Technical Assistance Document (TAD) for 

Precursor Gas Measurements in the NCore 

Multi-pollutant Monitoring Network 

Version 4
ii

EPA-454/R-05-003 

September 2005 

Technical Assistance Document (TAD) 

For Precursor Gas Measurements in the NCore Multi-Pollutant 

Monitoring Network 

VERSION 4 

Prepared by: 

BATTELLE 

505 King Avenue 

Columbus, Ohio 43201-2693 

Prepared for: 

Vickie Presnell, Project Officer 

Nealson Watkins, Work Assignment Manager 

Emissions, Monitoring, and Analysis Division 

Contract No. 68-D-02-061 

Work Assignment 3-02 

U.S. Environmental Protection Agency 

Office of Air Quality Planning and Standards 

Emissions, Monitoring, and Analysis Division 

Research Triangle Park, North Carolina 27711 
iii

DISCLAIMER

 This document is a work prepared for the United States Government by 

Battelle. In no event shall either the United States Government or Battelle have 

any responsibility or liability for any consequences of any use, misuse, inability to 

use, or reliance upon the information contained herein, nor does either warrant or 

otherwise represent in any way the accuracy, adequacy, efficacy, or applicability 

of the contents hereof. 
iv

ACKNOWLEDGMENTS 

 Significant contributions to the TAD content were made by Kevin Cavender, Dennis 

Mikel, Michael Papp, Joann Rice, Solomon Ricks, Nealson Watkins, and Lewis Weinstock of 

the U.S. EPA, Office of Air Quality Planning and Standards, and Anna Kelly, of the Hamilton 

County Department of Environmental Services (Ohio). 

The U.S. Environmental Protection Agency wishes to acknowledge the assistance and 

input provided by the following advisors in the preparation of this guidance document: George 

Allen, of the Northeast States of Coordinated Air Use Management (NESCAUM); James 

Schwab, of the State University of New York at Albany; William McClenny of the U.S. EPA 

Office of Research and Development; and Eric Edgerton of Atmospheric Research and Analysis, 

Inc. 
v

TABLE OF CONTENTS 

ACKNOWLEDGMENTS ......................................................................................................... iv 

ACRONYMS............................................................................................................................. ix 

1.0 INTRODUCTION ............................................................................................................... 1 

1.1 Development of the NCore Network .............................................................................. 2 

1.2 The Need for High Sensitivity Precursor Gas Data in NCore ........................................ 3 

1.3 Precursor Gas Monitoring in the NCore Network .......................................................... 5 

1.4 Data Quality Objectives.................................................................................................. 6 

1.5 Format and Purpose ........................................................................................................ 7 

1.6 References....................................................................................................................... 8 

2.0 HIGH SENSITIVITY CARBON MONOXIDE MEASUREMENTS................................ 1 

2.1 Introduction..................................................................................................................... 1 

2.1.1 Properties of Carbon Monoxide.............................................................................. 1 

2.1.2 Sources and Sinks of Carbon Monoxide................................................................. 1 

2.1.3 Historical Overview of CO Measurement Method................................................. 2 

2.2 Summary of Method ....................................................................................................... 3 

2.2.1 CO Measurement by NDIR Spectrophotometry..................................................... 3 

2.2.2 Gas Filter Correlation (GFC).................................................................................. 5 

2.3 Recommendations for NCore ......................................................................................... 6 

2.3.1 Recommended Method Performance Criteria ........................................................ 7 

2.3.2 Recommended Features for High Sensitivity CO Measurements ........................ 13 

2.3.3 Commercial High Sensitivity GFC CO Monitors................................................. 14 

2.3.4 Sampling Requirements........................................................................................ 19 

2.4 Potential Problems and Solutions ................................................................................. 21 

2.4.1 Interferences and Sources of Bias......................................................................... 21 

2.4.2 Detector Stability .................................................................................................. 23 

2.5 Supporting Equipment .................................................................................................. 23 

2.5.1 Data Acquisition Device....................................................................................... 23 

2.5.2 Calibration Equipment.......................................................................................... 23 

2.6 Reagents and Standards ................................................................................................ 25 

2.6.1 Calibration Standards............................................................................................ 25 

2.6.2 Zero Air................................................................................................................. 26 

2.7 Quality Control ............................................................................................................. 26 

2.7.1 Site Visit Checks and Remote Diagnostic Checks ............................................... 26 

2.7.2 Multipoint Calibrations......................................................................................... 26 

2.7.3 Level 1 Zero/Span Checks ................................................................................... 27 

2.7.4 Precision Checks................................................................................................... 29 

2.8 Preventive Maintenance and Troubleshooting.............................................................. 29 

2.8.1 Preventive Maintenance........................................................................................ 30 

2.8.2 Troubleshooting .................................................................................................... 31 

2.9 References..................................................................................................................... 32 
vi

3.0 HIGH SENSITIVITY SULFUR DIOXIDE MEASUREMENTS ...................................... 1 

3.1 Introduction..................................................................................................................... 1 

3.1.1 Properties of SO2..................................................................................................... 1 

3.1.2 Historical Overview of Measurement Method ....................................................... 2 

3.2 Summary of SO2 Measurement by UV Fluorescence..................................................... 2 

3.3 Recommendations for NCore ......................................................................................... 4 

3.3.1 Recommended Method Performance Criteria ........................................................ 4 

3.3.2 Recommended Features for High Sensitivity SO2 Measurements ....................... 10 

3.3.3 Commercial High Sensitivity UV Fluorescence SO2 Monitors............................ 12 

3.3.4 Sampling Requirements........................................................................................ 16 

3.4 Potential Problems and Solutions ................................................................................. 18 

3.4.1 Sources of Positive Interference or Bias............................................................... 19 

3.4.2 Sources of Negative Interference or Bias ............................................................. 20 

3.5 Supporting Equipment .................................................................................................. 20 

3.5.1 Data Acquisition Device....................................................................................... 21 

3.5.2 Calibration Equipment.......................................................................................... 21 

3.6 Reagents and Standards ................................................................................................ 23 

3.6.1 Calibration Standards............................................................................................ 23 

3.6.2 Zero Air................................................................................................................. 24 

3.7 Quality Control ............................................................................................................. 24 

3.7.1 Site Visit Checklists and Remote Diagnostic Checks........................................... 24 

3.7.2 Multipoint Calibrations......................................................................................... 24 

3.7.3 Level 1 Zero/Span Checks.................................................................................... 25 

3.7.4 Precision Checks................................................................................................... 27 

3.8 Preventive Maintenance and Troubleshooting.............................................................. 27 

3.8.1 Preventive Maintenance........................................................................................ 28 

3.8.2 Troubleshooting .................................................................................................... 29 

3.9 References..................................................................................................................... 30 

4.0 HIGH SENSITIVITY TOTAL REACTIVE NITROGEN OXIDES MEASUREMENTS 1 

4.1 Introduction..................................................................................................................... 1 

4.1.1 Properties of NOy .................................................................................................... 1 

4.1.2 Sources of NOy ....................................................................................................... 2 

4.1.3 Historical Overview of NOy Measurement Method................................................ 3 

4.2 Summary of NOy Measurement by Chemiluminescence Method.................................. 4 

4.3 Recommendations for NCore ......................................................................................... 8 

4.3.1 Recommended Method Performance Criteria ........................................................ 8 

4.3.2 Recommended Features for High Sensitivity Ambient NOy Measurements........ 14 

4.3.3 Commercial Chemiluminescent NOy Monitors.................................................... 16 

4.3.4 Sampling Requirements............................................................................................... 22 

4.4 Potential Problems and Solutions ................................................................................. 24 

4.4.1 Interferences.......................................................................................................... 25 

4.4.2 Converter Efficiency............................................................................................. 26 

4.5 Equipment and Supplies ............................................................................................... 28 

4.5.1 Data Acquisition Device....................................................................................... 28 

4.5.2 Calibration Equipment.......................................................................................... 29 
vii

4.6 Reagents and Standards ................................................................................................ 30 

4.6.1 Calibration Standards............................................................................................ 30 

4.6.2 Zero Air................................................................................................................. 31 

4.7 Quality Control ............................................................................................................. 31 

4.7.1 Site Visit Checklists and Remote Diagnostic Checks........................................... 31 

4.7.2 Multipoint Calibrations......................................................................................... 31 

4.7.3 Level 1 Zero/Span Checks.................................................................................... 33 

4.7.4 Precision Checks................................................................................................... 35 

4.8 Preventive Maintenance and Troubleshooting.............................................................. 35 

4.8.1 Preventive Maintenance........................................................................................ 35 

4.8.2 Troubleshooting .................................................................................................... 36 

4.9 References..................................................................................................................... 38 

5.0 QUALITY ASSURANCE/QUALITY CONTROL (QA/QC) PROCEDURES ................. 1 

5.1 Introduction..................................................................................................................... 1 

5.2 QA/QC Management ...................................................................................................... 1 

5.3 Network Calibration and Instrument Check Procedures ................................................ 2 

5.3.1 Multipoint Calibrations........................................................................................... 2 

5.3.2 Level 1 Zero/Span Checks...................................................................................... 5 

5.3.3 Precision Checks..................................................................................................... 7 

5.4 Independent Audits and Assessments............................................................................. 7 

5.4.1 Proficiency Test Samples........................................................................................ 8 

5.4.2 Technical Systems Audit ........................................................................................ 9 

5.4.3 Audits of Data Quality.......................................................................................... 10 

5.5 References..................................................................................................................... 10 

6.0 DATA ACQUISITION AND MANAGEMENT ................................................................ 1 

6.1 Introduction..................................................................................................................... 1 

6.2 Data Acquisition and Analysis........................................................................................ 1 

6.2.1 Example Data Logger: ESC 8832 Data System Controller......................................... 2 

6.2.2 Example Environmental Data System: ENVIDAS System................................... 4 

6.2.3 Summary Data Acquisition Process........................................................................ 6 

6.3 Data Acquisition System Quality Assurance.................................................................. 7 

6.3.1 Personnel................................................................................................................. 7 

6.3.2 Security ................................................................................................................... 8 

6.3.3 Data Entry and Formatting...................................................................................... 8 

6.3.4 Data Review............................................................................................................ 9 

6.3.5 Calibrations and Audits......................................................................................... 10 

6.4 Data and Records Management .................................................................................... 11 

6.4.1 Calibration Data.................................................................................................... 11 

6.4.2 Electronic Data Files............................................................................................. 12 

6.4.3 Hard Copies .......................................................................................................... 12 

6.5 References..................................................................................................................... 13 
viii

Appendix A Sample Manifold Design for Precursor Gas Monitoring ................................A-1 

Appendix B Standard Operating Procedures for Selected Trace Level Precursor Gas 

 Monitoring and Calibration Equipment ..........................................................B-1 

LIST OF TABLES 

2-1 Ecotech Model EC9830T High Sensitivity CO Analyzer Specifications......................16 

2-2 Thermo Electron Model 48C TLE CO Analyzer Specifications ..................................17 

2-3 Teledyne API Model 300E High Sensitivity CO Analyzer Specifications ...................18 

2-4 Example of a Preventive Maintenance Schedule for High Sensitivity CO Analyzers ..30 

2-5 Instrument Troubleshooting for High Sensitivity CO Analyzers ..................................31 

3-1 Ecotech EC9850T SO2 Analyzer Specifications ...........................................................13 

3-2 Thermo Electron Model 43C TLE SO2 Analyzer Specifications ..................................15 

3-3 Teledyne API Model 100AS SO2 Analyzer Specifications ..........................................16 

3-4 Example of a Preventive Maintenance Schedule for High Sensitivity SO2 Analyzers .27 

3-5 Instrument Troubleshooting for Precursor SO2 Analyzers ............................................29 

4-1 Thermo Electron Model 42C-Y NOy Analyzer Specifications......................................17 

4-2 API Model 200AU/501 NOy Analyzer Specifications ..................................................18 

4-3 Ecotech EC9841-NOy Analyzer Specifications.............................................................20 

4-4 ECO PHYSICS CLD 88 p and CLD 780 TR Analyzer Specifications ........................22 

4-5 Example of a Preventive Maintenance Schedule for NOy Monitoring .........................35 

4-6 Instrument Troubleshooting for High Sensitivity NOy Analyzers ................................36 

5-1 Concentration Levels for Biweekly Precision Checks.....................................................6 

5-2 Concentration Ranges for PT Samples ............................................................................7 

6-1 Example Internal Diagnostic Parameters of High Sensitivity Precursor Gas 

 Analyzers Accessible to a Digital Data Acquisition System...........................................6 

LIST OF FIGURES

2-1 General Schematic of a Typical GFC CO Analyzer........................................................5 

2-2 Ecotech EC9830T High Sensitivity CO Analyzer.........................................................15 

2-3 Thermo Electron Model 48C TLE CO Analyzer...........................................................17 

2-4 Teledyne API Model 300E CO Analyzer ......................................................................18 

3-1 Schematic Illustration of the Optical Chamber of a Precursor SO2 Analyzer .................3 

