NO Measurement y

Techniques. Submitted for Publication, J. Geophys. Research, Special Issue, Southern

Oxidant Study (1997).

12. Dahv, A.V., B.C. Daube, J.D. Burley, and S.C. Wofsy. Laboratory Investigation of the

Catalytic Reduction Technique for Measurement of Atmospheric NO . J. Geophys. y

Research, 102: 10759-10776 (1997).

13. Rehme, K.A., B.E. Martin, and J.A. Hodgeson. Tentative Method for the Calibration of

Nitric Oxide, Nitrogen Dioxide, and Ozone Analyzers by Gas Phase Titration. 

EPA-R2-73-246, Research Triangle Park, NC: U.S. Environmental Protection Agency,

1974.

14. Hodgeson, J.A., R.K. Stevens, and B.E. Martin. A Stable Ozone Source Applicable as a

Secondary Standard for Calibration of Atmospheric Monitors. ISA Transactions 11: 161

(1972).
Section: 4

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Page: 32 of 32

15. A Procedure for Establishing Traceability of Gas Mixtures to Certain National Bureau of

Standards Standard Reference Materials. EPA-600/7-81-010. Joint publication by NBS

and EPA. 1981.

16. Quality Assurance Handbook for Air Pollution Measurement Systems Volume II -

Ambient Air Specific Methods (Interim Edition). EPA-600/R-94/038a. U.S.

Environmental Protection Agency. 1994.

17. Ellis, E.C. Technical Assistance Document for the Chemiluminescence Measurement of

Nitrogen Dioxide. EPA-E600/4-75-003 Research Triangle Park, NC: U.S. Environmental

Protection Agency. 1992.
Section: 5

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Section 5.0 

Methodology for Determining Carbonyl Compounds 

in Ambient Air 

Determination of ambient concentrations of carbonyl compounds is a requirement of

40 CFR Part 58, Subpart E, enhanced O network monitoring programs. Carbonyl compounds 1

3

have been shown to contribute to the formation of photochemical O . Formaldehyde, 3

acetaldehyde, and acetone are specifically required target compounds for PAMS; however, other

carbonyl compounds may be added to the target list consistent with individual program

objectives. The methodology used to accomplish carbonyl compounds monitoring is

Compendium Method TO-11A. Method TO-11A, presented in Appendix D, provides sensitive 2

and accurate measurements of carbonyl compounds and involves sample collection and analysis

procedures. In this method, a cartridge(s) containing a solid sorbent is used to capture the target

compounds. Information on solid sorbents used is presented in Section 4.4 of Method TO-11A. 

Ozone has been identified as an interferent in the measurement of carbonyl compounds when

using Method TO-11A. To eliminate this interference, removal or scrubbing of O3 from the

sample air stream is mandatory. Section 5.1 presents information on O3 scrubbers. Sample

analysis is accomplished using high performance liquid chromatography (HPLC) with

ultraviolet/visible detection.

Under 40 CFR Part 58, Subpart E, States are required to obtain 3-hour and 24-hour 1

integrated measurements of carbonyl compounds at specified collection frequencies based on

individual enhanced O monitoring site type requirements. The sample collection frequencies 3

range from one 24-hour sample every sixth day to eight 3-hour samples every day. Specific

sample collection frequencies and minimum network monitoring requirements for carbonyl

compounds are presented in Table 5-1. (Note: This section is intended to be independent of other

sections. Figures, tables, and text from other sections are repeated as required.) The sample

collection frequencies necessitate the use of an automated multiple-event sample collection

approach. Section 5.2 presents information on multiple-event sample collection
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Table 5-1 . PAMS Minimum Monitoring Network Requirements

Population Required Sampling Compounds Sampling

of MSA/CMSA Site Type Frequency Frequency 1

Minimum VOCs Minimum Carbonyl

2 2

Less than 500,000 (1) A or C -

500,000 to 1,000,000 (1) A or C E

1,000,000 to (1) A or C E

2,000,000 (2) B E

More than 2,000,000 (1) A or C E

 (2) A or C D or F

(2) B -

(3) A or C

(2) B -

(3) A or C

(2) B E

(2) B -

(3) A or C -

(4) A or C

-

-

-

Whichever area is larger. 1

Frequency Requirements Are As Follows: 2

A = Eight 3-hour samples every third day and one additional 24-hour sample every sixth day during

the monitoring period.

B = Eight 3-hour samples every day during the monitoring period and one additional 24-hour sample

every sixth day year-round.

C = Eight 3-hour samples on the 5 peak O3 days plus each previous day, eight 3-hour samples every

sixth day and one additional 24-hour sample every sixth day during the monitoring period.

D = Eight 3-hour samples every third day during the monitoring period.

E = Eight 3-hour samples on the 5 peak O days plus each previous day and eight 3-hour samples 3

every sixth day during the monitoring period.

F = Eight 3-hour samples on the 5 peak O3 days plus each previous day, eight 3-hour samples every

sixthe day and one additional 24-hour sample every sixth day during the monitoring period.
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Table 5-1 . PAMS Minimum Monitoring Network Requirements (Continued)

The minimum sampling frequency requirements for speciated VOC monitoring are prescribed in 40 CFR

Part 58, Subpart E, Appendix D - Network Design for State and Local Air Monitoring Stations (SLAMS),

National Air Monitoring Stations (NAMS), and Photochemical Assessment Monitoring Stations (PAMS). 

Section 4.3 - Monitoring Period requires, at a minimum, that O3 precursor monitoring be conducted

annually throughout the months of June, July, and August when peak O values are expected. Section 4.4 - 3

Minimum Monitoring Network Requirements specifies the minimum required number and type of

monitoring sites and sampling frequency requirements based on the population of the affected

MSA/CMSA or nonattainment area, whichever is larger. The minimum speciated VOC sampling

frequency requirements are summarized by site type below:

C Site Type 1 - Eight 3-hour samples every third day and one additional 24-hour sample every sixth day

during the monitoring period; or eight 3-hour samples on the 5 peak O3 days plus each previous day

and eight 3-hour samples and one 24-hour sample every sixth day, during the monitoring period.

C Site Type 2 - (population less than 500,000) - Same as Site Type 1.

C Site Type 2 - (population greater than 500,000) - Eight 3-hour samples every day during the

monitoring period and one additional 24-hour sample every sixth day year around.

C Site Type 3 - (population greater than 500,000) - Same as Site Type 1.

C Site Type 4 - (population more than 2,000,000) - Same as Site Type 1.

Samples collected should represent a time-integrated average for the required sampling period. It is

important to understand that the 3-hour sample integration period is a maximum requirement in the sense

that samples can be collected more frequently at shorter sampling intervals (i.e., three 1-hour periods) but

not less frequently for longer sampling intervals. 
O3

% 2I

& % H2O 6 I

2

% O2% 2OH &

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(5-1)

systems, including a generic equipment description and operating procedure and recommended

specifications applicable to evaluation and procurement.

5.1 Ozone Scrubbers

The EPA has determined through laboratory tests that O present in ambient air 3

interferes with the measurement of carbonyl compounds when using Method TO-11A. Ozone

can interfere with carbonyl analyses in three ways:

C The ozone reacts with the 2,4-dinitrophenylhydrazine (DNPH) on the cartridge,

making the DNPH unavailable for derivatizing carbonyl compounds;

C The ozone also degrades the carbonyl derivatives formed on the cartridge during

sampling; and

C If the analytical separation is insufficient, the DNPH degradation products can

coelute with target carbonyl derivatives. 

The extent of interference depends on the temporal variations of both the ozone and the carbonyl

compounds and the duration of sampling. Carbonyl compound losses have been estimated to be

as great as 48% on days when the ambient O concentration reaches 120 ppbv. Eliminating this 3

measurement interference problem by removing or scrubbing O from the sample air stream prior 3

to collection of the carbonyl compounds is a mandatory facet of carbonyl compounds sample

collection for enhanced O3 monitoring programs. Two types of O3 scrubbers, the Denuder O3

scrubber and the Cartridge O3 scrubber, have been developed. Both the Denuder and Cartridge

O3 scrubbers use potassium iodide (KI) as the scrubbing agent. Scrubbing is based on the

reaction of O with KI, specifically: 3
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where:

O = ozone (ambient) 3

H O = water (ambient) 2

I) = the iodide ion from potassium iodide forming molecular iodine (I ), 2

oxygen (O ), and the hydroxide ion (OH)) 2

Both O3 scrubber designs effectively remove O3 at sample collection flow rates up to 1 L/minute

and have sufficient scrubbing capacity to meet the needs of carbonyl compounds measurement

for enhanced O monitoring programs. 3

This section presents details of the two types of O3 scrubber equipment and

recommended procedures for their use.

5.1.1 Denuder Ozone Scrubber

The Denuder O3 Scrubber is a copper tube coated internally with a saturated solution

of KI. The tube is coiled and housed in a temperature controlled chamber that is heated to, and

maintained at, 66EC during sample collection. Heating prevents condensation from occurring in

the tube during sampling. The scrubber is connected to the inlet of the sample collection system. 

Sample air is extracted from a sample probe and distribution manifold (see Section 5.2.3) and

pulled through the scrubber by an oilless vacuum pump. Ozone in the sample air is converted

(i.e., scrubbed) by the chemical reaction previously described in Section 5.1.

The Denuder O3 Scrubber is reusable. The copper tube should be recoated with a

saturated solution of KI after each six months of use. The Denuder O Scrubber prepared as 3

described in TO-11A has been found to effectively remove ozone from the air stream for up to

100,000 ppb-hours. Thus, the scrubber will last for six months of 24-hour sampling on every

sixth day when sampling air with an average ozone concentration of 120 ppbv. To recoat the
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denuder, fill the copper tube with a saturated solution of KI in water. Allow the solution to

remain in contact with the tube for a few minutes. Then, drain the tube. Dry the tube by blowing

a stream of clean air or nitrogen through the tube for about one hour. 

An alternative to using a KI coated copper tube is to use a modified Dasibi ozone

scrubber device. Replace the manganese dioxide coated screens with 15 KI coated copper or

stainless steel screens assembled in a cartridge holder. Wash the screens in pure water in a sonic

bath. Dry the screens. Then, coat the screens by dipping them into a saturated KI solution in

water. Air dry the KI coated screens. This procedure deposits about 4 mmoles or about 700 mg

of KI over a sandwich of 15 two-inch diameter screens. Assemble the coated screens in the

Dasibi encasement with a fiberglass filter at each end. Close and seal the encasement including

the O-rings with the screws. Based on this removal capacity, this scrubber will last

approximately 300 days when sampling air with an average ozone concentration of 120 ppbv at a

rate of 1 L/min.

5.1.1.1 Denuder Ozone Scrubber Equipment 

Figure 5-1 presents a cross-sectional view of the Denuder O Scrubber. The scrubber is 3

comprised of the following components: 

Copper tubing - A 3 foot length of 1/4-inch O.D. copper tubing, coiled into a spiral

approximately 2 inches in diameter. Used as the body of the O scrubber. 3

Potassium iodide - The inside surface of the copper coil is coated with a saturated

solution of ACS Reagent Grade KI. Used to provide the O scrubbing mechanism. 3

Cord heater - A 2 foot long cord heater, rated at approximately 80 watts, wrapped

around the outside of the copper coil. Used to provide heat to prevent condensation of

water or organic compounds from occurring within the coil.
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Figure 5-1. Cross-Sectional View of the Denuder O Scrubber 3
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Thermocouple - A Chromel-Alumel (Type K) thermocouple located between the

surface of the copper coil and the cord heater. Used to provide accurate temperature

measurement for temperature control.

Temperature controller - A Type K active temperature controller. Used to maintain

the O scrubber at 66EC as referenced by the Type K thermocouple. 3

Fittings - Bulkhead unions attached to the entrance and exit of the copper coil. Used to

allow connection to other components of the sampling system.

Chassis box - Conveniently sized aluminum enclosure. Used to contain the fittings,

coated copper tube, heater, and thermocouple.

5.1.1.2 Denuder Ozone Scrubber Operational Procedure

Recommended procedural steps for operation of the Denuder O Scrubber are as 3

follows:

(1) Connect the inlet of the Denuder O3 scrubber to the sample probe and

distribution manifold (see Figure 5-1).

(2) Connect the outlet of the Denuder O3 scrubber to the sample collection system

inlet.

(3) Set the temperature controller to maintain the scrubber at 66EC.

(4) Conduct sampling in accordance with the recommended procedures for operating

multiple-event sample collection systems as described in Section 5.2.2 and/or

Method TO-11A sampling procedures as described in Section 5.11 (see

Appendix D).

5.1.2 Cartridge Ozone Scrubber 

The Cartridge O3 Scrubber is a standard Sep-Pak Plus cartridge (i.e., identical in size ®

and shape to the precoated DNPH Silica Sep-Pak cartridge) filled with approximately 1 gram of ®

ACS Reagent Grade KI. The scrubber is positioned at the inlet of the sample collection system. 

Sample air is extracted from the sample probe and distribution manifold (see Figure 5-1) and
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pulled through the O3 scrubber by an oilless vacuum pump. Ozone in the sample air is converted

(i.e., scrubbed) by the chemical reaction previously described in Section 5.1.

The Cartridge O Scrubber is commercially available (i.e., Waters Corporation) and is 3

disposable. The theoretical removal capacity of the scrubber, based on 100% consumption of KI,

is 200 mg of O3. Based on experience in the field, the cartridge O3 scrubber should be replaced

every three weeks.

5.1.2.1 Cartridge Ozone Scrubber Equipment

Figure 5-2 presents a cross-sectional view of the Cartridge O Scrubber. The scrubber 3

is comprised of the following components: 

Cartridge housing - A two-part plastic vessel with an O.D. of approximately 1⁄2 inches

and an overall length of approximately 1-5/8 inches. One of the parts has a female Luer

style connector that serves as the scrubber inlet. The other part has a male Luer style

connector that serves as the scrubber outlet. Used to contain the scrubber media.

Potassium iodide - The scrubber medium is granular ACS Reagent Grade KI. Used to

provide the ozone scrubbing mechanism.

Inlet and outlet filters - Polyethylene fritted filters located inside the cartridge housing

at the inlet and outlet ends. Used to retain the scrubber media inside the cartridge

housing during sampling.

Compression ring - An aluminum ring sized to fit around the outside of the two

cartridge housing parts and seal them through compression. Used to provide a secure

leak-free seal between the two cartridge housing parts.

5.1.2.2 Cartridge Ozone Scrubber Operational Procedure

Recommended procedural steps for operation of the Cartridge O Scrubber are as 3

follows:
Connector (Luer Style)

Filter (Polyethylene)

Scrubber Media (Potassium Iodide)

Filter (Polyethylene)

Compression Ring (Aluminum)

Cartridge Housing

Connector (Luer Style)

o:/s/g/morris/3797/pams/hobson/hob2.ppt

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Figure 5-2. Cross-Section View of the Cartridge O Scrubber 3
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1. Connect the inlet of the Cartridge O3 scrubber to the sample probe and

distribution manifold (see Section 2.4.1.1).

2. Connect the outlet of the Cartridge O3 scrubber to the sample collection system

inlet.

3. Ensure that a leak-free connection is obtained.

4. Conduct sampling in accordance with the recommended procedures for operating

multiple-event sample collection systems as described in Section 5.2.2 and/or

Method TO-11A sampling procedures as described in Section 5.10 of Method

TO-11A (See Appendix D). Note: Heating of the cartridge ozone scrubbers

to 35EC may be advisable under certain circumstances to prevent

condensation of water.

5.2 Multiple-event Sample Collection Systems

The use of solid sorbent cartridge sample collection systems to satisfy the sample

collection frequencies specified in Table 5-1 necessitates the use of multiple-event sample

collection systems. Multiple-event collection systems should be capable of unattended operation

in order to allow for multiple sample collection in a practical, non-labor intensive manner. 

Multiple-event sampling systems are manufactured commercially or can be custom manufactured

by the user for a specific application. Several multiple-event sampling systems are commercially

available. 

The following sections generally describe multiple-event sampling equipment,

procedures, and specifications. Also, recommended system specifications applicable to the

evaluation and procurement of multiple-event sampling systems are presented.

5.2.1 Multiple-event Collection System Equipment 

A typical multiple-event sampling system configuration is presented in Figure 5-3. The

multiple-event cartridge sampling system is comprised of the following primary components: 
Manifold By-Pass Pump

Os

Scrubber

9 Mechanical

Check Valves

9 Solenoid

Valves

or

or

Rotary

Valve

Sample

Cartridges

9 Solenoid

Valves

Rotary

Valve

Heated Manifold

Assembly

Mass Flow

Controller

Mass Flow

Meter and

Variable Orifice

3-hr Duplicate

or

24-hr Sample

Mass Flow

Controller

3-hr

Samples

To

Atmosphere

Oilless Vacuum Pump

o:/s/g/morris/3797/pams/hobson/hob3.ppt

Figure 5-3. Schematic of a Typical Multiple-Event Carbonyl Cartridge Sampling System

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Inlet probe and manifold assembly - Constructed of glass (see Figure 5-1) or stainless

steel. Used as a conduit to extract sample air from the atmosphere at the required

sampling height and distribute it for collection.

By-pass pump - A single- or double-headed diaphragm pump, or a caged rotary

blower. Used to continuously draw sample air through the inlet probe and manifold

assembly at a rate in excess of the sampling system total uptake. All excess sample air

is exhausted back to the atmosphere.

Sample pump - An oilless vacuum pump, capable of achieving an inlet pressure of

-25 inches Hg continually. Used to extract sample air from the manifold assembly and

pull it through the sample cartridges during collection.

Sample inlet line - Chromatographic-grade stainless steel tubing. Used to connect the

sampler to the manifold assembly. This line should be kept as short as possible.

Ozone scrubber - A Denuder or Cartridge type of O3

 scrubber. Used to remove

ambient O from the sample air stream prior to exposure to the sample cartridge. 3

Sample cartridges - A plastic housing containing silica gel or C18 solid sorbent (see

Section 4.4 of Method TO-11A in Appendix D) coated with DNPH. Used to contain

the collected sample for transportation and analysis.

Adjustable orifice and mass flow meter assembly, or electronic mass flow

controller - An indicating flow control device(s). Used to maintain a constant flow rate

(± 10%) over a specific sampling period under conditions of changing temperature

(20-40EC) and humidity (0-100% relative).

Microprocessor - An event control and data acquisition device. Used to allow

unattended operation (i.e., activation and deactivation of each sampling event) of the

collection system, and to record sampling event specific process data (i.e., start and end

times, elapsed times, collection flow rates, etc.). 

Check valves, solenoid valves, or a multi-port rotary valve - Eight stainless steel

check valves, eight solenoid valves with electric-pulse-operated or low temperature

coils, stainless steel bodies, and Viton plunger seats and o-rings, or 1 multi-port ®

stainless steel body rotary valve with Viton o-rings. Used to provide access to or ®

isolation of the inlet side of the sample cartridges.

Solenoid valves or a multi-port rotary valve - Eight solenoid valves with

electric-pulse-operated or low temperature coils, stainless steel bodies, and Viton®

plunger seat and o-rings, or 1 multi-port stainless steel body rotary valve with Viton®

o-rings. Used to provide access to or isolation of the outlet side of the sample

cartridges. 
F '

Vx1000

Tx60

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(5-2)

Tubing and fittings (Stainless steel or Teflon ) - Hardware for isolation and ®

interconnection of components. Used to complete system interconnections. All

stainless steel tubing in contact with the sample prior to analysis should be

chromatographic grade stainless steel and all fittings should be 316 grade stainless steel. 

Note that if the manifold is heated, stainless steel tubing should be used because of the

potential of off-gassing of the tubing.

Note: Elapsed-time indicators installed in-line with sample pumps can provide

backup documentation that all samples ran for 180 minutes and can indicate that

a malfunction occurred with the programmable timers or that power was

interrupted.

5.2.2 Multiple-event Sampling Procedures

Samples are collected on individual solid sorbent sample cartridges using a single pump

and one or more flow control devices. An oil-less vacuum pump draws ambient air from the

sampling probe and manifold assembly through the sample cartridge at a constant flow rate

during each specific sampling event.

A flow control device(s) is used to maintain a constant sample flow rate through each

sample cartridge over each specific sampling period. The flow rate used is a function of the

desired total volume of ambient air sampled and the specified sampling period. The flow rate is

calculated as follows:

where:

F = flow rate (milliliters/minute)

V = desired total volume of ambient air sampled (liters)

1000 = milliliters in a liter

T = sample period (hours)
F '

168x1000

3x60

' 933 milliliters/minute

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(5-3)

60 = minutes in an hour

For example, if the desired total volume of ambient air to be sampled is 168 L over each

individual 3-hour cartridge collection episode, the flow rate specific to each cartridge collection

episode is calculated as follows:

During operation, the microprocessor control device is programmed to activate and

deactivate the components of the sample collection system, consistent with the beginning and

end of each individual sample collection period. 

Cartridge sampling systems can collect sample from a shared sample probe and

manifold assembly as described in Section 5.2.3 or from a dedicated stainless steel sample probe,

manifold assembly, and by-pass pump. If a dedicated probe, manifold assembly, and by-pass

pump are used, a separate timer device should be incorporated to start the by-pass pump several

hours prior to the first sampling event of a multiple-event collection period to flush and condition

the probe and manifold assembly components. The connecting lines between the manifold

assembly and the sampling system should be kept as short as possible to minimize the system

residence time. 

The flow rate through each sample cartridge should remain relatively constant over the

entire collection period of each sampling event. Each adjustable orifice and mass flow meter

assembly, or mass flow controller, used as a flow control device should be calibrated against a

primary flow measurement standard (i.e., a bubble flow meter, etc.). Calibrations should include

multiple points of comparison (i.e., indicated flow versus measured flow), across the entire range

of the flow control device at increments reflecting 10% of the range. Calibration curves are

generated from these comparisons and are used to set actual desired flow rates based on the flow
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rates indicated by the flow control devices. Calibration of the flow control devices should be

repeated periodically according to program specific QA/QC schedules as developed by the user.

Generic steps for operating a typical multiple-event sample collection system are as

follows:

1. Set the sampling system to the desired sample collection flow rate(s)

(i.e., referencing the corresponding calibration curve(s) and considering the

desired total volume of ambient air to be sampled and the sampling period for

each sampling event).

2. Program the microprocessor event control system to start and stop sample

collection consistent with program specific collection frequency requirements.

3. Attach all sample cartridges to the sampling system.

4. Record the start and end time of each collection event and the corresponding

flow rate onto the sampling field data sheet and calculate an average flow rate. 

The microprocessor event control and data acquisition system should

automatically store these data for each collection event. The final total volume

of ambient air sampled should be close to the desired total volume.

5. Remove each sample cartridge (i.e., one at a time), cap both ends, and attach an

identifier to each (i.e., again, one at a time to avoid mislabeling). Sample event

number, sample type, location, collection date, should be recorded on the field

data sheet.

6. Place cartridges in tightly enclosed transport containers and transport the samples

and corresponding information to the central laboratory for preparation and

analysis.

5.2.3 Sample Probe and Manifold

A sample probe and manifold assembly should be used to provide a representative air

sample for collection and subsequent analysis. Sample probe and manifold assemblies are

commercially available or can be custom fabricated.
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The sample probe is constructed of glass that is approximately 1 inch in outside

diameter (O.D.). The inlet of the sample probe is configured with an inverted funnel,

approximately 4 inches O.D. The sample manifold is constructed of glass, approximately 1 and

1⁄2 inches O.D. The manifold has ports used for sample distribution. The number of ports located

on the manifold must be equal to or greater than the total number of monitoring systems that

sample will be delivered to. The port nearest to the inlet of the manifold should be reserved for

VOC sampling; the second port or any other port may be used for carbonyl sampling.

Teflon bushings are used to connect sample lines to the manifold. Because the ®

manifold and ports are constructed of glass, care must be taken to not place excessive stress on

the assembly to avoid breakage. For VOC sampling, the sample lines should be constructed of

1/8 inch O.D. stainless steel tubing. The 1/8 inch tubing is flexible and will accommodate the

flow rates typically associated with VOC sample collection. The sample lines should be kept as

short as possible to reduce sample transfer time. For carbonyl sampling, the sample lines should

be constructed of 1/4 inch O.D. stainless steel tubing; the scrubber and the carbonyl sample

cartridge holder assembly should be positioned as close to the manifold as possible.

A blower and bleed adapter are located at the exit end of the sample manifold. The

blower is used to pull sample air through the probe and manifold and the bleed adapter is used to

control the rate at which the sample air is pulled through the manifold. An excess of sample air

is pulled through the sample probe and manifold to prevent back diffusion of room air into the

manifold and to ensure that the sample air is representative of outside ambient air. Sample air

flow through the sample probe and manifold should be at least two times greater than the total air

flow being removed for collection and analysis by all systems on the manifold.

The vertical placement of the sample probe and inlet funnel should be at a height of 3 to

15 meters above ground level. Because the O monitoring requirements involve multiple- 3

pollutant measurements, this range serves as a practical compromise for probe position. In

addition, the probe inlet should be positioned more than 1 meter, both vertically and horizontally,

away from the housing structure. The probe inlet should be positioned away from nearby
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obstructions such as a forest canopy or building. The vertical distance between the probe inlet

and any obstacle should be a least two times the height difference between the obstacle and the

probe inlet. Unrestricted air flow across the probe inlet should occur within an arc of at least

270 degrees. The predominant and second most predominant wind direction must be included in

this arc. If the probe inlet is positioned on the side of a building, a 180 degree clearance is

required. More specific details of probe positioning are presented in the “Enhanced Ozone

Monitoring Network Design and Siting Criteria Guideline Document.” The glass probe should 3

be reinforced or supported along the straight vertical axis of the assembly. Typically this support

is provided by routing the probe shaft through a rigid section of metal or plastic tubing that is

secured to the housing structure.

The manifold can be positioned in either a horizontal or vertical configuration. 

Figure 5-4 presents the manifold assembly in the vertical configuration. Figure 5-5 presents the

manifold assembly in the horizontal configuration. If the horizontal configuration is used, the

sample ports must point upward so that material that may be present in the manifold will not be

transferred into the sample lines.

With continuous use the sample probe and manifold can accumulate deposits of

particulate material and other potential contaminants. The sample probe and manifold should be

cleaned to remove these materials. The recommended frequency for cleaning is quarterly. To

clean the assembly, disconnect the sample lines and blower from the manifold. The sample lines

and blower are not cleaned. For safety, electric power to the blower should be terminated until

the cleaning process is completed. Disassemble the individual components by disconnecting the

probe, manifold, collection bottle, and coupling devices from each other. The individual

components should then be cleaned using heated high purity distilled water and a long handled

bottle brush. The components should then be rinsed with the distilled water and allowed to dry

completely before reassembling. If required, mild glass cleaner or detergent can be used to clean

particularly dirty components. However, care should be taken to select cleaners and detergents

that are advertised to have low organic compound content and the number of rinses performed

should be increased to ensure that all associated residues are removed.
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Figure 5-4. Vertical Configuration
Sampling cane

Sample

 in

Cane

support

Shelter roof

Shelter

wall

First port dedicated to VOC sampling

Second port dedicated to Carbonyl sampling

Sample manifold

(with sufficient number of

ports to individually support

all monitoring conducted)

Bleed adapter

(flow control)

Blower

and mount

Exhaust

tube

Collection

bottle

To

atmosphere

Shelter

wall

o/s/g/morr/3797/pams/shelt2.ppt

Figure 5-5. Horizontal Configuration

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5.2.4 Multiple-event System Specifications

The use of sample cartridges to practically address the sampling frequency and schedule

for carbonyl compounds specified in Table 5-1 requires the use of multiple-event cartridge

sampling systems. The use of a single-event system to collect eight back-to-back 3-hour

cartridge samples would require that an operator be physically present on site to manually

complete the activities associated with the start and stop of each sampling event.

To ensure that a multiple-event sample collection system will meet the user’s program

needs, system specifications and other pertinent general considerations should be presented to,

and addressed by, the candidate vendor(s) prior to procurement. Primary system specifications

are presented below. However, additional system specifications and considerations may be

added at the discretion of the user.

C An in-depth, detailed manual covering all aspects of the sample collection system

(i.e., operation, maintenance, etc.) must be provided by the vendor.

C The overall size of the sampling system should be kept as compact as possible. 

The sampling systems are usually installed into existing sampling site shelters

where many other parameters (i.e., criteria pollutants concentrations,

meteorological conditions, etc.) are also measured. Each of the other parameters

requires separate instrumentation and consequently the shelters can become very

crowded.

C The sample collection system should meet all applicable electrical and safety

codes, operate on standard 110 Vac power, and incorporate a main power fuse or

circuit breaker. Specific potential electrical hazards and/or other safety

considerations should be detailed in a supplied user’s manual.

C The overall configuration, and components comprising that configuration, should

allow for simple operation, maintenance, and service of the sample collection

system. Materials used in the construction of components of the sample

collection system should exhibit nonbiasing characteristics. The components

themselves should generally conform to the descriptions presented in

Section 5.2.1. All surfaces that come in direct contact with sampled air should

be constructed of glass, stainless steel, or Viton .

®
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C To avoid cross-contamination, the sample collection system must have

provisions to isolate the inlet and outlet of each sample cartridge when that

cartridge is not collecting sample.

C The sampling system must incorporate or provide for removal of O , consistent 3

with the O scrubber designs detailed in Section 5.1. 3

C Ideally, the sampling system should be able to accommodate the most intensive

sample collection event frequency presented in Figure 5-6 on an automated

unattended basis, and simultaneously accommodate a duplicate collection for one

of the 3-hour sampling events as recommended for quality control purposes. 

These requirements mean that the sampling system should have the capability to

collect the following during any given 24-hour period:

- Eight 3-hour cartridge samples;

- One 3-hour duplicate cartridge sample, collected concurrently with one of

the eight 3-hour cartridge samples; and

- One 24-hour cartridge sample, collected concurrently with the eight 3-hour

cartridge samples, but not concurrent with a duplicate 3-hour cartridge

sample.

It is imperative that the sample collection system have the collection capabilities

detailed above. If not, a second sampling system would be required to address

the 24-hour sample collection, and consequently more overall labor and space

would be needed to fully address the network monitoring requirements. 

The ability of the sampling system to perform sample collections as presented

above would require the operator to visit the site only twice during the 24-hour

period being characterized; once to install sample cartridges prior to sampling

and once to remove sample cartridges containing the collected samples. Each 

24-hour period is scheduled to begin at 12:00 A.M. (i.e., midnight) and end at

11:59 P.M. of the day being characterized. The sampling system must be able to

automatically address these periods (i.e., must be able to start and stop at the

specified times without requiring an operator to go to the site and manually

actuate the system).

C The sampling system should incorporate a microprocessor event control and data

acquisition device. At a minimum this microprocessor should be able to be

programmed to control the start and stop times of every collection event within a

given 24-hour sampling duration. The microprocessor should also be able to

simultaneously collect and store all the sample collection process data pertaining

to each sampling event as follows:
Isolated Area Network Design

Note: 

U1 and U2 represent the first and second most 

predominant high ozone day morning wind direction. 

U3 represents the high ozone day afternoon wind direction.

(4)

(3)

(1)

(2)

(2)

Central business district

Urbanized fringe

U1

U3

U2

o:s/g/morr/3797/pams/isolated.ppt

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(1), (2), (3), and (4) are different types of PAMS sites (See Table 5-1).

Figure 5-6. Isolated Area Network Design
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- Start and stop times for each sample collection; and

- Beginning and ending collection flow rates for each cartridge collection.

The microprocessor should incorporate a battery backup system to address power

failure situations. Incorporation of a battery backup system should result in

fewer invalidated sample collections and a higher sample collection completion

rate. The battery backup system would ensure that all programmed control

activities and collection process data would be retained for a predetermined

interval should standard power to the system be interrupted. Retaining the

programmed control activities would allow sampling to resume automatically at

the next programmed event time when standard power is once again established

to the sampling system. Retaining the collection process data obtained for

samples collected prior to the termination of standard power would allow these

samples to be qualified as valid or invalid based on sampling start and stop times

and initial and flow rates. Although not absolutely necessary, the incorporation

of a miniature printer that would allow for a report style listing of all sample

collection process data would be advantageous.

C Expedient and responsive vendor support should be a mandatory requirement and

primary consideration when procuring a multiple-event cartridge sampling

system. The user should specify that the vendor will maintain an adequate

supply of replacement parts and a staff of qualified service technicians to ensure

that the absolute minimum number of sample collection events are missed should

a sample collection system failure occur. The user should specify that the vendor

guarantee that parts/components be delivered to the sampling site within two

working days of order placement. The user should also specify that a sample

collection system delivered to the vendor for repair be serviced and returned to

the user within seven working days.

The manufacturer of a carbonyl sampling device and experience at some of the PAMS

sites indicate that the carbonyl sampler should not be located inside a shelter but outside to

alleviate the possibility of off-gassing from the shelter interfering with the samples. The

sampling methodology itself does not specify the location of the sampler. The wisdom of

locating the carbonyl sampler outside rather than inside a shelter would depend upon the

composition of the shelter and the security of the sampler if it is located in an outside area.
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5.3 Process Blanks

To ensure data quality and obtain quantitative carbonyl compound concentrations, the

collection of blanks is necessary. For the purposes of PAMS, there are three types of blanks used

to ensure data quality: certification blanks, field blanks, and trip blanks. The guidance given here

should be considered a minimum and users are encouraged to build upon this guidance as

necessary.

C Certification blanks consist of a minimum of three laboratory blank cartridges

that are eluted with acetonitrile and analyzed to verify the acceptability of a

specific cartridge lot from a commercial vendor. Certification blanks are

analyzed for each specific lot used for sampling. The mean mass plus 3 standard

deviations (0 + 3s) for the group of three laboratory blanks is used to assess

acceptability. 

C Field blanks are blank cartridges which are sent to the field, connected to the

sampling system and treated identically to the samples except that no air is drawn

through the cartridge. Field blanks are used to assess the background carbonyl

levels for cartridges used during the ambient sample collection process.

C Trip blanks are blank cartridges of the same lot that are sent to the field, stored,

and returned to the laboratory with the sample cartridges. Trip blanks are

optional and may be used to resolve contamination problems determined from

the field blanks. Trip blanks can be used to determine whether the contamination

occurred during the sampling process or during the shipping and storage process.

5.3.1 Blank Criteria

The acceptance criteria for blanks are discussed below. The criteria for certification are

considered conservative; most certification blank results will be well below these criteria. If the

mean mass plus 3 standard deviations (0 ± 3s) for the group of three laboratory blanks meets the

criteria, then no further certification or laboratory blanks are required for a particular lot. If large

differences are observed for the 3 laboratory blank samples, additional laboratory blanks should

be analyzed to obtain values for the mean and standard deviation. For the certification blanks to

be acceptable, the following criteria should be met:
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C Formaldehyde: <0.15 g/cartridge*

C Acetaldehyde: <0.10 g/cartridge

C Acetone: <0.30 g/cartridge

C Other aldehydes or ketones, concentration (per individual component):

<0.10 μg/cartridge.

* The equivalent formaldehyde concentration in ppbv as taken from Table 3 in EPA Compendium Method TO-11A

(see Appendix D) is 0.679 ppbv for a 180 L sample volume. 

Using good techniques and collection systems (not mixing lots or vendors), field blanks

should consistently be at levels that are less than 2 times the average measured laboratory blank

value for a specific lot. The laboratory blank is a cartridge blank used for lot certification that

has never been shipped to the field. If field blanks do not meet these criteria, corrective action is

required. Sites that are unable to achieve these levels for field blanks must determine the source

of contamination. An assessment of the air in the sampling shelter may also provide useful

information in the determination of sources for field blank and sample contamination.

As a minimum, a sampling system blank sample should be collected at least on an

annual basis before initiation of sampling. Collection of a pre- and post-sampling blank is

strongly recommended to aid in the qualification of data. If the sampler is subjected to only a

single blank audit, a failure to meet QA/QC limits will leave open the question of whether the

previous year’s data should be flagged or not. It is possible for a sampler to become

contaminated (or appear to become contaminated) during the down season, in which case there

would be no reason to invalidate the data from the previous year. Pre- and post-season audits

remove the ambiguity. Collect a sampler blank using carbonyl-free air when possible. Generate

carbonyl free air by purging air through acidic DNPH solution in a bubbling device or DNPHcoated cartridge. Alternatively, measure the carbonyl content of the air using a DNPH-coated

cartridge and subtract the carbonyl content in the air from that in the sampler blank. Before

collecting the sampler blank, flush the system using the same procedures as used for collecting a

sample. 
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5.3.2 Frequency of Collection

At least one field blank, or the square root of the field sample size, whichever is larger,

should be collected and analyzed with each sample lot collected at the site. The square root of the

sample size is used to result in more field blanks for a smaller sample size and fewer field blanks

for a larger sample size. For example, if 100 field samples will be taken at the site, then 10 field

blank samples (the square root of 100) are collected and analyzed. If multiple lots are used,

ensure that each lot has the necessary number of associated field blanks. Certification blanks are

not included in the number of field blanks. Certification blanks are analyzed in addition to field

blanks to verify acceptability of a specific cartridge lot from the vendor. At a minimum, three

laboratory blanks from each lot are used for certification. Table 5-2 gives an example collection

schedule for a field samples from a single lot.

Table 5-2. Example Schedule for the Collection of Blanks

Field Sample Size Certification the sample size)

Lab Blanks for Lot Field Blanks (square root of

50 3 7

100 3 10

200 3 16

Since field blank samples may not be collected on every sampling day, the issue of

maintaining consistency in the overall data treatment using blank subtraction is a challenge. For

PAMS blank subtraction must be performed using the average field blank mass obtained for each

field sample lot. Using the information in Table 5-2 as an example, for a sample size of 100, the 

average mass for the 10 field blank samples is subtracted from each of the 100 samples. Again,

it is important that cartridge lot be tracked and the appropriate number of field blanks be

collected and subtracted from the samples for each lot used.
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5.4 Breakthrough Analysis

Method TO-11A requires the use of a back-up cartridge during the first sampling event. 

If less than 10% of the analyte is collected on the back-up cartridge, then back-up cartridges are

only required for 10% of the field samples. If more than 10% of the analyte is collected on the

back-up cartridge, then use back-up cartridges for all sampling events. Breakthrough is more

likely to occur when sampling at high flow rates, when sampling very dry or very humid air,

when sampling air containing high levels of oxides, and when sampling air containing high levels

of carbonyl compounds. Perform breakthrough analyses on the 24-hour sample or on the

duplicate 3-hour sample. Be careful in determining the flow rate because two cartridges installed

in series create a higher pressure drop, decreasing the sampling rate. If breakthrough occurs,

minimize the breakthrough by replacing the ozone scrubber more frequently, sampling at a lower

flow rate, using larger capacity cartridges, or heating the cartridges slightly to prevent moisture

condensation when sampling very humid air. 

5.5 Collection of Collocated Samples

A collocated sample is collected from one manifold by two independent sampling

devices in the same sampling period. Collect collocated samples as indicated in Table 5-2. 

Analyze the collocated samples in replicate. The replicate analyses should agree to within ±10%

and the means of the replicate analyses for the collocated samples should agree to within ±20%. 

If the collocated samples do not agree to within ±20% and the replicate analyses are within

±10%, check the samples to ensure that they are truly collocated and check the sample flow rates

to ensure that the sampler is working correctly. Also verify that the sampler is not leaking by

performing a leak check as described in Section 10.2 of TO-11A (see Appendix D).

5.6 Quality Assurance and Quality Control

General quality assurance and quality control requirements are provided in Section 13.6

of Method TO-11A (see Appendix D). Each laboratory should develop SOPs for the sampling
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and analysis of carbonyls and should develop criteria for sampling and analysis that are specific

to the laboratory. Table 5-3 provides the quality assurance and quality control procedures

consistent with Method TO-11A. 

5.7 General Cartridge Handling Guidelines

Unintentional exposure of the DNPH cartridges and eluted samples to aldehyde and

ketone sources can result in contamination of the samples, creating a positive bias in the

collected data. Various aldehydes and ketones are ubiquitous in the environment. For example,

biological processes can produce formaldehyde, acetone, and acetaldehyde on peoples’ skin and

in peoples’ breath. Wear polyethylene gloves at all times when handling the DNPH cartridges

during sampling collection and analysis. In addition, laboratory air often holds high

concentrations of acetone (and sometimes formaldehyde). Measure background levels of

carbonyls in the laboratory air using a DNPH cartridge and sample pump. If high background

levels are present, handle the cartridges in a nitrogen-purged glove box or under a purge of

carbonyl free air. Labeling inks, adhesives, and packing containers are all additional sources of

contamination. Avoid packing cartridges in old newspapers, writing directly on the cartridges

with ink, or placing adhesive labels directly on the cartridges. Additionally, DNPH is light

sensitive. Always protect the cartridges from direct sunlight.
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Table 5-3. Quality Assurance and Quality Control Criteria

Parameter Frequency Limits Corrective Action

Flow calibration Each sampling event, ±10% Mark sample as

pre- and post-checks suspect

Mass flow meter Every quarter 1.0 ± 0.1 Repair mass flow

calibration factor meter

Leak check Each sampling event, No air flow Check for leaks

pre- and post-checks

Sampler blank Pre- and post-seasons > MDL Clean sampler,

qualify data if

required

Collocated samples 10% of field samples ±20% Mark sample as

suspect

Back-up cartridges 10% of field samples 10% of total on back-up Use back-up

cartridge cartridges for all

samples

Trip blanks 10% of field samples <0.15 μg Blank correct data

formaldehyde/cartridge

Field blanks 10% of field samples <0.15 μg Blank correct data

formaldehyde/cartridge

Spiked cartridges 10% of field samples 80 to 120% recovery Flag data

Multi-point Every 6 months 0.999 Recalibrate

calibration

Continuing Every analytical run ±10% Recalibrate

calibration standard

Method detection Annually or after <0.1 ppbv for 180 L Modify instrument

limits each instrument sample volume as needed

change

Replicate injections 10% of samples ±10% Reanalyze samples

Performance Before and after ±15% Reanalyze samples

evaluation sample samples
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1. U.S. Environmental Protection Agency. Code of Federal Regulations. Title 40, Part 58. 

Ambient Air Quality Surveillance, Final Rule Federal Register, Vol. 58, No. 28,

February 12, 1993.

2. Compendium of Methods for the Determination of Toxic Organic Compounds in

Ambient Air. Compendium Method TO-11A. Determination of Formaldehyde in

Ambient Air Using Adsorbent Cartridge Followed by High Performance Liquid

Chromatography (HPLC). EPA-625/R-96/010b. Cincinnati, OH: U.S. Environmental

Protection Agency, 1997.

3. Grassick, D. and R. Jongleux. Enhanced Ozone Monitoring Network—Design and Siting

Criteria Guideline Document. Contract No. 68-D0-0125. Research Triangle Park, NC:

U.S. Environmental Protection Agency, 1991.

5.8 References
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Section 6.0

Guidance for PAMS Meteorological Monitoring

6.1 Background

Title 40 Part 58 of the Code of Federal Regulations required the States to establish a 1

network of Photochemical Assessment Monitoring Stations (PAMS) in ozone nonattainment

areas which were classified as serious, severe, or extreme. The regulation states that each 

PAMS program must include provisions for enhanced monitoring of ozone, the precursors to

ozone, and both surface and upper-air meteorological conditions. Although the PAMS rule

establishes a requirement for meteorological monitoring, it does not provide specifics; e.g., a list

of the meteorological variables to be monitored. Discussions to develop such a list took place in

the Spring of 1994. Recommendations based on these discussions were issued in April 19942

and incorporated in an early draft of this document. The list of variables has since been revised

to reflect input from the review of this and subsequent drafts. Currently, the list of 

meteorological variables includes: wind direction, wind speed, temperature, humidity,

atmospheric pressure, precipitation, solar radiation, UV radiation, and mixing height. Table 6-1

provides an overview of the requirements for monitoring these variables.

The remainder of this section is organized as follows: Section 6.2 describes the PAMS

site types as established by the PAMS rule. Section 6.3 provides material on the application of

PAMS meteorological data. Sections 6.4 and 6.5 provide details related to measurement of

surface and upper-air meteorological variables, respectively. Section 6.6 provides a list of

references.

Users are referred to the “Quality Assurance Handbook for Air Pollution Measurement

Systems, Volume IV: Meteorological Measurements” for recommended procedures for quality 3

assurance and audit activities. The procedures provided in “On-Site Meteorological Program
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Table 6-1. Overview of PAMS Meteorological Monitoring Requirements

QUESTION ANSWER

 Where to monitor? All serious, severe, and extreme ozone nonattainment areas

 How many sites? 2 to 5 surface sites per network plus one upper-air site

 When to monitor? Routine continuous monitoring during the PAMS monitoring

season (3 months per year minimum)

 How long? Until the area is redesignated as attainment for ozone

 What variables? Wind Directiona

Wind Speeda

Air Temperaturea

Humiditya

Solar Radiationb

Ultraviolet Radiationb

Barometric Pressureb

Precipitationb,c

 What interval? Surface measurements should be continuous and should be

reported hourly.

Upper-air measurements (profiles of wind and temperature) should

be made at least 4 times per day.

 What levels? Surface measurements should be made at 2 meters (temperature

and humidity) or 10 meters (wind direction and wind speed). 

Other surface measurements are nominally made at about 2

meters.

 A required measurement for all PAMS sites. a

 A required measurement for at least one site per PAMS area. b

 Precipitation data from other sources (National Weather Service or others) are acceptable on a case-by-case basis. c

Guidance for Regulatory Modeling Applications” should be followed for processing of 4

meteorological measurements.
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6.2 PAMS Site Types

The PAMS requirements were designed to provide as much information as practicable on

the roles of ozone precursors, pollutant transport, and local meteorology in the photochemical

process. Specific provisions of the Rule require the establishment and operation of four

monitoring sites in each PAMS area; each of the sites has specific data quality objectives

(DQOs). The four sites are as follows:

Site #1 - Upwind and background characterization site. These sites are

established to characterize upwind background and transported ozone and

its precursor concentrations entering the area and will identify those areas

which are subjected to overwhelming incoming transport of ozone. The

#1 Sites are located in the predominant morning wind direction from the

local area of maximum precursor emissions and at a distance sufficient to

obtain urban scale measurements. Typically, these sites will be located

near the upwind edge of the photochemical grid model domain.

Site #2 - Maximum ozone precursor emissions impact site. These sites are

established to monitor the magnitude and type of precursor emissions in

the area where maximum precursor emissions representative of the

Metropolitan Statistical Area (MSA)/Consolidated Metropolitan Statistical

Area (CMSA) are expected to impact and are suited for the monitoring of

urban air toxic pollutants. The #2 Sites are located immediately

downwind (using the same morning wind direction as for locating Site #1)

of the area of maximum precursor emissions and are typically placed near

the downwind boundary of the central business district (CBD) or primary

area of precursor emissions mix to obtain neighborhood scale

measurements. Additionally, a second #2 Site may be required

depending on the size of the area, and it should be placed in the secondmost predominant morning wind direction.

Site #3 - Maximum ozone concentration site. These sites are intended to monitor

maximum ozone concentrations occurring downwind from the area of

maximum precursor emissions. Locations for #3 Sites should be chosen

so that urban scale measurements are obtained. Typically, these sites are

located 10 to 30 miles from the fringe of the urban area.

Site #4 - Extreme downwind monitoring site. These sites are established to

characterize the extreme downwind transported ozone and its precursor

concentrations exiting the area and will identify those areas which are
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potentially contributing to overwhelming ozone transport into other areas. 