3-2 Ecotech EC9850T SO2 Analyzer...................................................................................13 

3-3 Thermo Electron Model 43C TLE SO2 Analyzer..........................................................14 

3-4 Teledyne API Model 100AS SO2 Analyzer...................................................................16 

4-1 General Schematic of a Typical Chemiluminescence NOy Instrument ...........................7 

4-2 Thermo Electron Model 42C-Y NOy Analyzer .............................................................17 

4-3 API Model 200AU/501 NOy Analyzer..........................................................................18 

4-4 Ecotech EC9841-NOy Analyzer ....................................................................................20 

4-5 ECO PHYSICS Model CLD 88 p and CON 765 NOy Converter ................................22 

6-1 ESC 8832 Data System Controller ..................................................................................3 

6-2 Flow of Data from Precursor Gas Analyzers to Final Reporting ....................................7 
ix

ACRONYMS 

CFR Code of Federal Regulations 

CO carbon monoxide 

EPA U.S. Environmental Protection Agency 

FPD flame photometric detection 

FRM Federal Reference Method 

GFC gas filter correlation 

HCN hydrogen cyanide 

IR infrared 

LDL lower detectable limit 

MDL method detection limit 

Mo molybdenum 

N2 nitrogen 

NAAMS National Ambient Air Monitoring Strategy 

NAAQS National Ambient Air Quality Standards 

NAMS National Air Monitoring Station 

NCore national core monitoring network 

NDIR non-dispersive infrared 

NH3 ammonia 

NH4

+

 ammonium 

NIST National Institute of Standards and Technology 

NO nitrogen oxide 

NO2 nitrogen dioxide 

NOx nitrogen oxides 

NOy reactive nitrogen oxides 

NPN n-propyl nitrate 

O3 ozone 

Pd palladium 

Pt platinum 
x

PM particulate matter 

PMT photomultiplier tube 

ppb part per billion 

ppm part per million 

ppt part per trillion 

QA quality assurance 

QC quality control 

SLAMS State and Local Air Monitoring Station 

SO2 sulfur dioxide 

SOP standard operating procedure 

TAD technical assistance document 

VOC volatile organic compound 

UV ultraviolet 
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TECHNICAL ASSISTANCE DOCUMENT 

FOR PRECURSOR GAS MEASUREMENTS IN THE NCORE MULTI-POLLUTANT 

MONITORING NETWORK 

1.0 INTRODUCTION 

 The U.S. EPA is currently implementing the National Ambient Air Monitoring Strategy 

(NAAMS).[1] The NAAMS goals include improvement of the scientific and technical 

competency of the nation’s air monitoring networks and increased value in protecting public 

health and the environment. Monitoring of ambient air pollution is a critical part of the nation’s 

air program infrastructure. Monitoring data are used to characterize air quality and associated 

health and ecosystem impacts, develop emission strategies to reduce impacts, and account for 

progress over time. Substantial improvements in ambient air quality have been observed over 

the last two decades, despite increases in the U.S. population, vehicle usage, and industrial 

productivity. Ambient concentrations of several of the criteria air pollutants [specifically, lead 

(Pb), carbon monoxide (CO), sulfur dioxide (SO2), and nitrogen dioxide (NO2)] are now well 

below the applicable National Ambient Air Quality Standards (NAAQS). 

 While the obvious problems of widespread elevated concentrations have been largely 

solved for some criteria pollutants, problems related to particulate matter (PM), ozone (O3), and 

toxic air pollutants remain. It is now clear that even very low air pollution levels can be 

associated with adverse environmental and human health effects. As a result, new approaches in 

air monitoring are needed to measure these low levels and to incorporate these measurements 

with other data into comprehensive assessments of human and environmental health. 

 One of the major areas of investment in the NAAMS is the use of highly sensitive 

commercial air pollutant monitors for the characterization of the precursor gases CO, SO2, and 

total reactive oxides of nitrogen (NOy) in a new national core monitoring network (NCore). The 

high sensitivity CO and SO2 analyzers are fundamentally the same as those designated as Federal 

Reference and Equivalent methods (http://www.epa.gov/ttn/amtic/criteria.html), but with 
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modifications to improve sensitivity and accuracy or reduce interferences. The use of such 

precursor gas analyzers in the NCore network will still allow determination of compliance with 

the NAAQS, but will provide measurements at much lower detection limits than are achievable 

by current monitors. This capability for accurate measurements at low concentrations will 

support long-term epidemiological studies, reduce uncertainties in data for modeling of air 

pollution episodes, and support source apportionment and observational analyses. 

 The implementation of high sensitivity monitoring for CO, SO2, and NOy in the NCore 

network will require installation of new analyzers at selected sites, and implementation of new 

monitoring, calibration, and data acquisition procedures. The purpose of this Technical 

Assistance Document (TAD) is to provide state, local, and tribal (S/L/T) agencies with guidance 

on the equipment, procedures, data acquisition, and quality assurance/quality control (QA/QC) 

efforts needed to properly implement high sensitivity precursor gas monitoring. 

1.1 Development of the NCore Network 

 NCore is both a repackaging and an enhancement of existing networks. The emphasis on 

the term “Core” reflects a multi-faceted, multi-pollutant national network that can be 

complemented by more specific efforts, such as intensive field campaigns to understand 

atmospheric processes, or personal and indoor measurements to assess human exposure and 

health effects. The NCore network will replace the current National Air Monitoring Station 

(NAMS) and State and Local Air Monitoring Station (SLAMS) programs, and leverages all of 

the major existing networks to produce an integrated multi-pollutant approach to air monitoring. 

Emphasis is placed on a backbone of multi-pollutant sites, continuous monitoring methods, and 

measurement of important pollutants other than the criteria pollutants (e.g., ammonia and NOy). 

When complete, NCore will meet a number of important data needs: improved flow and timely 

reporting of data to the public, including supporting air quality forecasting and information 

systems such as AIRNow; continued determination of NAAQS compliance; improved 

development of emissions control strategies; enhanced accountability for the effectiveness of 
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emission control programs; and more complete information for scientific, public health, and 

ecosystem assessments. Structurally, NCore will establish three levels of monitoring sites: 

• Level 1– a small number of research-oriented sites accommodating the greatest 

diversity of instrumentation with specific targeted objectives, reasonably analogous to 

the current PM Supersite program; 

• Level 2 – the backbone network of approximately 75 long-term, nationwide 

multi-pollutant sites, encompassing both urban (about 55 sites) and rural (about 

20 sites) locations; 

• Level 3 – sites focused primarily on specific pollutants of greatest concern (PM and 

O3), with as few as one measured parameter. It is estimated that over 1,000 Level 3 

sites will be part of NCore. 

While each of these three levels has specific objectives, there will likely be a continuum of site 

capabilities. Level 2 sites, for example, may meet a minimum level of multi-pollutant 

measurements, or may be augmented as necessary with other measurements so that the most 

heavily equipped Level 2 sites approach Level 1 in scope. Similarly, Level 3 sites may be single 

pollutant sites, but as necessary, may be augmented by other monitors to approach Level 2 site 

capabilities. These variations will be dictated by the needs of the particular area or agency 

responsible for air monitoring programs. The Level 2 sites are the primary platform for new 

implementation of high sensitivity precursor gas monitors. 

1.2 The Need for High Sensitivity Precursor Gas Data in NCore 

 The precursor gases CO, SO2, and NOy play important roles in the formation of 

atmospheric ozone, air toxics, and PM, on both local and regional scales. This interconnection 

among distinct air quality issues requires an integrated multiple pollutant air quality monitoring 

and management approach. For example, multi-pollutant monitoring data can allow health 
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studies to separate confounding effects, particularly in the face of varying ambient 

concentrations and PM composition. Air quality models and source attribution methods can 

benefit because multi-pollutant data allow more robust diagnostic evaluations (i.e., ensuring the 

model produces correct results for the correct reasons). Many emission sources release multiple 

pollutants, and consequently source apportionment models may yield more conclusive results 

with the use of multi- pollutant monitoring data. The NCore Level 2 sites are focused on 

providing multi-pollutant monitoring data to address these issues. 

Equally important is that monitoring in NCore accurately quantify the low precursor gas 

concentrations that often typify conditions across the U.S. National health assessments and air 

quality model evaluations require data that are representative of broad urban (e.g., 5 to 40 km) 

and regional/rural (> 50 km) spatial scales, and long-term epidemiological studies must represent 

a variety of airshed characteristics across different population regimes. These requirements drive 

the mixed urban/rural placement of the NCore Level 2 sites. The NCore sites thus should be 

perceived as developing a representative report card on air quality across the nation, capable of 

delineating differences among geographic and climatological regions. While relatively high 

precursor gas concentrations may once have characterized all urban areas, emission reductions 

have changed that situation. For example, even in Atlanta, GA, median precursor gas 

concentrations are only a few times the detection limits of the conventional monitors currently in 

use.[2] Characterization of rural/regional environments is also important to understanding 

background conditions, transport corridors, regional-urban dynamics, and influences of global 

transport, as air quality modeling domains continue to expand. Localized source-oriented 

dispersion modeling evolved throughout the 1970's and 80's into broader urban scale modeling 

(e.g., EKMA and Urban airshed modeling for ozone), then into Regional approaches in the 

1980's and 1990's (e.g., the Regional Oxidant (ROM) and Acid Deposition (RADM) Models), 

and currently into national scale approaches (e.g., the Community Multiscale Air Quality 

(CMAQ) models). This movement toward broader spatial scale modeling coincides with 

increased recognition of the importance of the regional/rural transport environment on urban 

conditions. As peak urban air pollution levels decline, rural and regional levels also decline. For 

example, in rural Centreville, AL, median precursor gas concentrations are at or below the 
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detection limits of the conventional monitors currently in use.[2] Measurements of low precursor 

gas concentrations thus are needed throughout the NCore network so that models can incorporate 

these low concentrations accurately. 

 The overarching objective of the high sensitivity precursor gas monitoring in NCore is to 

determine concentrations in well-mixed representative rural and urban atmospheres. NCore 

provides an opportunity to address new directions in monitoring and to begin to fill measurement 

and technological gaps that have accumulated in the existing networks. The NAAMS recognizes 

that there are both nationally and locally oriented objectives in monitoring that require different 

design approaches. The multipollutant high sensitivity monitoring approach in NCore addresses 

national level needs and makes the most of available resources. 

 

1.3 Precursor Gas Monitoring in the NCore Network 

 The use of high sensitivity precursor gas monitors for the characterization of CO, SO2, 

and NOy at NCore Level 2 monitoring stations is one of the major areas of investment for the 

NAAMS. In most cases, the adoption of improved precursor gas monitoring methods and 

associated calibration procedures will be necessary given the low levels of these pollutants at 

many of the likely NCore Level 2 sites. The use of high sensitivity monitors will also be 

valuable at Level 2 sites in urban areas, since at many such locations the concentrations of these 

gases are not consistently at elevated levels. In addition, as emissions reductions are realized and 

concentrations shift downward, high sensitivity monitors in urban areas will support the 

detection of trends. The applicability of high sensitivity monitors to urban Level 2 sites will be 

addressed on a site-by-site basis. 

 Precursor gas monitoring of CO, SO2, and NOy at NCore Level 2 sites will be 

accomplished by use of commercially available, continuous high sensitivity monitors. This 

document provides the technical guidance needed for implementation of these monitors in the 

NCore network. The following is a brief summary of the measurement principles and limitations 

of these monitors: 
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• CO: Commercially available, non-dispersive infrared (NDIR) monitors will be used 

that include modifications to enhance performance and sensitivity. The principal 

constraints on lower detection limits of these devices are water vapor interference and 

background drift. These limitations are reduced by drying the sample air and by 

automated determination of the monitor’s baseline reading (i.e., auto-zeroing) using 

an appropriate CO oxidation system. 

• SO2: Commercially available, ultraviolet (UV) fluorescence monitors will be used 

that include modifications to enhance performance and sensitivity. A more intense 

UV light source and improved optical filtering to minimize interference from nitric 

oxide (NO), are modifications typically made to increase sensitivity of these 

monitors. As with CO measurements, precursor SO2 measurements also may be 

affected by water vapor and background drift. 

• NOy: Commercially available monitors based on the chemiluminescent reaction of 

NO with O3 will be used. Since the chemiluminescence method detects only NO, 

other trace nitrogen species including NO2 must first be converted to NO in order to 

be measured using this method. Consequently, appropriate means of sampling and 

converting the chemical species that constitute NOy are critical to accurate 

measurements. Typical improvements made to these monitors for high sensitivity 

measurements include increased sample flow rate, placement of the converter at the 

sample inlet, improved cooling of the detector, and reduction of interferences through 

a prereactor for baseline determination. 