The #4 Sites are located in the predominant afternoon downwind direction

from the local area of maximum precursor emissions at a distance

sufficient to obtain urban scale measurements. Typically, these sites will

be located near the downwind edge of the photochemical grid model

domain.

6.3 Applications of PAMS Meteorological Data

Meteorology is a critical element in the formation, transport, and ultimate disposition of

both ozone and its precursors. Consequently, meteorological data are essential to the

development and evaluation of ozone control strategies. Other types of evaluations which

depend on meteorological data include photochemical modeling, receptor modeling, emissions

tracking, and trends analysis. Other application areas associated with the PAMS meteorological

measurements are indicated in Table 6-2. Examples of applications can be found in the Draft

Guidelines for Quality Assurance and Management of PAMS Upper-Air Meteorological Data.5

Table 6-2. Application of the PAMS Meteorological Data

Variable Modeling Analysis Modeling

Photochemical Diagnostic Receptor

Wind Direction T T T

a

Wind Speed T T T

a

Air Temperature T T

a

Humidity T T

a

Pressure T T

b

Precipitation T T

b

Solar Radiation T T

b

UV Radiation T T

b

 To be measured at multiple sites in each PAMS area. a

 To be measured at one representative site in each PAMS area. b
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6.4 Surface Meteorological Monitoring

A minimum level of surface meteorological monitoring is required for each PAMS site

regardless of the site type (see Section 6.2). The minimum level includes measurements of wind

direction, wind speed, ambient temperature, and humidity (e.g., dew point or relative humidity). 

In addition, measurements of solar radiation, ultraviolet radiation, barometric pressure, and

precipitation are required for at least one site in each PAMS network. 

6.4.1 Siting and Exposure

The selection of an appropriate site for the surface meteorological measurements depends

on the intended use of the data; i.e., the Data Quality Objectives (DQOs). Ideally, for general

application, the site should be located in a level open area away from the influence of

obstructions such as buildings or trees. The area surrounding the site should have uniform

surface characteristics. Although it may be desirable to collocate the surface meteorological 6,7,8

measurements with the ambient air quality measurements, collocation of the two functions may

not be possible at all PAMS sites without violating one or more of the above criteria. Siting and

exposure requirements specific to each of the PAMS surface meteorological variables are

discussed in subsequent sections.

Surface meteorological measurements in urban areas, where compliance with siting and

exposure criteria may be precluded by the close proximity of buildings and other structures,

present special difficulties. In such cases, the individual involved in the site selection needs to

assess the likelihood that the data which may be collected at a given location will conform to the

DQOs. In all cases, the specific site characteristics should be well documented. This

documentation of the specific site characteristics is especially important in areas where surface

characteristics and/or terrain are not uniform and whenever standard exposure and siting criteria

cannot be met.
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6.4.2 Specifications

System specifications for the surface measurements are given in Table 6-3. The

recommended sampling interval of the meteorological sensors by the data acquisition system is

10 seconds. Data for all variables should be processed to obtain one hour averages. The data

acquisition system clock should have an accuracy of ±1 minute per week.

Table 6-3. System Specifications for Surface Meteorological Measurementsa

Variable Range Accuracy Resolution Constants

Time/Distance

Wind Speed 0.5 to 50 m/s ±0.2 m/s + 5% 0.1 m/s 5 m (63% response)

Wind Direction 0 to 360 deg. ±5 deg. 1 deg. 5 m (50% recovery)

Air Temperature -20 to 40 EC ±0.5 EC 0.1 EC 60 s (63% response)

Dew Point -30 to +30EC ±1.5EC 0.1EC 30 minutes

Relative Humidity 0 to 100 %RH ±3 %RH 0.5 %RH 60 s (63% response)

Solar Radiation 0 to 1200 W m ±5% 10 W m 60 s (99% response) -2 -2

UV Radiation 0 to 12 W m ±5% 0.01 W m 60 s (99% response) -2 -2

Barometric Pressure 800 to 1100 hPa ±3 hPa 0.5 hPa 60 s (63% response)

Precipitation 0 to 30 mm/hr ±10% 0.25 mm 60 s (63% response)

Quality assurance guidance for auditing these values is provided in Quality Assurance Handbook for Air Pollution a

Measurement Systems. Volume IV - Meteorological Measurements. EPA/600/R-94/038d. U.S. Environmental

Protection Agency, 1995.

6.4.3 Wind Speed and Wind Direction

Wind speed and direction are essential to the evaluation of transport and dispersion

processes of all atmospheric pollutants. Wind speed is typically measured with a cup or propeller

anemometer; wind direction is typically measured with a wind vane.
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The standard height for surface layer wind measurements is 10 m above ground level.3,7,9

The location of the site for the wind measurements should ensure that the horizontal distance to

obstructions (e.g., buildings, trees, etc.) is at least ten times the height of the obstruction. In 9

urban areas, where the “ten times” criterion may not be met, one should provide a protocol for

invalidating the measurements for the problem directions. Evans and Lee provide a discussion 10

of the validity of 10-meter wind data in an urban setting where the average obstruction height is

of the same order as the wind measurement height.

An open lattice tower is the recommended structure for monitoring of meteorological

variables at the 10-meter level. In the case of wind measurements, certain precautions are

necessary to ensure that the measurements are not significantly affected by turbulence in the

immediate wake of the meteorological tower. To avoid such tower effects, the wind sensor

should be mounted on a mast a distance at least one tower width above the top of the tower, or if

the tower is higher than 10 m, on a boom projecting horizontally from the tower. In the latter

case, the boom should extend a distance at least twice the diameter/diagonal of the tower from

the nearest point on the tower. The boom should project into the direction which provides the

least distortion for the most important wind direction (i.e., into the prevailing wind). 

There are several types of open lattice towers: Fixed, tilt-over, and telescopic. A fixed

tower is usually assembled as a one-piece structure from several smaller sections. This type of

tower must be sturdy enough so that it can be climbed safely to install and service the

instruments. Tilt-over towers are also one-piece structures, but are hinged at ground level. This

type of tower has the advantage of allowing the instruments to be serviced at the ground. 

Telescopic 10 m towers are usually composed of three sections, each approximately 4 m in

length. The top section is the smallest in diameter and fits inside the middle section which, in

turn, fits inside the base section. The tower can be extended to a height of 10 m by use of a hand

crank located at the lowest section. The top of the tower can be lowered to a height of about 4 m

providing easy access to the wind sensors. Telescopic and tilt-over towers are not generally

recommended for heights above 10 m. Regardless of which type of tower is used, the structure

should be sufficiently rigid and properly guyed to ensure that the instruments maintain a fixed
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orientation at all times. Instrumentation for monitoring wind speed and direction should never be

mounted on or near solid structures such as buildings, stacks, water storage tanks, cooling

towers, etc., because all such structures create significant distortions in the flow field.

A sensor with a high accuracy at low wind speeds and a low starting threshold is

recommended for PAMS applications. Light weight materials (e.g., molded plastic or

polystyrene foam) should be employed for cups and propeller blades to achieve a starting

threshold (lowest speed at which a rotating anemometer starts and continues to turn and produce

a measurable signal when mounted in its normal position) of # 0.5 m s . Wind vanes or tail fins -1

should also be constructed from light weight materials. The starting threshold (lowest speed at

which a vane will turn to within 5 of the true wind direction from an initial displacement of 10 )

o o

should be # 0.5 m s . Overshoot must be # 25% and the damping ratio should lie between 0.4 -1

and 0.7. The above information is summarized in Table 6-3.

6.4.4 Temperature

Temperature affects photochemical reaction rates and consequently, is an essential

variable for PAMS applications. Sensors used for monitoring ambient temperature include: wire

bobbins, thermocouples, and thermistors. Platinum resistance temperature detectors (RTD) are

among the more popular sensors used in ambient monitoring; these sensors provide accurate

measurements and maintain a stable calibration over a wide temperature range.

The standard height for surface layer ambient temperature measurements is 2 meters

above ground level. If a tower is used, the temperature sensor should be mounted on a boom 7

which extends at least one tower width/diameter from the tower. The measurement should be

made over a uniform plot of open, level ground at least 9 m in diameter. The surface should be

covered with non-irrigated or un-watered short grass or, in areas which lack a vegetation cover,

natural earth. Concrete, asphalt, and oil-soaked surfaces and other similar surfaces should be

avoided to the extent possible. The sensor should be at least 30 m from any paved area. Other

areas to avoid include large industrial heat sources, roof tops, steep slopes, hollows, high
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vegetation, swamps, snow drifts, standing water, and air exhausts. The distance to obstructions

for accurate temperature measurements should be at least four times the obstruction height. In

urban areas, one should be especially conscious of and avoid extraneous energy sources

(e.g., tunnels and subway entrances, roof tops, etc.).

Temperature measurements should be accurate to ±0.5EC over a range of -20 to +40EC

with a resolution of 0.1EC. The time constant (63.2%) should be # 60 seconds. Solar heating is

usually the greatest source of error and, consequently, adequate shielding is needed to provide a

representative ambient air temperature measurement. Ideally, the radiation shield should block

the sensor from view of the sun, sky, ground, and surrounding objects. The shield should reflect

all incident radiation and not reradiate any of that energy towards the sensor. The best type of

shield is one which provides forced aspiration at a rate of at least 3 m s over a radiation range of -1

-100 to +1100 W m . Errors in temperature should not exceed ±0.25EC when a sensor is placed -2

inside a forced aspiration radiation shield. The sensor must also be protected from precipitation

and condensation, otherwise evaporative effects and other forms of radiational heating or cooling

will lead to a depressed temperature measurement (i.e., wet bulb temperature). Temperatures may

also be reported to AIRS AQS in EF, but metric is the preferred and recommended system of

units for meteorological measurements.

6.4.5 Atmospheric Humidity

Measurements of atmospheric humidity are essential to understanding chemical reactions

involving ozone precursors and water vapor. Measures of atmospheric humidity include vapor

pressure, dew point temperature, specific humidity, absolute humidity, and relative humidity. 

There are several ways to measure the water vapor content of the atmosphere. The classical

measurement methods can be classified in terms of six scientific principles; examples are

provided in Table 6-4.

The standard height for humidity measurements is 2 m above ground level. The humidity

sensor should be installed using the same siting criteria as used for temperature. If possible, the
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Table 6-4. Principles of Humidity Measurementa

Principle Instrument/Method

Reduction of temperature by evaporation psychrometer

Dimensional changes due to absorption of hygrometers with sensors of hair, wood,

moisture, based on hygroscopic properties of natural and synthetic fibers

materials

Chemical or electrical changes due to absorption electric hygrometers such as the Dunmore

or adsorption Cell; lithium, carbon, and aluminum

oxide stirps; capacitance film

Formation of dew or frost by artificial cooling cooled mirror surfaces

Diffusion of moisture through porous membranes diffusion hygrometers

Adsorption spectra of water vapor infrared and UV absorption; Lyman-alpha

radiation hygrometers

Middleton, W.E.K. and A.F. Spillhaus, Meteorological Instruments, University of Toronto Press (1953). a

 humidity sensor should be housed in the same aspirated radiation shield as the temperature

sensor. The humidity sensor should be protected from contaminants such as salt, hydrocarbons,

and other particulates. The best protection is the use of a porous membrane filter which allows

the passage of ambient air and water vapor while keeping out particulate matter.

6.4.6 Solar Radiation

Solar radiation refers to the electromagnetic energy in the solar spectrum (0.10 to 4.0 μm

wavelength). The latter is commonly classified as ultraviolet (0.10 to 0.40 μm), visible light

(0.40 to 0.73 μm), and near-infrared (0.73 to 4.0 μm) radiation. About 97% of the solar radiation

reaching the earth's outer atmosphere lies between 0.29 and 3.0 μm. A portion of this energy 7

penetrates through the atmosphere and is either absorbed or reflected at the earth's surface. The

rest of the solar radiation is scattered and/or absorbed in the atmosphere before reaching the

surface. Solar radiation measurements are used in heat flux calculations, for estimating

atmospheric stability, and in modeling photochemical reactions.
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Energy fluxes in the spectrum of solar radiation are measured using a pyranometer. 

These instruments are configured to measure what is referred to as global solar radiation;

i.e., direct plus diffuse (scattered) solar radiation. The sensing element of the typical

pyranometer is protected by a clear glass dome to prevent entry of energy (wavelengths) outside

the solar spectrum (i.e., long-wave radiation). The glass domes used on typical pyranometers are

transparent to wavelengths in the range of 0.28 to 2.8 μm.

Solar radiation measurements should be taken in a location with an unrestricted view of

the sky in all directions. In general, locations should be avoided where there are obstructions that

could cast a shadow or reflect light on the sensor; light colored walls or artificial sources of

radiation should also be avoided. The horizon as viewed from the pyranometer should not

exceed 5 degrees. Sensor height is not critical for pyranometers; consequently, tall platforms or

roof tops are typical locations. Regardless of where the pyranometer is sited, it is important to

ensure that the level of instrument is maintained, and that the glass dome is cleaned as 11

necessary. To facilitate leveling, the pyranometers should be equipped with an attached circular

spirit level.

Manufacturer's specifications should match the requirements of the World Meteorological

Organization for either a secondary standard or first class pyranometer (see Table 6-5) especially 7

if the measurements are to be used for estimating heat flux. Photovoltaic pyranometers (which

usually fall under second class pyranometers) may be used for PAMS applications on a case-bycase basis. The cost of photovoltaic sensors is significantly less than that of thermocouple-type

sensors; however, their spectral response is limited to the visible spectrum.

6.4.7 Ultraviolet Radiation

Ultraviolet (UV) radiation may be divided into three sub-ranges: UV-A (0.315

to 0.400 μm), UV-B (0.280 - 0.315 μm), and UV-C (0.100 - 0.280 μm). Due to absorption by

stratospheric ozone, the UV radiation reaching the surface of the earth consists primarily of

wavelengths longer than 0.28 μm (UV-A and UV-B ranges). The most important
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Table 6-5. Classification of Pyranometers 7 a

Characteristic Units Standard Class Class

Secondary First Second 

Resolution W m ±1 ±5 ±10 -2

Stability %FS year ±1 ±2 ±5 -1

Cosine Response % < ±3 < ±7 < ±15

Azimuth Response % < ±3 < ±5 < ±10

Temperature Response % ±1 ±2 ±5

Nonlinearity %FS ±0.5 ±2 ±5

Spectral Sensitivity % ±2 ±5 ±10

Response Time (99%) seconds < 25 < 60 < 240

Quality Assurance guidance for auditing these parameters is provided in Quality Assurance Handbook for a

Air Pollution Measurement Systems. Volume IV - Meteorological Measurements. EPA/600/R-94/038d. 

U.S. Environmental Protection Agency, 1995.

photochemically active chemical species at these wavelengths are ozone, nitrogen dioxide, and

formaldehyde. All three of these chemical species are important in the formation of ozone. 

Pyranometers with a spectral response covering both the UV-A and UV-B (0.280 to 0.400 m)

ranges are recommended for PAMS applications. The same siting criteria used for “all wave”

global solar radiation measurements apply.

6.4.8 Barometric Pressure

Barometric pressure (station pressure) is used in the calculation of fundamental

thermodynamic quantities (e.g., air density). The type of sensor used to measure pressure is

called a pressure transducer. There are numerous commercially available pressure transducers

which meet the specifications in Table 6-3. Ideally, the pressure sensor should be located in a

ventilated shelter about 2 m above ground level. The height of the station above mean sea level
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and the height of the pressure sensor above ground level should be documented. If needed, the

pressure can then be adjusted to a standard height.

If the pressure sensor is placed indoors, accommodations should be made to vent the

pressure port to the outside environment. One end of a tube should be attached to the sensor's

pressure port and the other end vented to the outside of the trailer or shelter so that pressurization

due to the air conditioning or heating system is avoided. The wind can often cause dynamical

changes of pressure in a room where a sensor is placed. These fluctuations may be on the order

of 2 to 3 hPa when strong or gusty winds prevail.

6.4.9 Precipitation

Precipitation should be measured with a recording rain gauge such as a tipping bucket or

weighing bucket. The rain gauge should be located on level ground in an open area. 

Obstructions should not be closer than two to four times their height from the instrument. The

area around the rain gauge should be covered with natural vegetation. The mouth of the rain

gauge should be level and should be as low as possible while still precluding in-splashing from

the ground (30 cm above ground level is the recommended minimum height). A wind

shield/wind screen (such as an Alter-type wind shield, consisting of a ring with approximately 3

32 free-swinging separate metal leaves) should be employed to minimize the effects of high wind

speeds.

6.5 Upper-Air Meteorological Monitoring

The design of the upper-air monitoring program will depend upon region specific factors

such that the optimal design for a given PAMS region is expected to be some combination of

remote sensing and conventional atmospheric soundings - in special cases, the upper-air

monitoring plan may be augmented with data from aircraft and/or tall towers. Data from existing

sources, e.g., the National Weather Service (NWS) upper-air network, should be considered and

integrated with the PAMS monitoring plan.
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Remote sensing systems (e.g., doppler SODAR) provide continuous measurements of

wind speed and wind direction as a function of height. These data are needed to provide wind

data with the necessary temporal and vertical resolution to evaluate changes in transport flow

fields coincident with the evolution of the convective boundary layer. Such evaluations will aid

in the diagnosis of conditions associated with extreme ozone concentrations. Remote sensing

platforms for use in obtaining these data are discussed in Section 6.3.5.

Conventional atmospheric soundings obtained using rawinsondes or their equivalent are

needed to provide atmospheric profiles with the necessary vertical resolution for estimating the

mixing height (see Section 6.3.6) and for use in initializing the photochemical grid models used

for evaluating ozone control strategies. Such soundings should extend to the top of the CBL or

1000 meters, whichever is greater, and should include measurements of wind speed, wind

direction, temperature, and humidity. Four soundings per day are needed to adequately

characterize the development of the atmospheric boundary layer. These soundings should be

acquired just prior to sunrise when the atmospheric boundary layer is usually the most stable; in

mid-morning when the growth of the boundary layer is most rapid; during mid-afternoon when

surface temperatures are maximum; and in late-afternoon when the boundary layer depth is

largest. Soundings obtained from a NWS upper-air station may be used to fulfill part of this

requirement depending on the time of the sounding and the location of the NWS site. 

Rawinsondes for use in obtaining these data are discussed in Section 3.4.

The information presented in Sections 6.3.2 (Aircraft), 6.3.3 (Tall Towers), 6.3.4

(Balloon Systems), and 6.3.5 (Ground-Based Remote Sensors) provides background for use in

designing an upper air monitoring plan for PAMS. The capabilities of the various platforms for

upper-air meteorological monitoring (towers, balloon systems, and remote sensors) are compared

in Table 6-6.
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Table 6-6. Capabilities and Limitations of Meteorological Measurement Systems

for Vertical Profiling of the Lower Atmosphere

Typical Maximum Height/Range (meters agl)a

Measurement System

Variable Mini- RADAR Radio- TetherTower SODAR SODAR RADAR with sonde sonde

RASS

Wind Speed 100 600 300 2-3 km 2-3 km >10 km 1000 b

Wind Direction 100 600 300 2-3 km 2-3 km >10 km 1000 b

Wind Sigmas 100 600 300 2-3 km 2-3 km c b

d d

Relative Humidity 100 >10 km 1000 b

d d d d

Temperature 100 1.2 km >10 km 1000 b

d d d

Typical Minimum Height (meters agl)a

Measurement System

Variable Mini- RADAR Radio- TetherTower SODAR SODAR RADAR with sonde sonde 

RASS

Wind Speed 10 50 10 100 100 10 10

Wind Direction 10 50 10 100 100 10 10

Wind Sigmas 10 50 10 100 100 c

d d

Relative Humidity 2 10 10

d d d d

Temperature 2 100 10 10

d d d

Typical Resolution (meters)

Measurement System

Variable Mini- RADAR Radio- TetherTower SODAR SODAR RADAR with sonde sonde 

RASS

Wind Speed 2-10 25 10 60-100 60-100 5-10 10

Wind Direction 2-10 25 10 60-100 60-100 5-10 10

Wind Sigmas 2-10 25 10 60-100 60-100 c

d d

Relative Humidity 2-10 5-10 10

d d d d

Temperature 2-10 60-100 5-10 10

d d d

 Meters above ground level a

 Typically meteorological towers do not exceed 100 m. However, radio and TV towers may exceed 600 m. b

 The standard deviation of horizontal and vertical wind components. c

 No capability for this variable d
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6.5.1 Siting and Exposure

The upper-air measurements are intended for more macro-scale application than are the 3

surface meteorological measurements. Consequently, the location of the upper-air site need not

be associated with any particular PAMS surface site. Factors that should be considered in

selecting a site for the upper-air monitoring include whether the upper-air measurements for the

proposed location are likely to provide the necessary data to characterize the meteorological

conditions associated with high ozone concentrations, and the extent to which data for the

proposed location may augment an existing upper-air network. Near lake shores and in coastal

areas, where land/sea/lake breeze circulations may play a significant role in ozone formation and

transport, additional upper-air monitoring sites may be needed; this consideration would also

apply to areas located in complex terrain. All of the above are necessary components of the

DQOs for an upper-air monitoring plan.

6.5.2 Aircraft

Aircraft (both airplanes and helicopters) are a prime example of a mobile observation

station. They are capable of traversing large horizontal and vertical distances in a relatively short

period of time. An aircraft platform equipped with meteorological instrumentation can provide

detailed atmospheric observations over large areas. Traditionally, aircraft are used for episodic

field studies which often require extensive data sets for model evaluation. Lenschow provides 12

an excellent overview of aircraft measurements in boundary layer applications. While an aircraft

can provide detailed atmospheric observations over large areas, the total sampling time per flight

(typically 6 to 8 hours) is relatively short because of fuel considerations. Aircraft may also be

subject to Federal Aviation Administration (FAA) restrictions on flight paths over urban areas. 

In addition, the operating cost for this type of platform is extremely expensive.
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6.5.3 Tall Towers

In some instances it may be possible to use existing towers which may be located in

PAMS areas to acquire vertical profiles of atmospheric boundary layer data. Radio and

television transmission towers, which may be as tall as 600 m, can be equipped with in situ

meteorological sensors at many levels. An advantage to using a tower is the ability to run an

unattended data acquisition system. Also, data can normally be collected under all weather

conditions. However, the main disadvantage of using a tower is the inability to determine the

mixed layer height during most of the day. When moderate to strong convective conditions exist,

the mixed layer height easily exceeds that of the tallest towers. Another disadvantage is the

potentially high cost of maintenance, especially during instances when the instrumentation needs

to be accessed for adjustments or repairs.

6.5.4 Balloon Systems

Balloon based systems include rawinsonde (sometimes called radiosonde) and

tethersonde systems. The rawinsonde consists of a helium filled balloon, an instrument package,

a radio transmitter, and a tracking device. The instrument package includes sensors for

measuring atmospheric temperature, relative humidity, and barometric pressure. Data from

ground-based radar, which is used to track the balloon, are processed to determine wind speed

and direction. The height of the instrument package is determined by the ascent rate of the

balloon. Typical specifications for the sensors used in rawinsondes are given in Table 6-7.

Table 6-7. Manufacturers’ Specifications for Sensors Used in Rawinsondes

Sensor Range Accuracy Resolution

Pressure 1080 to 3 mb ±0.5 mb 0.1 mb

Temperature -90 to +60 EC ±0.2 EC 0.1 EC

Relative Humidity 5 to 100% RH
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Unlike surface measurements, there is no equivalent to system accuracy for upper-air

meteorological measurements from rawinsondes. Consequently, to assess the quality of

rawinsonde measurements, the NWS uses a special statistical parameter called the “functional

precision,” defined as the root-mean-square (rms) difference between measurements made by 

identical instruments at as nearly as possible the same time and same point in the atmosphere.13

The functional precision of NWS radiosonde measurements is given in Table 6-8.

Table 6-8. Functional Precision of Rawinsonde Measurements13

Variable Functional Precision

Wind Speed ±3.1 m/s a

Wind Direction ±18 deg [ # 3.1 m/s] a

±14 deg [ 5.1 m/s]

± 9 deg [10.3 m/s]

± 6 deg [15.4 m/s]

± 5 deg [20.6 m/s]

Temperature ±0.6EC

b

Dew Point Depression ±3.3EC

b

Height ±24 m b

 at the same height a

 at the same pressure b

A tethersonde system is comprised of a tethered balloon with one or more instrument

packages attached to the tether. The instrument package includes a radio transmitter and sensors

to measure atmospheric temperature, relative humidity, barometric pressure, wind speed, and

wind direction. Data are telemetered to the ground by radio or by conductors incorporated within

the tethering cable. Tethersondes are capable of providing data up to about 1000 m in good

conditions. Use of a tethersonde is limited by wind speed; they can only be used reliably in light

to moderate wind conditions (5 m/s at the surface to 15 m/s aloft). Tethered balloons are also

considered a hazard to aviation and thus are subject to FAA regulations. A permit is required to

operate such a system.
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6.5.5 Ground-Based Remote Sensors

Ground-based remote sensors have become effective tools for acquiring upper-air

information and have played an increasingly important role in atmospheric boundary layer

studies. There are two basic types of remote sensing systems used to acquire three-component

wind velocity profiles: Radar (radio detection and ranging) and sodar (sound detection and

ranging). Radars (also called wind profilers) transmit an electromagnetic signal (~ 915 MHZ)

into the atmosphere in a predetermined beam width which is controlled by the configuration of

the transmitting antenna. Sodars (also called acoustic sounders) transmit an acoustic signal

(~ 2 to 5 KHz) into the atmosphere in a predetermined beam width which is also controlled by

the transmitting antenna. The radar has a range of approximately 150 to 3000 m with a

resolution of 60 to 100 m. The sodar has a range of about 50 to 1500 m with a resolution of

about 25 to 50 m.

Both systems transmit their respective signals in pulses. Each pulse is both reflected and

absorbed by the atmosphere as it propagates upwards. The vertical range of each pulse is

determined by how high it can go before the signal becomes so weak that the energy reflected

back to the antenna can no longer be detected. As long as the reflected pulses can be discerned

from background noise, meaningful wind velocities can be obtained by comparing the doppler

shift of the return signal to that of the output signal. A positive or negative doppler shift

indicates whether the radial wind velocity is moving towards or away from the transmitting

antenna. The attenuation of a transmitted pulse is a function of signal type, signal power, signal

frequency, and atmospheric conditions. Radar signal reflection depends primarily on the

presence of an index of refraction gradient in the atmosphere which varies with temperature and

humidity. Sodar signal reflection depends primarily on the presence of small scale atmospheric

turbulence. The reflected signals received by either a radar or sodar are processed in a system

computer by signal conditioning algorithms.

In order to obtain a profile of the three-component wind velocity (U, V, W), one vertical

beam and two tilted beams are needed. The two tilted beams are usually between 15 and 30 o o
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from the vertical. These two beams are also at right angles to each other in azimuth. For

example, one tilted beam may be oriented towards the north while the second tilted beam points

east. Each antenna transmits a pulse and then listens for the reflected signal in succession. After

all three antennas perform this function, enough information is available to convert the radial

velocities into horizontal and vertical wind velocities by using simple trigonometric

relationships.

There are two types of antenna configurations for radars and sodars: Monostatic and

phased array. Monostatic systems consist of three individual transmit/receive antennas. Phased

array consist of a single antenna array which can electronically steer the beam in the required

directions. Vertical panels (also known as clutter fences) are usually placed around the antennas. 

This placement effectively acts to block out any stray side-lobe echoes from contaminating the

return signal of a radar. For sodars, these panels cut down on the side-lobe noise which may be a

nuisance to nearby residents and also prevents any background noise which may contaminate the

return signal.

A RASS (radio acoustic sounding system) utilizes a combination of electromagnetic and

acoustic pulses to derive a virtual air temperature profile. A RASS usually consists of several

acoustic antennas placed around a radar system. The antennas transmit a sweep of acoustic

frequencies vertically into the atmosphere. As the sound pulses rise, the speed of the acoustic

wave varies according to the virtual air temperature. Concurrently, a radar beam is emitted

vertically into the atmosphere. The radar beam will most strongly reflect off the sound wave

fronts created by the acoustic pulses. The virtual air temperature is computed from the speed of

sound which is measured by the reflected radar energy. The typical range of a RASS is

approximately 150 to 1500 m with a resolution of 60 to 100 m.

Unlike in situ sensors which measure by direct contact, remote sensors do not disturb the

atmosphere. Another fundamental difference is that remote sensors measure a volume of air

rather than a fixed point in space. The thickness of the volume is a function of the pulse length

and frequency used. The width of the volume is a function of beam spread and altitude. Siting
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of these profilers is sometimes a difficult task. Artificial and natural objects located near the

sensors can potentially interfere with the transmission and return signals, thereby contaminating

the wind velocity data.

Since sodars utilize sound transmission and reception to determine the overlying wind

field, a clear return signal with a sharply defined atmospheric peak frequency is required. Thus,

consideration of background noise may put limitations on where a sodar can be located. External

noise sources can be classified as active or passive, and as broad-band (random frequency) or

narrow-band (fixed frequency). General background noise is considered active and is broadband. If loud enough, it can cause the sodar software to reject data because it can not find a peak

or because the signal-to-noise ratio is too low. The net effect is to lower the effective sampling

rate due to the loss of many transmission pulses. A qualitative survey should be conducted to

identify any potential noise sources. A quantitative noise survey may be necessary to determine

if noise levels are within the instrument's minimum requirements.

Examples of active, broad-band noise sources include highways, industrial facilities,

power plants, and heavy machinery. Some of these noise sources have a pronounced diurnal,

weekly, or even seasonal pattern. A noise survey should at least cover diurnal and weekly

patterns. Examination of land-use patterns and other sources of information may be necessary to

determine if any seasonal activities may present problems.

Examples of active, fixed-frequency noise sources include rotating fans, a back-up beeper

on a piece of heavy equipment, birds, and insects. If these noise sources have a frequency

component in the sodar operating range, they may be misinterpreted as good data by the sodar. 

Some of these sources can be identified during the site selection process. One approach to

reducing the problem of fixed frequency noise sources is to use a coded pulse, i.e., the transmit

pulse has more than one peak frequency. A return pulse would not be identified as data unless

peak frequencies were found in the return signal the same distance apart as the transmit

frequencies.
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Passive noise sources are objects either on or above the ground (e.g., tall towers, power

transmission lines, buildings, trees) that can reflect a transmitted pulse back to the sodar antenna. 

While most of the acoustic energy is focused in a narrow beam, side-lobes do exist and are a

particular concern when antenna enclosures have degraded substantially. Side-lobes reflecting

off stationary objects and returning at the same frequency as the transmit pulse may be

interpreted by the sodar as a valid atmospheric return with a speed of zero. It is not possible to

predict precisely which objects may be a problem. Anything in the same general direction in

which the antenna is pointing and higher than 5 to 10 m may be a potential reflector. It is

therefore important to construct an “obstacle vista diagram” prior to sodar installation that

identifies the direction and height of potential reflectors in relation to the sodar. This diagram

can be used after some data have been collected to assess whether or not reflections are of

concern at some sodar height ranges. Note that reflections from an object at distance X from an

antenna will show up at height Xcos("), where " is the tilt angle of the antenna from the vertical.

The radar, sodar, and RASS antennas should be aligned and tilted carefully as small

errors in orientation or tilt angle can produce unwanted biases in the data. True North should

also be established for antenna alignment. Installation of the antennas should not be permanent

since problems are very likely to arise in siting the profilers in relation to the tower and other

objects that may be in the area. One final consideration is the effect of the instrument on its

surroundings. The sound pulse from a sodar and RASS is quite audible and could become a

nuisance to residents who might happen to live near the installation site. This audible pulse

should be a consideration in the siting process because of the potential irritation to nearby

residents.

6.5.6 Estimation of Mixing Height

In addition to the directly measured meteorological variables, estimates are also required

of the depth of the mixed layer (i.e., mixing height). The mixing height is a derived variable

indicating the depth through which vertical mixing of pollutants occurs. Reliable estimates of

the mixing height are essential to dispersion modeling in support of PAMS.
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1. U.S. Environmental Protection Agency. Code of Federal Regulations. Title 40, Part 58,

Ambient Air Quality Surveillance, Final Rule Federal Register, Vol. 58, No. 28,

February 12, 1993.

2. Recommendations for Meteorological Monitoring Requirements in Support of PAMS,

Internal Memorandum, Desmond Bailey, Emissions Monitoring and Analysis Division,

Research Triangle Park, NC: U.S. Environmental Protection Agency, April 1994.

3. Quality Assurance Handbook for Air Pollution Measurement Systems. Volume IV -

Meteorological Measurement, EPA-600/R-94/038d. U. S. Environmental Protection

Agency, 1994.

4. On-site Meteorological Program Guidance for Regulatory Modeling Applications, EPA450/4-87-013. Research Triangle Park, NC: U. S. Environmental Protection Agency,

1987b.

5. Draft Guidelines for Quality Assurance and Management of PAMS Upper-Air

Meteorological Data. Sonoma Technology, Inc., under EPA Contract No. 68-D3-0020. 

December, 1995.

6. On-Site Meteorological Instrumentation Requirements to Characterize Diffusion from

Point Sources, EPA-600/9-81-020. Research Triangle Park, NC: U.S. Environmental

Protection Agency, 1981.

7. Guide to Meteorological Instruments and Methods of Observation (Fifth Edition), WMO

No. 8 Geneva, Switzerland: World Meteorological Organization, 1983.

The EPA recommended method for estimating mixing height requires measurements of

the vertical temperature profile. In this method, the afternoon mixing height is calculated as 14,15

the height above the ground of the intersection of the dry adiabatic extension of the maximum

surface temperature with the 12 z morning temperature profile. This concept of a mixing layer in

which the lapse rate is roughly dry adiabatic is well founded on general theoretical principles and

on operational use in regulatory dispersion modeling over the last two decades. Comparisons of

mixing height estimates based on the Holzworth method with several other techniques indicate

that all methods perform similarly in estimating the maximum afternoon mixing depth. The 16,17

Holzworth method is normally preferred because of its simplicity.

6.6 References
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8. Instructor’s Handbook on Meteorological Instrumentation, NCAR/TN-237+IA. Boulder,

Colorado: National Center for Atmospheric Research, 1985.

9. Standard Practice for Characterizing Surface Wind Using a Wind Vane and Rotating

Cup Anemometer, ASTM Designation: D 5741-96, Annual Book of ASTM Standards,

Section 11, 1996.

10. Evans, R.A., and B.E. Lee. The Problems of Anemometer Exposure in Urban Areas - A

Wind-Tunnel Study. Meteorological Magazine, 110, 188-199 (1981).

11. Katsaros, K. B., and DeVault, J. E. On Irradiance Measurement Errors at Sea Due to Tilt

of Pyranometers. J. Atmos. Oceanic Technol. 3, 740-745 (1986).

12. Lenschow, D. H. Aircraft Measurements in the Boundary Layer. Probing the

Atmospheric Boundary Layer, American Meteorological Society, Boston, pp. 39-55

(1986).

13. Hoehne, W. E. Precision of National Weather Service Upper Air Measurements, NOAA

Technical Memorandum NWS T&ED-16, U.S. Department of Commerce, Sterling, VA. 

(1980).

14. Holzworth, G. C. Estimates of Mean Maximum Mixing Depths in the Contiguous United

States. Monthly Weather Review, 92, 235-242 (1964).

15. Holzworth, G. C. Mixing Heights, Wind Speeds, and Potential for Urban Air Pollution

Throughout the Contiguous United States, Publication No. AP-101. Research Triangle

Park, NC: U. S. Environmental Protection Agency, 1972.

16. Hanna, S. R. The Thickness of the Planetary Boundary Layer. Atmos. Environ. 3, 519-

536 (1969).

17. Irwin, J. S., and J. O. Paumier. Characterizing the Dispersive State of Convective

Boundary Layers for Applied Dispersion Modeling. Boundary-Layer Meteorology, 53,

267-296 (1990).
APPENDIX A

Method TO-15

Determination of Volatile Organic Compounds (VOCs) in Air Collected-Prepared

Canisters and Analyzed by Gas Chromatography/Mass Spectrometry (GC/MS)
EPA/625/R-96/010b

Compendium of Methods

for the Determination of 

Toxic Organic Compounds

in Ambient Air

Second Edition

Compendium Method TO-15

Determination Of Volatile Organic

Compounds (VOCs) In Air Collected In

Specially-Prepared Canisters And

Analyzed By Gas Chromatography/

Mass Spectrometry (GC/MS)

Center for Environmental Research Information

Office of Research and Development

U.S. Environmental Protection Agency

Cincinnati, OH 45268

January 1997
ii

Method TO-15

Acknowledgements

This Method was prepared for publication in the Compendium of Methods for the Determination of Toxic

Organic Compounds in Ambient Air, Second Edition (EPA/625/R-96/010b), which was prepared under

Contract No. 68-C3-0315, WA No. 3-10, by Midwest Research Institute (MRI), as a subcontractor to

Eastern Research Group, Inc. (ERG), and under the sponsorship of the U.S. Environmental Protection

Agency (EPA). Justice A. Manning and John O. Burckle, Center for Environmental Research

Information (CERI), and Frank F. McElroy, National Exposure Research Laboratory (NERL), both in the

EPA Office of Research and Development, were the project officers responsible for overseeing the

preparation of this method. Additional support was provided by other members of the Compendia

Workgroup, which include:

• John O. Burckle, EPA, ORD, Cincinnati, OH

• James L. Cheney, Corps of Engineers, Omaha, NB

• Michael Davis, U.S. EPA, Region 7, KC, KS

• Joseph B. Elkins Jr., U.S. EPA, OAQPS, RTP, NC

• Robert G. Lewis, U.S. EPA, NERL, RTP, NC

• Justice A. Manning, U.S. EPA, ORD, Cincinnati, OH

• William A. McClenny, U.S. EPA, NERL, RTP, NC

• Frank F. McElroy, U.S. EPA, NERL, RTP, NC

• Heidi Schultz, ERG, Lexington, MA

• William T. "Jerry" Winberry, Jr., MRI, Cary, NC

This Method is the result of the efforts of many individuals. Gratitude goes to each person involved in

the preparation and review of this methodology.

Author(s)

• William A. McClenny, U.S. EPA, NERL, RTP, NC

• Michael W. Holdren, Battelle, Columbus, OH

Peer Reviewers

• Karen Oliver, ManTech, RTP, NC

• Jim Cheney, Corps of Engineers, Omaha, NB

• Elizabeth Almasi, Varian Chromatography Systems, Walnut Creek, CA

• Norm Kirshen, Varian Chromatography Systems, Walnut Creek, CA

• Richard Jesser, Graseby, Smyrna, GA

• Bill Taylor, Graseby, Smyrna, GA

Finally, recognition is given to Frances Beyer, Lynn Kaufman, Debbie Bond, Cathy Whitaker, and Kathy

Johnson of Midwest Research Institute's Administrative Services staff whose dedication and persistence

during the development of this manuscript has enabled it's production.

DISCLAIMER

This Compendium has been subjected to the Agency's peer and administrative review, and it has been

approved for publication as an EPA document. Mention of trade names or commercial products does not

constitute endorsement or recommendation for use.
METHOD TO-15

Determination of Volatile Organic Compounds (VOCs) In Air Collected In

Specially-Prepared Canisters And Analyzed By Gas Chromatography/

Mass Spectrometry (GC/MS)

TABLE OF CONTENTS

Page

1. Scope .................................................................. 15-1

2. Summary of Method 15-2

3. Significance ............................................................. 15-3

4. Applicable Documents ..................................................... 15-4

4.1 ASTM Standards .................................................... 15-4

4.2 EPA Documents ..................................................... 15-4

5. Definitions .............................................................. 15-5

6. Interferences and Contamination ............................................. 15-6

7. Apparatus and Reagents .................................................... 15-6

7.1 Sampling Apparatus .................................................. 15-7

7.2 Analytical Apparatus ................................................. 15-8

7.3 Calibration System and Manifold Apparatus ............................... 15-10

7.4 Reagents ........................................................... 15-10

8. Collection of Samples in Canisters ........................................... 15-11

8.1 Introduction ......................................................... 15-11

8.2 Sampling System Description ........................................... 15-11

8.3 Sampling Procedure .................................................. 15-13

8.4 Cleaning and Certification Program ...................................... 15-14

9. GC/MS Analysis of Volatiles from Canisters ................................... 15-17

9.1 Introduction ......................................................... 15-17

9.2 Preparation of Standards ............................................... 15-18

10. GC/MS Operating Conditions ............................................... 15-21

10.1 Preconcentrator ...................................................... 15-21

10.2 GC/MS System ...................................................... 15-22

10.3 Analytical Sequence .................................................. 15-23

10.4 Instrument Performance Check .......................................... 15-23

10.5 Initial Calibration .................................................... 15-24

10.6 Daily Calibration .................................................... 15-27

10.7 Blank Analyses ...................................................... 15-28

10.8 Sample Analysis ..................................................... 15-29
TABLE OF CONTENTS (continued)

Page

11. Requirements for Demonstrating Method Acceptability for VOC Analysis from 

Canisters ................................................................ 15-31

11.1 Introduction ......................................................... 15-31

11.2 Method Detection Limit ............................................... 15-32

11.3 Replicate Precision ................................................... 15-32

11.4 Audit Accuracy ...................................................... 15-32

12. References .............................................................. 15-33
January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 15-1

METHOD TO-15

Determination of Volatile Organic Compounds (VOCs) In Air Collected In

Specially-Prepared Canisters And Analyzed By Gas Chromatography/

Mass Spectrometry (GC/MS)

1. Scope

1.1 This method documents sampling and analytical procedures for the measurement of subsets of the 97

volatile organic compounds (VOCs) that are included in the 189 hazardous air pollutants (HAPs) listed in

Title III of the Clean Air Act Amendments of 1990. VOCs are defined here as organic compounds having

a vapor pressure greater than 10-1 Torr at 25EC and 760 mm Hg. Table 1 is the list of the target VOCs along

with their CAS number, boiling point, vapor pressure and an indication of their membership in both the list

of VOCs covered by Compendium Method TO-14A (1) and the list of VOCs in EPA's Contract Laboratory

Program (CLP) document entitled: Statement-of-Work (SOW) for the Analysis of Air Toxics from Superfund

Sites (2).

Many of these compounds have been tested for stability in concentration when stored in specially-prepared

canisters (see Section 8) under conditions typical of those encountered in routine ambient air analysis. The

stability of these compounds under all possible conditions is not known. However, a model to predict

compound losses due to physical adsorption of VOCs on canister walls and to dissolution of VOCs in water

condensed in the canisters has been developed (3). Losses due to physical adsorption require only the

establishment of equilibrium between the condensed and gas phases and are generally considered short term

losses, (i.e., losses occurring over minutes to hours). Losses due to chemical reactions of the VOCs with

cocollected ozone or other gas phase species also account for some short term losses. Chemical reactions

between VOCs and substances inside the canister are generally assumed to cause the gradual decrease of

concentration over time (i.e., long term losses over days to weeks). Loss mechanisms such as aqueous

hydrolysis and biological degradation (4) also exist. No models are currently known to be available to

estimate and characterize all these potential losses, although a number of experimental observations are

referenced in Section 8. Some of the VOCs listed in Title III have short atmospheric lifetimes and may not

be present except near sources. 

1.2 This method applies to ambient concentrations of VOCs above 0.5 ppbv and typically requires VOC

enrichment by concentrating up to one liter of a sample volume. The VOC concentration range for ambient

air in many cases includes the concentration at which continuous exposure over a lifetime is estimated to

constitute a 10-6 or higher lifetime risk of developing cancer in humans. Under circumstances in which many

hazardous VOCs are present at 10-6 risk concentrations, the total risk may be significantly greater.

1.3 This method applies under most conditions encountered in sampling of ambient air into canisters.

However, the composition of a gas mixture in a canister, under unique or unusual conditions, will change

so that the sample is known not to be a true representation of the ambient air from which it was taken. For

example, low humidity conditions in the sample may lead to losses of certain VOCs on the canister walls,

losses that would not happen if the humidity were higher. If the canister is pressurized, then condensation

of water from high humidity samples may cause fractional losses of water-soluble compounds. Since the

canister surface area is limited, all gases are in competition for the available active sites. Hence an absolute

storage stability cannot be assigned to a specific gas. Fortunately, under conditions of normal usage for

sampling ambient air, most VOCs can be recovered from canisters near their original concentrations after

storage times of up to thirty days (see Section 8).
Method TO-15 VOCs

Page 15-2 Compendium of Methods for Toxic Organic Air Pollutants January 1997

1.4 Use of the Compendium Method TO-15 for many of the VOCs listed in Table 1 is likely to present two

difficulties: (1) what calibration standard to use for establishing a basis for testing and quantitation, and (2)

how to obtain an audit standard. In certain cases a chemical similarity exists between a thoroughly tested

compound and others on the Title III list. In this case, what works for one is likely to work for the other in

terms of making standards. However, this is not always the case and some compound standards will be

troublesome. The reader is referred to the Section 9.2 on standards for guidance. Calibration of compounds

such as formaldehyde, diazomethane, and many of the others represents a challenge.

1.5 Compendium Method TO-15 should be considered for use when a subset of the 97 Title III VOCs

constitute the target list. Typical situations involve ambient air testing associated with the permitting

procedures for emission sources. In this case sampling and analysis of VOCs is performed to determine the

impact of dispersing source emissions in the surrounding areas. Other important applications are prevalence

and trend monitoring for hazardous VOCs in urban areas and risk assessments downwind of industrialized

or source-impacted areas. 

1.6 Solid adsorbents can be used in lieu of canisters for sampling of VOCs, provided the solid adsorbent

packings, usually multisorbent packings in metal or glass tubes, can meet the performance criteria specified

in Compendium Method TO-17 which specifically addresses the use of multisorbent packings. The two

sample collection techniques are different but become the same upon movement of the sample from the

collection medium (canister or multisorbent tubes) onto the sample concentrator. Sample collection directly

from the atmosphere by automated gas chromatographs can be used in lieu of collection in canisters or on

solid adsorbents. 

2. Summary of Method

2.1 The atmosphere is sampled by introduction of air into a specially-prepared stainless steel canister. Both

subatmospheric pressure and pressurized sampling modes use an initially evacuated canister. A pump

ventilated sampling line is used during sample collection with most commercially available samplers.

Pressurized sampling requires an additional pump to provide positive pressure to the sample canister. A

sample of air is drawn through a sampling train comprised of components that regulate the rate and duration

of sampling into the pre-evacuated and passivated canister.

2.2 After the air sample is collected, the canister valve is closed, an identification tag is attached to the

canister, and the canister is transported to the laboratory for analysis.

2.3 Upon receipt at the laboratory, the canister tag data is recorded and the canister is stored until analysis.

Storage times of up to thirty days have been demonstrated for many of the VOCs (5). 

2.4 To analyze the sample, a known volume of sample is directed from the canister through a solid

multisorbent concentrator. A portion of the water vapor in the sample breaks through the concentrator during

sampling, to a degree depending on the multisorbent composition, duration of sampling, and other factors.

Water content of the sample can be further reduced by dry purging the concentrator with helium while

retaining target compounds. After the concentration and drying steps are completed, the VOCs are thermally

desorbed, entrained in a carrier gas stream, and then focused in a small volume by trapping on a reduced
VOCs Method TO-15

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 15-3

temperature trap or small volume multisorbent trap. The sample is then released by thermal desorption and

carried onto a gas chromatographic column for separation.