1.4 Data Quality Objectives 

Data Quality Objectives (DQOs) are qualitative and quantitative statements that clarify 

the monitoring objectives, define the appropriate type of data, and specify the tolerable levels of 

measurement errors for the monitoring program. By applying the DQO process to the 
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development of a quality system for NCore precursor gas monitoring, EPA guards against 

committing resources to data collection efforts that might not support the decisions for which the 

data are collected. The DQO process is iterative and allows for the incorporation of new 

information and modifying outputs from previous steps as inputs for a subsequent step. 

The final outcome of the DQO process is a design for collecting data (e.g., the type of 

measurements or number of samples to collect, and when, where, and how to collect samples), 

together with limits on the probabilities of making decision errors. During calendar year 2005 a 

Workgroup made up of personnel representing decision makers, technical experts, quality 

assurance manager, and statisticians will work their way through the seven step DQO process to 

address requirements for precursor gas monitoring in NCore. The results of that process will be 

reflected in additional guidance provided for the NCore network. 

1.5 Format and Purpose 

 Section 2 of this TAD provides detailed procedures for the use and calibration of high 

sensitivity CO monitoring equipment at Level 2 NCore sites. Sections 3 and 4 provide the same 

information for high sensitivity SO2 and NOy measurements, respectively. Section 5 of this TAD 

describes the QA/QC procedures needed to support precursor gas monitoring at the NCore 

Level 2 sites, and Section 6 provides guidance about the acquisition and management of data 

from the precursor gas monitors. Each major section concludes with a list of the references cited 

in that section. Appendix A of this TAD is a description prepared by EPA of sampling manifold 

designs for precursor gas monitoring. 

 Although this TAD is not intended to be a Standard Operating Procedure (SOP), several 

topics addressed here are discussed in the 2001 EPA guidance on preparing Standard Operating 

Procedures (SOPs).[3] S/L/T agencies will find this document useful in preparing SOPs for the 

specific precursor gas analyzers employed at their sites. Furthermore, SOP’s prepared by EPA 

for selected precursor gas monitoring and calibration equipment are included as Appendix B. 

Electronic versions of these SOP’s are also located at 

http://www.epa.gov/ttn/amtic/precursop.html. 
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 This TAD was written to help field operators, data managers, and data users understand 

why (not just how) key procedures are performed, what issues exist with the analyzers that they 

should be aware of, and how to address these issues. Special attention is paid to interferences, 

equipment selection, and calibration procedures. Users of this TAD should also consult Part 1, 

General Principles, of EPA’s Quality Assurance Handbook, Volume II,[4] which contains 

detailed information pertinent to all measurement methods. 

1.6 References 

1. “National Ambient Air Monitoring Strategy,” U.S. Environmental Protection Agency, 

Office of Air Quality Planning and Standards, Research Triangle Park, NC 27711, 

April 2004, Final Draft. 

2. Data from sites in the Southeastern Aerosol Research and Characterization (SEARCH) 

Study, summarized in personal communication by Eric Edgerton, Atmospheric Research 

and Analysis, Inc., June 10, 2005. SEARCH data are available at 

http://www.atmospheric-research.com/studies/SEARCH/index.html. 

3. “Guidance for Preparing Standard Operating Procedures (SOPs),” EPA QA/G-6, 

EPA/240/B-01/004, U.S. Environmental Protection Agency, Office of Environmental 

Information, Washington, DC, 20460, March 2001. 

4. “Quality Assurance Handbook for Air Pollution Measurements,” Volume II, EPA-454/R98-004, U. S. Environmental Protection Agency, Research Triangle Park, NC 27711, 

August 1998. 
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2.0 HIGH SENSITIVITY CARBON MONOXIDE MEASUREMENTS 

2.1 Introduction 

 The NAAMS[1] builds upon research from the late 1990s, which indicated that carbon 

monoxide (CO) could be used as a background tracer for industrial processes and as a worldwide tracer for long-range pollution transport.[2-4] The Strategy also calls for monitoring to 

ascertain whether CO can be used as an indicator for volatile organic compounds (VOCs). 

 In response to the need for ambient CO monitoring, researchers and academia have 

worked with commercial instrument manufacturers to create high sensitivity CO instruments, 

with manufacturer-stated detection limits as low as 0.04 parts per million (ppm) (40 parts per 

billion (ppb)) in air. 

2.1.1 Properties of Carbon Monoxide

 CO is a colorless, odorless, tasteless, and highly poisonous gas. It affects the oxygen 

carrying capacity of the blood by diffusing through the alveolar walls of the lungs and competing 

with oxygen for the four iron sites in the hemoglobin molecule. Since the affinity of the iron site 

for CO is approximately 240 times greater than for oxygen[5] even low levels of CO can cause a 

number of symptoms including headache, mental dullness, dizziness, weakness, nausea, 

vomiting, and loss of muscular control. In extreme cases, collapse, unconsciousness, and death 

can occur. CO is only slightly soluble in water (2.3 ml/100 ml H2O at 20 °C and 760 mm Hg)[5]

and consequently CO is not readily deposited or washed out of the atmosphere. 

2.1.2 Sources and Sinks of Carbon Monoxide

 CO has both natural and anthropogenic sources. The two primary CO production 

mechanisms are the oxidation of hydrocarbons in the atmosphere and the combustion of 

carbonaceous fuels. Global background concentrations of CO typically fall between 50 and 

120 ppb and fluctuate seasonally, as well as geographically. In general, higher concentrations 
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occur during winter and are found in the northern hemisphere, due to the preponderance of 

anthropogenic sources in that part of the world.[5] CO is also produced naturally from the 

photochemical oxidation of methane (CH4) and other hydrocarbons in the atmosphere. 

 In urban environments, human activity results in CO levels that can greatly exceed 

background levels. Along with carbon dioxide (CO2), CO is a primary gaseous product of the 

combustion of carbonaceous fuels and is emitted from both mobile and stationary sources. In 

most urban areas, automobiles are a substantial source of CO. Consequently, CO levels tend to 

build up during morning and evening commute times, and maximum mixing ratios exceeding 50 

ppm have been observed in congested intersections. Typically, however, one-hour average 

concentrations greater than 10 ppm are rare. 

 CO is relatively stable in the atmosphere and has an average global atmospheric lifetime 

of between 1 and 4 months.[5] The primary mechanism for removal of CO from the atmosphere 

is the oxidative reaction with hydroxyl radical to form CO2: 

• • CO + OH → CO2 + H

The hydroxyl radical coincidently is part of a chain reaction that also produces CO from 

hydrocarbons in the atmosphere. 

2.1.3 Historical Overview of CO Measurement Method

 The standard reference method for the determination of ambient CO is non-dispersive 

infrared spectrophotometry (NDIR). The NDIR CO measurement principle is the absorption of 

infrared (IR) radiation, with a wavelength of 4.7 micrometers (μm), by CO. The first 

instrumental method introduced, the Luft-type instrument, was granted Federal Reference 

Method (FRM) designation in 1976. In 1981, instrument manufacturers developed several 

modifications of the NDIR FRM and submitted those modified instruments for FRM 

designation. The gas filter correlation (GFC) method became the most popular modification in 
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the monitoring community because of its improved linearity and detection capabilities. EPA 

sponsored the development of the GFC technique at Ford AeroNutronics in Newport Beach, CA. 

Instrument manufacturers used the original analyzer developed in that work as a guide for 

designing commercial versions. Today, FRM-designated instruments are available from several 

manufacturers using both Luft-type and GFC methods, however in ambient applications the GFC 

method is almost exclusively used. 

 The lower detectable limit (LDL) for an ambient monitor is defined as that minimum 

concentration level that produces a signal of twice the baseline noise level (Code of Federal 

Regulations, Volume 40, Part 53.23c, or, in the shortened format used hereafter, 40 CFR 53.23c). 

Modifications in commercial GFC CO instruments have lowered estimated LDL values to 0.04 

ppm (40 ppb). This chapter focuses on the GFC method and on those modifications to the GFC 

method that allow for high sensitivity CO measurements. 

2.2 Summary of Method 

2.2.1 CO Measurement by NDIR Spectrophotometry

 GFC analyzers operate on the principle that the CO molecule has a sufficiently 

characteristic IR absorption spectrum that absorption can be used as a measure of CO 

concentration in the presence of other gases. CO absorbs IR radiation maximally at a 

wavelength of 4.7 μm, which is in a spectral region where few other atmospherically significant 

species absorb to interfere with the accurate quantification of CO. The few potential 

interferences are discussed in Section 2.5.1. 

 Since NDIR is a spectrophotometric method, the concentration of CO can be determined 

based upon the Beer-Lambert Law. The Beer-Lambert law relates the concentration of an 

absorbing species to the degree of light attenuation according to the equation shown below: 
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( )

0 / axC I I e − =

where: 

I = light intensity after absorption by absorbing species 

Io = light intensity before absorption by the absorbing species 

a = absorption coefficient for absorbing species 

x = path length between light source and detector 

C = concentration of the absorbing species. 

By measuring the degree of light attenuation through a sample cell of known length in both the 

presence and absence of CO, the concentration can be accurately determined if the absorption 

coefficient of CO is known. 

 In Luft-type instruments, IR radiation is passed alternately between a reference cell, 

containing a non-absorbing gas, and the sample cell. Prior to the introduction of sample gas 

containing CO to the sample cell, the intensity of the light passing through the sample cell is 

adjusted to match the intensity passing through the reference cell. As sample gas containing CO 

is introduced to the sample cell, an imbalance in the light transmitted through the two cells 

develops. This imbalance results in a detectable signal that is related to the CO concentration in 

the sample cell. However, although CO has a strong characteristic absorption at 4.7 μm, other 

gaseous atmospheric species can contribute to the light attenuation by the sample and, thus, 

interfere with the accurate quantification of CO. Consequently, gas filter correlation (GFC) 

techniques were developed to address this problem. 
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2.2.2 Gas Filter Correlation (GFC)

 A schematic of a GFC CO monitor is shown in Figure 2-1. In GFC monitors, there is 

only one sample cell, which acts both as the sample and reference cell. In this technique, a broad 

band of IR radiation is emitted from an IR source and enters the sample cell. Mirrors are used to 

reflect the light across the length of the cell multiple times which increases the effective 

pathlength and sensitivity of the monitor. Depending on instrument design, the light passes 

Figure 2-1. General schematic of a typical GFC CO analyzer. 
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through a bandpass filter either before or after the sample cell. This bandpass filter blocks most 

wavelengths from passing and allows only a narrow bandwidth of radiation centered on 4.7 μm 

to reach the detector. In GFC monitors, a mechanical chopper assembly with cells containing 

either pure nitrogen (N2) or pure CO is positioned between the IR source and the sample cell, and 

acts as a gas filter. As the gas filter assembly rotates, the IR energy alternately passes through 

the cells containing the CO or N2 gases. When the light passes through a cell containing CO, all 

the light at 4.7 μm is absorbed by the CO in the gas filter cell. This technique effectively “scrubs 

out” any light at wavelengths where CO absorbs prior to the sample cell, but allows other 

wavelengths of light to pass through the sample cell and reach the detector. As the chopper 

wheel spins, the gas filter cell containing N2 in the chopper assembly then crosses the IR energy 

beam. Since N2 is transparent to IR radiation, this gas filter cell allows all IR light to pass 

through unattenuated by the N2. A neutral attenuator is used in the gas filter to reduce the overall 

light intensity exiting the N2 cell to match the intensity exiting the CO cell. 

 In the absence of CO in the sample cell, no change in light intensity is detected as the gas 

filter rotates. However, when CO is introduced to the sample cell, some of the light that passes 

through the N2 cell of the wheel is absorbed by CO in the sample cell, resulting in a difference in 

light intensity at the detector that is proportional to the concentration of CO in the sample cell. 

As the gas filter rotates, the light intensity is modulated and creates a signal from the detector 

that is electronically demodulated using phase-sensitive amplifiers and subsequently processed to 

generate a CO concentration reading. 

2.3 Recommendations for NCore 

 Since the high sensitivity analyzers deployed at NCore sites are intended to monitor low 

ambient CO concentrations, it is important that they meet a variety of performance criteria as 

described below. Many of these performance criteria are more stringent than those for routine 

CO analyzers; consequently, there are a number of recommended features that the precursor CO 

analyzers should have in order to achieve the performance criteria. This section describes the 

recommended performance criteria and the analyzer features that are recommended in order to 
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achieve the performance criteria, and provides examples of commercial high sensitivity CO 

analyzers that are available for deployment at the NCore sites. Additionally, this section 

discusses some important sampling requirements that should be considered during the 

installation of the analyzers. 

2.3.1 Recommended Method Performance Criteria

 The U.S. EPA has recently assessed the measurement quality objectives needed for high 

sensitivity precursor gas monitoring in NCore, relative to the long-established statistics stated in 

40 CFR 58.[6] In particular, EPA recommends that measurement quality objectives for bias and 

precision be based on upper confidence limits at the monitoring site level, to provide a higher 

probability of reaching appropriate conclusions (e.g., in comparisons to NAAQS). The intent of 

this recommendation is to move S/L/T agencies to a performance-based quality system i.e., 

allowing organizations that show tight control of precision and bias to reduce the frequency of 

certain QC checks, and to focus their quality system efforts where most needed. 