As a simple alternative to the multisorbent/dry purge water management technique, the amount of water

vapor in the sample can be reduced below any threshold for affecting the proper operation of the analytical

system by reducing the sample size. For example, a small sample can be concentrated on a cold trap and

released directly to the gas chromatographic column. The reduction in sample volume may require an

enhancement of detector sensitivity.

Other water management approaches are also acceptable as long as their use does not compromise the

attainment of the performance criteria listed in Section 11. A listing of some commercial water management

systems is provided in Appendix A. One of the alternative ways to dry the sample is to separate VOCs from

condensate on a low temperature trap by heating and purging the trap. 

2.5 The analytical strategy for Compendium Method TO-15 involves using a high resolution gas

chromatograph (GC) coupled to a mass spectrometer. If the mass spectrometer is a linear quadrupole system,

it is operated either by continuously scanning a wide range of mass to charge ratios (SCAN mode) or by

monitoring select ion monitoring mode (SIM) of compounds on the target list. If the mass spectrometer is

based on a standard ion trap design, only a scanning mode is used (note however, that the Selected Ion

Storage (SIS) mode for the ion trap has features of the SIM mode). Mass spectra for individual peaks in the

total ion chromatogram are examined with respect to the fragmentation pattern of ions corresponding to

various VOCs including the intensity of primary and secondary ions. The fragmentation pattern is compared

with stored spectra taken under similar conditions, in order to identify the compound. For any given

compound, the intensity of the primary fragment is compared with the system response to the primary

fragment for known amounts of the compound. This establishes the compound concentration that exists in

the sample.

Mass spectrometry is considered a more definitive identification technique than single specific detectors such

as flame ionization detector (FID), electron capture detector (ECD), photoionization detector (PID), or a

multidetector arrangement of these (see discussion in Compendium Method TO-14A). The use of both gas

chromatographic retention time and the generally unique mass fragmentation patterns reduce the chances for

misidentification. If the technique is supported by a comprehensive mass spectral database and a

knowledgeable operator, then the correct identification and quantification of VOCs is further enhanced. 

3. Significance

3.1 Compendium Method TO-15 is significant in that it extends the Compendium Method TO-14A

description for using canister-based sampling and gas chromatographic analysis in the following ways:

• Compendium Method TO-15 incorporates a multisorbent/dry purge technique or equivalent (see

Appendix A) for water management thereby addressing a more extensive set of compounds (the VOCs

mentioned in Title III of the CAAA of 1990) than addressed by Compendium Method TO-14A.

Compendium Method TO-14A approach to water management alters the structure or reduces the

sample stream concentration of some VOCs, especially water-soluble VOCs.
Method TO-15 VOCs

Page 15-4 Compendium of Methods for Toxic Organic Air Pollutants January 1997

• Compendium Method TO-15 uses the GC/MS technique as the only means to identify and quantitate

target compounds. The GC/MS approach provides a more scientifically-defensible detection scheme

which is generally more desirable than the use of single or even multiple specific detectors.

• In addition, Compendium Method TO-15 establishes method performance criteria for acceptance of

data, allowing the use of alternate but equivalent sampling and analytical equipment. There are several

new and viable commercial approaches for water management as noted in Appendix A of this method

on which to base a VOC monitoring technique as well as other approaches to sampling (i.e., autoGCs

and solid adsorbents) that are often used. This method lists performance criteria that these alternatives

must meet to be acceptable alternatives for monitoring ambient VOCs.

• Finally, Compendium Method TO-15 includes enhanced provisions for inherent quality control. The

method uses internal analytical standards and frequent verification of analytical system performance

to assure control of the analytical system. This more formal and better documented approach to quality

control guarantees a higher percentage of good data.

3.2 With these features, Compendium Method TO-15 is a more general yet better defined method for VOCs

than Compendium Method TO-14A. As such, the method can be applied with a higher confidence to reduce

the uncertainty in risk assessments in environments where the hazardous volatile gases listed in the Title III

of the Clean Air Act Amendments of 1990 are being monitored. An emphasis on risk assessments for human

health and effects on the ecology is a current goal for the U.S. EPA.

4. Applicable Documents

4.1 ASTM Standards

• Method D1356 Definitions of Terms Relating to Atmospheric Sampling and Analysis.

• Method E260 Recommended Practice for General Gas Chromatography Procedures.

• Method E355 Practice for Gas Chromatography Terms and Relationships.

• Method D5466 Standard Test Method of Determination of Volatile Organic Compounds in

Atmospheres (Canister Sampling Methodology).

4.2 EPA Documents

• Quality Assurance Handbook for Air Pollution Measurement Systems, Volume II, U. S. Environmental

Protection Agency, EPA-600/R-94-038b, May 1994.

• Technical Assistance Document for Sampling and Analysis of Toxic Organic Compounds in Ambient

Air, U. S. Environmental Protection Agency, EPA-600/4-83-027, June 1983. 

• Compendium of Methods for the Determination of Toxic Organic Compounds in Ambient Air: Method

TO-14, Second Supplement, U. S. Environmental Protection Agency, EPA-600/4-89-018, March 1989.

• Statement-of-Work (SOW) for the Analysis of Air Toxics from Superfund Sites, U. S. Environmental

Protection Agency, Office of Solid Waste, Washington, D.C., Draft Report, June 1990.

• Clean Air Act Amendments of 1990, U. S. Congress, Washington, D.C., November 1990.
VOCs Method TO-15

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 15-5

5. Definitions

[Note: Definitions used in this document and any user-prepared standard operating procedures (SOPs)

should be consistent with ASTM Methods D1356, E260, and E355. Aside from the definitions given below,

all pertinent abbreviations and symbols are defined within this document at point of use.]

5.1 Gauge Pressure—pressure measured with reference to the surrounding atmospheric pressure, usually

expressed in units of kPa or psi. Zero gauge pressure is equal to atmospheric (barometric) pressure.

5.2 Absolute Pressure—pressure measured with reference to absolute zero pressure, usually expressed in

units of kPa, or psi.

5.3 Cryogen—a refrigerant used to obtain sub-ambient temperatures in the VOC concentrator and/or on

front of the analytical column. Typical cryogens are liquid nitrogen (bp -195.8EC), liquid argon (bp -

185.7EC), and liquid CO2 (bp -79.5EC ).

5.4 Dynamic Calibration—calibration of an analytical system using calibration gas standard concentrations

in a form identical or very similar to the samples to be analyzed and by introducing such standards into the

inlet of the sampling or analytical system from a manifold through which the gas standards are flowing.

5.5 Dynamic Dilution—means of preparing calibration mixtures in which standard gas(es) from pressurized

cylinders are continuously blended with humidified zero air in a manifold so that a flowing stream of

calibration mixture is available at the inlet of the analytical system.

5.6 MS-SCAN—mass spectrometric mode of operation in which the gas chromatograph (GC) is coupled

to a mass spectrometer (MS) programmed to SCAN all ions repeatedly over a specified mass range.

5.7 MS-SIM—mass spectrometric mode of operation in which the GC is coupled to a MS that is

programmed to scan a selected number of ions repeatedly [i.e., selected ion monitoring (SIM) mode].

5.8 Qualitative Accuracy—the degree of measurement accuracy required to correctly identify compounds

with an analytical system.

5.9 Quantitative Accuracy—the degree of measurement accuracy required to correctly measure the

concentration of an identified compound with an analytical system with known uncertainty.

5.10 Replicate Precision—precision determined from two canisters filled from the same air mass over the

same time period and determined as the absolute difference between the analyses of canisters divided by their

sum and expressed as a percentage (see Section 11 for performance criteria for replicate precision).

5.11 Duplicate Precision—precision determined from the analysis of two samples taken from the same

canister. The duplicate precision is determined as the absolute difference between the canister analyses

divided by their sum and expressed as a percentage (see Section 11 for performance criteria for duplicate

precision). 
Method TO-15 VOCs

Page 15-6 Compendium of Methods for Toxic Organic Air Pollutants January 1997

5.12 Audit Accuracy—the difference between the analysis of a sample provided in an audit canister and the

nominal value as determined by the audit authority, divided by the audit value and expressed as a percentage

(see Section 11 for performance criteria for audit accuracy).

6. Interferences and Contamination

6.1 Very volatile compounds, such as chloromethane and vinyl chloride can display peak broadening and

co-elution with other species if the compounds are not delivered to the GC column in a small volume of

carrier gas. Refocusing of the sample after collection on the primary trap, either on a separate focusing trap

or at the head of the gas chromatographic column, mitigates this problem.

6.2 Interferences in canister samples may result from improper use or from contamination of: (1) the

canisters due to poor manufacturing practices, (2) the canister cleaning apparatus, and (3) the sampling or

analytical system. Attention to the following details will help to minimize the possibility of contamination

of canisters.

6.2.1 Canisters should be manufactured using high quality welding and cleaning techniques, and new

canisters should be filled with humidified zero air and then analyzed, after “aging” for 24 hours, to determine

cleanliness. The cleaning apparatus, sampling system, and analytical system should be assembled of clean,

high quality components and each system should be shown to be free of contamination.

6.2.2 Canisters should be stored in a contaminant-free location and should be capped tightly during

shipment to prevent leakage and minimize any compromise of the sample.

6.2.3 Impurities in the calibration dilution gas (if applicable) and carrier gas, organic compounds

out-gassing from the system components ahead of the trap, and solvent vapors in the laboratory account for

the majority of contamination problems. The analytical system must be demonstrated to be free from

contamination under the conditions of the analysis by running humidified zero air blanks. The use of

non-chromatographic grade stainless steel tubing, non-PTFE thread sealants, or flow controllers with Buna-N

rubber components must be avoided.

6.2.4 Significant contamination of the analytical equipment can occur whenever samples containing high

VOC concentrations are analyzed. This in turn can result in carryover contamination in subsequent analyses.

Whenever a high concentration (>25 ppbv of a trace species) sample is encountered, it should be followed

by an analysis of humid zero air to check for carry-over contamination. 

6.2.5 In cases when solid sorbents are used to concentrate the sample prior to analysis, the sorbents

should be tested to identify artifact formation (see Compendium Method TO-17 for more information on

artifacts).

7. Apparatus and Reagents

[Note: Compendium Method To-14A list more specific requirements for sampling and analysis apparatus

which may be of help in identifying options. The listings below are generic.]
VOCs Method TO-15

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 15-7

7.1 Sampling Apparatus

[Note: Subatmospheric pressure and pressurized canister sampling systems are commercially available and

have been used as part of U.S. Environmental Protection Agency's Toxic Air Monitoring Stations (TAMS),

Urban Air Toxic Monitoring Program (UATMP), the non-methane organic compound (NMOC) sampling

and analysis program, and the Photochemical Assessment Monitoring Stations (PAMS).]

7.1.1 Subatmospheric Pressure (see Figure 1, without metal bellows type pump).

7.1.1.1 Sampling Inlet Line. Stainless steel tubing to connect the sampler to the sample inlet.

7.1.1.2 Sample Canister. Leak-free stainless steel pressure vessels of desired volume (e.g., 6 L), with

valve and specially prepared interior surfaces (see Appendix B for a listing of known manufacturers/resellers

of canisters).

7.1.1.3 Stainless Steel Vacuum/Pressure Gauges. Two types are required, one capable of measuring

vacuum (–100 to 0 kPa or 0 to - 30 in Hg) and pressure (0–206 kPa or 0–30 psig) in the sampling system and

a second type (for checking the vacuum of canisters during cleaning) capable of measuring at 0.05 mm Hg

(see Appendix B) within 20%. Gauges should be tested clean and leak tight. 

7.1.1.4 Electronic Mass Flow Controller. Capable of maintaining a constant flow rate (± 10%) over

a sampling period of up to 24 hours and under conditions of changing temperature (20–40EC) and humidity.

7.1.1.5 Particulate Matter Filter. 2-Fm sintered stainless steel in-line filter.

7.1.1.6 Electronic Timer. For unattended sample collection.

7.1.1.7 Solenoid Valve. Electrically-operated, bi-stable solenoid valve with Viton® seat and O-rings.

A Skinner Magnelatch valve is used for purposes of illustration in the text (see Figure 2).

7.1.1.8 Chromatographic Grade Stainless Steel Tubing and Fittings. For interconnections. All

such materials in contact with sample, analyte, and support gases prior to analysis should be chromatographic

grade stainless steel or equivalent.

7.1.1.9 Thermostatically Controlled Heater. To maintain above ambient temperature inside insulated

sampler enclosure. 

7.1.1.10 Heater Thermostat. Automatically regulates heater temperature.

7.1.1.11 Fan. For cooling sampling system.

7.1.1.12 Fan Thermostat. Automatically regulates fan operation.

7.1.1.13 Maximum-Minimum Thermometer. Records highest and lowest temperatures during

sampling period.

7.1.1.14 Stainless Steel Shut-off Valve. Leak free, for vacuum/pressure gauge.

7.1.1.15 Auxiliary Vacuum Pump. Continuously draws air through the inlet manifold at 10 L/min.

or higher flow rate. Sample is extracted from the manifold at a lower rate, and excess air is exhausted. 

[Note: The use of higher inlet flow rates dilutes any contamination present in the inlet and reduces the

possibility of sample contamination as a result of contact with active adsorption sites on inlet walls.]

7.1.1.16 Elapsed Time Meter. Measures duration of sampling.

7.1.1.17 Optional Fixed Orifice, Capillary, or Adjustable Micrometering Valve. May be used in

lieu of the electronic flow controller for grab samples or short duration time-integrated samples. Usually

appropriate only in situations where screening samples are taken to assess future sampling activity.

7.1.2 Pressurized (see Figure 1 with metal bellows type pump and Figure 3).

7.1.2.1 Sample Pump. Stainless steel, metal bellows type, capable of 2 atmospheres output pressure.

Pump must be free of leaks, clean, and uncontaminated by oil or organic compounds. 
Method TO-15 VOCs

Page 15-8 Compendium of Methods for Toxic Organic Air Pollutants January 1997

[Note: An alternative sampling system has been developed by Dr. R. Rasmussen, The Oregon Graduate

Institute of Science and Technology, 20000 N.W. Walker Rd., Beaverton, Oregon 97006, 503-690-1077, and

is illustrated in Figure 3. This flow system uses, in order, a pump, a mechanical flow regulator, and a

mechanical compensation flow restrictive device. In this configuration the pump is purged with a large

sample flow, thereby eliminating the need for an auxiliary vacuum pump to flush the sample inlet.] 

7.1.2.2 Other Supporting Materials. All other components of the pressurized sampling system are

similar to components discussed in Sections 7.1.1.1 through 7.1.1.17.

7.2 Analytical Apparatus

7.2.1 Sampling/Concentrator System (many commercial alternatives are available).

7.2.1.1 Electronic Mass Flow Controllers. Used to maintain constant flow (for purge gas, carrier

gas and sample gas) and to provide an analog output to monitor flow anomalies.

7.2.1.2 Vacuum Pump. General purpose laboratory pump, capable of reducing the downstream

pressure of the flow controller to provide the pressure differential necessary to maintain controlled flow rates

of sample air.

7.2.1.3 Stainless Steel Tubing and Stainless Steel Fittings. Coated with fused silica to minimize

active adsorption sites.

7.2.1.4 Stainless Steel Cylinder Pressure Regulators. Standard, two-stage cylinder regulators with

pressure gauges. 

7.2.1.5 Gas Purifiers. Used to remove organic impurities and moisture from gas streams. 

7.2.1.6 Six-port Gas Chromatographic Valve. For routing sample and carrier gas flows.

7.2.1.7 Multisorbent Concentrator. Solid adsorbent packing with various retentive properties for

adsorbing trace gases are commercially available from several sources. The packing contains more than one

type of adsorbent packed in series. 

7.2.1.7.1A pre-packed adsorbent trap (Supelco 2-0321) containing 200 mg Carbopack B (60/80 mesh)

and 50 mg Carbosieve S-III (60/80 mesh) has been found to retain VOCs and allow some water vapor to pass

through (6). The addition of a dry purging step allows for further water removal from the adsorbent trap.

The steps constituting the dry purge technique that are normally used with multisorbent traps are illustrated

in Figure 4. The optimum trapping and dry purging procedure for the Supelco trap consists of a sample

volume of 320 mL and a dry nitrogen purge of 1300 mL. Sample trapping and drying is carried out at 25EC.

The trap is back-flushed with helium and heated to 220EC to transfer material onto the GC column. A trap

bake-out at 260EC for 5 minutes is conducted after each run. 

7.2.1.7.2An example of the effectiveness of dry purging is shown in Figure 5. The multisorbent used

in this case is Tenax/Ambersorb 340/Charcoal (7). Approximately 20% of the initial water content in the

sample remains after sampling 500 mL of air. The detector response to water vapor (hydrogen atoms

detected by atomic emission detection) is plotted versus purge gas volume. Additional water reduction by

a factor of 8 is indicated at temperatures of 45EC or higher. Still further water reduction is possible using

a two-stage concentration/dryer system. 

7.2.1.8 Cryogenic Concentrator. Complete units are commercially available from several vendor

sources. The characteristics of the latest concentrators include a rapid, "ballistic" heating of the concentrator

to release any trapped VOCs into a small carrier gas volume. This facilitates the separation of compounds

on the gas chromatographic column. 

7.2.2 Gas Chromatographic/Mass Spectrometric (GC/MS) System.

7.2.2.1 Gas Chromatograph. The gas chromatographic (GC) system must be capable of temperature

programming. The column oven can be cooled to subambient temperature (e.g., -50EC) at the start of the gas
VOCs Method TO-15

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 15-9

chromatographic run to effect a resolution of the very volatile organic compounds. In other designs, the rate

of release of compounds from the focusing trap in a two stage system obviates the need for retrapping of

compounds on the column. The system must include or be interfaced to a concentrator and have all required

accessories including analytical columns and gases. All GC carrier gas lines must be constructed from

stainless steel or copper tubing. Non-polytetrafluoroethylene (PTFE) thread sealants or flow controllers with

Buna-N rubber components must not be used. 

7.2.2.2 Chromatographic Columns. 100% methyl silicone or 5% phenyl, 95% methyl silicone fused

silica capillary columns of 0.25- to 0.53-mm I.D. of varying lengths are recommended for separation of many

of the possible subsets of target compounds involving nonpolar compounds. However, considering the

diversity of the target list, the choice is left to the operator subject to the performance standards given in

Section 11.

7.2.2.3 Mass Spectrometer. Either a linear quadrupole or ion trap mass spectrometer can be used as

long as it is capable of scanning from 35 to 300 amu every 1 second or less, utilizing 70 volts (nominal)

electron energy in the electron impact ionization mode, and producing a mass spectrum which meets all the

instrument performance acceptance criteria when 50 ng or less of p-bromofluorobenzene (BFB) is analyzed.

7.2.2.3.1Linear Quadrupole Technology. A simplified diagram of the heart of the quadrupole mass

spectrometer is shown in Figure 6. The quadrupole consists of a parallel set of four rod electrodes mounted

in a square configuration. The field within the analyzer is created by coupling opposite pairs of rods together

and applying radiofrequency (RF) and direct current (DC) potentials between the pairs of rods. Ions created

in the ion source from the reaction of column eluates with electrons from the electron source are moved

through the parallel array of rods under the influence of the generated field. Ions which are successfully

transmitted through the quadrupole are said to possess stable trajectories and are subsequently recorded with

the detection system. When the DC potential is zero, a wide band of m/z values is transmitted through the

quadrupole. This "RF only" mode is referred to as the "total-ion" mode. In this mode, the quadrupole acts

as a strong focusing lens analogous to a high pass filter. The amplitude of the RF determines the low mass

cutoff. A mass spectrum is generated by scanning the DC and RF voltages using a fixed DC/RF ratio and

a constant drive frequency or by scanning the frequency and holding the DC and RF constant. With the

quadrupole system only 0.1 to 0.2 percent of the ions formed in the ion source actually reach the detector.

7.2.2.3.2Ion Trap Technology. An ion-trap mass spectrometer consists of a chamber formed between

two metal surfaces in the shape of a hyperboloid of one sheet (ring electrode) and a hyperboloid of two sheets

(the two end-cap electrodes). Ions are created within the chamber by electron impact from an electron beam

admitted through a small aperture in one of the end caps. Radio frequency (RF) (and sometimes direct

current voltage offsets) are applied between the ring electrode and the two end-cap electrodes establishing

a quadrupole electric field. This field is uncoupled in three directions so that ion motion can be considered

independently in each direction; the force acting upon an ion increases with the displacement of the ion from

the center of the field but the direction of the force depends on the instantaneous voltage applied to the ring

electrode. A restoring force along one coordinate (such as the distance, r, from the ion-trap's axis of radial

symmetry) will exist concurrently with a repelling force along another coordinate (such as the distance, z,

along the ion traps axis), and if the field were static the ions would eventually strike an electrode. However,

in an RF field the force along each coordinate alternates direction so that a stable trajectory may be possible

in which the ions do not strike a surface. In practice, ions of appropriate mass-to-charge ratios may be

trapped within the device for periods of milliseconds to hours. A diagram of a typical ion trap is illustrated

in Figure 7. Analysis of stored ions is performed by increasing the RF voltage, which makes the ions

successively unstable. The effect of the RF voltage on the ring electrode is to "squeeze" the ions in the xy

plane so that they move along the z axis. Half the ions are lost to the top cap (held at ground potential); the
Method TO-15 VOCs

Page 15-10 Compendium of Methods for Toxic Organic Air Pollutants January 1997

remaining ions exit the lower end cap to be detected by the electron multiplier. As the energy applied to the

ring electrode is increased, the ions are collected in order of increasing mass to produce a conventional mass

spectrum. With the ion trap, approximately 50 percent of the generated ions are detected. As a result, a

significant increase in sensitivity can be achieved when compared to a full scan linear quadrupole system.

7.2.2.4 GC/MS Interface. Any gas chromatograph to mass spectrometer interface that gives

acceptable calibration points for each of the analytes of interest and can be used to achieve all acceptable

performance criteria may be used. Gas chromatograph to mass spectrometer interfaces constructed of

all-glass, glass-lined, or fused silica-lined materials are recommended. Glass and fused silica should be

deactivated. 

7.2.2.5 Data System. The computer system that is interfaced to the mass spectrometer must allow the

continuous acquisition and storage, on machine readable media, of all mass spectra obtained throughout the

duration of the chromatographic program. The computer must have software that allows searching any

GC/MS data file for ions of a specified mass and plotting such ion abundances versus time or scan number.

This type of plot is defined as a Selected Ion Current Profile (SICP). Software must also be available that

allows integrating the abundance in any SICP between specified time or scan number limits. Also, software

must be available that allows for the comparison of sample spectra with reference library spectra. The

National Institute of Standards and Technology (NIST) or Wiley Libraries or equivalent are recommended

as reference libraries.

7.2.2.6 Off-line Data Storage Device. Device must be capable of rapid recording and retrieval of data

and must be suitable for long-term, off-line data storage.

7.3 Calibration System and Manifold Apparatus (see Figure 8)

7.3.1 Calibration Manifold. Stainless steel, glass, or high purity quartz manifold, (e.g.,1.25-cm I.D.

x 66-cm) with sampling ports and internal baffles for flow disturbance to ensure proper mixing. The

manifold should be heated to -50EC.

7.3.2 Humidifier. 500-mL impinger flask containing HPLC grade deionized water.

7.3.3 Electronic Mass Flow Controllers. One 0 to 5 L/min unit and one or more 0 to 100 mL/min units

for air, depending on number of cylinders in use for calibration.

7.3.4 Teflon Filter(s). 47-mm Teflon® filter for particulate collection.

7.4 Reagents

7.4.1 Neat Materials or Manufacturer-Certified Solutions/Mixtures. Best source (see Section 9).

7.4.2 Helium and Air. Ultra-high purity grade in gas cylinders. He is used as carrier gas in the GC.

7.4.3 Liquid Nitrogen or Liquid Carbon Dioxide. Used to cool secondary trap.

7.4.4 Deionized Water. High performance liquid chromatography (HPLC) grade, ultra-high purity (for

humidifier).

8. Collection of Samples in Canisters

8.1 Introduction

8.1.1 Canister samplers, sampling procedures, and canister cleaning procedures have not changed very

much from the description given in the original Compendium Method TO-14. Much of the material in this
VOCs Method TO-15

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 15-11

F '

P x V

T x 60

kPa gauge

101.2

% 1

section is therefore simply a restatement of the material given in Compendium Method TO-14, repeated here

in order to have all the relevant information in one place.

8.1.2 Recent notable additions to the canister technology has been in the application of canister-based

systems for example, to microenvironmental monitoring (8), the capture of breath samples (9), and sector

sampling to identify emission sources of VOCs (10).

8.1.3 EPA has also sponsored the development of a mathematical model to predict the storage stability

of arbitrary mixtures of trace gases in humidified air (3), and the investigation of the SilcoSteelTM process

of coating the canister interior with a film of fused silica to reduce surface activity (11). A recent summary

of storage stability data for VOCs in canisters is given in the open literature (5). 

8.2 Sampling System Description

8.2.1 Subatmospheric Pressure Sampling [see Figure 1 (without metal bellows type pump)].

8.2.1.1 In preparation for subatmospheric sample collection in a canister, the canister is evacuated to

0.05 mm Hg (see Appendix C for discussion of evacuation pressure). When the canister is opened to the

atmosphere containing the VOCs to be sampled, the differential pressure causes the sample to flow into the

canister. This technique may be used to collect grab samples (duration of 10 to 30 seconds) or timeweighted-average (TWA) samples (duration of 1-24 hours) taken through a flow-restrictive inlet (e.g., mass

flow controller, critical orifice).

8.2.1.2 With a critical orifice flow restrictor, there will be a decrease in the flow rate as the pressure

approaches atmospheric. However, with a mass flow controller, the subatmospheric sampling system can

maintain a constant flow rate from full vacuum to within about 7 kPa (1.0 psi) or less below ambient

pressure.

8.2.2 Pressurized Sampling [see Figure 1 (with metal bellows type pump)].

8.2.2.1 Pressurized sampling is used when longer-term integrated samples or higher volume samples

are required. The sample is collected in a canister using a pump and flow control arrangement to achieve

a typical 101-202 kPa (15-30 psig) final canister pressure. For example, a 6-liter evacuated canister can be

filled at 10 mL/min for 24 hours to achieve a final pressure of 144 kPa (21 psig).

8.2.2.2 In pressurized canister sampling, a metal bellows type pump draws in air from the sampling

manifold to fill and pressurize the sample canister.

8.2.3 All Samplers.

8.2.3.1 A flow control device is chosen to maintain a constant flow into the canister over the desired

sample period. This flow rate is determined so the canister is filled (to about 88.1 kPa for subatmospheric

pressure sampling or to about one atmosphere above ambient pressure for pressurized sampling) over the

desired sample period. The flow rate can be calculated by:

where:

F = flow rate, mL/min.

P = final canister pressure, atmospheres absolute. P is approximately equal to
Method TO-15 VOCs

Page 15-12 Compendium of Methods for Toxic Organic Air Pollutants January 1997

F '

2 x 6000

24 x 60

' 8.3 mL/min

V = volume of the canister, mL.

T = sample period, hours.

For example, if a 6-L canister is to be filled to 202 kPa (2 atmospheres) absolute pressure in 24 hours, the

flow rate can be calculated by:

8.2.3.2 For automatic operation, the timer is designed to start and stop the pump at appropriate times

for the desired sample period. The timer must also control the solenoid valve, to open the valve when

starting the pump and to close the valve when stopping the pump.

8.2.3.3 The use of the Skinner Magnelatch valve (see Figure 2) avoids any substantial temperature rise

that would occur with a conventional, normally closed solenoid valve that would have to be energized during

the entire sample period. The temperature rise in the valve could cause outgassing of organic compounds

from the Viton® valve seat material. The Skinner Magnelatch valve requires only a brief electrical pulse

to open or close at the appropriate start and stop times and therefore experiences no temperature increase.

The pulses may be obtained either with an electronic timer that can be programmed for short (5 to 60

seconds) ON periods, or with a conventional mechanical timer and a special pulse circuit. A simple electrical

pulse circuit for operating the Skinner Magnelatch solenoid valve with a conventional mechanical timer is

illustrated in Figure 2(a). However, with this simple circuit, the valve may operate unreliably during brief

power interruptions or if the timer is manually switched on and off too fast. A better circuit incorporating

a time-delay relay to provide more reliable valve operation is shown in Figure 2(b).

8.2.3.4 The connecting lines between the sample inlet and the canister should be as short as possible

to minimize their volume. The flow rate into the canister should remain relatively constant over the entire

sampling period. 

8.2.3.5 As an option, a second electronic timer may be used to start the auxiliary pump several hours

prior to the sampling period to flush and condition the inlet line.

8.2.3.6 Prior to field use, each sampling system must pass a humid zero air certification (see

Section 8.4.3). All plumbing should be checked carefully for leaks. The canisters must also pass a humid

zero air certification before use (see Section 8.4.1).

8.3 Sampling Procedure

8.3.1 The sample canister should be cleaned and tested according to the procedure in Section 8.4.1.

8.3.2 A sample collection system is assembled as shown in Figures 1 and 3 and must be cleaned

according to the procedure outlined in Sections 8.4.2 and 8.4.4. 

[Note: The sampling system should be contained in an appropriate enclosure.]

8.3.3 Prior to locating the sampling system, the user may want to perform "screening analyses" using

a portable GC system, as outlined in Appendix B of Compendium Method TO-14A, to determine potential

volatile organics present and potential "hot spots." The information gathered from the portable GC screening

analysis would be used in developing a monitoring protocol, which includes the sampling system location,

based upon the "screening analysis" results.
VOCs Method TO-15

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 15-13

8.3.4 After "screening analysis," the sampling system is located. Temperatures of ambient air and

sampler box interior are recorded on the canister sampling field test data sheet (FTDS), as documented in

Figure 9. 

[Note: The following discussion is related to Figure 1]

8.3.5 To verify correct sample flow, a "practice" (evacuated) canister is used in the sampling system.

[Note: For a subatmospheric sampler, a flow meter and practice canister are needed. For the pump-driven

system, the practice canister is not needed, as the flow can be measured at the outlet of the system.]

A certified mass flow meter is attached to the inlet line of the manifold, just in front of the filter. The

canister is opened. The sampler is turned on and the reading of the certified mass flow meter is compared

to the sampler mass flow controller. The values should agree within ±10%. If not, the sampler mass flow

meter needs to be recalibrated or there is a leak in the system. This should be investigated and corrected. 

[Note: Mass flow meter readings may drift. Check the zero reading carefully and add or subtract the zero

reading when reading or adjusting the sampler flow rate to compensate for any zero drift.]

After 2 minutes, the desired canister flow rate is adjusted to the proper value (as indicated by the certified

mass flow meter) by the sampler flow control unit controller (e.g., 3.5 mL/min for 24 hr, 7.0 mL/min for 12

hr). Record final flow under "CANISTER FLOW RATE" on the FTDS. 

8.3.6 The sampler is turned off and the elapsed time meter is reset to 000.0. 

[Note: Whenever the sampler is turned off, wait at least 30 seconds to turn the sampler back on.]

8.3.7 The "practice" canister and certified mass flow meter are disconnected and a clean certified (see

Section 8.4.1) canister is attached to the system.

8.3.8 The canister valve and vacuum/pressure gauge valve are opened.

8.3.9 Pressure/vacuum in the canister is recorded on the canister FTDS (see Figure 9) as indicated by

the sampler vacuum/pressure gauge.

8.3.10 The vacuum/pressure gauge valve is closed and the maximum-minimum thermometer is reset to

current temperature. Time of day and elapsed time meter readings are recorded on the canister FTDS.

8.3.11 The electronic timer is set to start and stop the sampling period at the appropriate times. Sampling

starts and stops by the programmed electronic timer.

8.3.12 After the desired sampling period, the maximum, minimum, current interior temperature and

current ambient temperature are recorded on the FTDS. The current reading from the flow controller is

recorded.

8.3.13 At the end of the sampling period, the vacuum/pressure gauge valve on the sampler is briefly

opened and closed and the pressure/vacuum is recorded on the FTDS. Pressure should be close to desired

pressure. 

[Note: For a subatmospheric sampling system, if the canister is at atmospheric pressure when the field final

pressure check is performed, the sampling period may be suspect. This information should be noted on the

sampling field data sheet.]

Time of day and elapsed time meter readings are also recorded.
Method TO-15 VOCs

Page 15-14 Compendium of Methods for Toxic Organic Air Pollutants January 1997

8.3.14 The canister valve is closed. The sampling line is disconnected from the canister and the canister

is removed from the system. For a subatmospheric system, a certified mass flow meter is once again

connected to the inlet manifold in front of the in-line filter and a "practice" canister is attached to the

Magnelatch valve of the sampling system. The final flow rate is recorded on the canister FTDS (see

Figure 9). 

[Note: For a pressurized system, the final flow may be measured directly.]

The sampler is turned off.

8.3.15 An identification tag is attached to the canister. Canister serial number, sample number, location,

and date, as a minimum, are recorded on the tag. The canister is routinely transported back to the analytical

laboratory with other canisters in a canister shipping case.

8.4 Cleaning and Certification Program

8.4.1 Canister Cleaning and Certification.

8.4.1.1 All canisters must be clean and free of any contaminants before sample collection.

8.4.1.2 All canisters are leak tested by pressurizing them to approximately 206 kPa (30 psig) with zero

air. 

[Note: The canister cleaning system in Figure 10 can be used for this task.]

The initial pressure is measured, the canister valve is closed, and the final pressure is checked after 24 hours.

If acceptable, the pressure should not vary more than ± 13.8 kPa (± 2 psig) over the 24 hour period.

8.4.1.3 A canister cleaning system may be assembled as illustrated in Figure 10. Cryogen is added

to both the vacuum pump and zero air supply traps. The canister(s) are connected to the manifold. The vent

shut-off valve and the canister valve(s) are opened to release any remaining pressure in the canister(s). The

vacuum pump is started and the vent shut-off valve is then closed and the vacuum shut-off valve is opened.

The canister(s) are evacuated to <0.05 mm Hg (see Appendix B) for at least 1 hour. 

[Note: On a daily basis or more often if necessary, the cryogenic traps should be purged with zero air to

remove any trapped water from previous canister cleaning cycles.]

Air released/evacuated from canisters should be diverted to a fume hood.

8.4.1.4 The vacuum and vacuum/pressure gauge shut-off valves are closed and the zero air shut-off

valve is opened to pressurize the canister(s) with humid zero air to approximately 206 kPa (30 psig). If a zero

gas generator system is used, the flow rate may need to be limited to maintain the zero air quality.

8.4.1.5 The zero air shut-off valve is closed and the canister(s) is allowed to vent down to atmospheric

pressure through the vent shut-off valve. The vent shut-off valve is closed. Repeat Sections 8.4.1.3 through

8.4.1.5 two additional times for a total of three (3) evacuation/pressurization cycles for each set of canisters.

8.4.1.6 At the end of the evacuation/pressurization cycle, the canister is pressurized to 206 kPa (30

psig) with humid zero air. The canister is then analyzed by a GC/MS analytical system. Any canister that

has not tested clean (compared to direct analysis of humidified zero air of less than 0.2 ppbv of targeted

VOCs) should not be used. As a "blank" check of the canister(s) and cleanup procedure, the final humid zero

air fill of 100% of the canisters is analyzed until the cleanup system and canisters are proven reliable (less

than 0.2 ppbv of any target VOCs). The check can then be reduced to a lower percentage of canisters.
VOCs Method TO-15

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 15-15

8.4.1.7 The canister is reattached to the cleaning manifold and is then reevacuated to <0.05 mm Hg

(see Appendix B) and remains in this condition until used. The canister valve is closed. The canister is

removed from the cleaning system and the canister connection is capped with a stainless steel fitting. The

canister is now ready for collection of an air sample. An identification tag is attached to the inlet of each

canister for field notes and chain-of-custody purposes. An alternative to evacuating the canister at this point

is to store the canisters and reevacuate them just prior to the next use.

8.4.1.8 As an option to the humid zero air cleaning procedures, the canisters are heated in an

isothermal oven not to exceed 100EC during evacuation of the canister to ensure that higher molecular weight

compounds are not retained on the walls of the canister. 

[Note: For sampling more complex VOC mixtures the canisters should be heated to higher temperatures

during the cleaning procedure although a special high temperature valve would be needed].

Once heated, the canisters are evacuated to <0.05 mm Hg (see Appendix B) and maintained there for 1 hour.

At the end of the heated/evacuated cycle, the canisters are pressurized with humid zero air and analyzed by

a GC/MS system after a minimum of 12 hrs of "aging." Any canister that has not tested clean (less than 0.2

ppbv each of targeted compounds) should not be used. Once tested clean, the canisters are reevacuated to

<0.05 mm Hg (see Appendix B) and remain in the evacuated state until used. As noted in Section 8.4.1.7,

reevacuation can occur just prior to the next use.

8.4.2 Cleaning Sampling System Components.

8.4.2.1 Sample components are disassembled and cleaned before the sampler is assembled.

Nonmetallic parts are rinsed with HPLC grade deionized water and dried in a vacuum oven at 50EC.

Typically, stainless steel parts and fittings are cleaned by placing them in a beaker of methanol in an

ultrasonic bath for 15 minutes. This procedure is repeated with hexane as the solvent.

8.4.2.2 The parts are then rinsed with HPLC grade deionized water and dried in a vacuum oven at

100EC for 12 to 24 hours. 

8.4.2.3 Once the sampler is assembled, the entire system is purged with humid zero air for 24 hours.

8.4.3 Zero Air Certification.

[Note: In the following sections, "certification" is defined as evaluating the sampling system with humid zero

air and humid calibration gases that pass through all active components of the sampling system. The system

is "certified" if no significant additions or deletions (less than 0.2 ppbv each of target compounds) have

occurred when challenged with the test gas stream.]

8.4.3.1 The cleanliness of the sampling system is determined by testing the sampler with humid zero

air without an evacuated gas sampling canister, as follows.

8.4.3.2 The calibration system and manifold are assembled, as illustrated in Figure 8. The sampler

(without an evacuated gas canister) is connected to the manifold and the zero air cylinder is activated to

generate a humid gas stream (2 L/min) to the calibration manifold [see Figure 8(b)].

8.4.3.3 The humid zero gas stream passes through the calibration manifold, through the sampling

system (without an evacuated canister) to the water management system/VOC preconcentrator of an

analytical system.

[Note: The exit of the sampling system (without the canister) replaces the canister in Figure 11.]

After the sample volume (e.g., 500 mL) is preconcentrated on the trap, the trap is heated and the VOCs are

thermally desorbed and refocussed on a cold trap. This trap is heated and the VOCs are thermally desorbed
Method TO-15 VOCs

Page 15-16 Compendium of Methods for Toxic Organic Air Pollutants January 1997

onto the head of the capillary column. The VOCs are refocussed prior to gas chromatographic separation.

Then, the oven temperature (programmed) increases and the VOCs begin to elute and are detected by a

GC/MS (see Section 10) system. The analytical system should not detect greater than 0.2 ppbv of any

targeted VOCs in order for the sampling system to pass the humid zero air certification test. Chromatograms

(using an FID) of a certified sampler and contaminated sampler are illustrated in Figures 12(a) and 12(b),

respectively. If the sampler passes the humid zero air test, it is then tested with humid calibration gas

standards containing selected VOCs at concentration levels expected in field sampling (e.g., 0.5 to 2 ppbv)

as outlined in Section 8.4.4.

8.4.4 Sampler System Certification with Humid Calibration Gas Standards from a Dynamic

Calibration System

8.4.4.1 Assemble the dynamic calibration system and manifold as illustrated in Figure 8.

8.4.4.2 Verify that the calibration system is clean (less than 0.2 ppbv of any target compounds) by

sampling a humidified gas stream, without gas calibration standards, with a previously certified clean canister

(see Section 8.1).

8.4.4.3 The assembled dynamic calibration system is certified clean if less than 0.2 ppbv of any

targeted compounds is found.

8.4.4.4 For generating the humidified calibration standards, the calibration gas cylinder(s) containing

nominal concentrations of 10 ppmv in nitrogen of selected VOCs is attached to the calibration system as

illustrated in Figure 8. The gas cylinders are opened and the gas mixtures are passed through 0 to 10 mL/min

certified mass flow controllers to generate ppb levels of calibration standards.

8.4.4.5 After the appropriate equilibrium period, attach the sampling system (containing a certified

evacuated canister) to the manifold, as illustrated in Figure 8(b).

8.4.4.6 Sample the dynamic calibration gas stream with the sampling system. 

8.4.4.7 Concurrent with the sampling system operation, realtime monitoring of the calibration gas

stream is accomplished by the on-line GC/MS analytical system [Figure 8(a)] to provide reference

concentrations of generated VOCs.

8.4.4.8 At the end of the sampling period (normally the same time period used for experiments), the

sampling system canister is analyzed and compared to the reference GC/MS analytical system to determine

if the concentration of the targeted VOCs was increased or decreased by the sampling system.

8.4.4.9 A recovery of between 90% and 110% is expected for all targeted VOCs.

8.4.5 Sampler System Certification without Compressed Gas Cylinder Standards.

8.4.5.1 Not all the gases on the Title III list are available/compatible with compressed gas standards.

In these cases sampler certification must be approached by different means. 

8.4.5.2 Definitive guidance is not currently available in these cases; however, Section 9.2 lists several

ways to generate gas standards. In general, Compendium Method TO-14A compounds (see Table 1) are

available commercially as compressed gas standards.

9. GC/MS Analysis of Volatiles from Canisters

9.1 Introduction

9.1.1 The analysis of canister samples is accomplished with a GC/MS system. Fused silica capillary

columns are used to achieve high temporal resolution of target compounds. Linear quadrupole or ion trap

mass spectrometers are employed for compound detection. The heart of the system is composed of the

sample inlet concentrating device that is needed to increase sample loading into a detectable range. Two
VOCs Method TO-15

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 15-17

examples of concentrating systems are discussed. Other approaches are acceptable as long as they are

compatible with achieving the system performance criteria given in Section 11. 

9.1.2 With the first technique, a whole air sample from the canister is passed through a multisorbent

packing (including single adsorbent packings) contained within a metal or glass tube maintained at or above

the surrounding air temperature. Depending on the water retention properties of the packing, some or most

of the water vapor passes completely through the trap during sampling. Additional drying of the sample is

accomplished after the sample concentration is completed by forward purging the trap with clean, dry helium

or another inert gas (air is not used). The sample is then thermally desorbed from the packing and

backflushed from the trap onto a gas chromatographic column. In some systems a "refocusing" trap is placed

between the primary trap and the gas chromatographic column. The specific system design downstream of

the primary trap depends on technical factors such as the rate of thermal desorption and sampled volume, but

the objective in most cases is to enhance chromatographic resolution of the individual sample components

before detection on a mass spectrometer.

9.1.3 Sample drying strategies depend on the target list of compounds. For some target compound lists,

the multisorbent packing of the concentrator can be selected from hydrophobic adsorbents which allow a high

percentage of water vapor in the sample to pass through the concentrator during sampling and without

significant loss of the target compounds. However, if very volatile organic compounds are on the target list,

the adsorbents required for their retention may also strongly retain water vapor and a more lengthy dry purge

is necessary prior to analysis.

9.1.4 With the second technique, a whole air sample is passed through a concentrator where the VOCs

are condensed on a reduced temperature surface (cold trap). Subsequently, the condensed gases are thermally

desorbed and backflushed from the trap with an inert gas onto a gas chromatographic column. This

concentration technique is similar to that discussed in Compendium Method TO-14, although a membrane

dryer is not used. The sample size is reduced in volume to limit the amount of water vapor that is also

collected (100 mL or less may be necessary). The attendant reduction in sensitivity is offset by enhancing

the sensitivity of detection, for example by using an ion trap detector.

9.2 Preparation of Standards

9.2.1 Introduction.

9.2.1.1 When available, standard mixtures of target gases in high pressure cylinders must be certified

traceable to a NIST Standard Reference Material (SRM) or to a NIST/EPA approved Certified Reference

Material (CRM). Manufacturer's certificates of analysis must be retained to track the expiration date.

9.2.1.2 The neat standards that are used for making trace gas standards must be of high purity;

generally a purity of 98 percent or better is commercially available. 

9.2.1.3 Cylinder(s) containing approximately 10 ppmv of each of the target compounds are typically

used as primary stock standards. The components may be purchased in one cylinder or in separate cylinders

depending on compatibility of the compounds and the pressure of the mixture in the cylinder. Refer to

manufacturer's specifications for guidance on purchasing and mixing VOCs in gas cylinders. 

9.2.2 Preparing Working Standards.

9.2.2.1 Instrument Performance Check Standard. Prepare a standard solution of BFB in humidified zero air at a concentration which will allow collection of 50 ng of BFB or less under the optimized concentration parameters.

9.2.2.2 Calibration Standards. Prepare five working calibration standards in humidified zero air at

a concentration which will allow collection at the 2, 5, 10, 20, and 50 ppbv level for each component under

the optimized concentration parameters.
Method TO-15 VOCs

Page 15-18 Compendium of Methods for Toxic Organic Air Pollutants January 1997

Manifold Conc. '

(Original Conc.) (Std. Gas Flowrate)

(Air Flowrate) % (Std. Gas Flowrate)

Manifold Conc. '

(10 ppm)(1 mL/min)(1000 ppb/1 ppm)

(1000 mL/min) % (1 mL/min)

' 10 ppb

9.2.2.3 Internal Standard Spiking Mixture. Prepare an internal spiking mixture containing bromochloromethane, chlorobenzene-d5

, and 1,4-difluorobenzene at 10 ppmv each in humidified zero air to be

added to the sample or calibration standard. 500 μL of this mixture spiked into 500 mL of sample will result

in a concentration of 10 ppbv. The internal standard is introduced into the trap during the collection time

for all calibration, blank, and sample analyses using the apparatus shown in Figure 13 or by equivalent

means. The volume of internal standard spiking mixture added for each analysis must be the same from run

to run.

9.2.3 Standard Preparation by Dynamic Dilution Technique.

9.2.3.1 Standards may be prepared by dynamic dilution of the gaseous contents of a cylinder(s)

containing the gas calibration stock standards with humidified zero air using mass flow controllers and a

calibration manifold. The working standard may be delivered from the manifold to a clean, evacuated

canister using a pump and mass flow controller.

9.2.3.2 Alternatively, the analytical system may be calibrated by sampling directly from the manifold

if the flow rates are optimized to provide the desired amount of calibration standards. However, the use of

the canister as a reservoir prior to introduction into the concentration system resembles the procedure

normally used to collect samples and is preferred. Flow rates of the dilution air and cylinder standards (all

expressed in the same units) are measured using a bubble meter or calibrated electronic flow measuring

device, and the concentrations of target compounds in the manifold are then calculated using the dilution

ratio and the original concentration of each compound.

9.2.3.3 Consider the example of 1 mL/min flow of 10 ppmv standard diluted with 1,000 mL/min of

humid air provides a nominal 10 ppbv mixture, as calculated below: 

9.2.4 Standard Preparation by Static Dilution Bottle Technique

[Note: Standards may be prepared in canisters by spiking the canister with a mixture of components

prepared in a static dilution bottle (12). This technique is used specifically for liquid standards.]

9.2.4.1 The volume of a clean 2-liter round-bottom flask, modified with a threaded glass neck to accept

a Mininert septum cap, is determined by weighing the amount of water required to completely fill up the

flask. Assuming a density for the water of 1 g/mL, the weight of the water in grams is taken as the volume

of the flask in milliliters.

9.2.4.2 The flask is flushed with helium by attaching a tubing into the glass neck to deliver the helium.

After a few minutes, the tubing is removed and the glass neck is immediately closed with a Mininert septum

cap.