 The U.S. EPA recommends that the high sensitivity CO analyzers that are deployed at 

NCore sites meet the following method performance criteria. 

2.3.1.1 Precision 

 Precision is defined as the measure of agreement among individual measurements of the 

same property taken under the same conditions. Precision is assessed from checks that are 

performed at least once every two weeks (see Sections 2.7.4 and 5.3.3). Calculations to assess 

precision are given below and should be used to assess precision on a quarterly basis. It is 

recommended that high sensitivity CO analyzers have a 95 percent probability limit for precision 

of ±15 percent or less. 

 Calculation of precision starts with the comparison of the known challenge concentration 

used in the precision checks to the corresponding measured concentrations reported by the 
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analyzer. The resulting percent differences are then used as described below. For each single 

point precision check, calculate the percent difference, di, as follows: 

Equation 1

 

where reported is the concentration indicated by the high sensitivity CO analyzer and challenge

is the concentration of the standard used in the precision check. The precision estimator is then 

calculated as the coefficient of variation (CV) upper bound, using Equation 2 as follows: 

Equation 2

 

 

where n is the number of data points (i.e., precision check comparisons), the di values are the 

resulting percent differences, and X 0.1,n-1 is the 10th percentile of a chi-squared distribution with 

n-1 degrees of freedom. 

2.3.1.2 Bias 

 Bias is defined as a systematic or persistent distortion of a measurement process that 

causes errors in one direction. Bias is assessed from the degree of agreement between a 

measured value and the true, expected, or accepted value. Analyzer bias is calculated using 

comparisons of known challenge concentrations to the corresponding measured concentrations 

reported by the analyzer. The challenge comparisons used to assess bias should be the same as 

those used to assess precision (see Section 2.3.1.1 above). The bias estimator is an upper bound 

on the mean absolute value of the percent differences as described in Equation 3 as follows: 

d reported challenge

challenge i = − ⋅100

( ) CV

nd d

n n

n

X

i

i

n

i

i

n

n

=

⋅ −

⎛

⎝

⎜

⎜

⎞

⎠

⎟

⎟

− ⋅ = = −

−

∑ ∑ 2

1 1

2

2

01 1 1

1

. ,
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Equation 3

where n is the number of challenge comparisons being aggregated; t0.95,n-1 is the 95th quantile of 

a t-distribution with n-1 degrees of freedom; the quantity AB is the mean of the absolute values 

of the individual di’s and is calculated using Equation 4 as follows: 

Equation 4

 

and the quantity AS is the standard deviation of the absolute value of the di’s and is calculated 

using Equation 5 as follows: 

Equation 5

 

 

 

Since the bias statistic as calculated in Equation 3 uses absolute values, it does not have a 

direction or sign (negative or positive) associated with it. The sign of the calculated bias is to be 

determined by rank ordering the percent differences of the QC check samples from a given 

analyzer for a particular assessment interval. Calculate the 25th and 75th percentiles of the 

percent differences for each analyzer. The absolute bias upper bound should be flagged as 

positive if both the 25th and 75th percentiles are positive, and as negative if both these percentiles 

are negative. The absolute bias upper bound would not be flagged if the 25th and 75th percentiles 

bias AB t

AS

n

=+ ⋅ 0. , 95 n −1

AB

n

d i

i

n

= ⋅

=

∑1

1

( ) AS

nd d

n n

i

i

n

i

i

n

=

⋅ −⎛

⎝

⎜

⎜

⎞

⎠

⎟

⎟

−

= =

∑ ∑ 2

1 1

2

1
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are of different signs. It is recommended that high sensitivity CO analyzers have an upper bound 

for the average bias of ± 15 percent or less. 

2.3.1.3 Representativeness 

 Representativeness refers to whether the data collected accurately reflect the conditions 

being measured. It is the data quality indicator most difficult to quantify. Unless the samples are 

truly representative, the other indicators are meaningless. Representativeness for monitoring of 

low ambient levels of CO in NCore is different than for routine monitoring, since the objectives 

of the monitoring are much different. Representativeness can only be assured in terms of the 

appropriate selection of the sampling site, proper implementation of ambient air sampling, and 

reasonable coverage of the sampling schedule (i.e., 24 hours per day, 7 days per week, ideally). 

2.3.1.4 Completeness 

 Completeness is defined as the amount of data collected relative to the total expected 

amount. Ideally, 100 percent of the expected amount of data would always be collected; in 

practice, completeness will be less for many reasons, ranging from calibration time and site 

relocation to power outages and equipment failure. For monitoring of ambient CO 

concentrations in NCore, EPA requires a minimum data completeness of 75 percent. In practice 

typical completeness values can often approach 90 to 95 percent. 

2.3.1.5 Comparability 

 Comparability is defined as the process of collecting data under conditions that are 

consistent with those used for other data sets of the same pollutant. The goal is to ensure that 

instruments purchased and operated by different states and local agencies produce comparable 

data. To promote comparability, this TAD describes the recommended characteristics of high 

sensitivity CO analyzers and the procedures for their installation and use. For example, all 
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monitoring agencies should purchase instruments that have the additional features described in 

Section 2.3.2, and should adhere to the sampling requirements described in Section 2.3.3. 

2.3.1.6 Method Detection Limit 

 The method detection limit (MDL) refers to the lowest concentration of a substance that 

can be reliably determined by a given procedure. The MDL is typically not provided by the 

vendor. Based on the objectives of the Precursor Gas Program, it is expected that most sites will 

be measuring pollutant concentrations at lower ranges than the typical SLAMS/NAMS network. 

Therefore, the ability to quantify concentrations at these lower levels will be very important. 

The use of a vendors advertised LDL is sufficient to make intelligent purchasing decisions. 

Vendors quantify LDLs under ideal conditions and therefore one might consider this value as the 

best possible detection that can be achieved. As these monitors are deployed into monitoring 

networks, where both environmental conditions, equipment (calibration, dilution devices, 

sampling lines, gaseous standards) and operator activities can vary, it is important to estimate 

what pollutant concentrations can truly be detected, above background noise (the potential 

conditions mentioned above). The site specific MDL establishes an estimate based on the 

routine operation (and conditions) of that instrument in the network and provides a more 

meaningful evaluation of data as it is aggregated across the precursor gas network. By 

establishing site specific MDLs, values less than the MDL can be flagged which would allow 

data users a more informed decision on the use of that data. 

 The MDL should be established on-site by supplying the analyzer at least seven times 

with a test atmosphere containing CO at a concentration that is approximately one to five times 

greater than the estimated MDL, and recording the response. To perform the MDL test, run zero 

air through the analyzer and establish an acceptable zero; dilute pollutant gas to the targeted 

concentration (one to five times the estimated MDL) and collect 20 to 25 one minute 

observations. Repeat this seven times over the course of 5 to 14 days. Average the concentration 

from the 20-25 readings; calculate the standard deviation (S) of the average readings and 

compute the MDL. The MDL is then calculated as the standard deviation of the response values 
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times the Student’s t-value for the number of test measurements (40 CFR Part 136, Appendix B). 

The MDL for high sensitivity CO analyzers should be established prior to putting the analyzers 

into service, and should be 0.080 ppm (80 ppb) or lower over an averaging time of no more than 

5 minutes. 

2.3.1.7 Lower Detectable Limit 

 The LDL is the minimum pollutant concentration that produces a signal of twice the 

noise level. To estimate the LDL, zero air is sampled and the noise level of the CO readings is 

determined according to 40 CFR 53.23(b). The vendor-specified LDL for the most sensitive 

range of high sensitivity CO analyzers should be 0.040 ppm (40 ppb) or lower, over an averaging 

time of no more than 5 minutes. 

2.3.1.8 Linear Range 

 The linear range of each high sensitivity CO analyzer should extend from approximately 

0.040 ppm to at least 5 ppm. Users should determine if their range should exceed 5 ppm and 

adjust accordingly. A range of 5 ppm may not be sufficient in all areas and situations. Note that 

some high sensitivity CO analyzers can operate simultaneously on a number of ranges, with each 

range recorded on a separate data logger channel with its own calibration curve. Although 

requiring slightly more effort to calibrate and maintain, recording of multiple ranges would allow 

capture of a wide range of CO concentrations. 

2.3.1.9 Zero/Span Drift 

 Zero drift is defined as the change in response to zero pollutant concentration, over 

12- and 24-hour periods of continuous unadjusted operation. Span drift is defined as the percent 

change in response to an upscale pollutant concentration over a 24-hour period of continuous 

unadjusted operation. Zero and span drift specifications should be obtained from the vendor 

prior to putting a high sensitivity CO analyzer into service. Such CO analyzers should have 12- 
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and 24-hour zero drift less than 100 ppb, and should have a span drift of less than ±1 percent of 

the full scale measurement range of the analyzer per 24 hours. Zero tests should be performed 

with the internal zero engaged. It is suggested that the zero trap of the analyzer be initially and 

periodically (annually) evaluated for efficiency or if the operator suspects a problem with the 

zero trap. A suggested means of confirming the functionality of the zero trap is to sample 

calibration air spiked with 1000 to 2000 ppb CO during the zero cycle, and review results for the 

automatic zeroing periods. This approach tests the key components of the zeroing/drying system 

and should meet the vendor-specified zero drift criterion. 

2.3.2 Recommended Features for High Sensitivity CO Measurements

 Continuous high sensitivity CO analyzers are commercially available from a number of 

vendors. The design of these analyzers is similar among vendors with some slight variations. A 

diagram of a typical GFC CO instrument is described in Section 2.2, and examples of specific 

instruments are provided in Section 2.3.3. In general, each of the analyzers contains the 

following systems: 

• Pneumatic System: This portion of the analyzer consists of a sample probe, sample 

inlet line, particulate filter, dryer, catalytic converter, flow meter, and pump, all used 

to condition the ambient sample air and bring it to the analyzer. 

• Analytical System: This portion of the analyzer consists of the IR source, the gas 

correlation filter, motor, optical multipass cell, detector, and bandpass filter. Being a 

mechanical device, the motor can and will wear out. The gas correlation filter can be 

subject to leakage and the IR source will eventually burn out. Extra IR sources 

should be stocked as replacement parts and the gas correlation filters should be 

replaced as necessary. 

• Electronic Hardware: This portion of the analyzer consists of the electronic 

components that control the analyzer and process the signals. This part of the 
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analyzer generally requires little or no maintenance. However, if the instrument is 

operated near the manufacturer’s recommended upper temperature limit, individual 

integrated chips can fail and cause problems with data storage or retrieval. 

 In addition to these general systems, the high sensitivity versions of the commercial GFC 

CO instruments typically have four distinct features that allow them to measure CO at ppb 

levels: 

• The sample stream is dried using a permeation tube or Nafion® Dryer prior to 

introduction to the sample cell; 

• The analyzer baseline is determined and corrected automatically and frequently by 

introducing into the sample cell CO-free air, that is generated using a heated, onboard, converter that is based on palladium (Pd), platinum (Pt), or other composition;

• The temperature of the optical bench is tightly controlled (i.e., within ± 1 °C) to 

maintain detector stability; 

• The instrument uses an ultra-sensitive detector, in order to detect very small changes 

in light intensity. 

It is recommended that the high sensitivity CO analyzers deployed in NCore employ these 

features. Examples of commercial analyzers with these features are presented below. 

2.3.3 Commercial High Sensitivity GFC CO Monitors

 Several vendors of commercial GFC CO analyzers supply instruments for both ambient 

and high sensitivity monitoring. Only high sensitivity GFC CO analyzers with nominal LDLs of 

40 ppb or below are discussed in detail in this document. Three such analyzers [from Ecotech, 

Thermo Electron Corporation, and Teledyne Advanced Pollution Instrumentation (API)] are 
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described here as examples of available high sensitivity CO monitors (no endorsement should be 

inferred). The descriptions provided for these instruments and the performance claimed for them 

are based solely on information provided by the respective vendors, and confirmation by EPA 

should not be inferred. 

2.3.3.1 Ecotech Model EC9830T 

 The Model EC9830T (Figure 2-2) is the high-sensitivity version of the Model EC9830, 

which has a U.S. EPA Reference Method designation of RFCA-0992-088.[7]

This analyzer has a vendor-specified LDL of 20 ppb, which is achieved in part by the 

implementation of the features described in Section 2.3.2 and through the use of a cell with a 6 m 

path length. This LDL is achieved by use of a Kalman digital filter to provide a compromise 

between response time and noise reduction. The 95% response time of the EC9830T is 300 

seconds with the Kalman filter. The recommended operating temperatures for the 

Model EC9830T are 20 °C to 30 °C, but it may be operated between 15 °C and 35 °C. Since 

temperature stability of the analyzer is crucial to maintaining its high sensitivity, an automatic 

background correction will be initiated if the internal temperature of the instrument changes by 

more than 4 °C. The automatic zeroing feature allows the analyzer to periodically check and 

Figure 2-2. Ecotech EC9830T high sensitivity CO analyzer (courtesy of Ecotech). 
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correct for background light intensity, and significantly reduces zero drift. The Model EC9830T 

incorporates a second order polynomial correction curve that is custom calibrated for each 

analyzer in the range of 0 to 3,000 ppb (3 ppm), with linearity within 5 percent. Outputs are 

provided in both analog and digital formats. Table 2-1 shows the specifications of the Model 

EC9820T.[7]

Table 2-1. Ecotech Model EC9830T high sensitivity CO analyzer specifications 

Parameter EC9830T Specifications 

Precision ± 5 % of reading for range 0-1 ppm 

± 1% of reading for range 1-20 ppm 

Bias Not Available 

Method Detection Limit Not Available 

Lower Detectable Limit 0.020 ppm (20 ppb) with Kalman 300 sec filter active 

Linearity ± 5% 0-1 ppm scale 

± 1% of full scale from 1-20 ppm 

Zero Drift 

Temperature dependence, 0.1% per degree C change. 

24 hours; less than 0.020 ppm (20 ppb) 

30 days; less than 0.020 ppm (20 ppb) 

Span Drift 

Temperature dependence, 0.05 % per degree C change. 

24 hours less than 0.5% of reading 

30 days less than 1.0% of reading 

2.3.3.2 Thermo Electron Corporation Model 48C-TLE 

 The Thermo Electron Corporation Model 48C-TLE Enhanced Trace Level CO 

analyzer[8-10] (Figure 2-3) is an improved version of the standard Model 48C Ambient CO 

analyzer (U.S. EPA Designation Method RFCA-0981-054). In addition to the features described 

in Section 2.3.2, the primary modifications to the Model 48C-TLE analyzer that improve its 

sensitivity over the Model 48C include the use of higher reflectance gold-coated mirrors, 

incorporation of a baseline auto-zeroing function, and the implementation of ± 1E C control of 

optical bench temperature. The recommended operating temperature for the instrument ranges 
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from 20 °C to 30 °C, but the Model 48C-TLE CO analyzer can be operated over the range of 

5 °C to 45°C. The Model 48C-TLE CO analyzer has an LDL of 0.02 ppm (20 ppb) with a 30 

second averaging time. The analyzer has ten operating ranges from 0 to 1 ppm through 0 to 

1,000 ppm, including a 0 to 5 ppm range. Data can be provided in analog or digital formats. 

Table 2-2 shows the specifications of the Model 48C-TLE CO. 

Table 2-2. Thermo Electron Model 48C-TLE CO analyzer specifications 

Performance Parameters Model 48C-TLE CO Analyzer Specifications 

Precision ±2% of reading or 0.02 ppm (20 ppb) (whichever is larger) 

Bias Not Available 

Method Detection Limit Not Available 

Lower Detectable Limit 0.04 ppm (40 ppb) ; 60 sec averaging time 

Linearity ± 1% full-scale 

Zero Drift < 0.100 ppm (100 ppb) (24 hour) 

Span Drift ± 1% full-scale (24 hour) 

Figure 2-3. Thermo Electron Model 48C-TLE CO analyzer (courtesy of 

Thermo Electron). 
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2.3.3.3 Teledyne Advanced Pollution Instrumentation (API) Model 300E 

 The Teledyne/API Model 300E high sensitivity CO analyzer[11-12] (Figure 2-4) has a 

U.S. EPA Reference Method designation of RFCA-1093-093. The Model 300E is a 

high-sensitivity version of the Model 300, which has the same Reference Method designation, 

and incorporates the recommended features described in Section 2.3.2 to achieve enhanced 

sensitivity. The Model 300E CO instrument has selectable measurement ranges that can be set 

anywhere from 0 to 1 ppm up to 0 to 1,000 ppm. The operational temperature range for the 

instrument is between 5 °C and 40 °C. Table 2-3 shows the specifications of the Model 300E. 

Table 2-3. Teledyne API Model 300E high sensitivity CO analyzer specifications 

Performance Parameters Model 300E CO Analyzer Specifications 

Precision 0.5% of reading 

Bias Not Available 

Method Detection Limit Not Available 

Lower Detectable Limit 0.04 ppm (40 ppb); 30 second averaging time 

Linearity 1% full-scale 

Zero Drift <0.1 ppm (100 ppb) per 24 hours; 0.2 ppm (200 

ppb) per 7 days 

Span Drift <0.5% reading per 24 hours, 1% reading per 

7 days 

Figure 2-4. Teledyne API Model 300E CO analyzer (courtesy of Teledyne API). 
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2.3.4 Sampling Requirements

 Proper siting of the sampling equipment and sampling probes is necessary to ensure that 

the precursor gas analyzers are obtaining representative samples of the ambient air. Likewise, 

proper environmental control and proper sampling is critical to ensuring that the analyzers are 

operating correctly and that the CO measurements are comparable to CO measurements recorded 

at other sites. 

2.3.4.1 Analyzer Siting 

 Analyzer siting should follow the criteria in 40 CFR 58, Appendix E. The installation of 

the CO analyzer should allow for the sample manifold inlet to be located between 3 and 

15 meters above ground level, with at least one meter of vertical and horizontal separation from 

supporting structures. The probe should be positioned with at least 270 degrees of unrestricted 

airflow including the predominant wind direction. The probe should be separated from the drip 

line of nearby trees or structures by at least 20 meters, and should be positioned at least twice as 

far from nearby obstacles as the height of the obstacles. 

2.3.4.2 Instrument Shelter 

 To help ensure proper performance, the precursor gas analyzers and supporting 

equipment should be installed and operated in a temperature controlled environment. An 

insulated instrument shelter should be used to protect the analyzers from precipitation and 

adverse weather conditions, maintain operating temperature within the analyzers’ temperature 

range requirements, and provide security and electrical power. The environmental control of the 

shelter should be sufficient to minimize fluctuations in shelter temperature. The recommended 

shelter temperature range is 20 °C to 30 °C, and daily changes in temperature should not exceed 

5 °C over a 24-hour period. Condensation of moisture must be prevented, and it may be 
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necessary to impose seasonal temperature ranges to assure remaining above the ambient 

dewpoint. 

2.3.4.3 Sample Inlet or Manifold 

Sample air for a high sensitivity CO analyzer should be drawn directly to the analyzer 

through FEP (Fluoroethylpropylene) or PTFE (Polytetrafluoroethylene) tubing (e.g., 1⁄4 inch 

outer diameter (OD)), equipped with a 1-micron Teflon® filter at the inlet to remove particles 

from the sample air. The filter should be changed weekly, or more often in excessively dirty 

conditions. In this configuration the CO analyzer does not share its inlet system with any other 

analyzer. 

 Some existing air monitoring stations may provide air to multiple analyzers through a 

common manifold. In such a case, it is recommended that manifolds for high sensitivity CO 

measurements be made of glass. Since neither zero air nor sample air is totally particulate-free, 

over time sample manifolds will collect particulate matter on the internal walls. A glass 

manifold is transparent, and can be inspected easily and cleaned readily by rinsing with distilled 

water and air drying. However, caution must be used with glass manifolds because of their 

fragility. The CO analyzer should be located as close to the inlet manifold as possible, to 

minimize the length of sampling lines, and sampling lines should be of constructed of FEP or 

PTFE . The sample manifold must be of sufficient diameter that outside air is drawn into the 

manifold at as close to atmospheric pressure as possible. The manifold must also allow for 

excess gas flow to be exhausted without over-pressurization (e.g., during delivery of gases from 

high-pressure cylinders.) If the pressure in the manifold differs from atmospheric pressure, the 

CO readings obtained will not be representative. A manifold of 1 inch inner diameter should be 

sufficient to avoid pressure differences. A detailed description of sample manifold designs is 

presented in Appendix A.
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2.4 Potential Problems and Solutions 

 This section describes several of the potential problems associated with high sensitivity 

CO measurements, and discusses the practical solutions to these problems, some of which the 

vendors have already implemented in their analyzers. In addition to these potential problems, 

other problems may arise in the routine operation of high sensitivity CO analyzers. Operators 

are encouraged to report any observations or anecdotal data that might add to the understanding 

or awareness of interferences or other anomalies in CO measurements. 

2.4.1 Interferences and Sources of Bias

 Preventing interferences or biases is crucial to the accurate measurement of low ambient 

levels of CO. The following sections describe several potential positive and negative sources of 

interference or bias. Section 2.4.1.1 describes the most common positive interferences (water 

vapor and CO2), and Section 2.4.1.2 describes the most common negative interferences and 

sources of bias (incomplete removal of CO during instrumental auto-zeroing and loss of CO by 

reaction or adsorption in dirty inlet lines or filters). In each section recommended procedures to 

minimize these interferences or sources of bias are described. 

2.4.1.1 Positive Interferences 

 GFC CO analyzers determine CO concentration by measuring the amount of light that is 

absorbed at a select wavelength (4.7 μm) as it passes through a sample cell containing CO. Any 

other gas in the air sample that also absorbs at those wavelengths could present an interference 

that results in an inaccurate determination of CO concentration. Removal of potential 

interferences must be done selectively such that these interferences are completely removed 

without affecting the CO concentration. For CO measurements at low ambient levels, this is 

particularly critical in order to achieve the desired sensitivity. Of particular concern are water 

vapor and CO2, which are both generally present in the atmosphere at concentrations greatly 

exceeding those of CO. Studies have shown conclusively that water vapor interferes with the 

ability of NDIR analyzers to accurately quantify CO. Water absorbs very strongly in the 3.1, 5.0 
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to 5.5, and 7.1 to 10.0 μm regions of the IR spectrum. Since water vapor absorbs light in regions 

in close proximity to the CO absorptions, removal of water vapor from the sample air is 

necessary to avoid positive interferences in the determination of CO concentration. To achieve 

this goal, high sensitivity CO analyzers are equipped with a permeation tube or NafionTM drier 

that selectively removes water vapor from the sample gas without removing CO. 

 CO2 absorbs in the IR spectrum at 2.7, 5.2, and 8.0 to 12.0 μm. These regions are also 

very close to the regions of CO absorption. Since atmospheric carbon dioxide is typically much 

higher in concentration than CO and has properties that are similar to CO, it is impractical to 

selectively remove CO2 from the sample air without removing a fraction of the CO. Therefore, it 

is important that the bandpass filter used to limit the interrogating radiation is sufficiently 

selective to restrict the wavelengths to a small region centered on the CO absorption band of 

4.7 μm. Manufacturers of high sensitivity CO analyzers select the bandpass filter to effectively 

remove CO2 interference. An added benefit of such filters is that they also limit interference 

from water vapor. 

2.4.1.2 Negative Interferences and Biases 

 High sensitivity CO analyzers are equipped with a solenoid switching system to draw 

sample air into a heated internal scrubber that converts all CO to CO2. The analyzer then 

measures the light absorption of this CO-free air and uses that light intensity to establish the zero 

reading. However, any CO that is not converted to CO2 would remain in the sample gas and 

decrease the light intensity (i.e., absorb the light) used to establish the zero reading, resulting in 

an artificially high zero reading and a negative bias when measuring the CO in ambient air. To 

avoid this situation, it is important that the heated scrubber be maintained at the manufacturer’s 

recommended temperature. Scrubber efficiency must be checked periodically, e.g., every 30 

days. A convenient means to check CO scrubber efficiency is to sample ambient air, then zero 

air, then a CO calibration mixture, all with the internal heated CO scrubber engaged. Zero air 

and sample air readings should be within ±0.010 ppm (10 ppb), and scrubber efficiency should 

be >99%. 
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2.4.2 Detector Stability

 The temperature of the detector in a high sensitivity CO analyzer must remain stable in 

order to allow for ppb sensitivity. Commercial high sensitivity CO analyzers provide a display 

of the detector temperature. This temperature should be checked periodically for compliance 

with the vendor’s required temperature setting. Bench temperature should be checked both with 

and without the zero scrubber engaged, to ensure that scrubber effluent does not cause heating of 

the optical bench. 

2.5 Supporting Equipment 

 In addition to the precursor gas analyzers, several pieces of supporting equipment should 

be maintained at each NCore site. At a minimum, this equipment includes a data acquisition 

device and calibration equipment. 

2.5.1 Data Acquisition Device

 Many types of equipment can be used to record the concentration measurements obtained 

from the analyzer. Recommended options for data acquisition are described in Section 6 of this 

TAD. 

2.5.2 Calibration Equipment

 The following equipment is recommended for calibration of a high sensitivity CO 

analyzer. 