9.2.4.3 The flask is placed in a 60EC oven and allowed to equilibrate at that temperature for about

15 minutes. Predetermined aliquots of liquid standards are injected into the flask making sure to keep the

flask temperature constant at 60EC.

9.2.4.4 The contents are allowed to equilibrate in the oven for at least 30 minutes. To avoid

condensation, syringes must be preheated in the oven at the same temperature prior to withdrawal of aliquots

to avoid condensation.
VOCs Method TO-15

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 15-19

Concentration, mg/L '

(Va)(d)

Vf

Concentration, ppbv '

Volumestandard

Volumedilution gas

x 109

9.2.4.5 Sample aliquots may then be taken for introduction into the analytical system or for further

dilution. An aliquot or aliquots totaling greater than 1 percent of the flask volume should be avoided.

9.2.4.6 Standards prepared by this method are stable for one week. The septum must be replaced with

each freshly prepared standard.

9.2.4.7 The concentration of each component in the flask is calculated using the following equation:

where: Va = Volume of liquid neat standard injected into the flask, μL.

d = Density of the liquid neat standard, mg/μL.

Vf = Volume of the flask, L.

9.2.4.8 To obtain concentrations in ppbv, the equation given in Section 9.2.5.7 can be used.

[Note: In the preparation of standards by this technique, the analyst should make sure that the volume of

neat standard injected into the flask does not result in an overpressure due to the higher partial pressure

produced by the standard compared to the vapor pressure in the flask. Precautions should also be taken to

avoid a significant decrease in pressure inside the flask after withdrawal of aliquot(s).] 

9.2.5 Standard Preparation Procedure in High Pressure Cylinders

[Note: Standards may be prepared in high pressure cylinders (13). A modified summary of the procedure

is provided below.]

9.2.5.1 The standard compounds are obtained as gases or neat liquids (greater than 98 percent purity).

9.2.5.2 An aluminum cylinder is flushed with high-purity nitrogen gas and then evacuated to better

than 25 in. Hg.

9.2.5.3 Predetermined amounts of each neat standard compound are measured using a microliter or

gastight syringe and injected into the cylinder. The cylinder is equipped with a heated injection port and

nitrogen flow to facilitate sample transfer.

9.2.5.4 The cylinder is pressurized to 1000 psig with zero nitrogen.

[Note: User should read all SOPs associated with generating standards in high pressure cylinders. Follow

all safety requirements to minimize danger from high pressure cylinders.]

9.2.5.5 The contents of the cylinder are allowed to equilibrate (-24 hrs) prior to withdrawal of aliquots

into the GC system.

9.2.5.6 If the neat standard is a gas, the cylinder concentration is determined using the following

equation:

[Note: Both values must be expressed in the same units.]
Method TO-15 VOCs

Page 15-20 Compendium of Methods for Toxic Organic Air Pollutants January 1997

V '

nRT

P

n '

(mL)(d)

MW

9.2.5.7 If the neat standard is a liquid, the gaseous concentration can be determined using the following

equations:

and:

where: V = Volume of injected compound at EPA standard temperature (25EC) and pressure

(760 mm Hg), L.

n = Moles.

R = Gas constant, 0.08206 L-atm/mole EK.

T = 273EK (standard temperature).

P = 1 standard pressure, 760 mm Hg (1 atm).

mL = Volume of liquid injected, mL. 

d = Density of the neat standard, gm/mL.

MW = Molecular weight of the neat standard expressed, gm/gm-mole.

The volume of injected compound is divided by the cylinder volume at STP and then multiplied by 109 to

obtain the component concentration in ppb units. 

9.2.6 Standard Preparation by Water Methods.

[Note: Standards may be prepared by a water purge and trap method (14) and summarized as follows].

9.2.6.1 A previously cleaned and evacuated canister is pressurized to 760 mm Hg absolute (1 atm) with

zero grade air.

9.2.6.2 The air gauge is removed from the canister and the sparging vessel is connected to the canister

with the short length of 1/16 in. stainless steel tubing. 

[Note: Extra effort should be made to minimize possible areas of dead volume to maximize transfer of

analytes from the water to the canister.]

9.2.6.3 A measured amount of the stock standard solution and the internal standard solution is spiked

into 5 mL of water.

9.2.6.4 This water is transferred into the sparge vessel and purged with nitrogen for 10 mins at

100 mL/min. The sparging vessel is maintained at 40EC.

9.2.6.5 At the end of 10 mins, the sparge vessel is removed and the air gauge is re-installed, to further

pressurize the canister with pure nitrogen to 1500 mm Hg absolute pressure (approximately 29 psia).

9.2.6.6 The canister is allowed to equilibrate overnight before use.

9.2.6.7 A schematic of this approach is shown in Figure 14.

9.2.7 Preparation of Standards by Permeation Tubes.

9.2.7.1 Permeation tubes can be used to provide standard concentration of a trace gas or gases. The

permeation of the gas can occur from inside a permeation tube containing the trace species of interest to an
VOCs Method TO-15

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 15-21

air stream outside. Permeation can also occur from outside a permeable membrane tube to an air stream

passing through the tube (e.g., a tube of permeable material immersed in a liquid). 

9.2.7.2 The permeation system is usually held at a constant temperature to generate a constant

concentration of trace gas. Commercial suppliers provide systems for generation and dilution of over

250 compounds. Some commercial suppliers of permeation tube equipment are listed in Appendix D.

9.2.8 Storage of Standards.

9.2.8.1 Working standards prepared in canisters may be stored for thirty days in an atmosphere free

of potential contaminants.

9.2.8.2 It is imperative that a storage logbook be kept to document storage time.

10. GC/MS Operating Conditions

10.1 Preconcentrator

The following are typical cryogenic and adsorbent preconcentrator analytical conditions which, however,

depend on the specific combination of solid sorbent and must be selected carefully by the operator. The

reader is referred to Tables 1 and 2 of Compendium Method TO-17 for guidance on selection of sorbents.

An example of a system using a solid adsorbent preconcentrator with a cryofocusing trap is discussed in the

literature (15). Oven temperature programming starts above ambient.

10.1.1 Sample Collection Conditions

Cryogenic Trap Adsorbent Trap

Set point -150EC Set point 27EC

Sample volume - up to 100 mL Sample volume - up to 1,000 mL

Carrier gas purge flow - none Carrier gas purge flow - selectable

[Note: The analyst should optimize the flow rate, duration of sampling, and absolute sample volume to be

used. Other preconcentration systems may be used provided performance standards (see Section 11) are

realized.]

10.1.2 Desorption Conditions

Cryogenic Trap Adsorbent Trap

Desorb Temperature 120EC Desorb Temperature Variable

Desorb Flow Rate - 3 mL/min He Desorb Flow Rate -3 mL/min He

Desorb Time <60 sec Desorb Time <60 sec

The adsorbent trap conditions depend on the specific solid adsorbents chosen (see manufacturers’

specifications).
Method TO-15 VOCs

Page 15-22 Compendium of Methods for Toxic Organic Air Pollutants January 1997

10.1.3 Trap Reconditioning Conditions.

Cryogenic Trap Adsorbent Trap

Initial bakeout 120EC (24 hrs) Initial bakeout

Variable (24 hrs)

After each run 120EC (5 min) After each run Variable (5 min)

10.2 GC/MS System

10.2.1 Optimize GC conditions for compound separation and sensitivity. Baseline separation of benzene

and carbon tetrachloride on a 100% methyl polysiloxane stationary phase is an indication of acceptable

chromatographic performance.

10.2.2 The following are the recommended gas chromatographic analytical conditions when using a 50-

meter by 0.3-mm I.D., 1 μm film thickness fused silica column with refocusing on the column.

Item Condition

Carrier Gas: Helium

Flow Rate: Generally 1-3 mL/min as recommended by manufacturer

Temperature Program: Initial Temperature: -50EC

Initial Hold Time: 2 min

Ramp Rate: 8E C/min 

Final Temperature: 200EC

Final Hold Time: Until all target compounds elute.

10.2.3 The following are the recommended mass spectrometer conditions:

Item Condition

Electron Energy: 70 Volts (nominal)

Mass Range: 35-300 amu [the choice of 35 amu excludes the detection of some target compounds

such as methanol and formaldehyde, and the quantitation of others such as ethylene

oxide, ethyl carbamate, etc. (see Table 2). Lowering the mass range and using

special programming features available on modern gas chromatographs will be

necessary in these cases, but are not considered here.

Scan Time: To give at least 10 scans per peak, not to exceed 1 second per scan].

A schematic for a typical GC/MS analytical system is illustrated in Figure 15.

10.3 Analytical Sequence

10.3.1 Introduction. The recommended GC/MS analytical sequence for samples during each 24-hour

time period is as follows:

• Perform instrument performance check using bromofluorobenzene (BFB).

• Initiate multi-point calibration or daily calibration checks.
VOCs Method TO-15

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 15-23

• Perform a laboratory method blank.

• Complete this sequence for analysis of #20 field samples.

10.4 Instrument Performance Check

10.4.1 Summary. It is necessary to establish that a given GC/MS meets tuning and standard mass

spectral abundance criteria prior to initiating any data collection. The GC/MS system is set up according to

the manufacturer's specifications, and the mass calibration and resolution of the GC/MS system are then

verified by the analysis of the instrument performance check standard, bromofluorobenzene (BFB).

10.4.2 Frequency. Prior to the analyses of any samples, blanks, or calibration standards, the Laboratory

must establish that the GC/MS system meets the mass spectral ion abundance criteria for the instrument

performance check standard containing BFB. The instrument performance check solution must be analyzed

initially and once per 24-hour time period of operation.

The 24-hour time period for GC/MS instrument performance check and standards calibration (initial

calibration or daily calibration check criteria) begins at the injection of the BFB which the laboratory records

as documentation of a compliance tune.

10.4.3 Procedure. The analysis of the instrument performance check standard is performed by trapping

50 ng of BFB under the optimized preconcentration parameters. The BFB is introduced from a cylinder into

the GC/MS via a sample loop valve injection system similar to that shown in Figure 13.

The mass spectrum of BFB must be acquired in the following manner. Three scans (the peak apex scan and

the scans immediately preceding and following the apex) are acquired and averaged. Background subtraction

is conducted using a single scan prior to the elution of BFB.

10.4.4 Technical Acceptance Criteria. Prior to the analysis of any samples, blanks, or calibration

standards, the analyst must establish that the GC/MS system meets the mass spectral ion abundance criteria

for the instrument performance check standard as specified in Table 3.

10.4.5 Corrective Action. If the BFB acceptance criteria are not met, the MS must be retuned. It may

be necessary to clean the ion source, or quadrupoles, or take other necessary actions to achieve the

acceptance criteria.

10.4.6 Documentation. Results of the BFB tuning are to be recorded and maintained as part of the

instrumentation log.

10.5 Initial Calibration

10.5.1 Summary. Prior to the analysis of samples and blanks but after the instrument performance

check standard criteria have been met, each GC/MS system must be calibrated at five concentrations that

span the monitoring range of interest in an initial calibration sequence to determine instrument sensitivity

and the linearity of GC/MS response for the target compounds. For example, the range of interest may be

2 to 20 ppbv, in which case the five concentrations would be 1, 2, 5, 10 and 25 ppbv.

One of the calibration points from the initial calibration curve must be at the same concentration as the daily

calibration standard (e.g., 10 ppbv).

10.5.2 Frequency. Each GC/MS system must be recalibrated following corrective action (e.g., ion

source cleaning or repair, column replacement, etc.) which may change or affect the initial calibration criteria

or if the daily calibration acceptance criteria have not been met.
Method TO-15 VOCs

Page 15-24 Compendium of Methods for Toxic Organic Air Pollutants January 1997

RRF '

AxCis

AisCx

RRF ' j

n

i'1

xi

n

If time remains in the 24-hour time period after meeting the acceptance criteria for the initial calibration,

samples may be analyzed.

If time does not remain in the 24-hour period after meeting the acceptance criteria for the initial calibration,

a new analytical sequence shall commence with the analysis of the instrument performance check standard

followed by analysis of a daily calibration standard.

10.5.3 Procedure. Verify that the GC/MS system meets the instrument performance criteria in

Section 10.4.

The GC must be operated using temperature and flow rate parameters equivalent to those in Section 10.2.2.

Calibrate the preconcentration-GC/MS system by drawing the standard into the system. Use one of the

standards preparation techniques described under Section 9.2 or equivalent.

A minimum of five concentration levels are needed to determine the instrument sensitivity and linearity. One

of the calibration levels should be near the detection level for the compounds of interest. The calibration

range should be chosen so that linear results are obtained as defined in Sections 10.5.1 and 10.5.5. 

Quantitation ions for the target compounds are shown in Table 2. The primary ion should be used unless

interferences are present, in which case a secondary ion is used. 

10.5.4 Calculations.

[Note: In the following calculations, an internal standard approach is used to calculate response factors.

The area response used is that of the primary quantitation ion unless otherwise stated.]

10.5.4.1 Relative Response Factor (RRF). Calculate the relative response factors for each target

compound relative to the appropriate internal standard (i.e., standard with the nearest retention time) using

the following equation:

where: RRF = Relative response factor.

Ax = Area of the primary ion for the compound to be measured, counts.

Ais = Area of the primary ion for the internal standard, counts. 

Cis = Concentration of internal standard spiking mixture, ppbv.

Cx = Concentration of the compound in the calibration standard, ppbv.

[Note: The equation above is valid under the condition that the volume of internal standard spiking mixture

added in all field and QC analyses is the same from run to run, and that the volume of field and QC sample

introduced into the trap is the same for each analysis. Cis and Cx must be in the same units.]

10.5.4.2 Mean Relative Response Factor. Calculate the mean RRF for each compound by averaging

the values obtained at the five concentrations using the following equation:
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January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 15-25

%RSD '

SDRRF

RRF

x 100

SDRRF ' j

N

i'1

(RRFi& RRF)

2

N & 1

RRT '

RTc

RTis

RRT ' j

n

i'1

RRT

n

where: RRF = Mean relative response factor.

xi = RRF of the compound at concentration i.

n = Number of concentration values, in this case 5.

10.5.4.3 Percent Relative Standard Deviation (%RSD). Using the RRFs from the initial calibration,

calculate the %RSD for all target compounds using the following equations:

and

where: SDRRF = Standard deviation of initial response factors (per compound).

RRFi = Relative response factor at a concentration level i.

RRF = Mean of initial relative response factors (per compound).

10.5.4.4 Relative Retention Times (RRT). Calculate the RRTs for each target compound over the

initial calibration range using the following equation:

where: RTc = Retention time of the target compound, seconds

RTis = Retention time of the internal standard, seconds.

10.5.4.5 Mean of the Relative Retention Times (RRT). Calculate the mean of the relative retention

times (RRT) for each analyte target compound over the initial calibration range using the following

equation:

where: RRT = Mean relative retention time for the target compound for each initial calibration

standard.

RRT = Relative retention time for the target compound at each calibration level.

10.5.4.6 Tabulate Primary Ion Area Response (Y) for Internal Standard. Tabulate the area

response (Y) of the primary ions (see Table 2) and the corresponding concentration for each compound and

internal standard.

10.5.4.7 Mean Area Response (Y) for Internal Standard. Calculate the mean area response (Y)

for each internal standard compound over the initial calibration range using the following equation:
Method TO-15 VOCs

Page 15-26 Compendium of Methods for Toxic Organic Air Pollutants January 1997

Y ' j

n

i'1

Yi

n

RT ' j

n

i'1

RTi

n

where: Y = Mean area response.

Y = Area response for the primary quantitation ion for the internal standard for each initial

calibration standard.

10.5.4.8 Mean Retention Times (RT). Calculate the mean of the retention times (RT) for each

internal standard over the initial calibration range using the following equation:

where: RT = Mean retention time, seconds

RT = Retention time for the internal standard for each initial calibration standard, seconds.

10.5.5 Technical Acceptance Criteria for the Initial Calibration. 

10.5.5.1 The calculated %RSD for the RRF for each compound in the calibration table must be less

than 30% with at most two exceptions up to a limit of 40%.

10.5.5.2 The RRT for each target compound at each calibration level must be withiin 0.06 RRT units

of the mean RRT for the compound.

10.5.5.3 The area response Y of at each calibration level must be within 40% of the mean area

response Y over the initial calibration range for each internal standard.

10.5.5.4 The retention time shift for each of the internal standards at each calibration level must be

within 20 s of the mean retention time over the initial calibration range for each internal standard.

10.5.6 Corrective Action. 

10.5.6.1 Criteria. If the initial calibration technical acceptance criteria are not met, inspect the system

for problems. It may be necessary to clean the ion source, change the column, or take other corrective actions

to meet the initial calibration technical acceptance criteria.

10.5.6.2 Schedule. Initial calibration acceptance criteria must be met before any field samples,

performance evaluation (PE) samples, or blanks are analyzed. 

10.6 Daily Calibration

10.6.1 Summary. Prior to the analysis of samples and blanks but after tuning criteria have been met,

the initial calibration of each GC/MS system must be routinely checked by analyzing a daily calibration

standard to ensure that the instrument continues to remain under control. The daily calibration standard,

which is the nominal 10 ppbv level calibration standard, should contain all the target compounds.

10.6.2 Frequency. A check of the calibration curve must be performed once every 24 hours on a

GC/MS system that has met the tuning criteria. The daily calibration sequence starts with the injection of

the BFB. If the BFB analysis meets the ion abundance criteria for BFB, then a daily calibration standard may

be analyzed.

10.6.3 Procedure. The mid-level calibration standard (10 ppbv) is analyzed in a GC/MS system that

has met the tuning and mass calibration criteria following the same procedure in Section 10.5.

10.6.4 Calculations. Perform the following calculations.
VOCs Method TO-15

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 15-27

%D '

RRFc& RRFi

RRFi

x 100

[Note: As indicated earlier, the area response of the primary quantitation ion is used unless otherwise

stated.]

10.6.4.1 Relative Response Factor (RRF). Calculate a relative response factor (RRF) for each target

compound using the equation in Section 10.5.4.1.

10.6.4.2 Percent Difference (%D). Calculate the percent difference in the RRF of the daily RRF

(24-hour) compared to the mean RRF in the most recent initial calibration. Calculate the %D for each target

compound using the following equation:

where: RRFc = RRF of the compound in the continuing calibration standard.

RRF = Mean RRF of the compound in the most recent initial calibration. i

10.6.5 Technical Acceptance Criteria. The daily calibration standard must be analyzed at the

concentration level and frequency described in this Section 10.6 and on a GC/MS system meeting the BFB

instrument performance check criteria (see Section 10.4).

The %D for each target compound in a daily calibration sequence must be within ±30 percent in order to

proceed with the analysis of samples and blanks. A control chart showing %D values should be maintained.

10.6.6 Corrective Action. If the daily calibration technical acceptance criteria are not met, inspect the

system for problems. It may be necessary to clean the ion source, change the column, or take other corrective

actions to meet the daily calibration technical acceptance criteria.

Daily calibration acceptance criteria must be met before any field samples, performance evaluation (PE)

samples, or blanks are analyzed. If the % D criteria are not met, it will be necessary to rerun the daily

calibration sample.

10.7 Blank Analyses

10.7.1 Summary. To monitor for possible laboratory contamination, laboratory method blanks are

analyzed at least once in a 24-hour analytical sequence. All steps in the analytical procedure are performed

on the blank using all reagents, standards, equipment, apparatus, glassware, and solvents that would be used

for a sample analysis.

A laboratory method blank (LMB) is an unused, certified canister that has not left the laboratory. The blank

canister is pressurized with humidified, ultra-pure zero air and carried through the same analytical procedure

as a field sample. The injected aliquot of the blank must contain the same amount of internal standards that

are added to each sample.

10.7.2 Frequency. The laboratory method blank must be analyzed after the calibration standard(s) and

before any samples are analyzed.

Whenever a high concentration sample is encountered (i.e., outside the calibration range), a blank analysis

should be performed immediately after the sample is completed to check for carryover effects.
Method TO-15 VOCs

Page 15-28 Compendium of Methods for Toxic Organic Air Pollutants January 1997

10.7.3 Procedure. Fill a cleaned and evacuated canister with humidified zero air (RH >20 percent, at

25EC). Pressurize the contents to 2 atm.

The blank sample should be analyzed using the same procedure outlined under Section 10.8.

10.7.4 Calculations. The blanks are analyzed similar to a field sample and the equations in

Section 10.5.4 apply.

10.7.5 Technical Acceptance Criteria. A blank canister should be analyzed daily.

The area response for each internal standard (IS) in the blank must be within ±40 percent of the mean area

response of the IS in the most recent valid calibration.

The retention time for each of the internal standards must be within ±0.33 minutes between the blank and

the most recent valid calibration.

The blank should not contain any target analyte at a concentration greater than its quantitation level (three

times the MDL as defined in Section 11.2) and should not contain additional compounds with elution

characteristics and mass spectral features that would interfere with identification and measurement of a

method analyte.

10.7.6 Corrective Action. If the blanks do not meet the technical acceptance criteria, the analyst should

consider the analytical system to be out of control. It is the responsibility of the analyst to ensure that

contaminants in solvents, reagents, glassware, and other sample storage and processing hardware that lead

to discrete artifacts and/or elevated baselines in gas chromatograms be eliminated. If contamination is a

problem, the source of the contamination must be investigated and appropriate corrective measures need to

be taken and documented before further sample analysis proceeds.

If an analyte in the blank is found to be out of control (i.e., contaminated) and the analyte is also found in

associated samples, those sample results should be "flagged" as possibly contaminated.

10.8 Sample Analysis

10.8.1 Summary. An aliquot of the air sample from a canister (e.g., 500 mL) is preconcentrated and

analyzed by GC/MS under conditions stated in Sections 10.1 and 10.2. If using the multisorbent/dry purge

approach, adjust the dry purge volume to reduce water effects in the analytical system to manageable levels.

[Note: The analyst should be aware that pressurized samples of high humidity samples will contain

condensed water. As a result, the humidity of the sample released from the canister during analysis will vary

in humidity, being lower at the higher canister pressures and increasing in humidity as the canister pressures

decreases. Storage integrity of water soluble compounds may also be affected.]

10.8.2 Frequency. If time remains in the 24-hour period in which an initial calibration is performed,

samples may be analyzed without analysis of a daily calibration standard.

If time does not remain in the 24-hour period since the injection of the instrument performance check

standard in which an initial calibration is performed, both the instrument performance check standard and

the daily calibration standard should be analyzed before sample analysis may begin.

10.8.3 Procedure for Instrumental Analysis. Perform the following procedure for analysis.

10.8.3.1 All canister samples should be at temperature equilibrium with the laboratory.
VOCs Method TO-15

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 15-29

Cx'

AxCisDF

AisRRF

10.8.3.2 Check and adjust the mass flow controllers to provide correct flow rates for the system.

10.8.3.3 Connect the sample canister to the inlet of the GC/MS analytical system, as shown in

Figure 15 [Figure 16 shows an alternate two stage concentrator using multisorbent traps followed by a trap

cooled by a closed cycle cooler (15)]. The desired sample flow is established through the six-port chromatographic valve and the preconcentrator to the downstream flow controller. The absolute volume of sample

being pulled through the trap must be consistent from run to run.

10.8.3.4 Heat/cool the GC oven and cryogenic or adsorbent trap to their set points. Assuming a sixport value is being used, as soon as the trap reaches its lower set point, the six-port chromatographic valve

is cycled to the trap position to begin sample collection. Utilize the sample collection time which has been

optimized by the analyst.

10.8.3.5 Use the arrangement shown in Figure 13, (i.e., a gastight syringe or some alternate method)

introduce an internal standard during the sample collection period. Add sufficient internal standard

equivalent to 10 ppbv in the sample. For example, a 0.5 mL volume of a mixture of internal standard

compounds, each at 10 ppmv concentration, added to a sample volume of 500 mL, will result in 10 ppbv of

each internal standard in the sample.

10.8.3.6 After the sample and internal standards are preconcentrated on the trap, the GC sampling

valve is cycled to the inject position and the trap is swept with helium and heated. Assuming a focusing trap

is being used, the trapped analytes are thermally desorbed onto a focusing trap and then onto the head of the

capillary column and are separated on the column using the GC oven temperature program. The canister

valve is closed and the canister is disconnected from the mass flow controller and capped. The trap is

maintained at elevated temperature until the beginning of the next analysis.

10.8.3.7 Upon sample injection onto the column, the GC/MS system is operated so that the MS scans

the atomic mass range from 35 to 300 amu. At least ten scans per eluting chromatographic peak should be

acquired. Scanning also allows identification of unknown compounds in the sample through searching of

library spectra.

10.8.3.8 Each analytical run must be checked for saturation. The level at which an individual

compound will saturate the detection system is a function of the overall system sensitivity and the mass

spectral characteristics of that compound.

10.8.3.9 Secondary ion quantitation is allowed only when there are sample matrix interferences with

the primary ion. If secondary ion quantitation is performed, document the reasons in the laboratory record

book. 

10.8.4 Calculations. The equation below is used for calculating concentrations.

where: Cx = Compound concentration, ppbv.

Ax = Area of the characteristic ion for the compound to be measured, counts.

Ais = Area of the characteristic ion for the specific internal standard, counts.

Cis = Concentration of the internal standard spiking mixture, ppbv.

RRF = Relative response factor from the analysis of the continuing calibration standard

or the mid level standard of the initial calibration.

DF = Dilution factor calculated as described in section 2. If no dilution is performed,

DF = 1.
Method TO-15 VOCs

Page 15-30 Compendium of Methods for Toxic Organic Air Pollutants January 1997

[Note: The equation above is valid under the condition that the volume (-500 μL) of internal standard

spiking mixture added in all field and QC analyses is the same from run to run, and that the volume

(-500 mL) of field and QC sample introduced into the trap is the same for each analysis.]

10.8.5 Technical Acceptance Criteria.

[Note: If the most recent valid calibration is an initial calibration, internal standard area responses and

RTs in the sample are evaluated against the corresponding internal standard area responses and RTs in the

mid level standard (10 ppbv) of the initial calibration.]

10.8.5.1 The field sample must be analyzed on a GC/MS system meeting the BFB tuning, initial

calibration, and continuing calibration technical acceptance criteria at the frequency described in

Sections 10.4, 10.5 and 10.6.

10.8.5.2 The field samples must be analyzed along with a laboratory method blank that met the blank

technical acceptance criteria.

10.8.5.3 All of the target analyte peaks should be within the initial calibration range.

10.8.5.4 The retention time for each internal standard must be within ±0.33 minutes of the retention

time of the internal standard in the most recent valid calibration.

10.8.6 Corrective Action. If the on-column concentration of any compound in any sample exceeds the

initial calibration range, an aliquot of the original sample must be diluted and reanalyzed. Guidance in

performing dilutions and exceptions to this requirement are given below. 

• Use the results of the original analysis to determine the approximate dilution factor required to get the

largest analyte peak within the initial calibration range.

• The dilution factor chosen should keep the response of the largest analyte peak for a target compound

in the upper half of the initial calibration range of the instrument.

• Do not submit data for more than two analyses, i.e., the original sample and one dilution, or, if the

screening procedure was employed, the most concentrated dilution analyzed and one further dilution.

[Note: Analysis involving dilution should be reported with a dilution factor and nature of the dilution gas.]

10.8.6.1 Internal standard responses and retention times must be evaluated during or immediately after

data acquisition. If the retention time for any internal standard changes by more than 20 sec from the latest

daily (24-hour) calibration standard (or mean retention time over the initial calibration range), the GC/MS

system must be inspected for malfunctions, and corrections made as required.

10.8.6.2 If the area response for any internal standard changes by more than ±40 percent between the

sample and the most recent valid calibration, the GC/MS system must be inspected for malfunction and

corrections made as appropriate. When corrections are made, reanalysis of samples analyzed while the

system was malfunctioning is necessary.

10.8.6.3 If, after reanalysis, the area responses or the RTs for all internal standards are inside the

control limits, then the problem with the first analysis is considered to have been within the control of the

Laboratory. Therefore, submit only data from the analysis with SICPs within the limits. This is considered

the initial analysis and should be reported as such on all data deliverables.

11. Requirements for Demonstrating Method Acceptability for VOC Analysis from Canisters
VOCs Method TO-15

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 15-31

percent difference '

*x1& x2*

x

x 100

11.1 Introduction

11.1.1 There are three performance criteria which must be met for a system to qualify under

Compendium Method TO-15. These criteria are: the method detection limit of #0.5 ppbv, replicate precision

within 25 percent, and audit accuracy within 30 percent for concentrations normally expected in

contaminated ambient air (0.5 to 25 ppbv). 

11.1.2 Either SIM or SCAN modes of operation can be used to achieve these criteria, and the choice of

mode will depend on the number of target compounds, the decision of whether or not to determine tentatively

identified compounds along with other VOCs on the target list, as well as on the analytical system

characteristics. 

11.1.3 Specific criteria for each Title III compound on the target compound list must be met by the

analytical system. These criteria were established by examining summary data from EPA's Toxics Air

Monitoring System Network and the Urban Air Toxics Monitoring Program network. Details for the

determination of each of the criteria follow.

11.2 Method Detection Limit

11.2.1 The procedure chosen to define the method detection limit is that given in the Code of Federal

Regulations (40 CFR 136 Appendix B). 

11.2.2 The method detection limit is defined for each system by making seven replicate measurements

of the compound of interest at a concentration near (within a factor of five) the expected detection limit,

computing the standard deviation for the seven replicate concentrations, and multiplying this value by 3.14

(i.e., the Student's t value for 99 percent confidence for seven values). Employing this approach, the

detection limits given in Table 4 were obtained for some of the VOCs of interest. 

11.3 Replicate Precision

11.3.1 The measure of replicate precision used for this program is the absolute value of the difference

between replicate measurements of the sample divided by the average value and expressed as a percentage

as follows:

where: x1 = First measurement value.

x2 = Second measurement value.

x = Average of the two values.

11.3.2 There are several factors which may affect the precision of the measurement. The nature of the

compound of interest itself such as molecular weight, water solubility, polarizability, etc., each have some

effect on the precision, for a given sampling and analytical system. For example, styrene, which is classified

as a polar VOC, generally shows slightly poorer precision than the bulk of nonpolar VOCs. A primary

influence on precision is the concentration level of the compound of interest in the sample, i.e., the precision

degrades as the concentration approaches the detection limit. A conservative measure was obtained from

replicate analysis of "real world" canister samples from the TAMS and UATMP networks. These data are
Method TO-15 VOCs

Page 15-32 Compendium of Methods for Toxic Organic Air Pollutants January 1997

Audit Accuracy, % '

Spiked Value & Observed Value

Spiked Value

x 100

summarized in Table 5 and suggest that a replicate precision value of 25 percent can be achieved for each

of the target compounds. 

11.4 Audit Accuracy

11.4.1 A measure of analytical accuracy is the degree of agreement with audit standards. Audit accuracy

is defined as the difference between the nominal concentration of the audit compound and the measured

value divided by the audit value and expressed as a percentage, as illustrated in the following equation:

11.4.2 Audit accuracy results for TAMS and UATMP analyses are summarized in Table 6 and were used

to form the basis for a selection of 30 percent as the performance criterion for audit accuracy.
VOCs Method TO-15

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 15-33

12. References

1. Compendium of Methods for the Determination of Toxic Organic Compounds in Ambient Air: Method

TO-14A, Second Edition, U. S. Environmental Protection Agency, Research Triangle Park, NC,

EPA 600/625/R-96/010b, January 1997.

2. Winberry, W. T., Jr., et al., Statement-of-Work (SOW) for the Analysis of Air Toxics From Superfund

Sites, U. S. Environmental Protection Agency, Office of Solid Waste, Contract Laboratory Program,

Washington, D.C., Draft Report, June 1990.

3. Coutant, R.W., Theoretical Evaluation of Stability of Volatile Organic Chemicals and Polar Volatile

Organic Chemicals in Canisters, U. S. Environmental Protection Agency, EPA Contract No. 68-DO-0007,

Work Assignment No. 45, Subtask 2, Battelle, Columbus, OH, June 1993.

4. Kelly, T.J., Mukund, R., Gordon, S.M., and Hays, M.J., Ambient Measurement Methods and Properties

of the 189 Title III Hazardous Air Pollutants, U. S. Environmental Protection Agency, EPA Contract No. 68-

DO-0007, Work Assignment 44, Battelle, Columbus, OH, March 1994.

5. Kelly T. J. and Holdren, M.W., "Applicability of Canisters for Sample Storage in the Determination of

Hazardous Air Pollutants," Atmos. Environ., Vol. 29, 2595-2608, May 1995.

6. Kelly, T.J., Callahan, P.J., Pleil, J.K., and Evans, G.E., "Method Development and Field Measurements

for Polar Volatile Organic Compounds in Ambient Air," Environ. Sci. Technol., Vol. 27, 1146-1153, 1993.

7. McClenny, W.A., Oliver, K.D. and Daughtrey, E.H.., Jr. "Dry Purging of Solid Adsorbent Traps to

Remove Water Vapor Before Thermal Desorption of Trace Organic Gases," J. Air and Waste Manag. Assoc.,

Vol. 45, 792-800, June 1995.

8. Whitaker, D.A., Fortmann, R.C. and Lindstrom, A.B. "Development and Testing of a Whole Air Sampler

for Measurement of Personal Exposures to Volatile Organic Compounds," Journal of Exposure Analysis and

Environmental Epidemiology, Vol. 5, No. 1, 89-100, January 1995. 

9. Pleil, J.D. and Lindstrom, A.B., "Collection of a Single Alveolar Exhaled Breath for Volatile Organic

Compound Analysis," American Journal of Industrial Medicine, Vol. 28, 109-121, 1995.

10. Pleil, J.D. and McClenny, W.A., "Spatially Resolved Monitoring for Volatile Organic Compounds Using

Remote Sector Sampling," Atmos. Environ., Vol. 27A, No. 5, 739-747, August 1993.

11. Holdren, M.W., et al., Unpublished Final Report, EPA Contract 68-DO-0007, Battelle, Columbus, OH.

Available from J.D. Pleil, MD-44, U. S. Environmental Protection Agency, Research Triangle Park, NC,

27711, 919-541-4680.

12. Morris, C.M., Burkley, R.E. and Bumgarner, J.E., "Preparation of Multicomponent Volatile Organic

Standards Using Dilution Bottles," Anal. Letts., Vol. 16 (A20), 1585-1593, 1983.
Method TO-15 VOCs

Page 15-34 Compendium of Methods for Toxic Organic Air Pollutants January 1997

13. Pollack, A.J., Holdren, M.W., “Multi-Adsorbent Preconcentration and Gas Chromatographic Analysis

of Air Toxics With an Automated Collection/Analytical System,” in the Proceedings of the 1990

EPA/A&WMA International Symposium of Measurement of Toxic and Related Air Pollutants, U. S.

Environmental Protection Agency, Research Triangle Park, NC, EPA/600/9-90-026, May 1990.

14. Stephenson, J.H.M., Allen, F., Slagle, T., "Analysis of Volatile Organics in Air via Water Methods" in

Proceedings of the 1990 EPA/A&WMA International Symposium on Measurement of Toxic and Related Air

Pollutants, U. S. Environmental Protection Agency, Research Triangle Park, NC, EPA 600/9-90-026,

May 1990.

15. Oliver, K. D., Adams, J. R., Davehtrey, E. H., Jr., McClenny, W. A., Young, M. J., and Parade, M. A.,

"Techniques for Monitoring Toxices VOCs in Air: Sorbent Preconcentration Closed-Cycle Cooler

Cryofocusing, and GC/MS Analysis," Environ. Sci. Technol., Vol. 30, 1938-1945, 1996.
VOCs Method TO-15

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 15-35

APPENDIX A.

LISTING OF SOME COMMERCIAL WATER 

MANAGEMENT SYSTEMS USED WITH AUTOGC SYSTEMS

Tekmar Dohrman Company

7143 East Kemper Road

Post Office Box 429576

Cincinnati, Ohio 45242-9576

(513) 247-7000

(513) 247-7050 (Fax)

(800) 543-4461

[Moisture control module]

Entech Laboratory Automation

950 Enchanted Way No. 101

Simi Valley, California 93065

(805) 527-5939

(805) 527-5687 (Fax)

[Microscale Purge and Trap]

Dynatherm Analytical Instruments

Post Office Box 159

Kelton, Pennsylvania 19346

(215) 869-8702

(215) 869-3885 (Fax)

[Thermal Desorption System]

XonTech Inc.

6862 Hayenhurst Avenue

Van Nuys, CA 91406

(818) 787-7380

(818) 787-4275 (Fax)

[Multi-adsorbent trap/dry purge]

Graseby

500 Technology Ct.

Smyrna, Georgia 30082

(770) 319-9999

(770) 319-0336 (Fax)

(800) 241-6898

[Controlled Desorption Trap]

Varian Chromatography System

2700 Mitchell Drive

Walnut Creek, California 94898

(510) 945-2196

(510) 945-2335 (FAX)

[Variable Temperature Adsorption Trap]
Method TO-15 VOCs

Page 15-36 Compendium of Methods for Toxic Organic Air Pollutants January 1997

APPENDIX B.

COMMENT ON CANISTER CLEANING PROCEDURES

The canister cleaning procedures given in Section 8.4 require that canister pressure be reduced to <0.05mm

Hg before the cleaning process is complete. Depending on the vacuum system design (diameter of

connecting tubing, valve restrictions, etc.) and the placement of the vacuum gauge, the achievement of this

value may take several hours. In any case, the pressure gauge should be placed near the canisters to

determine pressure. The objective of requiring a low pressure evacuation during canister cleaning is to

reduce contaminants. If canisters can be routinely certified (<0.2 ppbv for target compounds) while using

a higher vacuum, then this criteria can be relaxed. However, the ultimate vacuum achieved during cleaning

should always be <0.2mm Hg. 

Canister cleaning as described in Section 8.4 and illustrated in Figure 10 requires components with special

features. The vacuum gauge shown in Figure 10 must be capable of measuring 0.05mm Hg with less than

a 20% error. The vacuum pump used for evacuating the canister must be noncontaminating while being

capable of achieving the 0.05 mm Hg vacuum as monitored near the canisters. Thermoelectric vacuum

gauges and turbomolecular drag pumps are typically being used for these two components.

An alternate to achieving the canister certification requirement of <0.2 ppbv for all target compounds is the

criteria used in Compendium Method TO-12 that the total carbon count be <10ppbC. This check is less

expensive and typically more exacting than the current certification requirement and can be used if proven

to be equivalent to the original requirement. This equivalency must be established by comparing the total

nonmethane organic carbon (TNMOC) expressed in ppbC to the requirement that individual target

compounds be <0.2 ppbv for a series of analytical runs.
VOCs Method TO-15

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 15-37

APPENDIX C.

LISTING OF COMMERCIAL MANUFACTURERS AND RE-SUPPLIERS OF 

SPECIALLY-PREPARED CANISTERS

BRC/Rasmussen

17010 NW Skyline Blvd.

Portland, Oregon 97321

(503) 621-1435

Meriter

1790 Potrero Drive

San Jose, CA 95124

(408) 265-6482

Restek Corporation

110 Benner Circle

Bellefonte, PA 16823-8812

(814) 353-1300

(800) 356-1688

Scientific Instrumentation Specialists

P.O. Box 8941

815 Courtney Street

Moscow, ID 83843

(208) 882-3860

Graseby

500 Technology Ct.

Smyrna, Georgia 30082

(404) 319-9999

(800) 241-6898

XonTech Inc.

6862 Hayenhurst Avenue

Van Nuys, CA 91406

(818) 787-7380
Method TO-15 VOCs

Page 15-38 Compendium of Methods for Toxic Organic Air Pollutants January 1997

APPENDIX D.

LISTING OF COMMERCIAL SUPPLIERS OF PERMEATION TUBES AND SYSTEMS

Kin-Tek

504 Laurel St.

Lamarque, Texas 77568

(409) 938-3627

(800) 326-3627

Vici Metronics, Inc.

2991 Corvin Drive

Santa Clara, CA 95051

(408) 737-0550

Analytical Instrument Development, Inc.

Rt. 41 and Newark Rd.

Avondale, PA 19311

(215) 268-3181

Ecology Board, Inc.

9257 Independence Ave.

Chatsworth, CA 91311

(213) 882-6795

Tracor, Inc.

6500 Tracor Land

Austin, TX

(512) 926-2800

Metronics Associates, Inc.

3201 Porter Drive

Standford Industrial Park

Palo Alto, CA 94304

(415) 493-5632
January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 15-39 TABLE 1. VOLATILE ORGANIC COMPOUNDS ON THE TITLE III CLEAN AIR AMENDMEN

MEMBERSHIP IN COMPENDIUM METHOD TO-14A LIST AND THE SOW-CLP LIST OF 

Compound CAS No. BP (EC)

1 v.p. (mmHg)

1 MW1 TO-14

Methyl chloride (chloromethane); CH3Cl 74-87-3 -23.7 3.8 x 10

3 50.5

X

Carbonyl sulfide; COS 463-58-1 -50.0 3.7 x 10

3 60.1

Vinyl chloride (chloroethene); C2H3Cl 75-01-4 -14.0 3.2 x 10

3 62.5

X

Diazomethane; CH2N2 334-88-3 -23.0 2.8 x 10

3 42.1

Formaldehyde; CH2O 50-00-0 -19.5 2.7 x 10

3 30

1,3-Butadiene; C4H6 106-99-0 -4.5 2.0 x 10

3 54

Methyl bromide (bromomethane); CH3Br 74-83-9 3.6 1.8 x 10

3 94.9

X

Phosgene; CCl2O 75-44-5 8.2 1.2 x 10

3 99

Vinyl bromide (bromoethene); C2H3Br 593-60-2 15.8 l.l x 10

3 107

Ethylene oxide; C2H4O 75-21-8 10.7 1.1 x 10

3 44

Ethyl chloride (chloroethane); C2H5Cl 75-00-3 12.5 1.0 x 10

3 64.5

X

Acetaldehyde (ethanal); C2H4O 75-07-0 21.0 952 44Vinylidene chloride (1,1-dichloroethylene); C2H2Cl2 75-35-4 31.7 500 97

X

Propylene oxide; C3H6O 75-56-9 34.2 445 58Methyl iodide (iodomethane); CH3I 74-88-4 42.4 400 141.9Methylene chloride; CH2Cl2 75-09-2 40.0 349 84.9

X

Methyl isocyanate; C2H3NO 624-83-9 59.6 348 57.1Allyl chloride (3-chloropropene); C3H5Cl 107-05-1 44.5 340 76.5

X

Carbon disulfide; CS2 75-15-0 46.5 260 76Methyl ter-butyl ether; C5H12O 1634-04-4 55.2 249 86Propionaldehyde; C2H5CHO 123-38-6 49.0 235 58.1Ethylidene dichloride (1,1-dichloroethane); C2H4Cl2 75-34-3 57.0 230 99

X

Chloroprene (2-chloro-1,3-butadiene); C4H5Cl 126-99-8 59.4 226 88.5
Page 15-40 Compendium of Methods for Toxic Organic Air Pollutants January 1997 TABLE 1. (continued) Compound CAS No. BP (EC)

1 v.p. (mmHg)

1 MW1 TO-14

Acrolein (2-propenal); C3H4O 107-02-8 52.5 220 561,2-Epoxybutane (1,2-butylene oxide); C4H8O 106-88-7 63.0 163 72Chloroform; CHCl3 67-66-3 61.2 160 119

X

Ethyleneimine (aziridine); C2H5N 151-56-4 56 160.0 431,1-Dimethylhydrazine; C2H8N2 57-14-7 63 157.0 60.0Hexane; C6H14 110-54-3 69.0 120 86.2

X

1,2-Propyleneimine (2-methylaziridine); C3H7N 75-55-8 66.0 112 57.1Acrylonitrile (2-propenenitrile); C3H3N 107-13-1 77.3 100 53

X

Methyl chloroform (1,1,1-trichloroethane); C2H3Cl3 71-55-6 74.1 100 133.4

X

Methanol; CH4O 67-56-1 65.0 92.0 32Carbon tetrachloride; CCl4 56-23-5 76.7 90.0 153.8

X

Vinyl acetate; C4H6O2 108-05-4 72.2 83.0 86Methyl ethyl ketone (2-butanone); C4H8O 78-93-3 79.6 77.5 72Benzene; C6H6 71-43-2 80.1 76.0 78

X

Acetonitrile (cyanomethane); C2H3N 75-05-8 82 74.0 41.0Ethylene dichloride (1,2-dichloroethane); C2H4Cl2 107-06-2 83.5 61.5 99

X

Triethylamine; C6H15N 121-44-8 89.5 54.0 101.2Methylhydrazine; CH6N2 60-34-4 87. 8 49.6 46.1Propylene dichloride (1,2-dichloropropane); C3H6Cl2 78-87-5 97.0 42.0 113

X

2,2,4-Trimethyl pentane C8H18 540-84-l 99.2 40.6 1141,4-Dioxane (1,4-Diethylene oxide); C4H8O2 123-91-1 101 37.0 88Bis(chloromethyl) ether; C2H4Cl2O 542-88-1 104 30.0 115Ethyl acrylate; C5H8O2 140-88-5 100 29.3 100Methyl methacrylate-C5H8O2 80-62-6 101 28.0 100.11,3-Dichloropropene; C3H4Cl2 (cis) 542-75-6 112 27.8 111

X

Toluene; C7H8 108-88-3 111 22.0 92

X
January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 15-41 TABLE 1. (continued) Compound CAS No. BP (EC)

1 v.p. (mmgHg)

1 MW1 TO-14

Tetrachloroethylene; C2Cl4 127-18-4 121 14.0 165.8

X

Epichlorohydrin (1-chloro-2,3-epoxy propane); C3H5ClO 106-89-8 117 12.0 92.5Ethylene dibromide (1,2-dibromoethane); C2H4Br2 106-93-4 132 11.0 187.9

X

N-Nitroso-N-methylurea; C2H5N3O2 684-93-5 124 10.0 1032-Nitropropane; C3H7NO2 79-46-9 120 10.0 89Chlorobenzene; C6H5Cl 108-90-7 132 8.8 112.6

X

Ethylbenzene; C8H10 100-41-4 136 7.0 106

X

Xylenes (isomer & mixtures); C8H10 1330-20-7 142 6.7 106.2

X

Styrene; C8H8 100-42-5 145 6.6 104

X

p-Xylene; C8H10 106-42-3 138 6.5 106.2

X

m-Xylene; C8H10 108-38-3 139 6.0 106.2

X

Methyl isobutyl ketone (hexone); C6H12O 108-10-1 117 6.0 100.2Bromoform (tribromomethane); CHBr3 75-25-2 149 5.6 252.8l,l,2,2-Tetrachloroethane; C2H2Cl4 79-34-5 146 5.0 167.9

X

o-Xylene; C8H10 95-47-6 144 5.0 106.2

X

Dimethylcarbamyl chloride; C3H6ClNO 79-44-7 166 4.9 107.6N-Nitrosodimethylamine; C2H6N2O 62-75-9 152 3.7 74Beta-Propiolactone; C3H4O2 57-57-8 Decomposes at

162

3.4 72

Cumene (isopropylbenzene); C9Hl2 98-82-8 153 3.2 120Acrylic acid; C3H4O2 79-10-7 141 3.2 72N,N-Dimethylformamide; C3H7NO 68-12-2 153 2.7 731,3-Propane sultone; C3H6O3S 1120-71-4 180/30 mm 2.0 122.1Acetophenone; C8H8O 98-86-2 202 1.0 120Dimethyl sulfate; C2H6O4S 77-78-l 188 l.0 126.1
Page 15-42 Compendium of Methods for Toxic Organic Air Pollutants January 1997 TABLE 1. (continued) Compound CAS No. BP (EC)

1 v.p. (mmHg)

1 MW1 TO-14

Bis(2-Chloroethyl)ether; C4H8Cl2O 111-44-4 178 0.71 143Chloroacetic acid; C2H3ClO2 79-11-8 189 0.69 94.5Aniline (aminobenzene); C6H7N 62-53-3 184 0.67 931,4-Dichlorobenzene (p-); C6H4Cl2 106-46-7 173 0.60 147

X

Ethyl carbamate (urethane); C3H7NO2 51-79-6 183 0.54 89Acrylamide; C3H5NO 79-06-1 125/25 mm 0.53 71N,N-Dimethylaniline; C8H11N 121-69-7 192 0.50 121Hexachloroethane; C2Cl6 67-72-1 Sublimes at

186

0.40 236.7

Hexachlorobutadiene; C4Cl6 87-68-3 2l5 0.40 260.8

X

Isophorone; C9H14O 78-59-1 215 0.38 138.2N-Nitrosomorpholine; C4H8N2O2 59-89-2 225 0.32 116.1Styrene oxide; C8H8O 96-09-3 194 0.30 120.2Diethyl sulfate; C4H10O4S 64-67-5 208 0.29 154Cresylic acid (cresol isomer mixture) 1319-77-3 202 0.26 108o-Cresol; C7H8O 95-48-7 191 0.24 108Catechol (o-hydroxyphenol); C6H6O2 120-80-9 240 0.22 110Phenol; C6H6O 108-95-2 182 0.20 941,2,4-Trichlorobenzene; C6H3Cl3 120-82-1 213 0.18 181.5

X

Nitrobenzene; C6H5NO2 98-95-3 211 0.15 123

1Vapor pressure (v.p.), boiling point (BP) and molecular weight (MW) data from: 

(a) D. L. Jones and J. bursey, "Simultaneous Control of PM-10 and Hazardous Air Pollutants II: Rationale for Selection of Hazardo

Potential Particulate Matter," Report EPA-452/R-93/013, U. S. Environmental Protection Agency, Research Triangle Park, NC. 

(b) R. C. Weber, P. A. Parker, and M. Bowser. Vapor Pressure Distribution of Selected Organic Chemicals, Report EPA-600/2-81-

Environmental Protection Agency, Cincinnati, OH, February 1981; and

(c) R. C. Weast, ed., "CRC Handbook of Chemistry and Physics," 59th edition, CRC Press, Boca Raton, 1979.
VOCs Method TO-15

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 15-43

TABLE 2. CHARACTERISTIC MASSES (M/Z) USED FOR QUANTIFYING 

THE TITLE III CLEAN AIR ACT AMENDMENT COMPOUNDS

Compound CAS No. Primary Ion Secondary Ion

Methyl chloride (chloromethane); CH3Cl 74-87-3 50 52

Carbonyl sulfide; COS 463-S8-1 60 62

Vinyl chloride (chloroethene); C2H3Cl 7S-01-4 62 64

Diazomethane; CH2N2 334-88-3 42 41

Formaldehyde; CH20 50-00-0 29 30

1,3-Butadiene; C4H6 106-99-0 39 54

Methyl bromide (bromomethane); CH3Br 74-83-9 94 96

Phosgene; CCl2O 75-44-5 63 65

Vinyl bromide (bromoe hene); C2H3Br 593-60-2 106 108

Ethylene oxide; C2H4O 75-21-8 29 44

Ethyl chloride (chloroethane); C2H5Cl 75-00-3 64 66

Acetaldehyde (ethanal); C2H4O 75-07-0 44 29, 43

Vinylidene chloride (1,1-dichloroethylene); C2H2Cl2 75-35-4 61 96

Propylene oxide; C3H6O 75-56-9 58 57

Methyl iodide (iodomethane); CH3I 74-88-4 142 127

Methylene chloride; CH2Cl2 75-09-2 49 84, 86

Methyl isocyanate; C2H3N0 624-83-9 57 56

Allyl chloride (3-chloropropene); C3H5Cl 107-05-1 76 41, 78

Carbon disulfide; CS2 75-15-0 76 44, 78

Methyl ter-butyl ether; C5H12O 1634-04-4 73 41, 53

Propionaldehyde; C2H5CHO 123-38-6 58 29, 57

Ethylidene dichloride (1,1-dichloroethane); C2H4Cl2 75-34-3 63 65, 27

Chloroprene (2-chloro-1,3-butadiene); C4H5Cl 126-99-8 88 53, 90

Chloromethyl methyl ether; C2H5ClO 107-30-2 45 29, 49

Acrolein (2-propenal); C3H4O 107-02-8 56 55

1,2-Epoxybutane (1,2-butylene oxide); C4H8O 106-88-7 42 41, 72

Chloroform; CHCl3 67-66-3 83 85, 47

Ethyleneimine (aziridine); C2H5N 151-56-4 42 43

1,1-Dimethylhydrazine; C2H8N2 57-14-7 60 45, 59

Hexane; C6H14 110-54-3 57 41, 43

1,2-Propyleneimine (2-methylazindine); C3H7N 75-55-8 56 57, 42

Acrylonitrile (2-propenenitrile); C3H3N 107-13-1 53 52

Methyl chloroform (1,1,1 trichloroethane); C2H3Cl3 71-55-6 97 99, 61

Methanol; CH4O 67-56-1 31 29

Carbon tetrachloride; CCl4 56-23-5 117 119

Vinyl acetate; C4H6O2 108-05-4 43 86

Methyl ethyl ketone (2-butanone); C4H8O 78-93-3 43 72

Benzene; C6H6 71-43-2 78 77, 50

Acetonitrile (cyanomethane); C2H3N 75-05-8 41 40
Method TO-15 VOCs

Page 15-44 Compendium of Methods for Toxic Organic Air Pollutants January 1997

TABLE 2. (continued)

Compound CAS No. Primary Ion Secondary Ion

Ethylene dichloride (1,2-dichloroethane); C2H4Cl2 107-06-2 62 64, 27

Triethylamine; C6H15N 121-44-8 86 58, 101

Methylhydrazine; CH6N2 60-34-4 46 31, 45

Propylene dichloride (1,2-dichloropropane); C3H6Cl2 78-87-5 63 41, 62

2,2,4-Trimethyl pentane; C8H18 540-84-1 57 41, 56

1,4-Dioxane (1,4 Diethylene oxide); C4H8O2 123-91-1 88 58

Bis(chloromethyl) ether; C2H4Cl2O 542-88-1 79 49, 81

Ethyl acrylate; C5H8O2 140-88-5 55 73

Methyl methacrylate; C5H8O2 80-62-6 41 69, 100

1,3-Dichlompropene; C3H4Cl2 (cis) 542-75-6 75 39, 77

Toluene; C7H8 108-88-3 91 92

Trichloethylene; C2HCl3 79-01-6 130 132, 95

1,1,2-Trichloroethane; C2H3Cl3 79-00-5 97 83, 61

Tetrachloroethylene; C2Cl4 127-18-4 166 164, 131

Epichlorohydrin (l-chloro-2,3-epoxy propane); C3H5ClO 106-89-8 57 49, 62

Ethylene dibromide (1,2-dibromoethane); C2H4Br2 106-93-4 107 109

N-Nitrso-N-methylurea; C2H5N3O2 684-93-5 60 44, 103

2-Nitropropane; C3H7NO2 79-46-9 43 41

Chlorobenzene; C6H5Cl 108-90-7 112 77, 114

Ethylbenzene; C8H10 100-41-4 91 106

Xylenes (isomer & mixtures); C8H10 1330-20-7 91 106

Styrene; C8H8 100-42-5 104 78, 103

p-Xylene; C8H10 106-42-3 91 106

m-Xylene; C8H10 108-38-3 91 106

Methyl isobutyl ketone (hexone); C6H12O 108-10-1 43 58, 100

Bromoform (tribromomethane); CHBr3 75-25-2 173 171, 175

1,1,2,2-Tetrachloroethane; C2H2Cl4 79-34-5 83 85

o-Xylene; C8H10 95-47-6 91 106

Dimethylcarbamyl chloride; C3H6ClNO 79-44-7 72 107

N-Nitrosodimethylamine; C2H6N2O 62-75-9 74 42

Beta-Propiolactone; C3H4O2 57-57-8 42 43

Cumene (isopropylbenzene); C9H12 98-82-8 105 120

Acrylic acid; C3H4O2 79-10-7 72 45, 55

N,N-Dimethylformamide; C3H7NO 68-12-2 73 42, 44

1,3-Propane sultone; C3H6O3S 1120-71-4 58 65, 122

Acetophenone; C8H8O 98-86-2 105 77, 120

Dimethyl sulfate; C2H6O4S 77-78-1 95 66, 96

Benzyl chloride (a-chlorotoluene); C7H7Cl 100-44-7 91 126

1,2-Dibromo-3-chloropropane; C3H5Br2Cl 96-12-8 57 155, 157

Bis(2-Chloroethyl)ether; C4H8Cl2O 111-44-4 93 63, 95

Chloroacetic acid; C2H3ClO2 79-11-8 50 45, 60
VOCs Method TO-15

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 15-45

TABLE 2. (continued)

Compound CAS No. Primary Ion Secondary Ion

Aniline (aminobenzene); C6H7N 62-53-3 93 66

1,4-Dichlorobenzene (p-); C6H4Cl2 106-46-7 146 148, 111

Ethyl carbamate (urethane); C3H7NO2 51-79-6 31 44, 62

Acrylamide; C3H5NO 79-06-1 44 55, 71

N,N-Dimethylaniline; C8H11N 121-69-7 120 77, 121

Hexachloroethane; C2Cl6 67-72-1 201 199, 203

Hexachlorobutadiene; C4Cl6 87-68-3 225 227, 223

Isophorone; C9H14O 78-59-1 82 138

N-Nitrosomorpholine; C4H8N2O2 59-89-2 56 86, 116

Styrene oxide; C8H8O 96-09-3 91 120

Diethyl sulfate; C4H10O4S 64-67-5 45 59, 139

Cresylic acid (cresol isomer mixture) 1319-77-3

o-Cresol; C7H8O 95-48-7 108 107

Catechol (o-hydroxyphenol); C6H6O2 120-80-9 110 64

Phenol; C6H6O 108-95-2 94 66

1,2,4-Trichlorobenzene; C6H3Cl3 120-82-1 180 182, 184

Nitrobenzene; C6H5NO2 98-95-3 77 51, 123
Method TO-15 VOCs

Page 15-46 Compendium of Methods for Toxic Organic Air Pollutants January 1997

TABLE 3. REQUIRED BFB KEY IONS AND 

ION ABUNDANCE CRITERIA

Mass Ion Abundance Criteria1

50 8.0 to 40.0 Percent of m/e 95

75 30.0 to 66.0 Percent of m/e 95

95 Base Peak, 100 Percent Relative Abundance

96 5.0 to 9.0 Percent of m/e 95 (See note)

173 Less than 2.0 Percent of m/e 174

174 50.0 to 120.0 Percent of m/e 95

175 4.0 to 9.0 Percent of m/e 174

176 93.0 to 101.0 Percent of m/e 174

177 5.0 to 9.0 Percent of m/e 176

1All ion abundances must be normalized to m/z 95, the

 nominal base peak, even though the ion abundance of m/z

 174 may be up to 120 percent that of m/z 95.
VOCs Method TO-15

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 15-47

TABLE 4. METHOD DETECTION LIMITS (MDL)1

TO-14A List Lab #1, SCAN Lab #2, SIM

Benzene 0.34 0.29

Benzyl Chloride -- --

Carbon tetrachloride 0.42 0.15

Chlorobenzene 0.34 0.02

Chloroform 0.25 0.07

1,3-Dichlorobenzene 0.36 0.07

1,2-Dibromoethane -- 0.05

1,4-Dichlorobenzene 0.70 0.12

1,2-Dichlorobenzene 0.44 --

1,1-Dichloroethane 0.27 0.05

1,2-Dichloroethane 0.24 --

1,1-Dichloroethene -- 0.22

cis-1,2-Dichloroethene -- 0.06

Methylene chloride 1.38 0.84

1,2-Dichloropropane 0.21 --

cis-1,3-Dichloropropene 0.36 --

trans-1,3-Dichloropropene 0.22 --

Ethylbenzene 0.27 0.05

Chloroethane 0.19 --

Trichlorofluoromethane -- --

1,1,2-Trichloro-1,2,2-trifluoroethane --

1,2-Dichloro-1,1,2,2-tetrafluoroethane -- --

Dichlorodifluoromethane -- --

Hexachlorobutadiene -- --

Bromomethane 0.53 --

Chloromethane 0.40 --

Styrene 1.64 0.06

1,1,2,2-Tetrachloroethane 0.28 0.09

Tetrachloroethene 0.75 0.10

Toluene 0.99 0.20

1,2,4-Trichlorobenzene -- --

1,1,1-Trichloroethane 0.62 0.21

1,1,2-Trichloroethane 0.50 --

Trichloroethene 0.45 0.07

1,2,4-Trimethylbenzene -- --

1,3,5-Trimethylbenzene -- --

Vinyl Chloride 0.33 0.48

m,p-Xylene 0.76 0.08

o-Xylene 0.57 0.28

1Method Detection Limits (MDLs) are defined as the product of the standard

 deviation of seven replicate analyses and the student's "t" test value for 99%

 confidence. For Lab #2, the MDLs represent an average over four studies. 

 MDLs are for MS/SCAN for Lab #1 and for MS/SIM for Lab #2.

TABLE 5. SUMMARY OF EPA DATA ON REPLICATE PRECISION (RP)
Method TO-15 VOCs

Page 15-48 Compendium of Methods for Toxic Organic Air Pollutants January 1997

FROM EPA NETWORK OPERATIONS1

Monitoring Compound

Identification

EPA's Urban Air Toxics Monitoring

Program (UATMP)

EPA's Toxics Air Monitoring

Stations (TAMS)

%RP # ppbv %RP # ppbv

Dichlorodifluoromethane

Methylene chloride

1,2-Dichloroethane

1,1,1-Trichloroethane

Benzene

Trichloroethene

Toluene

Tetrachloroethene

Chlorobenzene

Ethylbenzene

m-Xylene

Styrene

o-Xylene

p-Xylene

1,3-Dichlorobenzene

1,4-Dichlorobenzene

--

16.3

36.2

14.1

12.3

12.8

14.7

36.2

20.3

14.6

14.7

22.8

--

--

49.1

14.7

07 

31 

44 

56 

08 

76 

12 

21 

32 

75 

592

06 

14 

--

4.3

1.6

1.0

1.6

1.3

3.1

0.8

0.9

0.7

4.0

1.1

--

0.6

6.5

13.9

19.4

--

10.6

4.4

--

3.4

--

--

5.4

5.3

8.7

6.0

--

--

47

47

--

47

47

--

47

--

--

47

47

47

47

--

--

0.9

0.6

--

2.0

1.5

--

3.1

--

--

0.5

1.5

0.22

0.5

--

--

1Denotes the number of replicate or duplicate analysis used to generate the statistic. The replicate precision is

 defined as the mean ratio of absolute difference to the average value.

2Styrene and o-xylene coelute from the GC column used in UATMP. For the TAMS entries, both values were

 below detection limits for 18 of 47 replicates and were not included in the calculation.

TABLE 6. AUDIT ACCURACY (AA) VALUES1 FOR SELECTED 

COMPENDIUM METHOD TO-14A COMPOUNDS

Selected Compounds From TO-14A List FY-88 TAMS AA(%), N=30 FY-88 UATMP AA(%), N=3

Vinyl chloride

Bromomethane

Trichlorofluoromethane

Methylene chloride

Chloroform

1,2-Dichloroethane

1,1,1-Trichloroethane

Benzene

Carbon tetrachloride

1,2-Dichloropropane

Trichloroethene

Toluene

Tetrachloroethene

Chlorobenzene

Ethylbenzene

o-Xylene

4.6

--

6.4

8.6

--

6.8

18.6

10.3

12.4

--

8.8

8.3

6.2

10.5

12.4

16.2

17.9

6.4

--

31.4

4.2

11.4

11.3

10.1

9.4

6.2

5.2

12.5

--

11.7

12.4

21.2

1Audit accuracy is defined as the relative difference between the audit measurement result and its nominal value divided

by the nominal value. N denotes the number of audits averaged to obtain the audit accuracy value. Information is not

available for other TO-14A compounds because they were not present in the audit materials.
VOCs Method TO-15

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 15-49

Figure 1. Sampler configuration for subatmospheric pressure or pressurized canister sampling.
Method TO-15 VOCs

Page 15-50 Compendium of Methods for Toxic Organic Air Pollutants January 1997

Figure 2. Electrical pulse circuits for driving Skinner magnelatch solenoid valve with

mechanical timer.
VOCs Method TO-15

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 15-51

Figure 3. Alternative sampler configuration for pressurized canister sampling.
Method TO-15 VOCs

Page 15-52 Compendium of Methods for Toxic Organic Air Pollutants January 1997

Figure 4. Illustration of three stages of dry purging of adsorbent trap.

778
January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 15-53Figure 5. Residual water vapor on VOC concentrator vs. dry He purge volume.
Method TO-15 VOCs

Page 15-54 Compendium of Methods for Toxic Organic Air Pollutants January 1997

Figure 6. Simplified diagram of a quadrupole mass spectrometer.

Figure 7. Simplified diagram of an ion trap mass spectrometer.
January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 15-55 Figure 8. Schematic diagram of calibration system and manifold for (a) analytical system calibration, (b) testing canister sampling system and (c) preparing canister transfer stand
Method TO-15 VOCs

Page 15-56 Compendium of Methods for Toxic Organic Air Pollutants January 1997

COMPENDIUM METHOD TO-15

CANISTER SAMPLING FIELD TEST DATA SHEET

A.GENERAL INFORMATION

SITE LOCATION: 

SITE ADDRESS: 

SAMPLING DATE: 

SHIPPING DATE: 

CANISTER SERIAL NO.: 

SAMPLER ID: 

OPERATOR: 

CANISTER LEAK

CHECK DATE: 

B. SAMPLING INFORMATION

TEMPERATURE PRESSURE

INTERIOR AMBIENT MAXIMUM MINIMUM CANISTER PRESSURE

START

STOP

SAMPLING TIMES FLOW RATES

LOCAL TIME ELAPSED TIME METER

READING

MANIFOLD

FLOW RATE

CANISTER FLOW

RATE

FLOW

CONTROLLER

READOUT

START

STOP

SAMPLING SYSTEM CERTIFICATION DATE: 

QUARTERLY RECERTIFICATION DATE: 

C. LABORATORY INFORMATION

DATA RECEIVED: 

RECEIVED BY: 

INITIAL PRESSURE: 

FINAL PRESSURE: 

DILUTION FACTOR: 

ANALYSIS

GC-FID-ECD DATE: 

GC-MSD-SCAN DATE: 

GC-MSD-SIM DATE: 

RESULTS*: 

GC-FID-ECD: 

GC-MSD-SCAN: 

GC-MSD-SIM: 

SIGNATURE/TITLE

Figure 9. Canister sampling field test data sheet (FTDS).
VOCs Method TO-15

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 15-57

Figure 10. Canister cleaning system.
Method TO-15 VOCs

Page 15-58 Compendium of Methods for Toxic Organic Air Pollutants January 1997

Figure 11. Canister analysis utilizing GC/MS/SCAN/SIM analytical system with optional flame ionization detector with 6-port

chromatographic valve in the sample desorption mode. 

[Alternative analytical system illustrated in Figure 16.]
VOCs Method TO-15

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 15-59

Figure 12. Example of humid zero air test results for a clean sample canister

(a) and a contaminated sample canister (b).
Method TO-15 VOCs

Page 15-60 Compendium of Methods for Toxic Organic Air Pollutants January 1997

Figure 13. Diagram of design for internal standard addition.
VOCs Method TO-15

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 15-61

Figure 14. Water method of standard preparation in canisters.
Method TO-15 VOCs

Page 15-62 Compendium of Methods for Toxic Organic Air Pollutants January 1997

Figure 15. Diagram of the GC/MS analytical system.
January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 15-63 Figure 16. Sample flow diagram of a commercially available concentrator showing the combination of multisorbent tu

(Trap 1 sampling; Trap 2 desorbing).
APPENDIX B

Humidity
%RH ' 100%

6 L

Vs

for Vs> Vr

McClenny, W.A., S.M. Schmidt, and K.G. Kronmiller. “Variation of the Relative 1

Humidity of Air Released from Canisters After Ambient Sampling.” In Proceedings of the

Measurement of Toxic and Related Air Pollutants International Symposium, Research Triangle

Park, NC, 1997.

B-1

Appendix B

Humidity1

Dalton’s Law of partial pressures and the hypothesis that water vapor equilibrium above a

canister surface is identical to that established above liquid water can be used to predict the

variation of the percent relative humidity (%RH) of air released from canisters used in ambient

air sampling, typically 6L canisters pressurized with 18L of air. During sampling, water vapor

partial pressure increases as air enters the canister. When (and if) the water vapor partial

pressure exceeds its saturation vapor pressure, the rate of water vapor condensation on the

canister walls equals its sampling rate into the canister. Under constant temperature conditions,

the %RH of air subsequently released from the canister can be calculated. This development

shows that the air released from the canister is initially less humid than the original sample, if the

ambient %RH >33% RH and increases as air is released from the canister according to the

relationship:

where:

V = Residual air volume in canister; s

Vr = The residual air volume at which water is predicted to be completely

removed (using the assumptions) from the canister wall. 

For V < V , the %RH is constant and equal to its value at V . V is shown to depend on s r r r

the %RH of the ambient air sample. Experimental values are shown to agree reasonably well
B-2

with predictions. However, experimental values were systematically lower than predicted

especially when ambient air with mid-range %RH was sampled. The difference appears to be

related to the mass of water vapor condensed on the sampling apparatus upstream of the canister. 

Near V , some effects due to strongly adsorbed water vapor may also be present. r

Note: The results of mathematical prediction of the %RH of air released from a

canister are summarized below and graphical information is provided to allow predictions

to be made for a variety of situations.

Three ranges of %RH of the ambient air that is initially sampled into the canister are

conveniently treated:

C 0%RH # original ambient %RH # 33.3%RH 

No condensation occurs and (neglecting any adsorbed water vapor) the relative

humidity of air released from the canister should be constant at its original

ambient air value although in practice some water vapor will be adsorbed on the

canister wall.

C 33.3%RH < original ambient %RH < 70%RH 

Locate the ambient sample %RH on the abscissa (the value of 60%RH was chosen

in Figure B-1 as an example) and the point of intersection of this value with the

curve A. 

Identify the value of canister volume on the ordinate scale corresponding to the

point of intersection (8L in the example). This value is the volume V at which all r

condensed water vapor on the canister walls has been evaporated during the

process of releasing the sample air from the canister. 

Use Vr to locate a point of intersection on curve B. This point V = Vs divides the r

curve B into two sections, (1) V # V and (2) V $V . s r s r

Note: In general (for any ambient %RH), as the sample is released from the

canister (at any stage having a volume V remaining in the canister), the s

curve B indicates the %RH (on the abscissa scale) of the released sample air

over the range 18L # V # 6L. s
30 40 50 60 70 80 90 100

0

6

12

18

-15

0

15

30

% Relative Humidity

A

Figure B-1. A - Original %RH of the sample air vs the remaining sample

 volume, V , in the canister when all condensed water is

 evaporated; B - residual sample volume, V , vs %RH of air

 released from canister.

r

s

 6L Canister Filled with

 18L Air, Constant T

Vr

Vs

B

B-3
B-4

For the example, for Vs # 8L, since all condensed water in the canister will have

been evaporated, the mixture of water vapor and air will be constant and the %RH 

of the remaining sample air will be released at its value at V = 8L. In the example s

this value if 74%RH. 

For Vs $Vr, the abscissa value (obtained with curve B) corresponding to Vs

indicates the predicted %RH value of released air. In the example, this applies for

any remaining sample volume between 18L and 8L. 

Figure B-2 shows the modification of Figure B-1 (curve B) to predict the %RH of

released sample air for the example (when the %RH of the ambient air sample

was 60%). To do this locate the ordinate value corresponding to the volume Vs

remaining in the canister [between 18L (30psig) and 6L (15psig)] and read the

abscissa value of %RH for the point of intersection of V and the curve. s

C 70%RH # original ambient %RH # 100%RH 

Refer to Figure B-1 and note from curve A that Vr # 6L which is equivalent to

stating that some condensed water is always on the canister wall for 18L # Vs

# 6L. The %RH of released air is determined by using curve B in Figure B-1 to

find the value of %RH corresponding to any residual volume Vs over the entire

range of values of V $ 6L. s 

Results of Experimental Determination of the %RH of Sample Air Released

from Pressurized Canisters—Figures B-3 and B-4 show the %RH of air released from

canisters initially pressurized to 18L when 34%, 61% and 90%RH (23 ± 3oC) ambient air

samples were made available to the sampling manifold. The predicted values are shown for

comparison. Some of the difference between experimental and predicted values appears to be

due to condensation of water vapor on the sampling apparatus. This condensation causes a

systematic displacement of the entire set of experimental points such as seen in Figure B-4.

The curves in Figure B-4 correspond to a 61% Relative Humidity value for ambient air

and involve both water vapor condensation followed by evaporation of available water from the

canister wall as the sample air is released. Two experimental approaches (Can 1 and Can 2) are

shown. The two differ as the sample value remaining approaches Vr. The Can 2 values show the

general features of the predicted characteristic. However, the value of Vr (constant % Relative

Humidity) occurs at a higher value (58% Relative Humidity) than predicted (76%), probably due
*

s

V =rVs

30 40 50 60 70 80 90 100

6

12

18

0

15

30

% Relative Humidity (From Can)

Sample Volume Left (L), V

Can Pressure (psig)

Figure B-2. Residual Sample Volume, Vs Versus %RH of Air Released From Canister

B-5
B-6

34% RH

30 40 50 60 70 80 90 100

6

12

18

0

15

30

% Relative Humidity (From Can)

90% RH

 

 Note:

 Arrows indicate % RH

 of Ambient Sample

 , Experimental

 Predicted

Figure B-3. Comparison of Predicted and Experimental %RH Values of Released Air Versus Volume of Sample

Remaining in Canister; 34% RH and 90% RH Ambient Air Sample

B-6
30 40 50 60 70 80 90 100

6

12

18

0

15

30

% Relative Humidity (From Can)

Sample Volume Remaining (L)

Can Pressure (psig)

Note:

 Arrows indicate % RH

 of Ambient Sample

 Can 1

 Can 2

 Predicted

Vr

Figure B-4. Comparison of Predicted and Experimental %RH Values of Released Air Versus Volume of Sample

Remaining in Canister; 61% RH Ambient Air Sample

B-7
B-8

to the condensation of water vapor on the inlet lines during sampling. Can 1 shows a

monotonically increasing value of % Relative Humidity as residual canister volume decreases.

Recent experimental work indicates that different canisters exhibit different behaviors near V . r

Additional experimental work is being carried out to investigate whether these differences may

be related to the condition of the interior surface of the canister.

Adjustments must be made to the predicted values when ambient conditions of

temperature change appreciably between sampling and release of air. Obviously, more or less

water is condensed in the canister when the ambient temperature at which the canister is held

becomes lower or higher than the temperature at which the sample was taken. Consideration

should also be given to the mass of water in the canister since the condensation of water in the

canister for the same %RH but different temperatures may lead to droplets with various surface

to volume ratios. Another factor that could make a difference in the response profile of %RH

versus canister pressure is the manner in which water is introduced into the canister. Water added

to synthetic samples for humidification by using a certain number of μL probably has a different

surface distribution in the canister than humidified samples introduced directly from the ambient

air. 
APPENDIX C

Method TO-12

Method for the Determination of Non-Methane Organic Compounds (NMOC) in

Ambient Air Using Cryogenic Preconcentration and Direct Flame Ionization

Detection (PDFID)
METHOD TO-12

METHOD FOR THE DETERMINATION OF NON-METHANE ORGANIC COMPOUNDS (NMOC)

IN AMBIENT AIR USING CRYOGENIC PRECONCENTRATION AND DIRECT FLAME

IONIZATION DETECTION (PDFID)

1. Scope

1.1 In recent years, the relationship between ambient concentrations

of precursor organic compounds and subsequent downwind

concentrations of ozone has been described by a variety of

photochemical dispersion models. The most important application

of such models is to determine the degree of control of precursor

organic compounds that is necessary in an urban area to achieve

compliance with applicable ambient air quality standards for ozone

(1,2).

1.2 The more elaborate theoretical models generally require detailed

organic species data obtained by multicomponent gas chromatography

(3). The Empirical Kinetic Modeling Approach (EKMA), however,

requires only the total non-methane organic compound (NMOC)

concentration data; specifically, the average total NMOC

concentration from 6 a.m. to 9 a.m. daily at the sampling

location. The use of total NMOC concentration data in the EKMA

substantially reduces the cost and complexity of the sampling and

analysis system by not requiring qualitative and quantitative

species identification.

1.3 Method TO1, "Method for The Determination of Volatile Organic

Compounds in Ambient Air Using Tenax Adsorption and Gas ®

Chromatography/Mass Spectrometry (GC/MS)", employs collection of

certain volatile organic compounds on Tenax GC with subsequent ®

analysis of thermal desorption/cryogenic preconcentration and

GC/MS identification. This method (TO12) combines the same type

of cryogenic concentration techniques used in Method TO1 for high

sensitivity with the simple flame ionization detector (FID) of the

GC for total NMOC measurements, without the GC columns and complex

procedures necessary for species separation.

1.4 In a flame ionization detector, the sample is injected into a

hydrogen-rich flame where the organic vapors burn producing

ionized molecular fragments. The resulting ion fragments are then

collected and detected. The FID is nearly a universal detector. 

However, the detector response varies with the species of

[functional group in] the organic compound in an oxygen

atmosphere. Because this method employs a helium or argon carrier

gas, the detector response is nearly one for all compounds. Thus,
TO12-2

the historical short-coming of the FID involving varying detector

response to different organic functional groups is minimized.

1.5 The method can be used either for direct, in situ ambient

measurements or (more commonly) for analysis of integrated samples

collected in specially treated stainless steel canisters. EKMA

models generally require 3-hour integrated NMOC measurements over

the 6 a.m. to 9 a.m. period and are used by State or local

agencies to prepare State Implementation Plans (SIPs) for ozone

control to achieve compliance with the National Ambient Air

Quality Standards (NAAQS) for ozone. For direct, in situ ambient

measurements, the analyst must be present during the 6 a.m. to 9

a.m. period, and repeat measurements (approximately six per hour)

must be taken to obtain the 6 a.m. to 9 a.m. average NMOC

concentration. The use of sample canisters allows the collection

of integrated air samples over the 6 a.m. to 9 a.m. period by

unattended, automated samplers. This method has incorporated both

sampling approaches.

2. Applicable Documents

2.1 ASTM Standards

D1356 - Definition of Terms Related to Atmospheric Sampling

and Analysis

 E260 - Recommended Practice for General Gas Chromatography

Procedures

 E355 - Practice for Gas Chromatography Terms and

Relationships

2.2 Other Documents

U. S. Environmental Protection Agency Technical Assistance

Documents (4,5)

Laboratory and Ambient Air Studies (6-10)

3. Summary of Method

3.1 A whole air sample is either extracted directly from the ambient

air and analyzed on site by the GC system or collected into a

precleaned sample canister and analyzed off site.

3.2 The analysis requires drawing a fixed-volume portion of the sample

air at a low flow rate through a glass-bead filled trap that is

cooled to approximately -186 C with liquid argon. The cryogenic o

trap simultaneously collects and concentrates the NMOC (either via

condensation or adsorption) while allowing the methane, nitrogen,

oxygen, etc. to pass through the trap without retention. The

system is dynamically calibrated so that the volume of sample
TO12-3

passing through the trap does not have to be quantitatively

measured, but must be precisely repeatable between the calibration

and the analytical phases.

3.3 After the fixed-volume air sample has been drawn through the trap,

a helium carrier gas flow is diverted to pass through the trap, in

the opposite direction to the sample flow, and into an FID. When

the residual air and methane have been flushed from the trap and

the FID baseline restablizes, the cryogen is removed and the

temperature of the trap is raised to approximately 90 C. o

3.4 The organic compounds previously collected in the trap revolatilize due to the increase in temperature and are carried into the

FID, resulting in a response peak or peaks from the FID. The area

of the peak or peaks is integrated, and the integrated value is

translated to concentration units via a previously-obtained

calibration curve relating integrated peak areas with known

concentrations of propane.

3.5 By convention, concentrations of NMOC are reported in units of

parts per million carbon (ppmC), which, for a specified compound,

is the concentration of volume (ppmV) multiplied by the number of

carbon atoms in the compound.

3.6 The cryogenic trap simultaneously concentrates the NMOC while

separating and removing the methane from air samples. The

technique is thus direct reading for NMOC and, because of the

concentration step, is more sensitive than conventional continuous

NMOC analyzers.

4. Significance

4.1 Accurate measurements of ambient concentrations of NMOC are

important for the control of photochemical smog because these

organic compounds are primary precursors of atmospheric ozone and

other oxidants. Achieving and maintaining compliance with the

NAAQS for ozone thus depends largely on control of ambient levels

of NMOC.

4.2 The NMOC concentrations typically found at urban sites may range

up to 5-7 ppmC or higher. In order to determine transport of

precursors into an area, measurement of NMOC upwind of the area

may be necessary. Upwind NMOC concentrations are likely to be

less than a few tenths of 1 ppm.

4.3 Conventional methods that depend on gas chromatography and

qualitative and quantitative species evaluation are excessively

difficult and expensive to operate and maintain when speciated

measurements are not needed. The method described here involves a
TO12-4

simple, cryogenic preconcentration procedure with subsequent,

direct, flame ionization detection. The method is sensitive and

provides accurate measurements of ambient NMOC concentrations

where speciated data are not required as applicable to the EKMA.

5. Definitions

[Note: Definitions used in this document and in any user-prepared

Standard Operating Procedures (SOPs) should be consistent with

ASTM Methods D1356 and E355. All abbreviations and symbols are

defined within this document at point of use.]

5.1 Absolute pressure - Pressure measured with reference to absolute

zero pressure (as opposed to atmospheric pressure), usually

expressed as pounds-force per square inch absolute (psia).

5.2 Cryogen - A substance used to obtain very low trap temperatures in

the NMOC analysis system. Typical cryogens are liquid argon

(bp-185.7) and liquid oxygen (bp-183.0).

5.3 Dynamic calibration - Calibration of an analytical system with

pollutant concentrations that are generated in a dynamic, flowing

system, such as by quantitative, flow-rate dilution of a high

concentration gas standard with zero gas.

5.4 EKMA - Empirical Kinetics Modeling Approach; an empirical model

that attempts to relate morning ambient concentrations of nonmethane organic compounds (NMOC) and NOx with subsequent peak,

downwind ambient ozone concentrations; used by pollution control

agencies to estimate the degree of hydrocarbon emission reduction

needed to achieve compliance with national ambient air quality

standards for ozone.

5.5 Gauge pressure - Pressure measured with reference to atmospheric

pressure (as opposed to absolute pressure). Zero gauge pressure

(0 psig) is equal to atmospheric pressure, or 14.7 psia (101 kPa).

5.6 In situ - In place; In situ measurements are obtained by direct,

on-the-spot analysis, as opposed to subsequent, remote analysis of

a collected sample.

5.7 Integrated sample - A sample obtained uniformly over a specified

time period and representative of the average levels of pollutants

during the time period.

5.8 NMOC - Nonmethane organic compounds; total organic compounds as

measured by a flame ionization detector, excluding methane.

5.9 ppmC - Concentration unit of parts per million carbon; for a

specific compound, ppmC is equivalent to parts per million by

volume (ppmv) multiplied by the number of carbon atoms in the

compound.
TO12-5

5.10 Sampling - The process of withdrawing or isolating a representative portion of an ambient atmosphere, with or without the

simultaneous isolation of selected components for subsequent

analysis.

6. Interferences

6.1 In field and laboratory evaluation, water was found to cause a

positive shift in the FID baseline. The effect of this shift is

minimized by carefully selecting the integration termination point

and adjusted baseline used for calculating the area of the NMOC

peak(s).

6.2 When using helium as a carrier gas, FID response is quite uniform

for most hydrocarbon compounds, but the response can vary

considerably for other types of organic compounds.

7. Apparatus

7.1 Direct Air Sampling (Figure 1)

7.1.1 Sample manifold or sample inlet line - to bring sample

air into the analytical system.

7.1.2 Vacuum pump or blower - to draw sample air through a

sample manifold or long inlet line to reduce inlet

residence time. Maximum residence time should be no

greater than 1 minute.

7.2 Remote Sample Collection in Pressurized Canisters (Figure 2)

7.2.1 Sample canister(s) - stainless steel, Summa -polished ®

vessel(s) of 4-6 L capacity (Scientific Instrumentation Specialists, Inc., P.O. Box 8941, Moscow, ID

83843), used for automatic collection of 3-hour

integrated field air samples. Each canister should

have a unique identification number stamped on its

frame.

7.2.2 Sample pump - stainless steel, metal bellows type

(Model MB-151, Metal Bellows Corp., 1075 Providence

Highway, Sharon, MA 02067) capable of 2 atmospheres

minimum output pressure. Pump must be free of leaks,

clean, and uncontaminated by oil or organic compounds.

7.2.3 Pressure gauge - 0-30 psig (0-240 kPa).

7.2.4 Solenoid valve - special electrically-operated,

bistable solenoid valve (Skinner Magnelatch Valve, New

Britain, CT), to control sample flow to the canister

with negligible temperature rise (Figure 3). The use

of the Skinner Magnelatch valve avoids any substantial

temperature rise that would occur with a conventional,
TO12-6

normally closed solenoid valve, which would have to be

energized during the entire sample period. This

temperature rise in the valve could cause outgasing of

organics from the Viton valve seat material. The

Skinner Magnelatch valve requires only a brief

electrical pulse to open or close at the appropriate

start and stop times and therefore experiences no

temperature increase. The pulses may be obtained with

an electronic timer that can be programmed for short

(5 to 60 seconds) ON periods or with a conventional

mechanical timer and a special pulse circuit. Figure

3[a] illustrates a simple electrical pulse circuit for

operating the Skinner Magnelatch solenoid valve with a

conventional mechanical timer. However, with this

simple circuit, the valve may operate unpredictably

during brief power interruptions or if the time is

manually switched on and off too fast. A better

circuit incorporating a time-delay relay to provide

more reliable valve operation is shown in Figure 3[b].

7.2.5 Stainless steel orifice (or short capillary) - capable

of maintaining a substantially constant flow over the

sampling period (see Figure 4).

7.2.6 Particulate matter filter - 2 micron stainless steel

sintered in-line type (see Figure 4).

7.2.7 Timer - used for unattended sample collection. 

Capable of controlling pump(s) and solenoid valve.

7.3 Sample Canister Cleaning (Figure 5)

7.3.1 Vacuum pump - capable of evacuating sample canister(s)

to an absolute pressure of <5 mm Hg.

7.3.2 Manifold - stainless steel manifold with connections

for simultaneously cleaning several canisters.

7.3.3 Shut off valve(s) - seven required.

7.3.4 Vacuum gauge - capable of measuring vacuum in the

manifold to an absolute pressure of 5 mm Hg or less.

7.3.5 Cryogenic trap (2 required) - U-shaped open tubular

trap cooled with liquid nitrogen or argon used to

prevent contamination from back diffusion of oil from

vacuum pump, and to provide clean, zero air to sample

canister(s).

7.3.6 Pressure gauge - 0-50 psig (0-345 kPa), to monitor

zero air pressure.
TO12-7

7.3.7 Flow control valve - to regulate flow of zero air into

canister(s).

7.3.8 Humidifier - water bubbler or other system capable of

providing moisture to the zero air supply.

7.4 Analytical System (Figure 1)

7.4.1 FID detector system - including flow controls for the

FID fuel and air, temperature control for the FID, and

signal processing electronics. The FID burner air,

hydrogen, and helium carrier flow rates should be set

according to the manufacturer's instructions to obtain

an adequate FID response while maintaining as stable a

flame as possible throughout all phases of the

analytical cycle.

7.4.2 Chart recorder - compatible with the FID output

signal, to record FID response.

7.4.3 Electronic integrator - capable of integrating the

area of one or more FID response peaks and calculating

peak area corrected for baseline drift. If a separate

integrator and chart recorder are used, care must be

exercised to be sure that these components do not

interfere with each other electrically. Range

selector controls on both the integrator and the FID

analyzer may not provide accurate range ratios, so

individual calibration curves should be prepared for

each range to be used. The integrator should be

capable of marking the beginning and ending of peaks,

constructing the appropriate baseline between the

start and end of the integration period, and

calculating the peak area.

Note: The FID (7.4.1), chart recorder (7.4.2),

integrator (7.4.3), valve heater (7.4.5), and a trap

heating system are conveniently provided by a standard

laboratory chromatograph and associated integrator. 

EPA has adapted two such systems for the PDFID method:

a Hewlett-Packard model 5880 (Hewlett-Packard Corp.,

Avondale, PA) and a Shimadzu model GC8APF (Shimadzu

Scientific Instruments Inc., Columbia, MD; see

Reference 5). Other similar systems may also be

applicable.

7.4.4 Trap - the trap should be carefully constructed from a

single piece of chromatographic-grade stainless steel
TO12-8

tubing (0.32 cm O.D, 0.21 cm I.D.) as shown in Figure

6. The central portion of the trap (7-10 cm) is

packed with 60/80 mesh glass beads, with small glass

wool (dimethyldichlorosilane-treated) plugs to retain

the beads. The trap must fit conveniently into the

Dewar flask (7.4.9), and the arms must be of an

appropriate length to allow the beaded portion of the

trap to be submerged below the level of liquid cryogen

in the Dewar. The trap should connect directly to the

six-port valve, if possible, to minimize line length

between the trap and the FID. The trap must be

mounted to allow the Dewar to be slipped conveniently

on and off the trap and also to facilitate heating of

the trap (see 7.4.13).

7.4.5 Six-port chromatographic valve - Seiscor Model VIII

(Seismograph Service Corp., Tulsa, OK), Valco Model

9110 (Valco Instruments Co., Houston, TX), or

equivalent. The six-port valve and as much of the

interconnecting tubing as practical should be located

inside an oven or otherwise heated to 80 - 90 C to o

minimize wall losses or adsorption/desorption in the

connecting tubing. All lines should be as short as

practical.

7.4.6 Multistage pressure regulators - standard two-stage,

stainless steel diaphram regulators with pressure

gauges, for helium, air, and hydrogen cylinders.

7.4.7 Pressure regulators - optional single stage, stainless

steel, with pressure gauge, if needed, to maintain

constant helium carrier and hydrogen flow rates.

7.4.8 Fine needle valve - to adjust sample flow rate through

trap.

7.4.9 Dewar flask - to hold liquid cryogen to cool the trap,

sized to contain submerged portion of trap.

7.4.10 Absolute pressure gauge - 0-450 mm Hg, (2 mm Hg [scale

divisions indicating units]), to monitor repeatable

volumes of sample air through cryogenic trap (Wallace

and Tiernan, Model 61C-ID-0410, 25 Main Street,

Belleville, NJ).

7.4.11 Vacuum reservoir - 1-2 L capacity, typically 1 L.

7.4.12 Gas purifiers - gas scrubbers containing Drierite or ®

silica gel and 5A molecular sieve to remove moisture
TO12-9

and organic impurities in the helium, air, and

hydrogen gas flows (Alltech Associates, Deerfield,

IL). Note: Check purity of gas purifiers prior to use

by passing zero-air through the unit and analyzing

according to Section 11.4. Gas purifiers are clean

if produce [contain] less than 0.02 ppmC hydrocarbons.

7.4.13 Trap heating system - chromatographic oven, hot water,

or other means to heat the trap to 80 to 90 C. A o o

simple heating source for the trap is a beaker or

Dewar filled with water maintained at 80-90 C. More o

repeatable types of heat sources are recommended,

including a temperature-programmed chromatograph oven,

electrical heating of the trap itself, or any type of

heater that brings the temperature of the trap up to

80-90 C in 1-2 minutes. o

7.4.14 Toggle shut-off valves (2) - leak free, for vacuum

valve and sample valve.

7.4.15 Vacuum pump - general purpose laboratory pump capable

of evacuating the vacuum reservoir to an appropriate

vacuum that allows the desired sample volume to be

drawn through the trap.

7.4.16 Vent - to keep the trap at atmospheric pressure during

trapping when using pressurized canisters.

7.4.17 Rotameter - to verify vent flow.

7.4.18 Fine needle valve (optional) - to adjust flow rate of

sample from canister during analysis.

7.4.19 Chromatographic-grade stainless steel tubing (Alltech

Applied Science, 2051 Waukegan Road, Deerfield, IL,

60015, (312) 948-8600) and stainless steel plumbing

fittings - for interconnections. All such materials

in contact with the sample, analyte, or support gases

prior to analysis should be stainless steel or other

inert metal. Do not use plastic or Teflon tubing or ®

fittings.

7.5 Commercially Available PDFID System (5)

7.5.1 A convenient and cost-effective modular PDFID system

suitable for use with a conventional laboratory

chromatograph is commercially available (NuTech

Corporation, Model 8548, 2806 Cheek Road, Durham, NC,

27704, (919) 682-0402).
TO12-10

7.5.2 This modular system contains almost all of the

apparatus items needed to convert the chromatograph

into a PDFID analytical system and has been designed

to be readily available and easy to assemble.

8. Reagents and Materials

8.1 Gas cylinders of helium and hydrogen - ultrahigh purity grade.

8.2 Combustion air - cylinder containing less than 0.02 ppm

hydrocarbons, or equivalent air source.

8.3 Propane calibration standard - cylinder containing 1-100 ppm (3-

300 ppmC) propane in air. The cylinder assay should be traceable

to a National Bureau of Standards (NBS) Standard Reference

Material (SRM) or to a NBS/EPA-approved Certified Reference

Material (CRM).

8.4 Zero air - cylinder containing less than 0.02 ppmC hydrocarbons. 

Zero air may be obtained from a cylinder of zero-grade compressed

air scrubbed with Drierite or silica gel and 5A molecular sieve ®

or activated charcoal, or by catalytic cleanup of ambient air. 

All zero air should be passed through a liquid argon cold trap for

final cleanup, then passed through a hydrocarbon-free water

bubbler (or other device) for humidification.

8.5 Liquid cryogen - liquid argon (bp -185.7 C) or liquid oxygen, (bp o

-183 C) may be used as the cryogen. Experiments have shown no o

differences in trapping efficiency between liquid argon and liquid

oxygen. However, appropriate safety precautions must be taken if

liquid oxygen is used. Liquid nitrogen (bp -195 C) should not be o

used because it causes condensation of oxygen and methane in the

trap.

9. Direct Sampling

9.1 For direct ambient air sampling, the cryogenic trapping system

draws the air sample directly from a pump-ventilated distribution

manifold or sample line (see Figure 1). The connecting line

should be of small diameter (1/8" O.D.) stainless steel tubing and

as short as possible to minimize its dead volume.

9.2 Multiple analyses over the sampling period must be made to

establish hourly or 3-hour NMOC concentration averages.