2.5.2.1 Calibration Standard and Standard Delivery System 

 The calibration standards used for the calibration of high sensitivity CO analyzers should 

be generated by dilution of a commercially-prepared and certified compressed gas CO standard 
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using a mass flow controlled (MFC) calibration unit. The method of generating calibration 

standards by dilution involves the accurate measurement of the analyte gas flow rate and the 

diluent gas flow rate prior to blending these gas streams. The calibration unit includes mass flow 

controllers that are based upon small thermistors that are sensitive to heat loss. A potential 

voltage is applied to the thermistor and, as the gas flow increases across the thermistor, the 

resistance of the thermistor changes proportionally with the flow rate. This change in resistance 

can be measured very accurately by electronic circuitry and a feedback loop within the MFC 

circuitry monitors the gas flow and controls the flow rate to maintain the desired rate. Using two 

channels in parallel, the MFC calibrator unit controls the analyte gas flow rate and the diluent 

gas flow rate such that upon mixing these gases generates a working standard with the desired 

concentration. Typical flow ranges of the MFC units are up to 10 L/min for the diluent gas flow 

and up to 100 cm3

/min for the analyte gas flow. These systems allow for accurate dilution of CO 

standard gases from high concentration (usually 200 to 250 ppm) to low ambient working 

standard concentrations (e.g., from 0.04 to 0.8 ppm). When the analyte concentration in the 

commercially-prepared standard cylinder is certified by reference to NIST standards, and the 

MFCs are calibrated to NIST-traceable standards, the resulting working standard concentration is 

considered to be NIST-traceable. 

 It is highly important when purchasing a MFC calibrator that it meet the 40 CFR 50 

requirements of ±2 percent flow accuracy, and that the calibrations of both MFC channels be 

checked periodically using a NIST traceable flow standard. Routine MFC checks must be 

standard procedure. To accomplish such check, a NIST traceable flow standard must be on hand 

as part of every calibration system. 

2.5.2.2 Zero Air Source/Generator 

 Zero air is required for the calibration of high sensitivity CO analyzers. This air must 

contain no detectable CO (i.e., CO content must be less than the LDL of the CO analyzer) and 

must be free of particulate matter. Suitable zero air may be supplied from compressed gas 

cylinders of purified air, with additional external CO scrubbers (e.g. hopcalite or carulite) to 
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remove residual CO in the commercial product. However, it is likely too expensive and 

impractical to maintain a sufficient supply of zero air cylinders to operate a high sensitivity CO 

analyzer continuously. As an alternative, many commercially available zero-air generation 

systems can greatly reduce CO levels in air. However, depending on the required zero air flow 

rates, it may be difficult to reduce CO levels to 0.040 ppm or less, unless a Pd or Pt scrubber is 

used. A recommended approach to test zero air quality is to compare the readings of the high 

sensitivity CO analyzer in zero air in sample mode vs. the analyzer output in the “auto zero” 

mode. This comparison should be done at least quarterly and can only be done with those 

analyzers that provide a digital recording of the output in the “auto zero” mode. 

2.6 Reagents and Standards 

 Routine operation of precursor CO analyzers requires the use of calibration standards and 

zero air to conduct periodic calibrations and instrument checks. This section describes the 

requirements for these gases. 

2.6.1 Calibration Standards

 The primary CO standards used must be certified, commercially-prepared compressed gas 

standards with a certified accuracy of no worse than ±2 percent. Standards in the concentration 

range of 200 to 250 ppm are suitable choices for dilution to prepare low concentration calibration 

mixtures. The commercially-prepared CO standard may contain only CO in an inert gas 

(e.g., N2), or may be a mixed component standard that also contains known concentrations of 

other precursor gases (e.g.,SO2, NO). (Note that mixtures containing both SO2 and NO may not 

be suitable for SO2 calibration, depending on the NO rejection ratio of the SO2 analyzer – see 

Section 3 SO2 Measurements.) 

 Every gas standard used in precursor gas monitoring must be accompanied by a certificate 

of calibration from the vendor stating the concentration of the standard, the uncertainty of that 

certification, and the expiration date of the certification. Standards traceable to NIST are 

preferred. Certification documents for all standards must be retained in a common location and 
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reviewed periodically so that standards for which the vendor’s certification has expired may be 

removed from service and replaced. 

2.6.2 Zero Air

 Zero air used as dilution gas for calibration purposes should have a CO concentration 

below the LDL of the high sensitivity CO monitor. Commercial cylinder gas grades such as 

Ultra Zero and CEM grade may be suitable as a starting point, provided additional cleanup is 

employed as noted in Section 2.5.2.2. Commercial zero air further scrubbed of CO may be used 

to crosscheck the purity of air provided by a commercial continuous air purification system. 

2.7 Quality Control 

 A thorough quality control program is critical to the collection of high sensitivity CO 

monitoring data, and must be implemented at each NCore site. Components of such a program 

are described below. 

2.7.1 Site Visit Checks and Remote Diagnostic Checks

 To determine whether the CO analyzer is working properly, field operators should 

conduct routine checks of instrument diagnostics and performance every time they visit the 

monitoring station. Each agency needs to develop diagnostic or maintenance checklists or 

electronic spreadsheets to document that all required checks have been made. Such lists and 

sheets should be useful both for collecting diagnostic information and for assessing the quality of 

the monitoring data. To the extent possible, diagnostic checks can be done remotely, provided 

the data acquisition system allows remote access to instrument diagnostic information (see 

Section 6). 

2.7.2 Multipoint Calibrations

 A multipoint calibration includes a minimum of four points (three spaced over the 

expected range and a zero point), generated by the calibration system. Although more points 
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may be preferable, current high sensitivity CO analyzers typically provide linear response over 

the entire operating range; therefore, four points should be sufficient. Multipoint calibrations 

must be done prior to the high sensitivity CO analyzer being put into service and should be 

repeated at least quarterly thereafter. An analyzer should be calibrated (or recalibrated) if any of 

the following conditions occur: 

• Upon initial installation; 

• The Level 1 span check or precision check difference exceeds 15 percent; 

• After repairs or service is conducted that may affect the calibration; 

• Following physical relocation or an interruption in operation of more than a few days; 

• Upon any indication that the analyzer has malfunctioned or a there has been a change 

in calibration; or 

• The measured concentration values during challenges with performance test samples 

(Section 5.4.1) differ from the certified standard values by ±15 percent. 

The analyzers should be calibrated in-situ without disturbing the normal sampling inlet system to 

the degree possible. 

2.7.3 Level 1 Zero/Span Checks 

 Level 1 zero and span calibrations are simplified, two-point calibrations used when 

adjustments may be made to the analyzer. When no adjustments are made to the analyzer, the 

Level 1 calibration may also be called a zero/span “check” and must not be confused with a level 

2 zero and span check. Level 1 zero and span checks should be conducted nightly. They are used 

to assess if the analyzers are operating properly and to assess if any drift in instrument response 
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has occurred. The level 1 check should not exceed ±15 percent. Zero drift is internally adjusted 

by the analyzer. The zero check is used to verify that the internal zero is working properly. 

They are conducted by challenging the analyzer with zero air and a test atmosphere containing 

CO at a concentration of between 70 percent and 90 percent of the full measurement range in 

which the analyzer is operating. The challenge gas should be sampled through as much of the 

sampling inlet system as practical to mimic the actual sampling of ambient air. The results of the 

Level 1 zero/span check should be plotted on control charts to graphically illustrate the trends in 

the response of the analyzer to the challenge gases. If the measured concentrations fall outside 

of the control limits, the accuracy of the MFC calibration system should be checked with a 

NIST-traceable flow standard. If the MFC flow accuracy is confirmed, the data recorded since 

the last successful Level 1 check should be flagged and the analyzer should be recalibrated using 

the multipoint calibration procedures described in Section 2.7.2. 

State-of-the-art calibration equipment now exists that is fully automated. These "new 

generation" calibration units are fully integrated with computers, mass flow calibrators, and the 

associated hardware and software where they can create test atmospheres manually or 

automatically. For the precursor gas program, it is recommended that the NCore sites have fully 

automated calibration capability. Below are a number of reasons why this is advantageous: 

• By performing the calibrations or checks automatically, agencies no longer spend the 

manpower needed to perform them. 

• Automated calibrations or checks can be triggered internally or by a DAS. Since newer 

DASs allow remote access, this allows a remote user to challenge the analyzers without 

actually being present. 

• High sensitivity precursor gas analyzers are expected to have more zero and span drift than 

less sensitive analyzers; therefore, it is important that a zero and Level I check be performed 

daily. 
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• New generation DASs can record calibration and check data and allow remote users to track 

daily Level I check and zero drift. This is important for data validation, verification and 

troubleshooting. 

2.7.4 Precision Checks

 At least once every two weeks a precision check should be conducted by challenging the 

CO analyzer with a known low CO concentration to assess the performance of the analyzer. The 

precision checks should be conducted by challenging the precursor CO analyzer with a standard 

gas of known concentration between 0.25 and 0.50 ppm (250 and 500 ppb). After completion of 

the precision check, the operator should calculate the percent difference between the measured 

value and the known standard value. Precision should be calculated quarterly, using the 

calculated percent differences from the precision checks, according to the equations provided in 

Section 2.3.1.1. For acceptable precision to be maintained it is recommended that the calibration 

system’s gas flows be verified frequently against a NIST flow standard, and adjusted if necessary 

before making any adjustments to the analyzer. 

2.8 Preventive Maintenance and Troubleshooting 

 Long-term operation of continuous high sensitivity precursor gas analyzers requires a 

preventive maintenance program to avoid instrument down-time and data loss. Despite active 

preventive maintenance, occasional problems may arise with the high sensitivity CO analyzers. 

This section briefly describes several key items that might be included in the preventive 

maintenance program established for high sensitivity CO analyzers deployed at NCore sites, as 

well as some of the troubleshooting activities that may be useful in resolving unexpected 

problems with these analyzers. This discussion is not meant to be exhaustive or comprehensive 

in detail. More thorough discussions can be found in the analyzer operation manuals, and should 

be included in SOPs developed for these analyzers. Example SOP’s prepared by EPA are 

included as Appendix B of this TAD. 
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2.8.1 Preventive Maintenance

 Routine preventive maintenance procedures should be in place to prevent down-time and 

data loss. Management and field operators should jointly develop their preventive maintenance 

program. A program designed by persons unfamiliar with analyzer operations may include 

unnecessary items or omit mandatory ones. Several factors linked to shelter and sampling 

manifold design can contribute to data loss. CO values can be low if the sample probe, manifold, 

and lines are dirty, cracked, or leaky. The sample probe and manifold should be cleaned at least 

every six months. FEP and PTFE sampling lines should be replaced every two years. Teflon® 

filters used in the sampling train to remove fine particles should be replaced at least once per 

month, but may need to be replaced as often as every week, depending on the condition of the 

filter and the particulate loading around the monitoring site. 

 Table 2-4 illustrates items that monitoring agencies should include in their preventive 

maintenance program for precursor CO monitoring. 

 In addition to a schedule, the preventive maintenance plan should also include more 

detailed task descriptions, such as illustrated below: 

• Because the analyzer pneumatic system requires so much preventive maintenance, the 

tubing, solenoids, and pump should be inspected regularly. Cracked tubing or loose 

fittings can cause the instrument to analyze room air rather than ambient air and lead 

to invalid data. A faulty pump can also cause problems with pneumatic systems. 

When oscillations in the flow rate force the operator to adjust the flow continually, 

the pump is failing and should be either repaired or replaced. 

• Check the instrument for vibration. When pumps get old, they sometimes will vibrate 

more than is normal. If this occurs, it can cause cracks if the tubing is touching 

another surface. 
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• Consult the analyzer operations manual for complete details on operation and 

maintenance. 

Table 2-4. Example of a preventive maintenance schedule for high sensitivity CO 

analyzers. 

Item Schedule

Replace particle filter Weekly 

Clean fan/fan filter Semi-annually 

Inspect internal, external tubing; replace if necessary Annually 

Rebuild or replace pump Every two years, or as needed 

Replace IR source As needed based on 

manufacturer’s diagnostics 

Clean optic bench As needed 

Replace wheel motor As needed 

Replace gases in correlation wheel As needed 

2.8.2 Troubleshooting

 High sensitivity CO analyzers are subject to many factors that can cause inaccurate 

measurements or down-time. Table 2-5 summarizes common problems seen with high 

sensitivity CO analyzers, their possible causes, and possible solutions. More specific 

information can be found in the manufacturer’s operations manual. 
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Table 2-5. Instrument troubleshooting for high sensitivity CO analyzers. 

Problem Possible Cause Possible Solution 

Defective DC power supply Replace power supply Noisy output Dirty optics Clean optics bench

High positive zero drift Defective bandpass filter Replace filter 

IR source is defective Replace IR source No Response to Span Gas IR power supply defective Replace IR power supply 

IR source is defective Replace IR source

Differential Signal at Zero IR power supply is defective Replace IR power supply 

CO leak from correlation wheel Replace wheel 

Pump failure Check pump 

Zero output at ambient levels IR source failure Replace IR source 

IR power supply defective Replace power supply 

No flow through analyzer Pump failure Replace/ rebuild pump head 

Reference signal at zero N2 leak from correlation wheel Replace wheel 

When troubleshooting, an operator must constantly be aware of environmental factors that may 

affect the instruments. Environmental factors can also cause sporadic problems that can be 

difficult to diagnose. Examples of factors that may affect the performance of the high sensitivity 

CO analyzers are: 

• Variable shelter temperature (fluctuations greater than several degrees); 

• Excessive vibration from other equipment; 

• Voltage instability; fluctuations in the 110 VAC line voltage; 

Air conditioning system blowing on the instrument; 

• Frequent opening of the door of the shelter.