10. Sample Collection in Pressurized Canister(s)

For integrated pressurized canister sampling, ambient air is sampled by

a metal bellows pump through a critical orifice (to maintain constant

flow), and pressurized into a clean, evacuated, Summa -polished sample ®

canister. The critical orifice size is chosen so that the canister is

pressurized to approximately one atmosphere above ambient pressure, at a
TO12-11

constant flow rate over the desired sample period. Two canisters are

connected in parallel for duplicate samples. The canister(s) are then

returned to the laboratory for analysis, using the PDFID analytical

system. Collection of ambient air samples in pressurized canisters

provides the following advantages:

! Convenient integration of ambient samples over a specific

time period

! Capability of remote sampling with subsequent central

laboratory analysis

! Ability to ship and store samples, if necessary

! Unattended sample collection

! Analysis of samples from multiple sites with one analytical

system

! Collection of replicate samples for assessment of

measurement precision

With canister sampling, however, great care must be exercised in

selecting, cleaning, and handling the sample canister(s) and sampling

apparatus to avoid losses or contamination of the samples.

10.1 Canister Cleanup and Preparation

10.1.1 All canisters must be clean and free of any

contaminants before sample collection.

10.1.2 Leak test all canisters by pressurizing them to

approximately 30 psig [200 kPa (gauge)] with zero air. 

The use of the canister cleaning system (see Figure 5)

may be adequate for this task. Measure the final

pressure - close the canister valve, then check the

pressure after 24 hours. If leak tight, the pressure

should not vary more than + 2 psig over the 24-hour

period. Note leak check result on sampling data

sheet, Figure 7.

10.1.3 Assemble a canister cleaning system, as illustrated in

Figure 5. Add cryogen to both the vacuum pump and

zero air supply traps. Connect the canister(s) to the

manifold. Open the vent shut off valve and the

canister valve(s) to release any remaining pressure in

the canister. Now close the vent shut off valve and

open the vacuum shut off valve. Start the vacuum pump

and evacuate the canister(s) to # 5.0 mm Hg (for at

least one hour). [Note: On a daily basis or more

often if necessary, blow-out the cryogenic traps with

zero air to remove any trapped water from previous

canister cleaning cycles.]

10.1.4 Close the vacuum and vacuum gauge shut off valves and

open the zero air shut off valve to pressurize the
TO12-12

canister(s) with moist zero air to approximately 30

psig [200 kPa (gauge)]. If a zero gas generator

systems is used, the flow rate may need to be limited

to maintain the zero air quality.

10.1.5 Close the zero shut off valve and allow canister(s) to

vent down to atmospheric pressure through the vent

shut off valve. Close the vent shut off valve. 

Repeat steps 10.1.3 through 10.1.5 two additional

times for a total of three (3) evacuation/

pressurization cycles for each set of canisters.

10.1.6 As a "blank" check of the canister(s) and cleanup

procedure, analyze the final zero-air fill of 100% of

the canisters until the cleanup system and canisters

are proven reliable. The check can then be reduced to

a lower percentage of canisters. Any canister that

does not test clean (compared to direct analysis of

humidified zero air of less than 0.02 ppmC) should not

be utilized.

10.1.7 The canister is then re-evacuated to # 5.0 mm Hg,

using the canister cleaning system, and remains in

this condition until use. Close the canister valve,

remove the canister from the canister cleaning system

and cap canister connection with a stainless steel

fitting. The canister is now ready for collection of

an air sample. Attach an identification tag to the

neck of each canister for field notes and chain-ofcustody purposes.

10.2 Collection of Integrated Whole-Air Samples

10.2.1 Assemble the sampling apparatus as shown in Figure 2. 

The connecting lines between the sample pump and the

canister(s) should be as short as possible to minimize

their volume. A second canister is used when a

duplicate sample is desired for quality assurance (QA)

purposes (see Section 12.2.4). The small auxiliary

vacuum pump purges the inlet manifold or lines with a

flow of several L/min to minimize the sample residence

time. The larger metal bellows pump takes a small

portion of this sample to fill and pressurize the

sample canister(s). Both pumps should be shockmounted to minimize vibration. Prior to field use,

each sampling system should be leak tested. The
F '

(P)(V)(N)

(T)(60)

F '

2 x 6000 x 1

3 x 60

' 67 cm 3/min

TO12-13

outlet side of the metal bellows pump can be checked

for leaks by attaching the 0-30 psig pressure gauge to

the canister(s) inlet via connecting tubing and

pressurizing to 2 atmospheres or approximately 29.4

psig. If pump and connecting lines are leak free

pressure should remain at +2 psig for 15 minutes. To

check the inlet side, plug the sample inlet and insure

that there is no flow at the outlet of the pump.

10.2.2 Calculate the flow rate needed so that the canister(s)

are pressurized to approximately one atmosphere above

ambient pressure (2 atmospheres absolute pressure)

over the desired sample period, utilizing the

following equation:

where:

F = flow rate (cm /min) 3

P = final canister pressure (atmospheres absolute)

= (Pg/Pa) + 1

V = volume of the canister (cm )

3

N = number of canisters connected together for 

simultaneous sample collection

T = sample period (hours)

 Pg = gauge pressure in canister, psig (kPa)

 Pa = standard atmospheric pressure, 14.7 psig

 (101 kPa)

For example, if one 6-L canister is to be filled to 2

atmospheres absolute pressure (14.7 psig) in 3 hours, the

flow rate would be calculated as follows:

10.2.3 Select a critical orifice or hypodermic needle

suitable to maintain a substantially constant flow at

the calculated flow rate into the canister(s) over the

desired sample period. A 30-gauge hypodermic needle,
TO12-14

2.5 cm long, provides a flow of approximately 65

cm /min with the Metal Bellows Model MBV-151 pump (see 3

Figure 4). Such a needle will maintain approximately

constant flow up to a canister pressure of about 10

psig (71 kPa), after which the flow drops with

increasing pressure. At 14.7 psig (2 atmospheres

absolute pressure), the flow is about 10% below the

original flow.

10.2.4 Assemble the 2.0 micron stainless steel in-line

particulate filter and position it in front of the

critical orifice. A suggested filter-hypodermic

needle assembly can be fabricated as illustrated in

Figure 4.

10.2.5 Check the sampling system for contamination by filling

two evacuated, cleaned canister(s) (See Section 10.1)

with humidified zero air through the sampling system. 

Analyze the canisters according to Section 11.4. The

sampling system is free of contamination if the

canisters contain less than 0.02 ppmC hydrocarbons,

similar to that of humidified zero air.

10.2.6 During the system contamination check procedure, check

the critical orifice flow rate on the sampling system

to insure that sample flow rate remains relatively

constant (+10%) up to about 2 atmospheres absolute

pressure (101 kpa). Note: A drop in the flow rate

may occur near the end of the sampling period as the

canister pressure approaches two atmospheres.

10.2.7 Reassemble the sampling system. If the inlet sample

line is longer than 3 meters, install an auxiliary

pump to ventilate the sample line, as illustrated in

Figure 2.

10.2.8 Verify that the timer, pump(s) and solenoid valve are

connected and operating properly.

10.2.9 Verify that the timer is correctly set for the desired

sample period, and that the solenoid valve is closed.

10.2.10 Connect a cleaned, evacuated canister(s) (Section

10.1) to the non-contaminated sampling system, by way

of the solenoid valve, for sample collection.

10.2.11 Make sure the solenoid valve is closed. Open the

canister valve(s). Temporarily connect a small

rotameter to the sample inlet to verify that there is
TO12-15

no flow. Note: Flow detection would indicate a

leaking (or open) solenoid valve. Remove the

rotameter after leak detection procedure.

10.2.12 Fill out the necessary information on the Field Data

Sheet (Figure 7).

10.2.13 Set the automatic timer to start and stop the pump or

pumps to open and close the solenoid valve at the

appropriate time for the intended sample period. 

Sampling will begin at the pre-determined time.

10.2.14 After the sample period, close the canister valve(s)

and disconnect the canister(s) from the sampling

system. Connect a pressure gauge to the canister(s)

and briefly open and close the canister valve. Note

the canister pressure on the Field Data Sheet (see

Figure 7). The canister pressure should be

approximately 2 atmospheres absolute [1 atmosphere or

101 kPa (gauge)]. Note: If the canister pressure is

not approximately 2 atmospheres absolute (14.7 psig),

determine and correct the cause before next sample. 

Re-cap canister valve.

10.2.15 Fill out the identification tag on the sample

canister(s) and complete the Field Data Sheet as

necessary. Note any activities or special conditions

in the area (rain, smoke, etc.) that may affect the

sample contents on the sampling data sheet.

10.2.16 Return the canister(s) to the analytical system for

analysis.

11. Sample Analysis

11.1 Analytical System Leak Check

11.1.1 Before sample analysis, the analytical system is

assembled (see Figure 1) and leak checked.

11.1.2 To leak check the analytical system, place the sixport gas valve in the trapping position. Disconnect

and cap the absolute pressure gauge. Insert a

pressure gauge capable of recording up to 60 psig at

the vacuum valve outlet.

11.1.3 Attach a valve and a zero air supply to the sample

inlet port. Pressurize the system to about 50 psig

(350 kPa) and close the valve.
Vs

'

()P)(Vr)

(Ps)

TO12-16

11.1.4 Wait approximately 3 hrs. and re-check pressure. If

the pressure did not vary more than + 2 psig, the

system is considered leak tight.

11.1.5 If the system is leak free, de-pressurize and

reconnect absolute pressure gauge.

11.1.6 The analytical system leak check procedure needs to be

performed during the system checkout, during a series

of analysis or if leaks are suspected. This should be

part of the user-prepared SOP manual (see Section

12.1).

11.2 Sample Volume Determination

11.2.1 The vacuum reservoir and absolute pressure gauge are

used to meter a precisely repeatable volume of sample

air through the cryogenically-cooled trap, as follows:

With the sample valve closed and the vacuum valve

open, the reservoir is first evacuated with the vacuum

pump to a predetermined pressure (e.g., 100 mm Hg). 

Then the vacuum valve is closed and the sample valve

is opened to allow sample air to be drawn through the

cryogenic trap and into the evacuated reservoir until

a second predetermined reservoir pressure is reached

(e.g., 300 mm Hg). The (fixed) volume of air thus

sampled is determined by the pressure rise in the

vacuum reservoir (difference between the predetermined

pressures) as measured by the absolute pressure gauge

(see Section 12.2.1).

11.2.2 The sample volume can be calculated by:

where:

Vs = volume of air sampled (standard cm )

3

)P = pressure difference measured by gauge (mm Hg)

Vr = volume of vacuum reservoir (cm )

3

usually 1 L

Ps = standard pressure (760 mm Hg)

For example, with a vacuum reservoir of 1000 cm and a 3

pressure change of 200 mm Hg (100 to 300 mm Hg), the volume
TO12-17

sampled would be 263 cm . [Note: Typical sample volume 3

using this procedure is between 200-300 cm .] 3

11.2.3 The sample volume determination need only be performed

once during the system check-out and shall be part of

the user-prepared SOP Manual (see Section 12.1).

11.3 Analytical System Dynamic Calibration

11.3.1 Before sample analysis, a complete dynamic calibration

of the analytical system should be carried out at five

or more concentrations on each range to define the

calibration curve. This should be carried out

initially and periodically thereafter [may be done

only once during a series of analyses]. This should

be part of the user-prepared SOP Manual (See Section

12.1). The calibration should be verified with two or

three-point calibration checks (including zero) each

day the analytical system is used to analyze samples.

11.3.2 Concentration standards of propane are used to

calibrate the analytical system. Propane calibration

standards may be obtained directly from low

concentration cylinder standards or by dilution of

high concentration cylinder standards with zero air

(see Section 8.3). Dilution flow rates must be

measured accurately, and the combined gas stream must

be mixed thoroughly for successful calibration of the

analyzer. Calibration standards should be sampled

directly from a vented manifold or tee. Note:

Remember that a propane NMOC concentration in ppmC is

three times the volumetric concentration in ppm.

11.3.3 Select one or more combinations of the following

parameters to provide the desired range or ranges

(e.g., 0-1.0 ppmC or 0-5.0 ppmC): FID attenuator

setting, output voltage setting, integrator resolution

(if applicable), and sample volume. Each individual

range should be calibrated separately and should have

a separate calibration curve. Note: Modern GC

integrators may provide automatic ranging such that

several decades of concentration may be covered in a

single range. The user-prepared SOP manual should

address variations applicable to a specific system

design (see Section 12.1).
TO12-18

11.3.4 Analyze each calibration standard three times

according to the procedure in Section 11.4. Insure

that flow rates, pressure gauge start and stop

readings, initial cryogen liquid level in the Dewar,

timing, heating, integrator settings, and other

variables are the same as those that will be used

during analysis of ambient samples. Typical flow

rates for the gases are: hydrogen, 30 cm /minute; 3

helium carrier, 30 cm /minute; burner air, 3

400 cm /minute. 3

11.3.5 Average the three analyses for each concentration

standard and plot the calibration curve(s) as average

integrated peak area reading versus concentration in

ppmC. The relative standard deviation for the three

analyses should be less than 3% (except for zero

concentration). Linearity should be expected; points

that appear to deviate abnormally should be repeated. 

Response has been shown to be linear over a wide range

(0-10,000 ppbC). If nonlinearity is observed, an

effort should be made to identify and correct the

problem. If the problem cannot be corrected,

additional points in the nonlinear region may be

needed to define the calibration curve adequately.

11.4 Analysis Procedure

11.4.1 Insure the analytical system has been assembled

properly, leaked checked, and properly calibrated

through a dynamic standard calibration. Light the FID

detector and allow to stabilize.

11.4.2 Check and adjust the helium carrier pressure to

provide the correct carrier flow rate for the system. 

Helium is used to purge residual air and methane from

the trap at the end of the sampling phase and to carry

the re-volatilized NMOC from the trap into the FID. A

single-stage auxiliary regulator between the cylinder

and the analyzer may not be necessary, but is

recommended to regulate the helium pressure better

than the multistage cylinder regulator. When an

auxiliary regulator is used, the secondary stage of

the two-stage regulator must be set at a pressure

higher than the pressure setting of the single-stage
TO12-19

regulator. Also check the FID hydrogen and burner air

flow rates (see 11.3.4).

11.4.3 Close the sample valve and open the vacuum valve to

evacuate the vacuum reservoir to a specific

predetermined valve (e.g., 100 mm Hg).

11.4.4 With the trap at room temperature, place the six-port

valve in the inject position.

11.4.5 Open the sample valve and adjust the sample flow rate

needle valve for an appropriate trap flow of 50-100

cm /min. Note: The flow will be lower later, when 3

the trap is cold.

11.4.6 Check the sample canister pressure before attaching it

to the analytical system and record on Field Data

Sheet (see Figure 7). Connect the sample canister or

direct sample inlet to the six-port valve, as shown in

Figure 1. For a canister, either the canister valve

or an optional fine needle valve installed between the

canister and the vent is used to adjust the canister

flow rate to a value slightly higher than the trap

flow rate set by the sample flow rate needle valve. 

The excess flow exhausts through the vent, which

assures that the sample air flowing through the trap

is at atmospheric pressure. The vent is connected to

a flow indicator such as a rotameter as an indication

of vent flow to assist in adjusting the flow control

valve. Open the canister valve and adjust the

canister valve or the sample flow needle valve to

obtain a moderate vent flow as indicated by the

rotameter. The sample flow rate will be lower (and

hence the vent flow rate will be higher) when the trap

is cold.

11.4.7 Close the sample valve and open the vacuum valve (if

not already open) to evacuate the vacuum reservoir. 

With the six-port valve in the inject position and the

vacuum valve open, open the sample valve for 2-3

minutes [with both valves open, the pressure reading

won't change] to flush and condition the inlet lines.

11.4.8 Close the sample valve and evacuate the reservoir to

the predetermined sample starting pressure (typically

100 mm Hg) as indicated by the absolute pressure

gauge.
TO12-20

11.4.9 Switch the six-port valve to the sample position.

11.4.10 Submerge the trap in the cryogen. Allow a few minutes

for the trap to cool completely (indicated when the

cryogen stops boiling). Add cryogen to the initial

level used during system dynamic calibration. The

level of the cryogenic liquid should remain constant

with respect to the trap and should completely cover

the beaded portion of the trap.

11.4.11 Open the sample valve and observe the increasing

pressure on the pressure gauge. When it reaches the

specific predetermined pressure (typically 300 mm Hg)

representative of the desired sample volume (Section

11.2), close the sample valve.

11.4.12 Add a little cryogen or elevate the Dewar to raise the

liquid level to a point slightly higher (3-15 mm) than

the initial level at the beginning of the trapping. 

Note: This insures that organics do not bleed from

the trap and are counted as part of the NMOC peak(s).

11.4.13 Switch the 6-port valve to the inject position,

keeping the cryogenic liquid on the trap until the

methane and upset peaks have diminished (10-20

seconds). Now close the canister valve to conserve

the remaining sample in the canister.

11.4.14 Start the integrator and remove the Dewar flask

containing the cryogenic liquid from the trap.

11.4.15 Close the GC oven door and allow the GC oven (or

alternate trap heating system) to heat the trap at a

predetermined rate (typically, 30 C/min) to 90 . 

o o

Heating the trap volatilizes the concentrated NMOC

such that the FID produces integrated peaks. A

uniform trap temperature rise rate (above 0 C) helps o

to reduce variability and facilitates more accurate

correction for the moisture-shifted baseline. With a

chromatograph oven to heat the trap, the following

parameters have been found to be acceptable: initial

temperature, 30 C; initial time, 0.20 minutes o

(following start of the integrator); heat rate,

30 /minute; final temperature, 90 C. o o

11.4.16 Use the same heating process and temperatures for both

calibration and sample analysis. Heating the trap too

quickly may cause an initial negative response that
TO12-21

could hamper accurate integration. Some initial

experimentation may be necessary to determine the

optimal heating procedure for each system. Once

established, the procedure should be consistent for

each analysis as outlined in the user-prepared SOP

Manual.

11.4.17 Continue the integration (generally, in the range of

1-2 minutes is adequate) only long enough to include

all of the organic compound peaks and to establish the

end point FID baseline, as illustrated in Figure 8. 

The integrator should be capable of marking the

beginning and ending of peaks, constructing the

appropriate operational baseline between the start and

end of the integration period, and calculating the

resulting corrected peak area. This ability is

necessary because the moisture in the sample, which is

also concentrated in the trap, will cause a slight

positive baseline shift. This baseline shift starts

as the trap warms and continues until all of the

moisture is swept from the trap, at which time the

baseline returns to its normal level. The shift

always continues longer than the ambient organic

peak(s). The integrator should be programmed to

correct for this shifted baseline by ending the

integration at a point after the last NMOC peak and

prior to the return of the shifted baseline to normal

(see Figure 8) so that the calculated operational

baseline effectively compensates for the water-shifted

baseline. Electronic integrators either do this

automatically or they should be programmed to make

this correction. Alternatively, analyses of

humidified zero air prior to sample analyses should be

performed to determine the water envelope and the

proper blank value for correcting the ambient air

concentration measurements accordingly. Heating and

flushing of the trap should continue after the

integration period has ended to insure all water has

been removed to prevent buildup of water in the trap. 

Therefore, be sure that the 6-port valve remains in

the inject position until all moisture has purged from

the trap (3 minutes or longer).
TO12-22

11.4.18 Use the dynamic calibration curve (see Section 11.3)

to convert the integrated peak area reading into

concentration units (ppmC). Note that the NMOC peak

shape may not be precisely reproducible due to

variations in heating the trap, but the total NMOC

peak area should be reproducible.

11.4.19 Analyze each canister sample at least twice and report

the average NMOC concentration. Problems during an

analysis occasionally will cause erratic or

inconsistent results. If the first two analyses do

not agree within + 5% relative standard deviation

(RSD), additional analyses should be made to identify

inaccurate measurements and produce a more accurate

average (see also Section 12.2).

12. Performance Criteria and Quality Assurance

This section summarizes required quality assurance measures and provides

guidance concerning performance criteria that should be achieved within

each laboratory.

12.1 Standard Operating Procedures (SOPs)

12.1.1 Users should generate SOPs describing and documenting

the following activities in their laboratory: (1)

assembly, calibration, leak check, and operation of

the specific sampling system and equipment used; (2)

preparation, storage, shipment, and handling of

samples; (3) assembly, leak check, calibration, and

operation of the analytical system, addressing the

specific equipment used; (4) canister storage and

cleaning; and (5) all aspects of data recording and

processing, including lists of computer hardware and

software used.

12.1.2 SOPs should provide specific stepwise instructions and

should be readily available to, and understood by, the

laboratory personnel conducting the work.

12.2 Method Sensitivity, Accuracy, Precision and Linearity

12.2.1 The sensitivity and precision of the method is

proportional to the sample volume. However, ice

formation in the trap may reduce or stop the sample

flow during trapping if the sample volume exceeds 500

cm . Sample volumes below about 100-150 cm may cause 3 3

increased measurement variability due to dead volume

in lines and valves. For most typical ambient NMOC
TO12-23

concentrations, sample volumes in the range of 200-400

cm appear to be appropriate. If a response peak 3

obtained with a 400 cm sample is off scale or exceeds 3

the calibration range, a second analysis can be

carried out with a smaller volume. The actual sample

volume used need not be accurately known if it is

precisely repeatable during both calibration and

analysis. Similarly, the actual volume of the vacuum

reservoir need not be accurately known. But the

reservoir volume should be matched to the pressure

range and resolution of the absolute pressure gauge so

that the measurement of the pressure change in the

reservoir, hence the sample volume, is repeatable

within 1%. A 1000 cm vacuum reservoir and a pressure 3

change of 200 mm Hg, measured with the specified

pressure gauge, have provided a sampling precision of

+ 1.31 cm . A smaller volume reservoir may be used 3

with a greater pressure change to accommodate absolute

pressure gauges with lower resolution, and vice versa.

12.2.2 Some FID detector systems associated with laboratory

chromatographs may have autoranging. Others may

provide attenuator control and internal full-scale

output voltage selectors. An appropriate combination

should be chosen so that an adequate output level for

accurate integration is obtained down to the detection

limit; however, the electrometer or integrator must

not be driven into saturation at the upper end of the

calibration. Saturation of the electrometer may be

indicated by flattening of the calibration curve at

high concentrations. Additional adjustments of range

and sensitivity can be provided by adjusting the

sample volume use, as discussed in Section 12.2.1.

12.2.3 System linearity has been documented (6) from 0 to

10,000 ppbC.

12.2.4 Some organic compounds contained in ambient air are

"sticky" and may require repeated analyses before they

fully appear in the FID output. Also, some adjustment

may have to be made in the integrator off time setting

to accommodate compounds that reach the FID late in

the analysis cycle. Similarly, "sticky" compounds

from ambient samples or from contaminated propane
TO12-24

standards may temporarily contaminate the analytical

system and can affect subsequent analyses. Such

temporary contamination can usually be removed by

repeated analyses of humidified zero air.

12.2.5 Simultaneous collection of duplicate samples decreases

the possibility of lost measurement data from samples

lost due to leakage or contamination in either of the

canisters. Two (or more) canisters can be filled

simultaneously by connecting them in parallel (see

Figure 2(a)) and selecting an appropriate flow rate to

accommodate the number of canisters (Section 10.2.2). 

Duplicate (or replicate) samples also allow assessment

of measurement precision based on the differences

between duplicate samples (or the standard deviations

among replicate samples).

13. Method Modification

13.1 Sample Metering System

13.1.1 Although the vacuum reservoir and absolute pressure

gauge technique for metering the sample volume during

analysis is efficient and convenient, other techniques

should work also.

13.1.2 A constant sample flow could be established with a

vacuum pump and a critical orifice, with the six-port

valve being switched to the sample position for a

measured time period. A gas volume meter, such as a

wet test meter, could also be used to measure the

total volume of sample air drawn through the trap. 

These alternative techniques should be tested and

evaluated as part of a user-prepared SOP manual.

13.2 FID Detector System

13.2.1 A variety of FID detector systems should be adaptable

to the method.

13.2.2 The specific flow rates and necessary modifications

for the helium carrier for any alternative FID

instrument should be evaluated prior to use as apart

of the user-prepared SOP manual.

13.3 Range

13.3.1 It may be possible to increase the sensitivity of the

method by increasing the sample volume. However,

limitations may arise such as plugging of the trap by

ice.
TO12-25

13.3.2 Any attempt to increase sensitivity should be

evaluated as part of the user-prepared SOP manual.

13.4 Sub-Atmospheric Pressure Canister Sampling

13.4.1 Collection and analysis of canister air samples at

sub-atmospheric pressure is also possible with minor

modifications to the sampling and analytical

procedures.

13.4.2 Method TO-14, "Integrated Canister Sampling for

Selective Organics: Pressurized and Sub-atmospheric

Collection Mechanism," addresses sub-atmospheric

pressure canister sampling. Additional information

can be found in the literature (11-17).
TO12-26

1. Uses, Limitations, and Technical Basis of Procedures for Quantifying

Relationships Between Photochemical Oxidants and Precursors, EPA-450/2-

77-21a, U.S. Environmental Protection Agency, Research Triangle Park,

NC, November 1977.

2. Guidance for Collection of Ambient Non-Methane Organic Compound (NMOC)

Data for Use in 1982 Ozone SIP Development, EPA-450/4-80-011, U.S.

Environmental Protection Agency, Research Triangle Park, NC, June 1980.

3. H.B. Singh, Guidance for the Collection and Use of Ambient Hydrocarbons

Species Data in Development of Ozone Control Strategies, EPA-450/4-80-

008, U.S. Environmental Protection Agency, Research Triangle Park, NC,

April 1980.

4. R.M. Riggin, Technical Assistance Document for Sampling and Analysis of

Toxic Organic Compounds in Ambient Air, EPA-600/4-83-027, U.S.

Environmental Protection Agency, Research Triangle Park, NC, 1983.

5. M.J. Jackson, et al., Technical Assistance Document for Assembly and

Operation of the Suggested Preconcentration Direct Flame Ionization

Detection (PDFID) Analytical System, publication scheduled for late

1987; currently available in draft form from the Quality Assurance

Division, MD-77, U.S. Environmental Protection Agency, Research Triangle

Park, NC 27711. 

6. R.K.M. Jayanty, et al., Laboratory Evaluation of Non-Methane Organic

Carbon Determination in Ambient Air by Cryogenic Preconcentration and

Flame Ionization Detection, EPA-600/54-82-019, U.S. Environmental

Protection Agency, Research Triangle Park, NC, July 1982.

7. R.D. Cox, et al., "Determination of Low Levels of Total Non-Methane

Hydrocarbon Content in Ambient Air," Environ. Sci. Technol., 16 (1):57.

1982.

8. F.F. McElroy, et al., A Cryogenic Preconcentration - Direct FID (PDFID)

Method for Measurement of NMOC in the Ambient Air, EPA-600/4-85-063,

U.S. Environmental Protection Agency, Research Triangle Park, NC, August

1985.

9. F.W. Sexton, et al., A Comparative Evaluation of Seven Automated Ambient

Non-Methane Organic Compound Analyzers, EPA-600/54-82-046, U.S.

Environmental Protection Agency, Research Triangle Park, NC, August

1982.

10. H.G. Richter, Analysis of Organic Compound Data Gathered During 1980 in

Northeast Corridor Cities, EPA-450/4-83-017, U.S. Environmental

Protection Agency, Research Triangle Park, NC, April 1983.

11. Cox, R.D. "Sample Collection and Analytical Techniques for Volatile

Organics in Air," presented at APCA Specialty Conference, Chicago, IL,

March 22-24, 1983.

12. Rasmussen, R.A. and Khalil, M.A.K. "Atmospheric Halocarbons: 

Measurements and Analyses of Selected Trace Gases," Proc. NATO ASI on

Atmospheric Ozone, 1980, 209-231.

13. Oliver, K.D., Pleil, J.D. and McClenny, W.A. "Sample Integrity of Trace

Level Volatile Organic Compounds in Ambient Air Stored in "SUMMA "

®

Polished Canisters," accepted for publication in Atmospheric Environment

as of January 1986. Draft available from W.A. McClenny, MD-44, EMSL,

EPA, Research Triangle Park, NC 27711.
TO12-27

14. McClenny, W.A. Pleil, J.D., Holdren, J.W. and Smith, R.N.; 1984.

"Automated Cryogenic Preconcentration and Gas Chromatographic

Determination of Volatile Organic Compounds," Anal. Chem. 56:2947.

15. Pleil, J.D. and Oliver, K.D., 1985, "Evaluation of Various

Configurations of Nafion Dryers: Water Removal from Air Samples Prior

to Gas Chromatographic Analysis." EPA Contract No. 68-02-4035.

16. Oliver, K.D.; Pleil, J.D. and McClenny, W.A.; 1986. "Sample Integrity

of Trace Level Volatile Organic Compounds in Ambient Air Stored in

"SUMMA " Polished Canisters," Atmospheric Environ. 20:1403. ®

17. Oliver, K.D. and Pleil, J.D., 1985, "Automated Cryogenic Sampling and

Gas Chromatographic Analysis of Ambient Vapor-Phase Organic Compounds:

Procedures and Comparison Tests," EPA Contract No. 68-02-4035, Research

Triangle Park, NC, Northrop Services, Inc. - Environmental Sciences. 
TO12-28
TO12-29
TO12-30
TO12-31
TO12-32
TO12-33
TO12-34

PRESSURIZED CANISTER SAMPLING DATA SHEET

GENERAL INFORMATION:

PROJECT: OPERATOR: 

SITE: ORIFICE IDENTIFICATION: 

LOCATION: FLOW RATE: 

MONITOR STATION NUMBER: CALIBRATED BY: 

PUMP SERIAL NUMBER: LEAK CHECK 

 Pass Fail

FIELD DATA:

Date

Canister

Serial

Number

Sample

Number

Sample Time Average Atmospheric Conditions

Canister pressure

Final, Laboratory Comments

Start Stop Temperature Pressure Relative Humidity

 

Date Title Signature

FIGURE 7. EXAMPLE SAMPLING DATA SHEET
TO12-35
APPENDIX D

Compendium Method TO-11A

Determination of Formaldehyde in Ambient Air Using Adsorbent Cartridge

Followed by High Performance Liquid Chromatography (HPLC)

[Active Sampling Methodology]
EPA/625/R-96/010b

Compendium of Methods

for the Determination of

Toxic Organic Compounds

in Ambient Air

Second Edition

Compendium Method TO-11A

Determination of Formaldehyde in Ambient Air

Using Adsorbent Cartridge Followed by High

Performance Liquid Chromatography (HPLC)

[Active Sampling Methodology]

Center for Environmental Research Information

Office of Research and Development

U.S. Environmental Protection Agency

Cincinnati, OH 45268

January 1997
iii

Method TO-11A

Acknowledgements

This Method was prepared for publication in the Compendium of Methods for the Determination of Toxic

Organic Compounds in Ambient Air, Second Edition (EPA/625/R-96/010b), which was prepared under

Contract No. 68-C3-0315, WA No. 3-10, by Midwest Research Institute (MRI), as a subcontractor to Eastern

Research Group, Inc. (ERG), and under the sponsorship of the U.S. Environmental Protection Agency (EPA).

Justice A. Manning and John O. Burckle, Center for Environmental Research Information (CERI), and Frank

F. McElroy, National Exposure Research Laboratory (NERL), both in the EPA Office of Research and

Development, were the project officers responsible for overseeing the preparation of this method. Additional

support was provided by other members of the Compendia Workgroup, which include:

• John O. Burckle, U.S. EPA, ORD, Cincinnati, OH

• James L. Cheney, Corps of Engineers, Omaha, NB

• Michael Davis, U.S. EPA, Region 7, KC, KS

• Joseph B. Elkins Jr., U.S. EPA, OAQPS, RTP, NC

• Robert G. Lewis, U.S. EPA, NERL, RTP, NC

• Justice A. Manning, U.S. EPA, ORD, Cincinnati, OH

• William A. McClenny, U.S. EPA, NERL, RTP, NC

• Frank F. McElroy, U.S. EPA, NERL, RTP, NC

• Heidi Schultz, ERG, Lexington, MA

• William T. "Jerry" Winberry, Jr., MRI, Cary, NC

Method TO-11 was originally published in March of 1989 as one of a series of peer reviewed methods in the

second supplement to "Compendium of Methods for the Determination of Toxic Organic Compounds in

Ambient Air," EPA 600/4-89-018. In an effort to keep these methods consistent with current technology,

Method TO-11 has been revised and updated as Method TO-11A in this Compendium to incorporate new or

improved sampling and analytical technologies.

This Method is the result of the efforts of many individuals. Gratitude goes to each person involved in the

preparation and review of this methodology.

Author(s)

• William T. "Jerry" Winberry, Jr., Midwest Research Institute, Cary, NC

• Silvestre Tejada, U.S. EPA, NERL, RTP, NC

• Bill Lonneman, U.S. EPA, NERL, RTP, NC

• Ted Kleindienst, ManTech, RTP, NC

Peer Reviewers

• Robert G. Lewis, U.S. EPA, NERL, RTP, NC

• Sucha S. Parmar, Atmospheric Analysis and Consulting, Ventura, CA

• Joette Steger, Eastern Research Group, Morrisville, NC

Finally, recognition is given to Frances Beyer, Lynn Kaufman, Debbie Bond, Cathy Whitaker, and Kathy

Johnson of Midwest Research Institute's Administrative Services staff whose dedication and persistence during

the development of this manuscript has enabled it's publication.
iv

DISCLAIMER

This Compendium has been subjected to the Agency's peer and administrative review, and it has been

approved for publication as an EPA document. Mention of trade names or commercial products does

not constitute endorsement or recommendation for use.
v

Method TO-11A

Determination of Formaldehyde in Ambient Air Using Adsorbent Cartridge Followed by High

Performance Liquid Chromatography (HPLC) [Active Sampling Methodology]

TABLE OF CONTENTS

Page

1. Scope .................................................................. 11A-1

2. Applicable Documents ...................................................... 11A-3

2.1 ASTM Standards ...................................................... 11A-3

2.2 Other Documents ...................................................... 11A-3

2.3 Other Documents ...................................................... 11A-3

3. Summary of Method ........................................................ 11A-3

4. Significance ............................................................... 11A-4

5. Definitions ................................................................ 11A-6

5.1 C18 ................................................................ 11A-6

5.2 HPLC ............................................................... 11A-6

5.3 Method Detection Limit (MDL) .......................................... 11A-6

5.4 Photochemical Reaction ................................................ 11A-6

5.5 Photochemical Smog ................................................... 11A-6

5.6 ppbv ................................................................ 11A-6

5.7 ppmv ............................................................... 11A-6

5.8 Silica Gel ............................................................ 11A-7

5.9 Denuder ............................................................. 11A-7

5.10 Certification Blank ................................................... 11A-7

5.11 Cartridge Blank ...................................................... 11A-7

5.12 Scrubber ........................................................... 11A-7

6. Extended Methodology and Common Interferences ................................ 11A-7

7. Apparatus ................................................................ 11A-8

7.1 Isocratic HPLC ....................................................... 11A-8

7.2 Cartridge sampler. .................................................... 11A-9

7.3 Sampling system ...................................................... 11A-10

7.4 Stopwatch. ........................................................... 11A-11

7.5 Polypropylene shipping container 

with polyethylene-air bubble padding. ................................... 11A-11

7.6 Thermometer ......................................................... 11A-11

7.7 Barometer (optional). ................................................... 11A-11

7.8 Volumetric flasks. ..................................................... 11A-11

7.9 Pipets. .............................................................. 11A-11

7.10 Erlenmeyer flask, 1 L. ................................................. 11A-11

7.11 Graduated cylinder, 1 L. ............................................... 11A-11

7.12 Syringe, 100-250 FL. ................................................. 11A-11

7.13 Sample vials. ....................................................... 11A-11
TABLE OF CONTENTS (continued)

Page

vi

7.14 Melting point apparatus ............................................... 11A-11

7.15 Rotameters .......................................................... 11A-11

7.16 Calibrated syringes ................................................... 11A-11

7.17 Soap bubble meter or wet test meter ...................................... 11A-11

7.18 Mass flow meters and mass flow controllers ................................ 11A-11

7.19 Positive displacement ................................................. 11A-12

7.20 Cartridge drying manifold .............................................. 11A-12

7.21 Liquid syringes ...................................................... 11A-12

7.22 Syringe rack ......................................................... 11A-12

7.23 Luer® fittings/plugs. .................................................. 11A-12

7.24 Hot plates, beakers, flasks, measuring and 

disposable pipets, volumetric flasks, etc. ................................... 11A-12

7.25 Culture tubes (20 mm x 125 mm) with polypropylene screw caps ............... 11A-12

7.26 Polyethylene gloves. .................................................. 11A-12

7.27 Dry test meter. ....................................................... 11A-12

7.28 User-prepared copper tubing for ozone scrubber ............................. 11A-12

7.29 Cord heater and Variac. ............................................... 11A-12

7.30 Fittings. ............................................................ 11A-12

8. Reagents and Materials ...................................................... 11A-12

8.1 2,4-Dinitrophenylhydrazine (DNPH) ...................................... 11A-13

8.2 DNPH coated cartridges ................................................

8.3 High purity acetonitrile. ................................................ 11A-13

8.4 Deionized-distilled water. ............................................... 11A-13

8.5 Perchloric acid. ....................................................... 11A-13

8.6 Ortho-phosphoric acid. ................................................. 11A-13

8.7 Formaldehyde. ....................................................... 11A-13

8.8 Aldehydes and ketones, analytical grade, best source. ......................... 11A-13

8.9 Carbonyl hydrazone ....................................................

 8.10Ethanol or methanol ................................................... 11A-13

8.11 Nitrogen ............................................................ 11A-13

8.12 Charcoal ........................................................... 11A-13

8.13 Helium ............................................................. 11A-13

8.14 Potassium Iodide ..................................................... 11A-13

9. Preparation of Reagents and Cartridges .......................................... 11A-13

9.1 Purity of the Acetonitrile ................................................ 11A-13

9.2 Purification of 2,4-Dinitrophenylhydrazine (DNPH) ........................... 11A-14

9.3 Preparation of DNPH-Formaldehyde Derivative .............................. 11A-16

9.4 Preparation of DNPH-Formaldehyde Standards .............................. 11A-16

9.5 Preparation of DNPH-Coated Cartridges .................................... 11A-16

9.6 Equivalent Formaldehyde Cartridge Concentration ............................ 11A-19

10. Sampling Procedure ....................................................... 11A-19

11. Sample Analysis .......................................................... 11A-22
TABLE OF CONTENTS (continued)

Page

vii

11.1 Sample Preparation ................................................... 11A-22

11.2 Sample Extraction .................................................... 11A-23

11.3 HPLC Analysis ...................................................... 11A-24

11.4 HPLC Calibration .................................................... 11A-25

12. Calculations .............................................................. 11A-26

13. Performance Criteria and Quality Assurance ..................................... 11A-28

13.1 Standard Operating Procedures (SOPs). ................................... 11A-28

13.2 HPLC System Performance ............................................. 11A-29

13.3 Process Blanks ....................................................... 11A-29

13.4 Method Precision and Accuracy ......................................... 11A-29

13.5 Method Detection Limits ............................................... 11A-30

13.6 General QA/QC Requirements .......................................... 11A-30

14. Detection of Other Aldehydes and Ketones ..................................... 11A-31

14.1 Introduction ......................................................... 11A-31

14.2 Sampling Procedures .................................................. 11A-32

14.3 HPLC Analysis ...................................................... 11A-32

15. Precision and Bias ......................................................... 11A-33

16. References ............................................................... 11A-33
January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 11A-1

METHOD TO-11A

Determination of Formaldehyde in Ambient Air Using Adsorbent

Cartridge Followed by High Performance Liquid 

Chromatography (HPLC)

[Active Sampling Methodology]

1. Scope

1.1 This document describes a method for the determination of formaldehyde and other carbonyl compounds

(aldehydes and ketones) in ambient air utilizing a coated-solid adsorbent followed by high performance liquid

chromatographic detection. Formaldehyde has been found to be a major promoter in the formation of

photochemical ozone. In particular, short term exposure to formaldehyde and other specific aldehydes

(acetaldehyde, acrolein, crotonaldehyde) is known to cause irritation of the eyes, skin, and mucous membranes

of the upper respiratory tract.

1.2 Over the last several years, numerous methods have been developed for the sampling and analysis of

carbonyl compounds. Because of the role which formaldehyde plays in photochemistry, most of the more

recent methods were designed to quantitate formaldehyde specifically. Early methods centered around wet

chemical technology involving a bubbler or impinger containing a reactive reagent (1). In some cases the

reactive reagent produced a color in the presence of formaldehyde. Examples of the more commonly used

reagents were: 3-methyl-2-benzothiazolone hydrazone (MBTH), sodium sulfite, 4-hexylresorcinol, water,

sodium tetrachloromercurate, and chromatropic acid. These reagents demonstrated high collection efficiency

(>95%), provided fairly stable non-volatile products and minimized formation of undesirable by-products.

Indeed, as part of U. S. Environmental Protection Agency's (EPA's) effort to quantitate atmospheric

concentrations of formaldehyde, the National Air Sampling Network utilized the impinger technique for

several years containing chromatrophic acid specifically for formaldehyde. However, impinger sampling had

numerous weaknesses which eventually lead to its demise. They were:

• Labor intense.

• Used acidic/hazardous reagents.

• Lacked sensitivity.

• Prone to interferences.

• Poor reproducibility at ambient concentration levels.

As EPA's interest focused upon formaldehyde and it's sources, the development of passive personal

sampling devices (PSDs) developed (2). These devices were mainly used by industrial hygienists to assess

the efforts of respiratory exposure for formaldehyde on workers. However, because of the design and flow rate

limitation, they require long exposures (up to 7 days) to the atmosphere to meet traditional bubbler technique

sensitivities. Consequently, the passive PSD had limited application to ambient monitoring.

To address the need for a monitoring method to sample carbonyl compounds in the air at sensitivities

needed to reach health-base detection limits (10 risk level), a combination of wet chemistry and solid

-6

adsorbent methodology was developed (3-6). Activating or wetting the surface of an adsorbent with a

chemical specific for reacting with carbonyl compounds allowed greater volumes of air to be sampled, thus

enabling better sensitivity in the methodology. Various chemicals and adsorbents combinations have been

utilized with various levels of success. The most commonly used technique is based on reacting airborne

carbonyls with 2,4-dinitrophenylhydrazine (2,4-DNPH) coated on an adsorbent cartridge followed by

separation and analysis of the hydrazone derivative by high performance liquid chromatography (HPLC) with

ultraviolet (UV) detection.

1.3 Historically, Compendium Method TO-5, "Method For the Determination of Aldehydes and Ketones in

Ambient Air Using High Performance Liquid Chromatography (HPLC)" was used to quantitate formaldehyde
Method TO-11A Formaldehyde

Page 11A-2 Compendium of Methods for Toxic Organic Air Pollutants January 1997

in ambient air. This method involved drawing ambient air through a midget impinger sampling train

containing 10 mL of 2N HCl/0.05% 2,4-DNPH reagent. Formaldehyde (and other aldehydes and ketones)

readily formed a stable derivative with the DNPH reagent, and the DNPH derivative is analyzed for aldehydes

and ketones utilizing HPLC. Compendium Method T0-11 modifies the sampling procedures outlined in

Method TO-5 by introducing a coated adsorbent. Compendium Method TO-11 is based on the specific

reaction of organic carbonyl compounds (aldehydes and ketones) with DNPH-coated silica gel cartridges in

the presence of a strong acid, as a catalyst, to form a stable color hydrazone derivative according to the

following reaction:

where R and R are organic alkyl or aromatic group (ketones) or either substituent is a hydrogen (aldehydes). 1

The reaction proceeds by nucleophilic addition to the carbonyl followed by 1,2-elimination of water to form

the 2,4-diphenylhydrazone derivative. The determination of formaldehyde from the DNPH-formaldehyde

derivative is similar to Method TO-5 in incorporating HPLC as the analytical methodology. 

1.4 Due to recent requirements in atmospheric carbonyl monitoring, EPA has determined a need to update

the present methodology found in Compendium Method TO-11. The revised Compendium Method TO-11A,

as published here, includes:

• Guidance on collocated sampling.

• Addition of ozone denuder or scrubber to reduce interferences.

• Sampler design update to allow heated-inlet and sequential sampling.

• Update HPLC procedure for column alternatives.

• Use of commercially prepared low pressure drop DNPH-coated cartridges.

The target compound for this method is formaldehyde; however, at least 14 other carbonyl compounds can

be detected and quantified.

1.5 The sampling method gives a time-weighted average (TWA) sample. It can be used for long-term 

(1-24 hr) sampling of ambient air where the concentration of formaldehyde is generally in the low ppb (v/v)

or for short-term (5-60 min) sampling of source-impacted atmospheres where the concentration of

formaldehyde could reach the ppm (v/v) levels.

1.6 The method instructs the user to purchase commercially pre-coated DNPH cartridges. The method still

includes the instructions of Compendium Method TO-11 for the preparation of DNPH-coated cartridges.

However due to the tedious preparation and clean room requirements, the method recommends the purchase

of pre-coated DNPH cartridges that are now commercially available from at least three major suppliers.

Different from previous cartridges identified in Compendium Method TO-11, the pressure drop across the

newer low-pressure drop cartridges are less than 37 inches of water at a sampling flow of up to 2.0
Formaldehyde Method TO-11A

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 11A-3

liters/minute, allowing compatibility with pumps used in personal sampling equipment. These pre-coated

commercial cartridges have generally lower and more consistent background (7) concentration of carbonyls

than cartridges prepared under normal chemical laboratory environment, as specified in the original

Compendium Method TO-11.

1.7 The commercially-prepared pre-coated cartridges are used as received and are discarded after use. The

collected and uncollected cartridges are stored in culture tubes with polypropylene caps and placed in cold

storage when not in use.

1.8 This method may involve hazardous materials, operations, and equipments. This method does not purport

to address all the safety problems associated with its use. It is the responsibility of whoever uses this method

to consult and establish appropriate safety and health practices and determine the applicability of regulatory

limitations prior to use.

2. Applicable Documents

2.1 ASTM Standards

• D1193 Specification for Reagent Water

• D1356 Terminology Relating to Atmospheric Sampling and Analysis

• D3195 Practice for Rotameter Calibration

• D3631 Method for Measuring Surface Atmospheric Pressure

• D5197 Determination of Formaldehyde and Other Carbonyl Compounds in Air (Active Sampler

Methodology)

• E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods

• E682 Practice for Liquid Chromatography Terms and Relationships

2.2 Other Documents

• Technical Assistance Document for Sampling and Analysis Toxic Organic Compounds in Ambient Air,

U. S. Environmental Protection Agency, EPA-600/4-83-027, June 1983.

• Quality Assurance Handbook for Air Pollution Measurement Systems, U. S. Environmental Protection

Agency, EPA-600/R-94-D38b, May 1994.

• Compendium of Methods for the Determination of Toxic Organic Compounds in Ambient Air: Method

TO-11, Second Supplement, U. S. Environmental Protection Agency, EPA-600/4-89-018, March 1989.

2.3 Other Documents

• Existing Procedures (8-10).

• Ambient Air Studies (11-15).

3. Summary of Method

3.1 A known volume of ambient air is drawn through a prepacked cartridge coated with acidified DNPH at

a sampling rate of 100-2000 mL/min for an appropriate period of time. Sampling rate and time are dependent

upon carbonyl concentration in the test atmosphere.
Method TO-11A Formaldehyde

Page 11A-4 Compendium of Methods for Toxic Organic Air Pollutants January 1997

3.2 After sampling, the sample cartridges and field blanks are individually capped and placed in shipping

tubes with polypropylene caps. Sample identifying tags and labels are then attached to the capped tubes. The

capped tubes are then placed in a polypropylene shipping container cooled to subambient temperature (~4EC),

and returned to the laboratory for analysis. Alternatively, the sample vials can be placed in a thermallyinsulated styrofoam box with appropriate padding for shipment to the laboratory. The cartridges may either

be placed in cold storage until analysis or immediately washed by gravity feed elution with 5 mL of acetonitrile

from a plastic syringe reservoir to a graduated test tube or a 5 mL volumetric flask.

3.3 The eluate is then diluted to a known volume and refrigerated until analysis.

3.4 For determining formaldehyde, the DNPH-formaldehyde derivative can be determined using isocratic

reverse phase HPLC with an ultraviolet (UV) absorption detector operated at 360 nm. To determine

formaldehyde and 14 other carbonyls, the HPLC system is operated in the linear gradient program mode.

3.5 For quantitative evaluation of formaldehyde and other carbonyl compounds, a cartridge blank is likewise

desorbed and analyzed.

3.6 Formaldehyde and other carbonyl compounds in the sample are identified and quantified by comparison

of their retention times and peak heights or peak areas with those of standard solutions. Typically, C1-C7

carbonyl compounds, including benzaldehyde, are measured effectively to less than 0.5 ppbv. 

4. Significance

4.1 Formaldehyde is a major compound in the formation of photochemical ozone (16). Short term exposure

to formaldehyde and other specific aldehydes (acetaldehyde, acrolein, crotonaldehyde) is known to cause

irritation of the eyes, skin, and mucous membranes of the upper respiratory tract (19). Animal studies indicate

that high concentrations can injure the lungs and other organs of the body (19). In polluted atmospheres,

formaldehyde may contribute to eye irritation and unpleasant odors that are common annoyances.

4.2 Over the last several years, carbonyl compounds including low molecular weight aldehydes and ketones

have received increased attention in the regulatory community. This is due in part to their effects on humans

and animals as primary irritation of the mucous membranes of the eyes, the upper respiratory tract, and the

skin. Animal studies indicate that high concentrations of carbonyl compounds, especially formaldehyde, can

injure the lungs, may contribute to eye irritation and effect other organs of the body. Aldehydes, either directly

of indirectly, may also cause injury to plants. Sources of carbonyl compounds into the atmosphere range from

natural occurrences to secondary formation through atmospheric photochemical reactions. Consequently,

carbonyl compounds are both primary (directly emitted) and secondary (formed in the atmosphere) air

pollutants (19).

4.2.1 Natural Occurrence. Natural sources of carbonyls do not appear to be important contributors to

air pollution. Acetaldehyde is found in apples and as a by-product of alcoholic fermentation process. Other

lower molecular weight aliphatic aldehydes are not found in significant quantities in natural products. Olefinic

and aromatic aldehydes are present in some of the essential oils in fruits and plants. These include citronella,

in rose oil; citral, in oil of lemongrass; benzaldehyde, in oil of bitter almonds; and cinnamaldehyde, in oil of

cinnamon.

4.2.2 Production Sources. Aldehydes are commercially manufactured by various processes, depending

on the particular aldehyde. In general, they are prepared via oxidation reactions of hydrocarbons,

hydroformulation of alkenes, dehydrogenation of alcohols, and addition reactions between aldehydes and other
[cat.]

CH3OH 6 CH2O % H2

Formaldehyde Method TO-11A

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 11A-5

compounds. Formaldehyde is manufactured from the oxidation of methanol as illustrated in the following

equation:

Formaldehyde and other aldehyde production in the United States has shown a substantial growth over the last

several years. This is due, in part, to their use in a wide variety of industries, such as the chemical, rubber,

tanning, paper, perfume, and food industries. The major use is as an intermediate in the synthesis of organic

compounds, including, alcohols, carboxylic acids, dyes, and medicinals.

4.2.3 Mobile Combustion Sources. A major source of carbonyl compounds in the atmosphere may be

attributed to motor vehicle emissions. In particular, formaldehyde is the major carbonyl in automobile exhaust,

accounting for 50-70 percent of the total carbonyl burden to the atmosphere (19). Furthermore, motor vehicles

emit reactive hydrocarbons that undergo photochemical oxidation to produce formaldehyde and other

carbonyls in the atmosphere.

4.3 Secondary Pollutant. As a secondary pollutant (formed in the atmosphere), carbonyls are formed by very

complex photo-oxidation mechanism involving volatile organic compounds (VOCs) with nitrogen oxide

(20,21). Both anthropogenic and biogenic (e.g., isoprene) hydrocarbons leads to in situ formation of carbonyls,

especially formaldehyde compounds. Aldehydes are both primary pollutants and secondary products of

atmospheric photochemistry. 

The complete photo-oxidation mechanism is indeed complex and not well understood. However, a brief

discussion is warranted (22). When VOCs and oxides of nitrogen (NOx) are in the atmosphere and are

irradiated with sunlight, their equilibrium in the photostationary state is changed. The photostationary state

is defined by the equilibrium between nitrogen dioxide (NO ), nitrous oxide (NO) and ozone (O ). This 2 3

equilibrium is theoretically maintained until VOCs are introduced. Various reactions occur to produce OH

radicals. The VOCs react with the OH radicals and produce RO2 radicals that oxidizes NO to NO2, destroying

the photostationary state. Carbonyls react with OH to produce RO2 radicals. Likewise carbonyls, particularly

formaldehyde in sunlight, are sources of the OH radicals.

The results of these processes lead to the following:

• Accumulation of ozone.

• Oxidation of hydrocarbons (HCs) to aldehydes and ketones which lead to the continued production of

HO @ and OH@ radicals, the real driving force in photochemistry smog. 2

Consequently, the determination of formaldehyde and other carbonyl compounds in the atmosphere is of

interest because of their importance as precursors in the production of photochemical smog, as photochemical

reaction products and as major source of free radicals in the atmosphere.

4.4 Historically, DNPH impinger techniques have been widely used to determine atmospheric carbonyls.

However, due to the limitation of applying this technique to remote locations, the solid adsorbent methodology

has become a convenient alternative to impinger sampling. A number of solid adsorbents have been used over

the years to support the DNPH coating. They are: glass beads, glass fiber filters, silica gel, Chromosorb® P,

Florisil®, Carbopack® B, XAD-2, and C18. Several of these adsorbents are available commercially as prepacked cartridges. The commercially available cartridges provide convenience of use, reproducibility and low

formaldehyde blanks. Two of the more widely used pre-packed adsorbents are silica gel and C18.

4.4.1 Silica Gel. Silica gel is a regenerative adsorbent, consisting of amorphous silica (SiO2) with surface

OH groups, making it a polar material and enhancing surface absorption. DNPH-coated silica gel cartridges
Method TO-11A Formaldehyde

Page 11A-6 Compendium of Methods for Toxic Organic Air Pollutants January 1997

have been used by numerous investigators since 1980 for sampling formaldehyde in ambient air. Tejada (3,4)

evaluated several adsorbents, including C18, Florsil, silanized glass wool, and silica gel as possible supports

for the DNPH coating. Results indicated that silica gel provided the best support with minimum interferences.

The studies did document that olefinic aldehydes such as acrolein and crotonaldehyde degraded partially and

formed unknown species. For stable carbonyls such as formaldehyde, acetaldehyde, propionaldehyde,

benzaldehyde, and acetone, correlation with an DNPH-impinger technique was excellent. However, further

studies by Arnts and Tejada identified a severe loss of carbonyl-DNPH derivative due to the reaction of

atmospheric ozone on DNPH-coated silica gel cartridges while sampling ambient air. This bias was eliminated

when sampling continued with the application of an ozone scrubber system (KI denuder) preceding the

cartridge.

4.4.2 C18 Cartridge. C18 is an octadecylsilane bonded silica substrate which is non-polar, hydrophobic,

and relatively inert, whose surface has been passivated with non-polar paraffinic groups. Because of these

qualities, C18 has been used historically as an adsorbent trap for trace organics in environmental aqueous

samples through hydrophobic interactions. The adsorbed trace organic molecules are then eluted from the

adsorbent with various organic solvents. In early 1990, C18 was used in an ambient air study as the support

for DNPH. While C18 showed promising results (23), it's use today as the support for DNPH is limited.

4.5 Both adsorbents have historically performed adequately as the support for the DNPH coating. The

comparison between silica gel and C18 as the adsorbent for the DNPH is illustrated in Table 1. The user is

encouraged to review the weaknesses and strengths outlined in Table 1 for using silica gel or C18 as the

adsorbent for the DNPH coating.

5. Definitions

[Note: Definitions used in this document and any user-prepared Standard Operating Procedures (SOPs)

should be consistent with those used in ASTM D1356. All abbreviations and symbols are defined within this

document at the point of first use.]

5.1 C18— C18 is an octadecylsilane bonded silica substrate, which is non-polar, hydrophobic, and relatively

inert. 

5.2 HPLC— high performance liquid chromatography.

5.3 Method Detection Limit (MDL)— the minimum concentration of an analyte that can be reported with

95% confidence that the value is above zero, based on a standard deviation of at least seven repetitive

measurements of the analyte in the matrix of concern at a concentration near the low standard.

5.4 Photochemical Reaction— any chemical reaction that is initiated as a result of absorption of light.

5.5 Photochemical Smog— air pollution resulting from photochemical reactions.

5.6 ppbv— a unit of measure of the concentration of gases in air expressed as parts of the gas per billion (10 )

9

parts of the air-gas mixture, normally both by volume.

5.7 ppmv— a unit of measure of the concentration of gases in air expressed as parts of the gas per million

(10 ) parts of the air-gas mixture, normally both by volume.

6
Formaldehyde Method TO-11A

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 11A-7

5.8 Silica Gel—silica gel is a regenerative adsorbent consisting of amorphous silica (SiO2) with OH surface

groups making it a polar material and enhancing surface reactions.

5.9 Denuder— A device designed to remove gases from an air sampling stream by the process of molecular

diffusion to a collecting surface.

5.10 Certification Blank— certification blank is defined as the mean value of the cartridge blank plus three

standard deviations. For Compendium Method TO-11A, the Certification Blank should be less than

0.15 μg/cartridge for formaldehyde. 

5.11 Cartridge Blank— cartridge blank is the measured value of the carbonyl compounds on an unsampled,

DNPH-coated cartridge. This is the value used in the calculations delineated in section 12.

5.12 Scrubber— to remove a specific gas from the air stream by passing through a pack bed.

6. Extended Methodology and Common Interferences

6.1 This procedure has been written specifically for the sampling and analysis of formaldehyde. Other

carbonyl compounds found in ambient air are also observed in the HPLC analysis. Resolution of these

compounds depend upon column and mobile phase conditions during HPLC analysis. Organic compounds

that have the same retention time and significant absorbance at 360 nm as the DNPH derivative of

formaldehyde will interfere. Such interferences (24) can often be overcome by altering the separation

conditions (e.g., using alternative HPLC columns or mobile phase compositions). In addition, other aldehydes

and ketones can be detected with a modification of the basic procedure. In particular, chromatographic

conditions can be optimized to separate acetone and propionaldehyde and 12 other higher molecular weight

aldehydes and ketones (within an analysis time of about one hour), as identified below, by utilizing one or two

Zorbax ODS columns in series under a linear gradient program:

Formaldehyde Isovaleraldehyde Propionaldehyde p-Tolualdehyde

Acetaldehyde Valeraldehyde Crotonaldehyde Hexanaldehyde

o-Tolualdehyde Butyraldehyde 2,5-Dimethylbenzaldehyde Methyl ethyl ketone

Acetone m-Tolualdehyde Benzaldehyde

The linear gradient program varies the mobile phase composition periodically to achieve maximum resolution

of the C-3, C-4, and benzaldehyde region of the chromatogram. 

6.2 Formaldehyde may be a contamination of the DNPH reagent. If user- prepared cartridges are employed,

the DNPH must be purified by multiple recrystallizations in UV grade carbonyl-free acetonitrile.

Recrystallization is accomplished at 40-60EC by slow evaporation of the solvent to maximize crystal size. The

purified DNPH crystals are stored under UV grade carbonyl-free acetonitrile until use. Impurity levels of

carbonyl compounds in the DNPH are determined by HPLC prior to use and should be less than the

Certification Blank value of 0.15 Fg/cartridge.

6.3 The purity of acetonitrile is an important consideration in the determination of allowable formaldehyde

blank concentration in the reagent. Background concentrations of formaldehyde in acetonitrile will be

quantitatively converted to the hydrazone, adding a positive bias to the ambient air formaldehyde

concentration. Within the project quality control procedures, the formaldehyde in the acetonitrile reagent

should be checked on a regular basis (see Section 9.1).
Method TO-11A Formaldehyde

Page 11A-8 Compendium of Methods for Toxic Organic Air Pollutants January 1997

6.4 Ozone at high concentrations has been shown to interfere negatively by reacting with both the DNPH and

its carbonyl derivatives (hydrazones) on the cartridge (25,26). The extent of interference depends on the

temporal variations of both the ozone and the carbonyl compounds and the duration of sampling. Significant

negative interference from ozone was observed even at concentrations of formaldehyde and ozone typical of

clean ambient air ( i.e., 2 and 40 ppb, respectively).

6.5 Exposure of the DNPH-coated sampling cartridges to direct sunlight may produce artifacts and should be

avoided.

6.6 The presence of ozone in the sample stream is readily inferred from the appearance of new compounds

with retention times different from the other carbonyl hydrazone compounds. 

6.7 The most direct solution to the ozone interference is to remove the ozone before the sample stream reaches

the coated cartridge. This process entails constructing an ozone denuder (9) or scrubber and placing it in front

of the cartridge. The denuder can be constructed of 1 m of 0.64-cm outside diameter (O.D.) by 0.46-cm inside

diameter (I.D.) copper tubing, that is filled with a saturated solution of KI, allowed to stand for a few minutes,

drained and dried with a stream of clean air or nitrogen for about 1 h. The capacity of the ozone denuder as

described is about 100,000 ppb-hour of ozone. Packed-bed granular potassium iodide (KI) scrubbers can also

be used in place of the denuder and are commercially available. Very little work has been done on long term

usage of a denuder or KI scrubber to remove ozone from the ambient air gas stream. The ozone removal

devices should be replaced periodically (e.g., monthly) in the sample train to maintain the integrity of the data

generated.

6.8 Test aldehydes or carbonyls (formaldehyde, acetaldehyde, acrolein, propionaldehyde, benzaldehyde, and

p-tolualdehyde) that were dynamically spiked into an ambient sample air stream passed through the KI denuder

with practically no losses (7). Similar tests were also performed for formaldehyde (26).

6.9 Ozone scrubbers (cartridge filled with granular KI) are also available from suppliers of pre-coated DNPH

cartridges. These scrubbers are optimized when the ambient air contains a minimum of 15% relative humidity.

7. Apparatus

7.1 Isocratic HPLC. System consisting of a mobile phase reservoir a high pressure pump; an injection valve

(automatic sampler with an optional 25-μL loop injector); a Zorbax ODS (DuPont Instruments, Wilmington,

DE) reverse phase (RP) column, or equivalent (25-cm x 4.6-mm ID); a variable wavelength UV detector

operating at 360 nm; and a data system, as illustrated in Figure 1.

[Note: Most commercial HPLC analytical systems will be adequate for this application.]

7.2 Cartridge sampler. Prepacked, pre-coated cartridge (see Figure 2), commercially available or coated in

situ with DNPH according to Section 9. 

[Note: This method was developed using the Waters Sep-Pak cartridge, coated in situ with DNPH on silica

gel by the users, as delineated in the original Compendium Method TO-11 as a guideline. EPA has

experience in use of this cartridge during various field monitoring programs over the last several years. Other

manufacturer's cartridges should work as well. However, modifications to these procedures may be necessary

if another commercially available cartridge is selected.]
Formaldehyde Method TO-11A

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 11A-9

Major suppliers of pre-coated cartridges are: 

• Supelco, Supelco Park, Bellefonte, PA 16823-0048, (800) 247-6628.

• SKC Inc., 334 Valley View Road, Eighty Four, PA 15330-9614, (800) 752-8472.

• Millipore/Waters Chromatography, P.O. Box 9162, Marlborough, MA 01752-9748,

(800) 252-4752.

• Atmospheric Analysis and Consulting (AAC) Inc., 4572 Telephone Rd., Suite 920, Ventura, CA 93003,

(805) 650-1642.

[Note: The SKC cartridge (see Figure 2) is an example of a dual bed tube. The glass cartridge contains a

front bed of 300 mg DNPH-coated silica gel with the back bed of 150 mg DNPH-coated silica gel. Air flow

through the tube should be from front to back bed, as indicated by the arrows enscribed on the cartridge. The

dual bed tube cartridge may be used in atmospheres containing carbonyl concentrations in excess of the

American Conference of Government Industrial Hygienists (ACGIH) 8-hour exposure limit, where

breakthrough of carbonyls on the adsorbent might occur. If used in routine ambient air monitoring

applications, the tube is recovered as one unit, as specified in Section 11.2.]

If commercially prepared DNPH-coated cartridges are purchased, ensure that a "Certification Blank for

Formaldehyde" is provided for the specific batch of which that cartridge is a member. For a commercial

cartridge to be acceptable, the following criteria must be met:

• Formaldehyde concentration: <0.15 μg/cartridge.

If the enhanced carbonyl analysis is being performed, the following Certification Blank criteria must also be

met:

• Speciated carbonyl concentration:

- Acetaldehyde: <0.10 μg/cartridge

- Acetone: <0.30 μg/cartridge

- Other: <0.10 μg/cartridge

Typical physical and chemical characteristics of commercial cartridge adsorbents are listed in Table 2 and

illustrated in Figure 2.

7.3 Sampling system. the DNPH-cartridge approach is capable of accurately and precisely sampling

100-2000 mL/min of ambient air. The monitoring of carbonyl compounds has recently been enhanced by the

promulgation of new ambient air quality surveillance regulations outlined in Title 40, Part 58. These

regulations require States to establish additional air monitoring stations as part of their existing State

Implementation Plan (SIP) monitoring network as part of EPA's Photochemical Assessment Monitoring

Stations (PAMS) to include provisions for enhanced (1) monitoring of ozone and oxides of nitrogen (NO ), x

(2) monitoring of volatile organic compounds (VOCs), (3) monitoring of meteorological parameters, and (4)

monitoring selected carbonyl compounds (formaldehyde, acetone, and acetaldehyde). Specifically, monitoring

for carbonyl involves:

• 8, 3 h sequential samples starting at midnight.

• 1, 24 h time-integrated "reality check" sample.

Consequently, the sampler must be able to accommodate numerous regulatory and practical needs. Practical

needs would include:
Method TO-11A Formaldehyde

Page 11A-10 Compendium of Methods for Toxic Organic Air Pollutants January 1997

• Ability to sequence two cartridges in series for breakthrough volume confirmation for a 24-hour

sampling event.

• Ability to collocate with any of the 8, 3 h samples.

Traditionally, three sampling approaches have been used to monitor carbonyl compounds in the ambient air.

They are:

• Manual single-port carbonyl sampler.

• Programmable single-port carbonyl sampler.

• Automated multi-port sampler.

Components of the single-port carbonyl sampler, for both manual and semi-automatic, are illustrated in

Figure 3. Components usually include a heated manifold/sample inlet, a denuder/cartridge assembly, a flow

meter, a vacuum gauge/pump, a timer and a power supply. In operation, ambient air is drawn through the

denuder/cartridge assembly with a vacuum pump at a fixed flow rate between 0.1 to 2 Lpm. The vacuum

gauge is used to measure the net vacuum in the system for all flow-rate corrections. Controlling the system

is usually a 7-day, 14-event timer to coordinate sampling events to allow a sample to be extracted continuously

or intermittently over a period of time. Finally, an elapsed-time counter is employed to measure the actual time

the sampling took place. This is particularly suitable for unattended sampling when power fails for short

periods.

The automated multi-port sampler is especially designed to collect numerous short-term (2 to 3 hours) sample

sequentially over a 24 hour, 7 day a week, nighttime and weekend monitoring period. This arrangement allows

for the sampling of short periods where the objectives of the project are to identify progress of atmospheric

reactions involving carbonyls. As illustrated in Figure 4, components of the fully automated multi-port

carbonyl sampler includes a heated inlet, ozone denuder (or scrubber) inlet manifold assembly, inlet check

valves, DNPH multi-port cartridge assembly, exhaust manifold, mass flow controller and sample pump. The

multi-port sampler automatically switches between sampling ports at preselected times, as programmed by the

user. Typically, a sequential air sampler contains a microprocessor timer/controller that provides precise

control over each sampling event. The microprocessor allows the user to program individual start date and

time, sample duration, and delays between samples. The timer also allows activation of the flow system prior

(approximately 10 min) to sequencing to allow purging of the sampler inlet with fresh sample. Finally, the

automated sequential sampler can be operated from an external signal, such as an ozone monitor, so that

sampling starts above certain preset ozone levels or via a modem. As a final option, various manufacturers

provide wind sensor instrumentation (wind speed and direction) which is connected to the automated

sequential sampler so that sampling begins when the wind is from a preset direction and speed.

Major suppliers of commercially available carbonyl samplers are:

• Supelco, Supelco Park, Bellefonte, PA 16823-0048, (800) 247-6628.

• SKC Inc., 334 Valley View Road, Eighty Four, PA 15330-9614, (800) 752-8472.

• Millipore/Waters Chromatography, P.O. Box 9162, Marlborough, MA 01752-9748, (800) 252-4752.

• XonTech, Inc. 6862 Hayvenhurst Avenue, Van Nuys, CA 91406, (818) 787-7380.

• ATEC Atmospheric Technology, P.O. Box 8062, Calabasas, CA 91372-8062, (310) 457-2671.

• Atmospheric Analysis and Consulting (AAC) Inc., 4572 Telephone Road, Suite 920, Ventura, CA

93003, (805) 650-1642.

• Scientific Instrumentation Specialists, P.O. Box 8941, Moscow, ID, (209) 882-3860.

7.4 Stopwatch.
Formaldehyde Method TO-11A

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 11A-11

7.5 Polypropylene shipping container (see Figure 5) with polyethylene-air bubble padding. To hold

sample cartridges.

7.6 Thermometer. To record ambient temperature.

7.7 Barometer (optional).

7.8 Volumetric flasks. Various sizes, 5-2000 mL.

7.9 Pipets. Various sizes, 1-50 mL.

7.10 Erlenmeyer flask, 1 L. For preparing HPLC mobile phase.

7.11 Graduated cylinder, 1 L. For preparing HPLC mobile phase. 

7.12 Syringe, 100-250 FL. For HPLC injection, with capacity at least four times the loop value.

7.13 Sample vials. 

7.14 Melting point apparatus (optional).

7.15 Rotameters. 

7.16 Calibrated syringes. 

7.17 Soap bubble meter or wet test meter.

7.18 Mass flow meters and mass flow controllers. For metering/setting air flow rate through sample

cartridge of 100-2000 mL/min.

[Note: The mass flow controllers are necessary because cartridges may develop a high pressure drop and

at maximum flow rates, the cartridge behaves like a "critical orifice." Recent studies have shown that critical

flow orifices may be used for 24-hour sampling periods at a maximum rate of 2 L/min for atmospheres not

heavily loaded with particulates without any problems.]

7.19 Positive displacement. Repetitive dispensing pipets (Lab-Industries, or equivalent), 0-10 mL range.

7.20 Cartridge drying manifold. With multiple standard male Luer® connectors. 

7.21 Liquid syringes. 10 mL (polypropylene syringes are adequate) for preparing DNPH-coated cartridges.

7.22 Syringe rack. Made of an aluminum plate (0.16 cm x 36 cm x 53 cm) with adjustable legs on four

corners. A matrix (5 cm x 9 cm) of circular holes of diameter slightly larger than the diameter of the 10-mL

syringes was symmetrically drilled from the center of the plate to enable batch processing of 45 cartridges for

cleaning, coating, and/or sample elution.

7.23 Luer® fittings/plugs. To connect cartridges to sampling system and to cap prepared cartridges.
Method TO-11A Formaldehyde

Page 11A-12 Compendium of Methods for Toxic Organic Air Pollutants January 1997

7.24 Hot plates, beakers, flasks, measuring and disposable pipets, volumetric flasks, etc. Used in the

purification of DNPH. 

7.25 Culture tubes (20 mm x 125 mm) with polypropylene screw caps. Used to transport coated cartridges

for field applications (see Figure 5), Fisher Scientific, Pittsburgh, PA, or equivalent.

7.26 Polyethylene gloves. Used to handle cartridges, best source. 

7.27 Dry test meter.

7.28 User-prepared copper tubing for ozone scrubber (see Figure 6a). A 36 inch length of 1⁄4-inch O.D.

copper tubing is used as the body of the ozone scrubber. The tubing should be coiled into a spiral

approximately 2 inches in O.D. EPA has considerable field experience with the use of this denuder.

[Note: Ozone scrubbers (cartridge filled with granular KI) are also available from suppliers of pre-coated

DNPH cartridges, as illustrated in Figure 6(b).]

7.29 Cord heater and Variac. A 24 inch long cord heater, rated at approximately 80 watts, wrapped around

the outside of the copper coil denuder, controlled by a Variac, to provide heat (~50EC) to prevent condensation

of water or organic compounds from occurring within the coil.

7.30 Fittings. Bulkhead unions are attached to the entrance and exit of the copper coil to allow attachment

to other components of the sampling system.

8. Reagents and Materials 

[Note: Purity of Reagents—Reagent grade chemicals shall be used in all tests. Unless otherwise indicated,

it is intended that all reagents conform to the specifications of the Committee on Analytical Reagents of the

American Chemical Society where such specifications are available; Purity of Water—Unless otherwise

indicated, references to water shall be understood to mean reagent water as defined by Type II of ASTM

Specifications D 1193.]

 

8.1 2,4-Dinitrophenylhydrazine (DNPH). Aldrich Chemical or J.T. Baker, reagent grade or equivalent.

Recrystallize at least twice with UV grade acetonitrile before use. 

8.2 DNPH coated cartridges. DNPH coated cartridge systems are available from several commercial

suppliers.

8.3 High purity acetonitrile. UV grade, Burdick and Jackson "distilled-in-glass," or equivalent. The

formaldehyde concentration in the acetonitrile should be <1.5 ng/mL. It is imperative (mandatory) that the

user establish the purity of the acetonitrile before use (see Section 9.1).

8.4 Deionized-distilled water. Charcoal filtered. 

8.5 Perchloric acid. Analytical grade, best source, 60%, specific gravity 1.51. 

8.6 Ortho-phosphoric acid. Analytical grade, best source, 36.5-38%, specific gravity 1.19. 
Formaldehyde Method TO-11A

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 11A-13

8.7 Formaldehyde. Analytical grade, best source, 37% solution (w/w).

8.8 Aldehydes and ketones, analytical grade, best source. Used for preparation of DNPH derivative 

standards (optional). 

8.9 Carbonyl hydrazones. Formaldehyde and other carbonyl hydrazones are available for use as standards

from commercial sources at various levels of purity.

8.10 Ethanol or methanol. Analytical grade, best source. 

8.11 Nitrogen. High purity grade, best source. 

8.12 Charcoal. Granular, best source. 

8.13 Helium. High purity grade, best source. 

8.14 Potassium Iodide. Analytical grade, best source. Used for coating inside of copper tubing of denuder

system to remove ozone interference.

9. Preparation of Reagents and Cartridges

9.1 Purity of the Acetonitrile

9.1.1 The purity of acetonitrile is an important consideration in the determination of the formaldehyde

blank concentration. Formaldehyde in the reagent will be quantitatively converted to the hydrazone and

measured as part of the blank. The contribution to the blank from the reagent is dependent on the

formaldehyde concentration in the reagent and the amount of the reagent used for extraction. Some examples

will illustrate these considerations.

Example A

• Silica gel DNPH cartridge has a blank level of 60 ng.

• Cartridge is eluted with 5-mL of acetonitrile reagent containing a formaldehyde of 3 ng/mL.

• Analyst measures a blank level of 75 ng of which 80% comes from the cartridge and 20% comes from

the reagent.

Example B

• Silica gel DNPH cartridge has a blank level of 30 ng.

• Cartridge is eluted with 5 mL of acetonitrile reagent containing a formaldehyde of 6 ng/mL.

• Analyst measures a blank level of 60 ng of which 50% comes from the cartridge and 50% comes from

the reagent.

9.1.2 As a quality control procedure, the formaldehyde in the acetonitrile reagent should be checked on

a regular basis. This can be done by mixing known proportions of the acetonitrile reagent and a DNPH

solution having a measured formaldehyde blank. (The extract from a blank cartridge can serve as the DNPH

solution.) After analyzing the resultant solution, a mass balance is performed on the observed formaldehyde

level and the contribution from the DNPH reagent as shown in the following example.
HCHO ng/mL '

(1.55ng/mL x 10ml&2.1ng/mL x 1mL)

9mL

' 1.49ng/mL

Method TO-11A Formaldehyde

Page 11A-14 Compendium of Methods for Toxic Organic Air Pollutants January 1997

• 1 mL of a DNPH solution containing 2.1 ng/mL of formaldehyde (as carbonyl) is mixed with 9 mL of

acetonitrile reagent containing as unknown formaldehyde blank. The analyst measures a resultant

solution concentration of 1.55 ng of formaldehyde. This data can be used to calculate the formaldehyde

in the reagent:

The formaldehyde contribution to the cartridge blank should be as low as possible but certainly less than 20%

of the total measured blank. Using a cartridge blank level of 30 ng/cartridge, the formaldehyde concentration

in the reagent would have to be less than 1.5 ng/mL (i.e., 50 nM) to give a blank level less than 20% of the

measured blank.

9.2 Purification of 2,4-Dinitrophenylhydrazine (DNPH)

[Note: This procedure should be performed under a properly ventilated hood, as inhalation of acetonitrile

can result in nose and throat irritation. Various health effects are resultant from the inhalation of acetonitrile.

At 500 ppm in air, brief inhalation has produced nose and throat irritation. At 160 ppm, inhalation for 4

hours has caused flushing of the face (2 hour delay after exposure) and bronchial tightness (5 hour delay).

Heavier exposures have produced systemic effects with symptoms ranging from headache, nausea, and

lassitude to vomiting, chest or abdominal pain, respiratory depression, extreme weakness, stupor, convulsions

and death (dependent upon concentration and time).]

[Note: Purified DNPH, suitable for preparing cartridges, can be purchased commercially.]

9.2.1 Prepare a supersaturated solution of DNPH by boiling excess DNPH in 200 mL of acetonitrile for

approximately one hour.

9.2.2 After one hour, remove and transfer the supernatant to a covered beaker on a hot plate and allow

gradual cooling to 40-60EC.

9.2.3 Maintain the solution at this temperature (40-60EC) until 95% of solvent has evaporated.

9.2.4 Decant solution to waste, and rinse crystals twice with three times their apparent volume of

acetonitrile.

9.2.5 Transfer crystals to another clean beaker, add 200 mL of acetonitrile, heat to boiling, and again let

crystals grow slowly at 40-60EC until 95% of the solvent has evaporated.

9.2.6 Repeat rinsing process as described in Section 9.2.4. 

9.2.7 Take an aliquot of the second rinse, dilute 10 times with acetonitrile, acidify with 1 mL of 3.8 M

perchloric acid per 100 mL of DNPH solution, and analyze by HPLC.

[Note: An acid is necessary to catalyze the reaction of the carbonyls with DNPH. Most strong inorganic

acids such as hydrochloric, sulfuric, phosphoric, or perchloric acids will do the job. Perchloric or phosphoric

acids are the preferred catalyst for using acetonitrile solution of DNPH as the absorbing solution. The DNPH

derivatives do not precipitate from solution as readily as when hydrochloric or phosphoric acids are used as

the catalyst. This is an ideal situation for an HPLC analytical finish as this minimizes sample handling. For

most ambient air sampling, precipitation is not a problem because the carbonyl concentration is generally

in the ppb range.]
Formaldehyde Method TO-11A

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 11A-15

9.2.8 An impurity level of <0.15 Fg/cartridge of formaldehyde in DNPH-coated cartridge is acceptable

(based on the Certification Blank section 5.10). An acceptable impurity level for an intended sampling

application may be defined as the mass of the analyte (e.g., DNPH-formaldehyde derivative) in a unit volume

of the reagent solution equivalent to less than one tenth (0.1) the mass of the corresponding analyte from a

volume of an air sample when the carbonyl (e.g., formaldehyde) is collected as DNPH derivative in an equal

unit volume of the reagent solution. An impurity level unacceptable for a typical 10 L sample volume may be

acceptable if sample volume is increased to 100 L. If the impurity level is not acceptable for intended

sampling application, repeat recrystallization.

9.2.9 If the impurity level is not satisfactory, pipet off the solution to waste, then add 25 mL of acetonitrile

to the purified crystals. Repeat rinsing with 20 mL portions of acetonitrile until a satisfactorily low impurity

level in the supernatant is confirmed by HPLC analysis.

9.2.10 If the impurity level is satisfactory, add another 25 mL of acetonitrile, stopper and shake the reagent

bottle, then set aside. The saturated solution above the purified crystals is the stock DNPH reagent.

9.2.11 Maintain only a minimum volume of saturated solution adequate for day to day operation. This will

minimize wastage of purified reagent should it ever become necessary to re-rinse the crystals to decrease the

level of impurity for applications requiring more stringent purity specifications.

9.2.12 Use clean pipets when removing saturated DNPH stock solution for any analytical applications.

Do not pour the stock solution from the reagent bottle.

9.3 Preparation of DNPH-Formaldehyde Derivative

[Note: Purified crystals or solutions of DNPH-derivatives can be purchased commercially.]

9.3.1 To a portion of the recrystallized DNPH, add sufficient 2N HCl to obtain an approximately saturated

solution. Add to this solution formaldehyde (other aldehydes or ketones may be used if their detection is

desirable), in molar excess of the DNPH. Allow it to dry in air.

9.3.2 Filter the colored precipitate, wash with 2N HCl and water and let the precipitate air dry.

9.3.3 Check the purity of the DNPH-formaldehyde derivative by melting point determination or HPLC

analysis. The DNPH-formaldehyde derivative should melt at 167EC ± 1EC. If the impurity level is not

acceptable, recrystallize the derivative in ethanol. Repeat purity check and recrystallization as necessary until

acceptable level of purity (e.g., 99%) is achieved.

9.3.4 DNPH derivatives of formaldehyde and other carbonyls suitable for use as standards are

commercially available both in the form of pure crystals and as individual or mixed stock solutions in

acetonitrile.

9.4 Preparation of DNPH-Formaldehyde Standards

9.4.1 Prepare a standard stock solution of the DNPH-formaldehyde derivative by dissolving accurately

weighed amounts in acetonitrile.

9.4.2 Prepare a working calibration standard mix from serial dilution of the standard stock solution. The

concentration of the DNPH-formaldehyde compound in the standard mix solutions should be adjusted to

reflect relative distribution in a real sample.

[Note: Individual stock solutions of approximately 100 mg/L are prepared by dissolving 10 mg of the solid

derivative in 100 mL of acetonitrile. The individual solution is used to prepare calibration standards

containing the derivative of interest at concentrations of 0.5-20 Fg/mL, which spans the concentration of

interest for most ambient air work.]
Method TO-11A Formaldehyde

Page 11A-16 Compendium of Methods for Toxic Organic Air Pollutants January 1997

9.4.3 Store all standard solutions in a refrigerator. They should be stable at least one month.

9.4.4 DNPH-formaldehyde standards can also be purchased from various commercial suppliers. If

purchased, ensure that a "Certification of Concentration" is provided.

9.5 Preparation of DNPH-Coated Cartridges

[Note: This procedure must be performed in an atmosphere with a very low aldehyde background. All

glassware and plastic ware must be scrupulously cleaned and rinsed with deionized water and carbonyl free

acetonitrile. Contact of reagents with laboratory air must be minimized. Polyethylene gloves must be worn

when handling the cartridges. If the user wishes to purchase commercially prepared DNPH-coated

cartridges, they are available from various vendors. If commercial prepared DNPH-coated cartridges are

purchased, ensure that a "Certification Blank for Formaldehyde" is provided for the specific batch of which

that cartridge is a member. For a commercial cartridge to be acceptable, the following criteria must be met:

• Formaldehyde concentration: <0.15 μg/cartridge.

If the enhanced carbonyl analysis is being performed, the following Certification Blank criteria must also be

met:

• Speciated carbonyl concentration:

- Acetaldehyde: <0.10 μg/cartridge

- Acetone: <0.30 μg/cartridge

- Other: <0.10 μg/cartridge

One who is not experienced in the preparation of DNPH-coated cartridge is strongly advised to use certified

commercially available cartridges.]

9.5.1 DNPH Coating Solution 

9.5.1.1 Pipet 30 mL of saturated DNPH stock solution to a 1000 mL volumetric flask, then add 500 mL

acetonitrile.

9.5.1.2 Acidify with 1.0 mL of ortho-phosphoric acid (H PO ). 3 4

[Note: The atmosphere above the acidified solution should preferably be filtered through a DNPH-coated

cartridge to minimize contamination from laboratory air. Shake solution, then make up to volume with

acetonitrile. Stopper the flask, invert and shake several times until the solution is homogeneous. Transfer the

acidified solution to a reagent bottle with a 0-10 mL range positive displacement dispenser.]

9.5.1.3 Prime the dispenser and slowly dispense 10-20 mL to waste.

9.5.1.4 Dispense an aliquot solution to a sample vial, and check the impurity level of the acidified

solution by HPLC according to Section 9.2.

9.5.1.5 The impurity level should be less than the Certification Blank of <0.15 Fg/cartridge for

formaldehyde, similar to that in the DNPH coating solution. 

9.5.2 Coating of Cartridges 

9.5.2.1 Open the pre-packed cartridge package, connect the short end to a 10-mL syringe, and place it

in a syringe rack (see Figure 7).

[Note: Prepare as many cartridges (~100) and syringes as possible.]
Formaldehyde Method TO-11A

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 11A-17

9.5.2.2 Using a positive displacement repetitive pipet, add 10 mL of acetonitrile to each of the syringes

(see Figure 7).

9.5.2.3 Let liquid drain to waste by gravity. 

[Note: Remove any air bubbles that may be trapped between the syringe and the silica cartridge by displacing

them with the acetonitrile in the syringe.]

9.5.2.4 Set the repetitive dispenser containing the acidified DNPH coating solution to dispense 7 mL

into the cartridges.

9.5.2.5 Once the effluent flow at the outlet of the cartridge has stopped, dispense 7 mL of the DNPH

coating reagent into each of the syringes (see Figure 7).

9.5.2.6 Let the coating reagent drain by gravity through the cartridge until flow at the other end of the

cartridge stops.

9.5.2.7 Wipe the excess liquid at the outlet of each of the cartridges with clean tissue paper. 

9.5.2.8 Assemble a drying manifold with a scrubber or "guard cartridge" connected to each of the ports

(see Figure 7). These "guard cartridges" are DNPH-coated and serve to remove any trace of formaldehyde in

the nitrogen gas supply. 

9.5.2.9 Insert cartridge connectors (flared at both ends, 0.64 by 2.5-cm outside diameter TFEfluorocarbon FEP tubing with inside diameter slightly smaller than the outside diameter of the cartridge port)

onto the long end of the scrubber cartridges.

9.5.2.10 Remove the cartridges from the syringes and connect the short ends to the exit end of the

scrubber cartridge. 

9.5.2.11 Pass nitrogen through each of the cartridges at about 300-400 mL/min for 5-10 minutes.

9.5.2.12 Within 10 minutes of the drying process, rinse the exterior surfaces and outlet ends of the

cartridges with acetonitrile using a Pasteur pipet. 

9.5.2.13 Stop the flow of nitrogen after 15 minutes, wipe the cartridge exterior free of rinsed acetonitrile

and remove the dried cartridge.

9.5.2.14 Plug both ends of the coated cartridge with standard polypropylene Luer® male plugs, place

the plugged cartridge in a shipping tube with polypropylene screw caps. 

9.5.2.15 Put a serial number and a lot number label on each of the individual shipping tubes.

9.5.2.16 Store shipping tubes containing the DNPH-coated cartridges in a refrigerator at 4EC until use.

[Note: Plugged cartridges may also be placed in screw-capped glass culture tubes and placed in a

refrigerator until use. Cartridges will maintain their integrity for up to 90 days stored in refrigerated, capped

shipping tubes.]

9.5.2.17 Take a minimum of 3 blank cartridges from the cartridge batch and analyze for formaldehyde,

as delineated in Section 11. The batch of user-prepared DNPH-coated cartridges is acceptable if the following

criteria are met:

• Formaldehyde Certification Blank: <0.15 μg/cartridge.

If the enhanced carbonyl analysis is being performed, the following certification criteria must also be met:
Method TO-11A Formaldehyde

Page 11A-18 Compendium of Methods for Toxic Organic Air Pollutants January 1997

• Speciated carbonyl concentration:

- Acetaldehyde: <0.10 μg/cartridge

- Acetone: <0.30 μg/cartridge

- Other: <0.10 μg/cartridge

9.5.2.18 If analysis meets the above criteria, provide documentation with all cartridges associated with

that batch involving "Certification Blank for Formaldehyde." This certificate must be part of the project

records.

9.5.2.19 If the cartridge results are close to, but above the Certification Blank, run a few more blank

cartridges to check background level.

9.5.2.20 If analysis indicates failure of the cartridge, then all cartridges in that batch are unacceptable.

Prepare a new batch of cartridges according to Section 9.5 until certification is achieved.

9.5.2.21 Store all certified cartridges in a refrigerator at 4EC until use.

9.5.2.22 Before transport, remove the shipping container (or screw-capped glass culture tubes)

containing the adsorbent tubes from the refrigerator and place culture tubes in a friction-top metal can

containing 1-2 inches of charcoal for shipment to sampling location. Alternately, acidified DNPH-coated filters

can be used in place of charcoal filters to remove impurity carbonyl compounds in the air.

9.5.2.23 As an alternative to friction-top cans for transporting sample cartridges, the coated cartridges

could be shipped in their individual glass containers (see Figure 5a). A batch of coated cartridges may also

be packed in a polypropylene shipping container for shipment to the field (see Figure 5b). The container

should be padded with clean tissue paper or polyethylene-air bubble padding. Do not use polyurethane foam

or newspaper as padding material.

9.5.2.24 The cartridges should be immediately stored in a refrigerator or freezer (<4EC) upon arrival

in the field.

9.6 Equivalent Formaldehyde Cartridge Concentration

9.6.1 One can calculate the equivalent formaldehyde background concentration (ppbv) contributed from

a commercial or user-prepared DNPH-coated cartridge following exposure to formaldehyde-free air.

9.6.2 The equivalent formaldehyde background concentration includes the contribution of formaldehyde

from both the acetonitrile and the cartridge. 

9.6.3 Knowing the equivalent background concentration, as determined by the user (see Section 9.5.2)

or supplied by the commercial supplier (see Note, Section 9.5), of formaldehyde in the cartridge (ng/cartridge),

the formaldehyde background concentration contributed by the DNPH-coated cartridge (thus the method

minimum detection limits) can be related to the total sample volume, as identified in Table 3.

9.6.4 For example, if the averaged background formaldehyde concentration supplied by the manufacturer

is 70 ng/cartridge, then that cartridge can add 0.95 ppbv of equivalent formaldehyde, to the final ambient air

concentration value, as delineated in Table 3 for a total air volume of 60 L.

9.6.5 The user should use DNPH-coated cartridges with the lowest background concentration to improve

accuracy and detection limits.

10. Sampling Procedure

10.1 The sampling system is assembled and should be similar to that shown in Figures 3 and 4. 

[Note: Figures 3 and 4 illustrate different tube/pump configurations. The tester should ensure that the pump

is capable of constant flow rate throughout the sampling period.]
Formaldehyde Method TO-11A

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 11A-19

It is recommended that the sampling system employ a heated inlet (~50EC) coupled to an ozone denuder or

scrubber to minimize water and ozone interference associated with the DNPH-coated adsorbent tube.

Historically, the coated cartridges have been used as direct probes and traps for sampling ambient air when

the ambient temperature was above freezing. 

[Note: As illustrated in Figure 8, the ozone denuder has been effective for up to 80 hours without

breakthrough at ozone levels of approximately 700 ppb. Other studies have evaluated both denuders and

scrubbers at ozone concentrations between 125 and 200ppbv and found they have effectively removed ozone

from the air stream for up to 100,000 ppb-hours; however, moisture was required (-10% RH) in the gas

stream (26). The user should evaluate the length of time of the application of the denuder or scrubber to his

field work. Caution should be utilized when using these devices for extensive periods of time at high humidity

(>65%). Regarding the 24 hour samples, special caution shoud be taken while sampling nighttime periods

when relative humidities approaching 100% are frequently encountered. It is recommended that routine

schedule of ozone removal device replacement should be implemented as part of the sampling program.]

[Note: For sampling ambient air below freezing, a short length (30-60 cm) of heated (50-60EF) stainless steel

tubing must be added to condition the air sample prior to collection on the DNPH-coated cartridges.]

10.2 Before sample collection, the system must be checked for leaks. Plug the inlet of the system so no flow

is indicated at the output end of the pump. The mass flow meter should not indicate any air flow through the

sampling apparatus.

10.3 Air flow through the DNPH-adsorbent cartridge may change during sampling as airborne particles

deposit on the front of the cartridge. The flow change could be significant when sampling particulate-laden

atmospheres. Particle concentrations greater than 50 ug/m are likely to represent a problem. For unattended 3

or extended sampling periods, a mass flow controller is highly recommended to maintain constant flow. The

mass flow controller should be set at least 20% below the maximum air flow through the cartridge.

10.4 The entire assembly (including a "test" sampling cartridge) is installed and the flow rate checked at a

value near the desired sampling rate. In general, flow rates of 1,000-2,000 mL/min should be employed. The

total sample volume should be selected to ensure that the collected formaldehyde concentration exceeds the

background formaldehyde DNPH-cartridge concentration, as illustrated in Table 3. The total moles of

carbonyl in the volume of air sampled should not exceed that of the DNPH concentration (i.e., 2 mg cartridge).

In general, a safe estimate of the sample size should be 75% of the DNPH loading of the cartridge.

[Note: If the user suspects that there will be breakthrough of a DNPH-coated cartridge during the sampling

event, a backup cartridge should be used during the first sampling event. One would analyze the back-up

cartridge for formaldehyde. If the back-up cartridge concentration exceeds 10% of the formaldehyde

concentration on the front cartridge, then continue to use back-up cartridges in the monitoring program.

However, if formaldehyde is not detected above the average blank level in the back-up cartridge after the first

sampling event, then one can continue to use only one cartridge under normal representative conditions.]

[Note: The SKC tube is a dual bed configuration, allowing one to analyze the back bed (see Figure 2) for

quantifying breakthrough.]

Generally, calibration is accomplished using a soap bubble flow meter or calibrated wet test meter connected

to the flow exit, assuming the system is sealed.
Method TO-11A Formaldehyde

Page 11A-20 Compendium of Methods for Toxic Organic Air Pollutants January 1997

[Note: ASTM Method D3686 describes an appropriate calibration scheme that does not require a sealed flow

system downstream of the pump.]

10.5 The operator must measure and record the sampling flow rate at the beginning and end of the sampling

period to determine sample volume. A dry gas meter may be included in the system to measure total sample

volume and to compare against the in-line mass flow controller. Some commerical systems use flow monitors

with data loggers to make these measurements.