2.9 References 

1. “National Ambient Air Monitoring Strategy,” U.S. Environmental Protection Agency, 

Office of Air Quality Planning and Standards, Research Triangle Park, NC 27711, 

April 2004, Final Draft. 
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2. Parrish, D.D., Holloway, J.S., Fehsenfeld, F.C, “Routine Continuous Measurement of 

Carbon Monoxide with Parts per Billion Precision,” Environmental Science and 

Technology, 28:9, 1615-1618, 1994. 

3. Lobert, J.M., Harris, J.M., “Precursors and Air Mass Origin at Kaashidhoo, Indian 

Ocean,” Journal of Geophysical Research, Volume 107(D19), 8013, doi: 

10.1029/2001JD000731, 2002. 

4. Cogan, M., Lobert. J.M., “Instrumentation for Trace-Level Measurements of Carbon 

Monoxide in Pristine Environments,” Instrument Society of America, Proceedings of the 

43rd Annual ISA Analysis Division Symposium, Volume 31, 1998. 

5. “Air Quality Criteria for Carbon Monoxide,” EPA/600/8-90/045F, U.S. Environmental 

Protection Agency, Office of Research and Development, Washington, DC, 20460, 

December 1991. 

6. Rhodes, R.C., Guidelines on the Meaning and Use of Precision and Accuracy Data 

Required by 40CFR Part 58, Appendices A and B, EPA60014-83-023, U.S. 

Environmental Protection Agency, Research Triangle Park, NC, June 1983. 

7. Ecotech Pty Ltd. (2004). “EC9830T Trace Carbon Monoxide Analyzer Product 

Specification Sheet.” Accessed September, 2004. Available at 

http://www.ecotech.com.au/brochures_new/EC9830T.pdf. 

8. Thermo Electron Corporation (2004a). “Instruction Manual, Model 48C Precursor Gas 

Filter Correlation CO Analyzer.” Accessed September, 2004. Available at 

https://www.thermo.com/eThermo/CMA/PDFs/Various/156File_17817.pdf. 

9. Thermo Electron Corporation (2004b). “Model 48C Gas Filter Correlation CO Analyzer 

Data Sheet.” Accessed September, 2004. Available at http://www.thermo.com/eThermo/

CMA/PDFs/Product/productPDF_12767.pdf 

10. Thermo Electron Corporation (2004c). Personal Communication with Michael 

Nemergut. 

11. Teledyne Advanced Pollution Instrumentation (2004a). “Model 300E Gas Filter 

Correlation CO Analyzer Data Sheet.” Accessed September, 2004. Available at 

http://www.teledyne-api.com/products/model_300e.asp. 

12. Teledyne Advanced Pollution Instrumentation (2004b). “Instruction Manual, Model 

300E Gas Filter Correlation CO Analyzer.” Accessed September, 2004. Available at 

http://www.teledyne-api.com/manuals/04288A5.M300E.Manual.pdf. 
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3.0 HIGH SENSITIVITY SULFUR DIOXIDE MEASUREMENTS 

3.1 Introduction 

 

 Sulfur dioxide (SO2) has been identified as a key precursor of fine particulate matter 

(PM2.5) and, thus, plays an important role in PM-related health effects. A variety of sulfur 

compounds are released to the atmosphere from both natural and anthropogenic sources. 

Ninety-five percent of sulfur emitted to the air from anthropogenic sources is released as sulfur 

dioxide, mainly from stationary sources that burn fossil fuels (e.g., coal and oil) that contain 

sulfur. The major human sources of SO2 are coal-burning electrical utilities, refineries, and ore 

smelters. The amount of SO2 released depends on the sulfur content of the fuel; high-sulfur coal 

may contain as much as six percent sulfur by weight. 

3.1.1 Properties of SO2

 SO2 is a colorless gas that can be detected by taste and odor in ambient air at 

concentrations as low as 0.3 ppm. Above 3 ppm, SO2 has a pungent, irritating odor similar to a 

struck match. In addition to having a bad odor, high concentrations of sulfur dioxide can affect 

breathing, cause respiratory illnesses, and aggravate existing respiratory and cardiovascular 

diseases. 

 SO2 is found at appreciable levels (i.e., low ppb) in the lower atmosphere (troposphere), 

where it is oxidized to sulfuric acid (H2SO4), by both gas-phase photochemical reactions and 

aqueous-phase reactions with hydrogen peroxide and other oxidants in cloud water. The 

gas-phase and aqueous-phase oxidation pathways are roughly equally important in converting 

SO2 to H2SO4. Sulfuric acid is non-volatile and condenses into particulate form, typically with 

partial to complete neutralization by atmospheric ammonia (NH3). Sulfates account for a 

substantial fraction of suspended particulate matter in urban air. They can be transported long 

distances and return to the earth as a major component of acid rain. 
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3.1.2 Historical Overview of Measurement Method

 The UV fluorescence monitoring method for atmospheric SO2 was developed to improve 

upon the flame photometric detection (FPD) method for SO2, which in turn had displaced the 

pararosaniline wet chemical method for SO2 measurement. The pararosaniline method is still the 

U.S. EPA’s Reference Method for atmospheric SO2, but is rarely used because of its complexity 

and slow response, even in its automated forms. Both the UV fluorescence and FPD methods are 

designated as Equivalent Methods by EPA, but UV fluorescence has largely supplanted the FPD 

approach because of the UV method’s inherent linearity, sensitivity, and the absence of 

consumables, such as the hydrogen gas needed for the FPD method. Numerous vendors supply 

UV fluorescence SO2 analyzers, including a few who supply high sensitivity analyzers 

(examples are provided below). 

3.2 Summary of SO2 Measurement by UV Fluorescence 

 The current method for the measurement of SO2 is based on the principle that SO2

molecules absorb ultraviolet (UV) light at one wavelength and emit UV light at a different 

wavelength. This process is known as fluorescence, and involves the excitation of the SO2

molecule to a higher energy electronic state by light absorption. Once excited, the molecule 

decays non-radiatively to a lower energy electronic state from which it then decays to the 

original, or ground, electronic state by emitting a photon of light at a longer wavelength 

(i.e., lower energy) than the original excitation light. The process can be summarized in the 

following equations: 

[Eq. 3-1] 

[Eq. 3-2] 

* SO2 + hv1 → SO2

2 2

* SO2 → SO + hv
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where SO2* represents the excited state of SO2, hv1 and hv2 represent the energy of the excitation 

and fluorescence photons, respectively, and hv2 < hv1. The intensity of the emitted light is 

proportional to the number of SO2 molecules in the sample gas. 

 Figure 3-1 shows a schematic illustration of the optical chamber of a commercial SO2

analyzer. Light from a high intensity UV lamp passes through a bandwidth filter, allowing only 

photons with wavelengths around the SO2 absorption peak (near 214 nm) to enter the optical 

chamber. The light passing through the source bandwidth filter is collimated using a UV lens 

and passes through the optical chamber, where it is detected on the opposite side of the chamber 

by the reference detector. A photomultiplier tube (PMT) is offset from and placed perpendicular 

to the light path to detect the SO2 fluorescence. Since the SO2 fluorescence (330 nm) is at a 

wavelength that is different from the excitation wavelength, an optical bandwidth filter is placed 

in front of the PMT to filter out any stray light from the UV lamp. A lens is located between the 

filter and the PMT to focus the fluorescence onto the active area of the detector and optimize the 

fluorescence signal. 

Figure 3-1. Schematic illustration of the optical chamber of a precursor SO2 analyzer. 
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3.3 Recommendations for NCore 

 Since the high sensitivity SO2 analyzers deployed at NCore sites are intended to monitor 

low ambient SO2 concentrations, it is important that they meet a variety of performance criteria. 

Many of these performance criteria are more stringent than those for routine SO2 analyzers; 

consequently, a number of features are required in the high sensitivity SO2 analyzers in order to 

achieve the performance criteria. This section describes the recommended performance criteria 

and the analyzer features that are recommended in order to achieve the performance criteria, and 

provides examples of commercial high sensitivity SO2 analyzers that are available for 

deployment at the NCore sites. Additionally, this section discusses some important sampling 

requirements that should be considered during the installation of the analyzers. 

3.3.1 Recommended Method Performance Criteria

 The U.S. EPA has recently assessed the measurement quality objectives needed for high 

sensitivity precursor gas monitoring in NCore, relative to the long-established statistics stated in 

40 CFR 58.[1] In particular, EPA recommends that measurement quality objectives for bias and 

precision be based on upper confidence limits at the monitoring site level, to provide a higher 

probability of reaching appropriate conclusions (e.g., in comparisons to NAAQS). The intent of 

this recommendation is to move S/L/T agencies to a performance-based quality system i.e., 

allowing organizations that show tight control of precision and bias to reduce the frequency of 

certain QC checks, and to focus their quality system efforts where most needed. 

 The U.S. EPA recommends that the high sensitivity SO2 analyzers that are deployed at 

NCore sites meet the following method performance criteria. 
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3.3.1.1 Precision 

 Precision is defined as the measure of agreement among individual measurements of the 

same property taken under the same conditions. Precision is assessed from checks that are 

performed at least once every two weeks (see Sections 3.7.4 and 5.3.3). Calculations to assess 

precision are given below and should be used to assess precision on a quarterly basis. It is 

recommended that high sensitivity SO2 analyzers have a 95 percent probability limit for 

precision of ±15 percent or less. 

 Calculation of precision starts with the comparison of the known challenge concentration 

used in the precision checks to the corresponding measured concentrations reported by the 

analyzer. The resulting percent differences are then used as described below. For each single 

point precision check, calculate the percent difference, di, as follows: 

Equation 1

 

where reported is the concentration indicated by the high sensitivity SO2 analyzer and challenge

is the concentration of the standard used in the precision check. The precision estimator is then 

calculated as the coefficient of variation (CV) upper bound, using Equation 2 as follows: 

Equation 2

 

 

where n is the number of data points (i.e., precision check comparisons), the di values are the 

resulting percent differences, and X 0.1,n-1 is the 10th percentile of a chi-squared distribution with 

n-1 degrees of freedom. 

d reported challenge

challenge i = − ⋅100

( ) CV

nd d

n n

n

X

i

i

n

i

i

n

n

=

⋅ −

⎛

⎝

⎜

⎜

⎞

⎠

⎟

⎟

− ⋅ = = −

−

∑ ∑ 2

1 1

2

2

01 1 1

1

. ,
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3.3.1.2 Bias 

 Bias is defined as a systematic or persistent distortion of a measurement process that 

causes errors in one direction. Bias is assessed from the degree of agreement between a 

measured value and the true, expected, or accepted value. Analyzer bias is calculated using 

comparisons of known challenge concentrations to the corresponding measured concentrations 

reported by the analyzer. The challenge comparisons used to assess bias should be the same as 

those used to assess precision (see Section 3.3.1.1 above). The bias estimator is an upper bound 

on the mean absolute value of the percent differences as described in Equation 3 as follows: 

Equation 3

where n is the number of challenge comparisons being aggregated; t0.95,n-1 is the 95th quantile of 

a t-distribution with n-1 degrees of freedom; the quantity AB is the mean of the absolute values 

of the individual di’s and is calculated using Equation 4 as follows: 

Equation 4

 

and the quantity AS is the standard deviation of the absolute value of the di’s and is calculated 

using Equation 5 as follows: 

Equation 5

 

 

bias AB t

AS

n

=+ ⋅ 0. , 95 n −1

AB

n

d i

i

n

= ⋅

=

∑1

1

( ) AS

nd d

n n

i

i

n

i

i

n

=

⋅ −⎛

⎝

⎜

⎜

⎞

⎠

⎟

⎟

−

= =

∑ ∑ 2

1 1

2

1
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Since the bias statistic as calculated in Equation 3 uses absolute values, it does not have a 

direction or sign (negative or positive) associated with it. The sign of the calculated bias is to be 

determined by rank ordering the percent differences of the QC check samples from a given 

analyzer for a particular assessment interval. Calculate the 25th and 75th percentiles of the 

percent differences for each analyzer. The absolute bias upper bound should be flagged as 

positive if both the 25th and 75th percentiles are positive, and as negative if both these percentiles 

are negative. The absolute bias upper bound would not be flagged if the 25th and 75th percentiles 

are of different signs. It is recommended that high sensitivity SO2 analyzers have an upper 

bound for the average bias of ± 15 percent or less. 

3.3.1.3 Representativeness 

 Representativeness refers to whether the data collected accurately reflect the conditions 

being measured. It is the data quality indicator most difficult to quantify. Unless the samples are 

truly representative, the other indicators are meaningless. Representativeness for monitoring of 

low ambient levels of SO2 in NCore is different than for routine monitoring, since the objectives 

of the monitoring are much different. Representativeness can only be assured in terms of the 

appropriate selection of the sampling site, proper implementation of ambient air sampling, and 

reasonable coverage of the sampling schedule (i.e., 24 hours per day, 7 days per week, ideally). 