10.6 Before sampling, flush the inlet (denuder/manifold, etc.) for approximately 15 min at the established flow

rate to condition the system. Remove the glass culture tube from the friction-top metal can or styrofoam box.

Let the cartridge warm to ambient temperature in the glass tube before connecting it to the sample train.

10.7 Using polyethylene gloves, remove the DNPH-coated cartridge from the shipping container and connect

it to the sampling system with a Luer® adapter fitting. Most commercially available cartridges are

bidirectional. However, review manufacturer suggestions for orientation of the cartridge to the inlet of the

sampler.

[Note: If using the SKC dual bed tube, ensure the ambient air is pulled through the tube in the direction

enscribed on the tube by an arrow.]

Record the following parameters on Compendium Method TO-11A field test data sheet (FTDS), as illustrated

in Figure 9: date, sampling location, time, ambient temperature, barometric pressure (if available), relative

humidity (if available), dry gas meter reading (if appropriate), flow rate, rotameter setting, cartridge batch

number, and dry gas meter pump identification numbers.

10.8 The sampler is turned on and the flow is adjusted to the desired rate. A typical flow rate through one

cartridge is 1.0 L/min and 0.8 L/min for two tandem cartridges.

10.9 The sampler is operated for the desired period, with periodic recording of the variables listed in Figure 9.

10.10 If the ambient air temperature during sampling is below 15EC, a heated inlet probe is recommended.

However, no pronounced effect of relative humidity (between 25% - 90%) has been observed for sampling

under various weather conditions--cold, wet, and dry winter months and hot and humid summer months.

However, a negative bias has been observed when the relative humidity is <25%. At high humidity, the

possibility of condensation must be guarded against, especially when sampling is an air conditioned trailer.

10.11 At the end of the sampling period, the parameters discussed in Section 10.7 are recorded and the sample

flow is stopped. If a dry gas meter is not used, the flow rate must be checked at the end of the sampling

interval. If the flow rates at the beginning and end of the sampling period differ by more than 10%, the sample

should be marked as suspect.

10.12 Immediately after sampling, remove the cartridge (using polyethylene gloves) from the sampling system,

cap with Luer® end plugs, and place it back in the original labeled glass shipping container or culture tube.

Cap, seal with TFE-fluorocarbon tape, and place it in appropriate padding. Refrigerate at 4EC until analysis.

Refrigeration period prior to analysis should not exceed 2 weeks. If a longer storage period is expected, the

cartridge should be extracted with 5 mL of acetonitrile (see Section 11.2.4 and 11.2.5) and the eluant placed

in a vial for long term storage.
QA

'

Q1% Q2% ... QN

N

Vs' Vm×

P A

760

×

298

273 % T A

P A

TA

Formaldehyde Method TO-11A

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 11A-21

[Note: If samples are to be shipped to a central laboratory for analysis, the duration of the non-refrigerated

period should be kept to a minimum, preferably less than two days.]

10.13 If a dry gas meter or equivalent total flow indicator is not used, the average sample flow rate must be

calculated according to the following equation:

where:

QA = average flow rate, L/min.

Q , Q . ... Q = flow rates determined at beginning, end, and intermediate points during sampling, 1 2 N

L/min.

N = number of points averaged.

10.14 The total flow rate is then calculated using the following equation:

Vm = (T2 - T1) x QA

where:

Vm = total volume sampled at measured temperature and pressure, L.

T = stop time, minutes. 2

T = start time, minutes. 1

T - T = total sampling time, minutes. 2 1

QA = average flow rate, L/min.

10.15 The total volume (Vs) at EPA standard conditions, 25EC and 760 mm Hg, is calculated from the

following equation: 

where:

V = total sample volume at 25EC and 760 mm Hg pressure, L. s

Vm = total sample volume at measured temperature and pressure, L.

 = average ambient pressure, mm Hg.

 = average ambient temperature, EC.

11. Sample Analysis

11.1 Sample Preparation
Method TO-11A Formaldehyde

Page 11A-22 Compendium of Methods for Toxic Organic Air Pollutants January 1997

11.1.1 The samples (trip blank, field blank and field samples) are returned to the laboratory in a shipping

container and stored in a refrigerator at (<4EC) until analysis. Alternatively, the samples may also be stored

alone in their individual containers. 

11.1.2 The time between sampling and extraction should not exceed 2 weeks. Since background levels

may change during storage, always compare field samples to those associates with field and trip to a blank

samples, stored under the same conditions.

11.2 Sample Extraction

[Note: Beware of unintentional exposure of samplers and eluted samples to aldehyde and ketone sources.

Laboratory air often holds high concentrations of acetone. Labeling inks, adhesives, and packaging

containers (including vials with plastic caps) are all possible sources on contamination.]

[Note: Contamination is most likely to occur during sample extraction. Before eluting derivatives, clean all

glassware by rinsing with acetonitrile, then heating in a 60EC vacuum oven for at least 30 minutes. Eluting

the samples in a nitrogen-purged glove bag further reduces the risk of contamination.

The acetonitrile used to elute the DNPH derivatives is a typical source of contamination. Formaldehyde-free

acetonitrile used to elute samples should be used only for this purpose, and stored in a carbonyl free

environment. A concentrations of 10 μg/L of any aldehyde or ketone in the acetonitrile adds 0.05 μg of that

carbonyl to sampler blank values if using 5 mL extraction volumes.]

11.2.1 Remove the sample cartridge from the labeled shipping tube or container. Connect the sample

cartridge to a clean syringe.(Some commerical cartridges do not require the addition of a syringe for elution.)

[Note: The liquid flow during desorption should be in the reverse direction of air flow during sample

collection.]

11.2.2 Place the sample cartridge syringe in the syringe rack (see Figure 7).

[Note: If the two beds in the SKC tube are being recovered separately for breakthrough studies, break the

tube and place the beds in separate vials. Proceed with recovery, as specified in Section 11.2.3 through

Section 11.2.6.]

11.2.3 Backflush the cartridge (gravity feed) by passing 5 mL of acetonitrile from the syringe through the

cartridge to a 5-mL volumetric flask. The backflush elution approach may add particulate particles also

collected on the cartridge to the acetonitrile solution which can cause sample valve failure and increase column

back pressure. To minimize this, frontflush the cartridge contents with the acetonitrile reagent rather than

blackflush. The use of 5mL of acetonitrile is sufficient for quantitative cartridge sample elution in either mode.

[Note: A dry cartridge has an acetonitrile holdup volume of about 0.3 mL. The eluant flow may stop before

the acetonitrile in the syringe is completely drained into the cartridge because of air trapped between the

cartridge filter and the syringe Luer® tip. If this happens, displace the trapped air with the acetonitrile in the

syringe using a long-tip disposable Pasteur pipet.]

11.2.4 Dilute to the 5-mL mark with acetonitrile. Label the flask with sample identification. Store in

refrigerated conditions until the sample is analyzed by HPLC. Pipet two aliquots into sample vials with TFE-
Formaldehyde Method TO-11A

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 11A-23

fluorocarbon-lined septa. Analyze the first aliquot for the derivative carbonyls by HPLC. Store the second

aliquot in the refrigerator until the results of the analysis of the first aliquot are complete and validated. The

second aliquot can be used for confirmatory analysis, if necessary.

11.2.5 Sample eluates are stable at 4EC for up to one month. 

11.3 HPLC Analysis

11.3.1 The HPLC system is assembled and calibrated as described in Section 11.4. The operating

parameters are as follows when formaldehyde is the only carbonyl of interest:

Column: Zorbax ODS (4.6-mm ID x 25-cm), or equivalent.

Mobile Phase: 60% acetonitrile/40% water, isocratic.

Detector: ultraviolet, operating at 360 nm.

Flow Rate: 1.0 mL/min.

Retention Time: 7 minutes for formaldehyde with one Zorbax ODS column. Thirteen

minutes for formaldehyde with two Zorbax ODS columns.

Sample Injection Volume: 25 μL.

Before each analysis, the detector baseline is checked to ensure stable conditions.

11.3.2 The HPLC mobile phase is prepared by mixing 600 mL of acetonitrile and 400 mL of water. This

mixture is filtered through a 0.22-Fm polyester membrane filter in an all-glass and Teflon® suction filtration

apparatus. The filtered mobile phase is degassed by purging with helium for 10-15 minutes (100 mL/min) or

by heating to 60EC for 5-10 minutes in an Erlenmeyer flask covered with a watch glass. A constant back

pressure restrictor (350 kPa) or short length (15-30 cm) of 0.25-mm (0.01 inch) ID Teflon® tubing should be

placed after the detector to eliminate further mobile phase outgassing.

11.3.3 The mobile phase is placed in the HPLC solvent reservoir and the pump is set at a flow rate of 1.0

mL/min and allowed to pump for 20-30 minutes before the first analysis. The detector is switched on at least

30 minutes before the first analysis, and the detector output is displayed on a strip chart recorder or similar

output device. The isocratic flow of 60% acetonitrile/40% water is adequate for the analysis of formaldehyde;

however, sufficient time between air sample analyses is required to assure that all other carbonyl compounds

are eluted from the HPLC column prior to the next sample. The gradient flow approach ,mentioned later (see

Section 14.3) is properly programmed to elute other carbonyl compounds. 

11.3.4 A 100-μL aliquot of the sample is drawn into a clean HPLC injection syringe. The sample injection

loop (25-μL) is loaded and an injection is made. The data system, if available, is activated simultaneously with

the injection. If a strip chart recorder is used, mark the point of injection on the chart paper.

11.3.5 After approximately one minute, the injection valve is returned to the "load" position and the

syringe and valve are rinsed or flushed with acetonitrile/water mixture in preparation for the next sample

analysis.

[Note: The flush/rinse solvent should not pass through the sample loop during flushing.] 

The loop is cleaned while the valve is in the "load" mode.

11.3.6 After elution of the DNPH-formaldehyde derivative (see Figure 10), data acquisition is terminated

and the component concentrations are calculated as described in Section 12.

11.3.7 After a stable baseline is achieved, the system can be used for further sample analyses as described

above. Be sure to examine the chromatogram closely to ensure that background DNPH-formaldehyde

derivative peaks are not on the solvent slope of the DNPH peak.
Method TO-11A Formaldehyde

Page 11A-24 Compendium of Methods for Toxic Organic Air Pollutants January 1997

[Note: After several cartridge analyses, background buildup on the column may be removed by flushing with

several column volumes of 100% acetonitrile.] 

11.3.8 If the concentration of analyte exceeds the linear range of the instrument, the sample should be

diluted with mobile phase, or a smaller volume can be injected into the HPLC.

11.3.9 If the retention time is not duplicated (+10%), the acetonitrile/water ratio may be increased or

decreased to obtain the correct elution time. If the elution time is too long, increase the ratio; if it is too short,

decrease the ratio. If retention time is not reproducing, the problem may be associated with the HPLC flow

system. A control chart is recommended to evaluate retention time changes.

[Note: The chromatographic conditions described here have been optimized for the detection of formaldehyde.

Analysts are advised to experiment with their HPLC system to optimize chromatographic conditions for their

particular analytical needs. If a solvent change is necessary, always recalibrate before running samples.]

11.4 HPLC Calibration

11.4.1 Calibration standards can be prepared by the user in acetonitrile from the solid

DNPH-formaldehyde derivative or liquid standards can be purchased from various manufacturers. From the

solid compound, individual stock solutions of 100 ug/mL are prepared by dissolving 10 mg of solid derivative

in 100 mL of acetronitrile. Since the MW of HCHO-hydrazone is 210 g/mol, and the MW of HCHO is 30

g/mol, the stock solution concentration converts to 14.3 ug/mL as formaldehyde (30/210 x 100mg/mL). The

solid compound is weighed using a 5-place analytical balance and liquid dilutions are made with volumetric

glassware. Stock solutions obtained from commercial suppliers generally range from 1 to 50 ug/mL as the

carbonyl compound. These stock solutions are typically provided in 1 mL ampules. 

11.4.2 Using the stock solution, working calibration standards are produced. To generate the highest

concentration working standard, use a pipette to quantitatively transfer 1.00 ml of the stock solution to a 25

mL volumetric flask. For example, using a 14.3 ug/mL stock solution produces a working standard solution

of 570 ng/mL ( 14300 ng/mL x 1/25 ). The high concentration working standard diluted serially, using 1 to

5 mL pipettes and volumetric flasks, can produce working standards ranging between 28.5 and 570 ng/mL.

11.4.3 Each calibration standard (at least five levels) is analyzed three times and area response is tabulated

against mass concentration injected (see Figure 11). All calibration runs are performed as described for sample

analyses in Section 11.3. The results are used to prepare a calibration curve, as illustrated in Figure 12. The

slope of the calibration curve gives the response factor, RF. Linear response is indicated where a correlation

coefficient of at least 0.999 for a linear least-squares fit of the data ( mass concentration versus area response)

is obtained. The intercept of the calibration curve should pass through the origin. If it does not, check your

reagents and standard solutions preparation procedure for possible contamination. If the calibration curve does

not pass through the origin, the equation for the calibration curve should include the intercept. 

11.4.4 Once linear response has been documented, a concentration standard near the anticipated levels

of each carbonyl component, but at least 10 times the detection limit, should be chosen for daily calibration.

The day to day response for the various components should be within 10% of the calibration value. If greater

variability is observed, prepare a fresh calibration check standard. If the variability using a freshly prepared

calibration check standard is greater than 15% , a new calibration curve must be developed from fresh

standards. A plot of the daily values on a Quality Control Chart ( day versus concentration ) is helpful to check

for long term drift of the concentration value.

11.4.5 The response for each component in the daily calibration standard is used to calculate a response

factor according to the following equation shown for formaldehyde:
RFHCHO '

(P&Po)

CHCHO

MBL&HCHOi

'

PBL&HCHOi× VE

RFHCHO

Formaldehyde Method TO-11A

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 11A-25

where:

RFHCHO = response factor for formaldehyde given as area counts per ng/mL.

CHCHO = concentration of analyte in the calibration standard in units of ng/mL.

 P = peak area counts for the formaldehyde standard.

 P = calibration curve intercept; in most cases this is zero. o

11.4.2 The RF for each carbonyl compound is determined in the same way as that given for formaldehyde.

The concentration of HCHO and other carbonyl compounds is determined with the calibration curves for each

component in the analyzed sample. Example calculation for HCHO is given in section 12.

12. Calculations

Determination of the carbonyl compound air concentration requires three steps: (1) determination of the

average blank and the standard deviation of the blank; (2) determination of the collected carbonyl compound

mass of the cartridge; (3) calculation of the carbonyl compound air concentration. The following discusion

provides these steps for formaldehyde.

12.1 Blank Determination

Since the blank level for any arbitary cartridge is unknown, an average value for the blank is used in the

calculation. As noted earlier, the average blank value is determined for each lot of cartridges. For a given lot

size, N, a minimum of /N& cartridge blanks (rounded to the next whole number) should be analyzed; i.e., for

a lot size of 200, a minimum of /200 or 14 cartridge blanks should be analyzed. A minimum of 3 of these

blanks are used for the Certification Blank, and the remaining 11 are used for field blanks. The mass of HCHO

on each cartridge is determined by multiplying the observed peak area for blank cartridge solution by the

acetonotrile extract volume ( typically 5 mL ) and dividing by the response factor as provided in the following

equation:

where:

MBL-HCHO = the blank HCHO mass for cartridge , i. i

RFHCHO = HCHO response factor calculated in Section 11.4.5.

PBL-HCHO = area counts for HCHO in blank sample extract. i

 V = extract volume in mL ( usually 5 mL). E

Once all blank cartridges have been measured, the average blank value is determined by the following

equation:
MBL&HCHO '

1

N

x j

i'1

N

MBL&HCHOi

MSAi

'

PSAix VE

RFHCHO

MHCHOi

' MSAi

& MBL&HCHO

Method TO-11A Formaldehyde

Page 11A-26 Compendium of Methods for Toxic Organic Air Pollutants January 1997

where:

 M&BL-HCHO = the average HCHO mass for all cartridges.

 MBL-HCHO = blank HCHO mass for cartridge, i. i

 N = the number of blank cartridges.

[Note: Measurement of cartridge blanks should be destributed over the period that this particular cartridge

lot is used for ambient air sampling. It is recommended that a trend plot of blank results be constructed to

evaluate background carbonyl results over the period of cartridge lot utilization in the sampling program. If

significant drifting is observed, blank average values should be segmented to be more representative of

carbonyl background.]

12.2 Carbonyl Analyte Mass

The calculation equation for the mass of the collected carbonyl compound mass for an individual

cartridge is the as that for the cartrigde blanks. The gross measured carbonyl mass is determined with an

equation analogous to that given in section 12.1. The equation for formaldehyde is given as:

where: 

 M = gross HCHO mass for cartridge, i. SAi

 P = HCHO peak area counts for cartridge, i. SAi

RFHCHO = the response factor for HCHO.

 V = acetonitrile extract volume in mL ( typically 5 mL). E

The net HCHO mass for an individual cartridge is determined by substracting the average blank value from

the gross HCHO mass obtained for sample i, and is given as:
VHCHOi

'

MHCHOi

MW

x (R x TAMB) x

760

PAMB

VHCHOi

' 1.2276 x MHCHOi

CHCHOppbv '

VHCHOi

VAIR

Formaldehyde Method TO-11A

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 11A-27

12.3 Carbonyl Compound Concentration

The sample air concentration for carbonyl compounds cannot be determined directly from the mass

measurement and requires conversion to units of volume. The conversion calculation for HCHO is determined

using the ideal gas law and is given by the following equation:

where:

 VHCHO = gas volume of HCHO on cartridge, i. i

MHCHOi = mass of HCHO on cartridge, i.

 MW = molecular weight of HCHO, 30.03 g/mole.

 R = gas constant, 0.082 L-atm/mol-deg.

 TAMB = ambient air temperature in degrees Kelvin, 273 + T (C ). o

 PAMB = ambient air pressure in torr.

For an ambient air temperature of 25 C and a pressure of 760 torr, the ideal law equation reduces to: o

In this equation, the HCHO mass in ng is converted to a volume in nL. The volume of air that was passed

through the cartridge was measured by either a mass flow controller or dry test meter calibrated at a known

temperature and pressure. To determine HCHO concentration in the units of ppbv, apply the following

equation:

where: 

VHCHOi = volume of formaldehyde in nL

VAIR = volume of sample air through the cartridge
N ' 5.54

t

r

W1/2

2

Method TO-11A Formaldehyde

Page 11A-28 Compendium of Methods for Toxic Organic Air Pollutants January 1997

13. Performance Criterial and Quality Assurance

This section summarizes required quality assurance measures and provides guidance concerning performance

criteria that should be achieved within each laboratory.

13.1 Standard Operating Procedures (SOPs).

13.1.1 Users should generate SOPs describing the following activities in their laboratory: (1) assembly,

calibration, and operation of the sampling system, with make and model of equipment used; (2) preparation,

purification, storage, and handling of sampling reagent and samples; (3) assembly, calibration, and operation

of the HPLC system, with make and model of equipment used; and (4) all aspects of data recording and

processing including lists of computer hardware and software used.

13.1.2 SOPs should provide specific stepwise instructions and should be readily available to and

understood by the laboratory personnel conducting the work.

13.2 HPLC System Performance

13.2.1 The general appearance of the HPLC system should be similar to that illustrated in Figure 1.

13.2.2 HPLC system efficiency is calculated according to the following equation:

where:

N = column efficiency, theoretical plates.

t = retention time of analyte, seconds. r

W = width of component peak at half height, seconds. 1/2

A column efficiency of >5,000 theoretical plates should be utilized.

13.2.3 Precision of response for replicate HPLC injections should be ±10% or less, day to day, for analyte

calibration standards at 150 ng/mL or greater levels (as the carbonyl compound). At 75 ng/mL levels and

below, precision of replicate analyses could vary up to 25%. Precision of retention times should be ±7% on

a given day.

13.3 Process Blanks

13.3.1 At least one field blank should be used for each day of field sampling, shipped and analyzed with

each group of samples. The number of samples within a group and/or time frame should be recorded so that

a specified minimum number of blanks is obtained for a given cartridge lot used for field samples. The field

blank is treated identically to the samples except that no air is drawn through the cartridge. The performance

criteria described in Section 9.2 should be met for field blanks. It is also desirable to analyze trip and

laboratory blank cartridges as well, to distinguish between possible field and lab contamination.

[Note: Remember to use the field blank value for each cartridge lot when calculating concentration. Do not

mix cartridge lots in the blank value determinations ]
Formaldehyde Method TO-11A

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 11A-29

13.4 Method Precision and Accuracy

13.4.1 At least 50% of the sampling events should include a collocated sample. A collocated sample is

defined as a second sampling port off the common sampling manifold. If more than five samples are collected

per sampling event, a collocated sample should be collected for each sampling event. Precision for the

collocated samples should be ±20% or better. EPA historical data has demonstrated effectiveness in reaching

±20%, as illustrated in Figure 13.

13.4.2 Precision for replicate HPLC injections should be ±10% or better, day to day, for calibration

standards.

13.4.3 Cartridges spiked with analytes of interest can be used in round-robin studies to intercompare

several laboratories performing carbonyl analyses. The spiked samples are prepared in the laboratory by

spiking a blank cartridge with a solution of derivatized carbonyls in acetonitrile. The laboratory preparing the

spike samples should analyze at a minimum 3 of the prepared spiked samples to evaluate the consistency of

prepared samples. 

13.4.4 Before initial use of the method, each laboratory should generate triplicate spiked samples at a

minimum of three concentration levels, bracketing the range of interest for each compound. Triplicate

nonspiked samples must also be processed. Spike recoveries of >80 ±10% and blank levels should be achieved.

13.4.5 For ambient air sampling, an ozone denuder must be used as part of the sampling system. As

discussed in Section 6.4, ozone effects the ultimate method precision and accuracy by reacting with its

carbonyl derivative (hydrazones) on the cartridge. To illustrate this point, Figure 14 documents the

concentration of formaldehyde captured on collocated DNPH-cartridges, one with a denuder (see Figure 14a)

and the other without a denuder (see Figure 14b). The formaldehyde peak is considerably higher with use of

an ozone denuder.

13.5 Method Detection Limits

13.5.1 Determine method detection limits using the procedures in 40 CFR Part 136B. Prepare a low level

standard of the carbonyl derivatives at a concentration within two to five times the estimated method detection

limit. Inject the standard into the analytical system seven times.

13.5.2 Calculate the measured concentration using the calibration curve.

13.5.3 Determine the standard deviation for the seven analyses and use the standard deviation to calculate

the detection limit as described in 40 CFR Part 136B.

13.6 General QA/QC Requirements

13.6.1 General QA/QC requirements associated with the performance of Compendium Method TO-11A

include:

Sampling

• Each sampling event, flow calibration with bubble meter, both pre- and post-checks.

• Mass flow meter calibration factor determined every quarter.

• Each sampling event, leak check, both pre- and post-checks.

• 10 percent of field samples collocated to help calculate method precision and evaluate biases.

• 10 percent of field samples operated with back-up cartridge to evaluate analyte breakthrough.
Method TO-11A Formaldehyde

Page 11A-30 Compendium of Methods for Toxic Organic Air Pollutants January 1997

• Field and trip (optional) blank cartridges are included with each field sample collection program.

• Sample volumes calculated and reviewed project QA officer.

Reagents

• Coating solution prepared from concentrated stock solution immediately before each coating.

• Solution analyzed before each coating to determine acceptability (less than 0.10 μg/cartridge for

each aldehyde), control chart of contaminant concentration maintained.

• Three blank cartridges per lot for immediate elution/analysis to determine Certification Blank for

the carbonyl compounds.

Analysis

• Multi point calibration curve performed each six months.

• Continuing calibration standard (mid-level) analyzer every analytical run to evaluate precision, peak

resolution and retention time drift.

• Method detection limits (MDLs) verified annually or after each instrument change.

• Replicate analysis of approximately 10 percent of sample eluents to evaluate precision.

• Samples quantitated against least squares calibration line.

• Performance evaluation (PE) sample acquired from independent sources analyzed prior to and after

field samples.

• Random collocated samples shipped to independent laboratory for analysis and compared to inhouse collocated sample.

• Testing of acetonitrile used for sample extraction for background carbonyl evaluation.

Data Acquisition

• Sample chromatograms and standards checked daily for peak shape and integration quality,

resolution of carbonyls, overall sensitivity and retention time drift.

• Separate tape backups made of raw data immediately after completion of each analysis.

• Peaks in each sample checked for correct ID and integration using system software before export

to ASCII file.

• Final results checked and edited by project QA officer before producing final report.

• Tape backups of final data files produced.

13.6.2 All results should be reviewed by the project QA officer, independent of the field and

laboratory operations, to evaluate the overall adherence to the methodology in meeting the program data quality

objectives (DQOs).

14. Detection of Other Aldehydes and Ketones 

14.1 Introduction

14.1.1 The procedure outlined above has been written specifically for the sampling and analysis of

formaldehyde in ambient air using an adsorbent cartridge and HPLC. Ambient air contains other aldehydes

and ketones. Optimizing chromatographic conditions by using two Zorbax ODS columns in series and varying

the mobile phase composition through a gradient program will enable the analysis of other aldehydes and

ketones. Alternatively, other aldehydes and ketones may also be analyzed using a single C-18, reverse phase

column and a ternary gradient as described by Waters or Smith, et al. (J. Chromatography, 483, 1989, 431-

436). Thus, other aldehydes and ketones can be detected with a modification of the basic procedure.
Formaldehyde Method TO-11A

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 11A-31

14.1.2 In particular, chromatographic conditions can be optimized to separate acetaldehyde, acetone,

propionaldehyde, and some higher molecular weight carbonyls within an analysis time of about 1 h by utilizing

two Zorbax ODS columns in series, and a linear mobile phase program. Operating the HPLC in a gradient

mode with one Zorbax ODS column may also provide adequate resolution and separation. Carbonyl

compounds covered within the scope of this modification include:

Formaldehyde Crotonaldehyde

o-Tolualdehyde

Aceteldehyde Butyraldehyde

m-Tolualdehyde

Acetone Benzaldehyde

p-Tolualdehyde

Propionaldehdye Isovaleraldehyde

Hexanaldehyde

Valeraldehyde 2,5-Dimethylbenzaldehyde Methyl ethyl ketone

14.1.3 The linear gradient program varies the mobile phase composition periodically to achieve maximum

resolution of the C-3, C-4 and benzaldehyde region of the chromatogram. The following gradient program

was found to be adequate to achieve this goal: Upon sample injection, linear gradient from 65% acetonitrile

(ACN)/35% water to 55% ACN/45% water in 36 min; to 100% ACN in 20 min; 100% ACN for 5 min; reverse

linear gradient from 100% ACN to 60% ACN/40% water in 1 min; maintain at 60% ACN/40% water for 15

min.

14.2 Sampling Procedures

Same as Section 10.

14.3 HPLC Analysis

14.3.1 The HPLC system is assembled and calibrated as described in Section 11. The operating parameters

are as follows:

Column: Zorbax ODS, two columns in series

Mobile Phase: Acetonitrile/water, linear gradient

Step 1. 60-75% acetonitrile/40-25% water in 30 minutes.

Step 2. 75-100% acetonitrile/25-0% water in 20 minutes.

Step 3. 100% acetonitrile for 5 minutes.

Step 4. 60% acetonitrile/40% water reverse gradient in 1 minute.

Step 5. 60% acetonitrile/40% water, isocratic, for 15 minutes.

Detector: Ultraviolet, operating at 360 nm

Flow Rate: 1.0 mL/min

Sample Injection Volume: 25 μL

14.3.2 The gradient program allows for optimization of chromatographic conditions to separate

acetaldehyde, acetone, propionaldehyde, and other higher molecular weight aldehydes and ketones in an

analysis time of about one hour. 

14.3.3 The chromatographic conditions described here have been optimized for a gradient HPLC

system equipped with a UV detector (variable wavelength), an automatic sampler with a 25-μL loop injector
Method TO-11A Formaldehyde

Page 11A-32 Compendium of Methods for Toxic Organic Air Pollutants January 1997

and two DuPont Zorbax ODS columns (4.6 x 250-mm), a recorder, and an electronic integrator. Analysts are

advised to experiment with their HPLC systems to optimize chromatographic conditions for their particular

analytical needs. Highest chromatographic resolution and sensitivity are desirable but may not be achieved.

The separation of acetaldehyde, acetone, and propionaldehyde should be a minimum goal of the optimization.

14.3.4 The carbonyl compounds in the sample are identified and quantified by comparing their

retention times and area counts with those of standard DNPH derivatives. Formaldehyde, acetaldehyde,

acetone, propionaldehyde, crotonaldehyde, benzaldehyde, and o-, m-, p-tolualdehydes can be identified with

a high degree of confidence. The identification of butyraldehyde is less certain because it coelutes with

isobutyraldehyde and is only partially resolved from methyl ethyl ketone under the stated chromatographic

conditions. A typical chromatogram obtained with the gradient HPLC system for detection of other aldehydes

and ketones is illustrated in Figure 15.

14.3.5 The concentrations of individual carbonyl compounds are determined as outlined in Section 12.

14.3.6 Performance criteria and quality assurance activities should meet those requirements outlined

in Section 13.

15. Precision and Bias

15.1 This test method has been evaluated by round robin testing. It has also been used by two different

laboratories for analysis of over 1,500 measurements of formaldehyde and other aldehydes in ambient air for

EPA's Urban Air Toxics Program (UATP), conducted in 14 cities throughout the United States.

15.2 The precision of 45 replicate HPLC injections of a stock solution of formaldehyde-DNPH derivative

over a 2-month period has been shown to be 0.85% relative standard deviation (RSD).

15.3 Triplicate analyses of each of twelve identical samples of exposed DNPH cartridges provided

formaldehyde measurements that agreed within 10.9% RSD.

15.4 A total of 16 laboratories in the U.S., Canada, and Europe participated in a round robin test that

included 250 blank DNPH-cartridges, three sets of 30 cartridges spiked at three levels with DNPH derivatives,

and 13 sets of cartridges exposed to diluted automobile exhaust gas. All round robin samples were randomly

distributed to the participating laboratories. A summary of the round robin results is shown in Table 4.

15.5 The absolute percent differences between collocated duplicate sample sets from the 1988 UATP

program were 11.8% for formaldehyde (n=405), 14.5% for acetaldehyde (n=386), and 16.7% for acetone

(n=346).

15.6 Collocated duplicate samples collected in the 1989 UATP program and analyzed by a different

laboratory showed a mean RSD of 0.07, correlation coefficient of 0.98, and bias of -0.05 for formaldehyde.

Corresponding values for acetaldehyde were 0.12, 0.95 and -0.54, respectively. In the 1988 UATP program,

single laboratory analyses of spiked DNPH cartridges provided over the year showed an average bias of +6.2%

for formaldehyde (n=14) and +13.8% for acetaldehyde (n=13).

15.7 Single laboratory analyses of 30 spiked DNPH cartridges during the 1989 UATP program showed an

average bias of +1.0% (range -49 to +28%) for formaldehyde and 5.1% (range -38% to +39%) for

acetaldehyde.

16. References
Formaldehyde Method TO-11A

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 11A-33

 1. Riggin, R. M., "Determination of Aldehydes and Ketones in Ambient Air: Method TO-5," in

Compendium of Methods for the Determination of Toxic Organic Compounds in Ambient Air, U. S.

Environmental Protection Agency, EPA-600/4-84-041, Research Triangle Park, NC, April 1984.

 2. Winberry, W. T. Jr., et al., "Determination of Formaldehyde and Other Aldehydes in Indoor Air Using

Passive Sampling Device, Method IP-6C," in Compendium of Methods for the Determination of Air

Pollutants in Indoor Air, U. S. Environmental Protection Agency, EPA-600/4-90-010, May 1990.

3. Tejada, S.B., "Standard Operating Procedure For DNPH-coated Silica Cartridges For Sampling

Carbonyl Compounds In Air And Analysis by High-performance Liquid Chromatography,"

Unpublished, U. S. Environmental Protection Agency, Research Triangle Park, NC, March 1986.

 4. Tejada, S.B., "Evaluation of Silica Gel Cartridges Coated in situ with Acidified

2,4-Dinitrophenylhydrazine for Sampling Aldehydes and Ketones in Air," Intern. J. Environ. Anal.

Chem., Vol. 26:167-185, 1986.

 5. Winberry, W. T. Jr., et al., "Determination of Formaldehyde in Ambient Air Using Adsorbent

Cartridge Followed by HPLC: Method TO-11," in Compendium of Methods for the Determination

of Toxic Organic Compounds in Ambient Air, Second Supplement, U. S. Environmental Protection

Agency, EPA-600/4-89-018, Research Triangle Park, NC, March 1989.

 6. Winberry, W. T. Jr., et al., "Determination of Formaldehyde and Other Aldehydes in Indoor Air Using

a Solid Adsorbent Cartridge: Method IP-6A," in Compendium of Methods for the Determination of

Air Pollutants in Indoor Air, U. S. Environmental Protection Agency, EPA-600/4-90-010, May 1990.

7. Nolan, L., et al., "Monitoring Carbonyls in Ambient Air Using the New SupelcleanTM LPD (Low

Pressure Drop) DNPH Cartridge," in Proceedings of the 1995 EPA/AWMA International Symposium

on Measurement of Toxic and Related Air Pollutants, VIP-50, pp. 279, May 1995.

 8. Quality Assurance Handbook for Air Pollution Measurement Systems, Volume II - Ambient Air

Specific Methods, EPA-600/R-94-038b, U. S. Environmental Protection Agency, Research Triangle

Park, NC, May 1994. 

 9. Technical Assistance Document for Sampling and Analysis of O Precursors, U. S. Environmental 3

Protection Agency, EPA-600/8-9-215, Research Triangle Park, NC, October 1991.

10. Ahonen, I., Priha, E., and Aijala, M-L, "Specificity of Analytical Methods Used to Determine the

Concentration of Formaldehyde in Workroom Air," Chemosphere, Vol. 13:521-525, 1984.

11. Levin, J. O., et al., "Determination of Sub-part-per-Million Levels of Formaldehyde in Air Using

Active or Passive Sampling on 2,4-Dinitrophenylhydrazine-Coated Glass Fiber Filters and

High-Performance Liquid Chromatography," Anal. Chem., Vol. 57:1032-1035, 1985.

12. Perez, J. M., Lipari, F., and Seizinger, D. E., "Cooperative Development of Analytical Methods for

Diesel Emissions and Particulates - Solvent Extractions, Aldehydes and Sulfate Methods", presented

at the Society of Automotive Engineers International Congress and Exposition, Detroit, MI,

February-March 1984. 
Method TO-11A Formaldehyde

Page 11A-34 Compendium of Methods for Toxic Organic Air Pollutants January 1997

13. Kring, E. V., et al., "Sampling for Formaldehyde in Workplace and Ambient Air EnvironmentsAdditional Laboratory Validation and Field Verification of a Passive Air Monitoring Device

Compared with Conventional Sampling Methods," J. Am. Ind. Hyg. Assoc., Vol. 45:318-324, 1984.

14. Sirju, A., and Shepson, P. B., "Laboratory and Field Evaluation of the DNPH-Cartridge Technique

for the Measurement of Atmospheric Carbonyl Compounds," Environ. Sci. Technol. Vol. 29:384-392,

1995.

15. Chasz, E. et al., "Philadelphia Air Management Lab, Summary of Procedures and Analytical Data for

Enhanced Ambient Monitoring of PAMS Carbonyls," in Proceedings of the 1995 EPA/AWMA

International Symposium on Measurement of Toxic and Related Air Pollutants, VIP-50, pp. 293, May

1995.

16. Grosjean, D., "Ambient Levels of Formaldehyde, Acetaldehyde, and Formic Acid in Southern

California: Results of a One-Year Base-Line Study," Environ. Sci. Technol., Vol. 25, 710-715, 1991.

17. Bufalini, J.J., and Brubaker, K.L., "The Photooxidation of Formaldehyde at Low Pressures." In:

Chemical Reaction in Urban Atmospheres, (C.S. Tuesday), American Elsevier Publishing Co., New

York, pp. 225-240. 1971.

18. Altshuller, A.P., and Cohen, I.R., “Photooxidation of Formaldehyde in the Pressence of Aliphatic

Aldehydes”, Science, Vol. 7:1043-1049, 1963.

19. "Formaldehyde and Other Aldehydes," Committee on Aldehydes, Board of Toxicology and

Environmental Hazards, National Research Council, National Academy Press, Washington, DC, 1981.

20. Altshuller, A. P., "Production of Aldehydes as Primary Emissions and Secondary Atmospheric

Reactions of Alkenes and Alkanes During the Night and Early Morning Hours," Atmos. Environ., Vol.

27A:21-31, 1993.

21. Tanner, R. L., et al., "Atmospheric Chemistry of Aldehydes; Enhanced PAN Formation From Ethanol

Fuel Vehicles," Environ. Sci. Technol., Vol. 22:1026-1034, 1988.

22. Ciccioli, P., and Cecinato, A., "Advanced methods for the Evaluation of Atmospheric Pollutants

Relevant to Photochemical Smog and Dry Acid Deposition: Chapter 11" in Gaseous Pollutants:

Characterization and Cycling, edited by Jerome O. Nriagu, ISBN 0-471-54898-7, John Wiley and

Sons, Inc., 1992.

23. Parmar, S. S., et al., "A Study of Ozone Interferences in Carbonyl Monitoring Using DNPH Coated

C18 and Silica Cartridges," in Proceedings of the 1995 EPA/AWMA International Symposium on

Measurement of Toxic and Related Air Pollutants, VIP-50, pp. 306, May 1995.

24. Parmar, S. S., et al., "Effect of Acidity on the Sampling and analysis of Carbonyls Using DNPH

Derivatization Method," in Proceedings of the 1996 EPA/AWMA International Symposium on

Measurement of Toxic and Related Air Pollutants, VIP-64, pp. 311, May 1996.
Formaldehyde Method TO-11A

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 11A-35

25. Arnts, R. R., and Tejada, S. B., "2,4-Dinitrophenylhydrazine-Coated Silica Gel Cartridge Method for

Determination of Formaldehyde in Air: Identification of an Ozone Interference," Environ. Sci.

Technol. Vol. 23:1428-1430, 1989.

26. Kleindienst, T. E., et al., "Measurement of C1-C4 Carbonyls on DNPH-Coated Silica Gel and C18

Cartridges in the Presence of Ozone," in Proceedings of the 1995 EPA/AWMA International

Symposium on Measurement of Toxic and Related Air Pollutants, VIP-50, pp 29T, May 1995. 
Method TO-11A Formaldehyde

Page 11A-36 Compendium of Methods for Toxic Organic Air Pollutants January 1997

TABLE 1. COMPARISON OF DNPH COATED CARTRIDGES: SILICA GEL VS. C18

Topic Comparison Discussion

Background Silica gel < C18 Silica gel is purer, therefore less background contamination

from acetone and formaldehyde as compared to C18.

Breakthrough Silica gel < C18 C18 allows carbonyl compounds to breakthrough easier with

longer sampling periods, thus causing bias results. C18 has a

lower capacity for carbonyls in general. Loading of DNPH on

C18 plays an important role in breakthrough for carbonyls.

Ozone interference Silica gel C18 Ozone interference with silica gel is documented. Ozone

interference with C18 is not clear at this time. Therefore, must

use denuder with both systems.

Extraneous chromato- Silica gel C18 Researchers have detected extraneous peaks in the

graphic peaks chromatography of both C18 and silica gel when ozone is

present.

TABLE 2. TYPICAL DNPH-CARTRIDGE SPECIFICATIONS

Category Typical Specifications

Adsorbent chromatographic grade silica or C18 coated with 2,4-

dinitrophenylhydrazine (DNPH)

Particle size 150-1000 μm (60/100 mesh to 18/35 mesh)

DNPH loading 0.3-0.9% (~1-3 mg/cartridge) 1

Bed weight approx. 350 mg 2

Capacity approx. 75 μg formaldehyde, assuming a 50% consumption of DNPH

Background <0.15 μg formaldehyde

(per cartridge) <0.10 μg acetaldehyde

<0.10 Fg other carbonyls

<0.30 μg acetone

Pressure drop 7 inches of water @ 0.5 L/min

15 inches of water @ 1.0 L/min

37 inches of water @ 2.0 L/min

Sampling temperature 10EC to 100EC

Collection efficiency >95% for formaldehyde for sampling rates up to 2.0 L/min

Solvent hold-up volume ~1.0 mL

Tube dimensions From ~2 inches to ~5 inches in length

~1 inch O.D. at widest point

Loading is variable among commercial suppliers. 1

The SKC tube is a dual bed cartridge with 300 mg of DNPH-coated silica gel in the front bed and 150 mg of 2

DNPH-coated silica gel in the back bed. 
Formaldehyde Method TO-11A

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 11A-37

TABLE 3. EQUIVALENT FORMALDEHYDE CONCENTRATION (ppbv) RELATED TO 

BACKGROUND FORMALDEHYDE CONCENTRATION (ng/cartridge)

Equivalent formaldehyde concentration

(ppbv) 60 120 180 1440

Sample volume, L

Background formaldehyde

cartridge concentration,

ng/cartridge 70 0.950 0.475 0.317 0.040

100 1.358 0.679 0.453 0.057

150 2.037 1.018 0.679 0.085

TABLE 4. ROUND ROBIN TEST RESULTSa

Sample Type Formaldehyde Acetaldehyde Propionaldehyde Benzaldehyde

Blank cartridges:

μg aldehyde 0.13 0.18 0.12 0.06

(% RSD) 46 70 47 44

n 33 33 23 8

Spiked cartridges: b

% recovery (%

RSD)

low 89.0 (6.02) 92.6 (13.8) 108.7 (32.6) 114.7 (36.1)

medium 97.2 (3.56) 97.8 (7.98) 100.9 (13.2) 123.5 (10.4)

high 97.5 (2.15) 102.2 (6.93) 100.1 (6.77) 120.0 (8.21)

n 12 13 12 14

Exhaust samples:

μg aldehyde 5.926 7.990 0.522 0.288

% RSD 12.6 16.54 26.4 19.4

n 31 32 32 17

tistics shown after removal of outliers.

Sixteen participating laboratories. Sta a

Normal spiking levels were approximately 0.5, 5 and 10 μg of aldehyde, designated as low, medium, and high in this table. b
ANALYTICAL

COLUMN

WASTE

DETECTOR

360 nm

RECORDER

INTEGRATOR

WASTE

AUTOSAMPLER

GUARD COLUMN

INJECTION VALVE

WATER ACN

SAMPLE LOOP

SBTejada

9/24/97

Method TO-11A Formaldehyde

Page 11A-38 Compendium of Methods for Toxic Organic Air Pollutants January 1997

Figure 1. Basic high-performance liquid chromatographic (HPLC) system used for carbonyl analysis.
Formaldehyde Method TO-11A

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 11A-39

Figure 2. Example of commercially available DNPH-cartridges.
Method TO-11A Formaldehyde

Page 11A-40 Compendium of Methods for Toxic Organic Air Pollutants January 1997

Figure 3. Example of configuration of a single-port carbonyl sampler using DNPH-coated cartridges.
Heated Sample Inlet

Sample Inlet

Ozone

Denuder

Inlet Manifold

Heated Zone

Purge

Pump

FC Pump

Exhaust Manifold

Timer-controlled DNPH Cartridge

Solenoid Valves

0.5 - 1.0 LPM

1 LPM

SBTejada

9/24/97

Formaldehyde Method TO-11A

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 11A-41

Figure 4. Example of components of an automated multi-port sampler for 

carbonyls monitoring using DNPH-coated cartridges.
Method TO-11A Formaldehyde

Page 11A-42 Compendium of Methods for Toxic Organic Air Pollutants January 1997

Figure 5. Example of commercially available shipping containers for DNPH cartridges.
Top View (cutaway)

Heated Cord

3' Potassium

Iodide Coated

1/4" O.D. Copper

Tubing

Potassium Iodide

Cartridge Ozone

Scrubber

Female Luer

®

Polyethylene Frit

Male Luer

®

(a) Cross-sectional view of EPA's ozone denuder assembly

(b) Commercially available packed granular potassium iodide (KI) ozone scrubber

1"

3/4"

SBTejada

9/24/97

Formaldehyde Method TO-11A

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 11A-43

Figure 6. Example of (a) cross-sectional view of EPA's ozone denuder assembly, and 

(b) commercially available packed granular potassium iodide (KI) ozone scrubber.
Method TO-11A Formaldehyde

Page 11A-44 Compendium of Methods for Toxic Organic Air Pollutants January 1997

Figure 7. Example of a typical syringe rack for coating (a) and drying (b) sample cartridges.
Formaldehyde Method TO-11A

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 11A-45

Figure 8. Example of capacity of 3' x 0.25" O.D. x 4.6-mm I.D. copper KI ozone

denuder at 2 L/min flow.
Vm

'

Q1% Q2% Q3... QN

N

×

1

1000 × (Sampling Time in Minutes)

Method TO-11A Formaldehyde

Page 11A-46 Compendium of Methods for Toxic Organic Air Pollutants January 1997

= ___ L

COMPENDIUM METHOD TO-11A

CARBONYL SAMPLING FIELD TEST DATA SHEET

(One Sample per Data Sheet)

I. GENERAL INFORMATION

PROJECT: DATES(S) SAMPLED: 

SITE: 

LOCATION: 

INSTRUMENT MODEL NO.: 

PUMP SERIAL NO.: 

ADSORBENT CARTRIDGE INFORMATION:

 Type: 

Adsorbent: 

Serial Number: 

Sample Number: 

TIME PERIOD SAMPLED: 

OPERATOR: 

CALIBRATED BY: 

OZONE DENUDER USE TIME (Hr): 

HEATED INLET: _____ YES _____ NO

II. SAMPLING DATA INFORMATION

Start Time: Stop Time: 

Time Reading Reading *Q mL/min EC mm Hg Humidity, % Comments

Dry Gas Ambient Barometric

Meter Rotameter Flow Rate, Temperature, Pressure, Relative

Avg.

* Flow rate from rotameter or soap bubble calibrator (specify which).

Total Volume Data (Vm) (use data from dry gras meter, if available)

Vm = (Final - Initial) Dry Gas Meter Reading, or = _______ L

or

III. COMMENTS

Figure 9. Example of Compendium Method TO-11A field test data sheet (FTDS).
Formaldehyde Method TO-11A

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 11A-47

Figure 10. Example of chromatogram of DNPH-formaldehyde derivative.
Method TO-11A Formaldehyde

Page 11A-48 Compendium of Methods for Toxic Organic Air Pollutants January 1997

Figure 11. Example of HPLC chromatogram of varying 

concentration of DNPH-formaldehyde derivative.
Formaldehyde Method TO-11A

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 11A-49

Figure 12. Example of calibration curve for formaldehyde.
Method TO-11A Formaldehyde

Page 11A-50 Compendium of Methods for Toxic Organic Air Pollutants January 1997

Figure 13. Historical data associated with collocated samples for 

formaldehyde (ppbv) in establishing 20% precision.
Formaldehyde Method TO-11A

January 1997 Compendium of Methods for Toxic Organic Air Pollutants Page 11A-51

Figure 14. Example of analysis demonstrating DNPH-coated cartridges sampling air with (A) and

without (B) ozone denuders, in the determination of formaldehyde.
Page 11A-52 Compendium of Methods for Toxic Organic Air Pollutants January 1997Figure 15. Typical chromatogram of a linear gradient program for analyzing other aldehydes/ketones from a DNPH-