3.3.1.4 Completeness 

 Completeness is defined as the amount of data collected relative to the total expected 

amount. Ideally, 100 percent of the expected amount of data would always be collected; in 

practice, completeness will be less for many reasons, ranging from calibration time and site 

relocation to power outages and equipment failure. For monitoring of ambient SO2

concentrations in NCore, EPA requires a minimum data completeness of 75 percent. In practice 

typical completeness values can often approach 90 to 95 percent. 
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3.3.1.5 Comparability 

 Comparability is defined as the process of collecting data under conditions that are 

consistent with those used for other data sets of the same pollutant. The goal is to ensure that 

instruments purchased and operated by different states and local agencies produce comparable 

data. To promote comparability, this TAD describes the recommended characteristics of high 

sensitivity SO2 analyzers and the procedures for their installation and use. For example, all 

monitoring agencies should purchase instruments that have the additional features described in 

Section 3.3.2, and should adhere to the sampling requirements described in Section 3.3.3. 

3.3.1.6 Method Detection Limit 

 The MDL refers to the lowest concentration of a substance that can be reliably 

determined by a given procedure. The MDL is typically not provided by the vendor. Based on 

the objectives of the Precursor Gas Program, it is expected that most sites will be measuring 

pollutant concentrations at lower ranges than the typical SLAMS/NAMS network. Therefore, 

the ability to quantify concentrations at these lower levels will be very important. The use of a 

vendors advertised LDL is sufficient to make intelligent purchasing decisions. Vendors quantify 

LDLs under ideal conditions and therefore one might consider this value as the best possible 

detection that can be achieved. As these monitors are deployed into monitoring networks, where 

both environmental conditions, equipment (calibration, dilution devices, sampling lines, gaseous 

standards) and operator activities can vary, it is important to estimate what pollutant 

concentrations can truly be detected, above background noise (the potential conditions 

mentioned above). The site specific MDL establishes an estimate based on the routine operation 

(and conditions) of that instrument in the network and provides a more meaningful evaluation of 

data as it is aggregated across the precursor gas network. By establishing site specific MDLs, 

values less than the MDL can be flagged which would allow data users a more informed decision 

on the use of that data. 
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 The MDL should be established on-site by supplying the analyzer at least seven times 

with a test atmosphere containing SO2 at a concentration that is approximately one to five times 

greater than the estimated MDL, and recording the response. To perform the MDL test, run zero 

air through the analyzer and establish an acceptable zero; dilute pollutant gas to the targeted 

concentration (one to five times the estimated MDL) and collect 20 to 25 one minute 

observations. Repeat this seven times over the course of 5 to 14 days. Average the concentration 

from the 20-25 readings; calculate the standard deviation (S) of the average readings and 

compute the MDL. The MDL is then calculated as the standard deviation of the response values 

times the Student’s t-value for the number of test measurements (40 CFR Part 136, Appendix B). 

The MDL for high sensitivity SO2 analyzers should be 0.30 ppb or lower over an averaging time 

of no more than 5 minutes. 

3.3.1.7 Lower Detectable Limit 

 The LDL is the minimum pollutant concentration that produces a signal of twice the 

noise level. To estimate the LDL, zero air is sampled and the noise level of the SO2 readings is 

determined according to 40 CFR 53.23(b). The vendor-specified LDL for the most sensitive 

range of high sensitivity SO2 analyzers should be 0.20 ppb or lower, over an averaging time of 

no more than 5 minutes. 

3.3.1.8 Linear Range 

 The linear range of each high sensitivity SO2 analyzer should extend from approximately 

0.20 ppb to at least 100 ppb. Users should determine if their range should exceed 100 ppb and 

adjust accordingly. A range of 100 ppb may not be sufficient in all areas and situations. Note 

that some high sensitivity SO2 analyzers can operate simultaneously on a number of ranges, with 

each range recorded on a separate data logger channel with its own calibration curve. Although 

requiring slightly more effort to calibrate and maintain, recording of multiple ranges would allow 

capture of a wide range of SO2 concentrations. 
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3.3.1.9 Zero/Span Drift 

 Zero drift is defined as the change in response to zero pollutant concentration, over 

12- and 24-hour periods of continuous unadjusted operation. Span drift is defined as the percent 

change in response to an upscale pollutant concentration over a 24-hour period of continuous 

unadjusted operation. Zero and span drift specifications should be obtained from the vendor 

prior to putting a high sensitivity SO2 analyzer into service. Such SO2 analyzers should have 12- 

and 24-hour zero drift less than 0.20 ppb, and should have a span drift of less than ±1 percent of 

the full scale measurement range of the analyzer per 24 hours. 

3.3.1.10 NO Rejection Ratio 

 The NO rejection ratio refers to the effectiveness with which fluorescent emission from 

nitric oxide (NO) is blocked in a UV fluorescence SO2 analyzer. This interfering emission can 

be greatly reduced by optical filtering of the light reaching the PMT. For high sensitivity SO2

monitoring in NCore, it is recommended that the NO rejection ratio of the SO2 analyzer be at 

least 100 to 1, i.e., 100 ppb of NO must produce a response equivalent to that from no more than 

1 ppb of SO2. 

3.3.2 Recommended Features for High Sensitivity SO2 Measurements

 Continuous UV fluorescence SO2 analyzers are commercially available from a number of 

vendors. The design of these analyzers is similar among vendors with some slight variations. A 

diagram of the typical UV fluorescence instrument is shown above in Section 3.2, and examples 

of specific instruments are provided in Section 3.3.3. In general, each of the analyzers contains 

the following systems: 

• Pneumatic System: This portion of the analyzer consists of sample probe, 

sample inlet line, particulate filter, hydrocarbon scrubber/kicker, dryer (if 
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needed), sample cell, flow meter, and pump, all used to bring ambient air from 

the inlet to the defector. 

• Analytical System: This portion of the analyzer consists of the UV source 

with the associated source filters, lenses, and optics, as well as the light 

baffles, the detector (photomultiplier tube), and bandpass filters. 

• Electronic Hardware: This portion of the analyzer consists of the electronic 

components that control the analyzer and process the signals. This part of the 

analyzer generally requires little or no maintenance. If the instrument is 

operated outside the manufacturer’s recommended temperature range, 

however, individual integrated chips can fail and cause problems with 

operation, data storage, or retrieval. 

 In addition to these general systems, the high sensitivity versions of the commercial 

UV fluorescence SO2 analyzers typically have the following features that allow them to measure 

SO2 at sub-ppb levels: 

• A high intensity pulsed UV light source that provides a greater degree of 

sensitivity; 

• Multiple reflective optical filters that allow only light at the wavelength 

causing excitation of the SO2 molecules to enter the optical chamber, while 

excluding all light at wavelengths that may cause interference; and 

• Optical filtering to maximize the rejection of fluorescence from NO 

molecules. 
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It is recommended that the high sensitivity SO2 analyzers deployed in NCore employ these 

features. Examples of commercial analyzers with these features are presented below. 

3.3.3 Commercial High Sensitivity UV Fluorescence SO2 Monitors

 High sensitivity SO2 analyzers are commercially available from a number of vendors. 

Examples of such analyzers discussed in this section are closely similar to instrumentation 

designated as Federal Equivalent Methods; however, modifications to improve measurement 

sensitivity have been made. The following three instruments are shown as examples of 

commercially available high sensitivity SO2 analyzers (no endorsement should be inferred). The 

descriptions provided for these instruments and the performance claimed for them are based 

solely on information provided by the respective vendors, and confirmation by EPA should not 

be inferred. 

3.3.3.1 Ecotech Model EC9850T 

The Ecotech Model EC9850T SO2 analyzer[2] shown in Figure 3-2 is a UV fluorescence 

SO2 analyzer specifically designed to measure background concentrations of SO2 with a lower 

detection limit of 200 ppt (0.2 ppb). The EC9850T is a high sensitivity version of the Ecotech 

ML9850/EC9850 that has a U.S. EPA Equivalent Method Designation of EQSA-0193-092. The 

higher sensitivity is achieved in part by using a specially selected high output UV lamp operating 

at 214 nm, a Kalman digital filter that continuously provides a compromise between response 

time and noise reduction, and a special high performance SO2 scrubber impregnated with 

Na2CO3 solution. Scrubbed sample air is used for zeroing of the analyzer’s response. The 

EC9850T SO2 analyzer uses a 360 nm filter to reduce interference from NO and potential 

interference from other species. The analyzer has multiple range settings up to 0 to 200 ppb full 

scale, and has a recommended operating temperature range of 20 °C to 30 °C, but may be 

operated between 15 °C and 35 °C. The EC9850T SO2 analyzer has both analog and digital 

outputs. Table 3-1 shows the specifications of the Model EC9850T. 
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Table 3-1. Ecotech EC9850T SO2 analyzer specifications. 

Performance 

Parameters EC9850T SO2 Analyzer Specifications 

Precision ± 2% of reading 

Bias Not available 

Method Detection Limit Not available 

Lower Detectable Limit 200 ppt (0.2 ppb) (with Kalman or 300 sec filter active) 

Linearity Not available 

Zero Drift Temperature dependence, 0.1% per degree C changes. 

24 hours; less than 200 ppt (0.2 ppb) 

Span Drift 

Temperature dependence, 0.05 % per degree C changes. 

24 hours less than 0.5% of reading 

30 days less than 1.0% of reading 

NO Rejection Ratio Not availablea 

a

: Vendor states rejection ratio is high, but difficult to quantify; dependent on water vapor content of air. 

 

3.3.3.2 Thermo Electron Corporation Model 43C-TLE

 The Model 43C-TLE enhanced high sensitivity pulsed fluorescence SO2 analyzer[3] is 

shown in Figure 3-3. The Model 43C-TLE SO2 analyzer is a successor to the Model 43C 

analyzer, which has a U.S. EPA Equivalent Method Designation of EQSA-0486-060. As 

Figure 3-2. Ecotech EC9850T SO2 analyzer (courtesy of Ecotech). 
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recommended in Section 3.3.2, the Model 43C-TLE achieves higher sensitivity than the 

Model 43C through the use of additional reflective bandpass filters to further reduce stray light, 

and by operation of the UV flash lamp at a higher voltage, which increases the total output light 

intensity. Additionally, the Model 43C-TLE also includes a longer optical bench that increases 

the effective sample path length and improves sensitivity. Furthermore, optimization of the 

optical properties of the detector filter allows for greater rejection of NO interference. This 

feature allows an instrument originally designed for rural background monitoring applications to 

also be used in urban monitoring programs such as NCore Level 2. 

 The Model 43C-TLE SO2 analyzer has multiple range settings up to 1 ppm full scale and 

may be safely operated in the temperature range of 0 °C to 45 °C. The Model 43C-TLE analyzer 

displays the SO2 concentration on a screen on the front panel of the analyzer, and has both 

analog and digital outputs. An optional capability of the 43C-TLE is for generation of internal 

zero and span mixtures using an SO2 permeation tube, although this means of calibration is not 

recommended for use in NCore. Table 3-2 shows the specifications of the Model 43C-TLE. 

Figure 3-3. Thermo Electron Model 43C-TLE SO2 analyzer (courtesy Thermo 

Electron).
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Table 3-2. Thermo Electron Model 43C-TLE SO2 analyzer specifications. 

Performance 

Parameters Model 43C-TLE SO2 Analyzer Specifications 

Precision 1% of reading or 0.2 ppb 

Bias Not available 

Method Detection Limit Not available 

Lower Detectable Limit 

0.2 ppb (10 sec avg. time) 

0.10 ppb (60 sec avg. time) 

0.05 ppb (300 sec avg. time) 

Linearity ± 1% of full scale 

Zero Drift less than 0.2 ppb per day 

Span Drift ± 1% per week 

NO Rejection Ratio <2.5 ppb equivalent with 500 ppb NO interference 

3.3.3.3 Teledyne Advanced Pollution Instrumentation (API) Model 100AS 

 The Teledyne API Model l00AS SO2 analyzer[4, 5] shown in Figure 3-4 is based on the 

Model 100A fluorescence SO2 Analyzer. Both the Model 100A and the Model 100AS analyzers 

are designated as U.S. EPA Equivalent Method Number EQSA-0495-100. The sensitivity and 

stability of the Model 100AS analyzer is achieved in part through the use of an optical shutter to 

compensate for PMT drift and a reference detector to correct for changes in UV lamp intensity. 

A hydrocarbon “kicker” and advanced optical design combine to minimize inaccuracies due to 

interferents, including NO. The Model 100AS has sensitivity ranges of 0 to 10 ppb full scale up 

to 0 to 1 ppm full scale and can measure SO2 with a lower detectable limit of 0.10 ppb. The 

analyzer may be safely operated in the temperature range of 5 °C to 40 °C. The Model 100AS 

has both analog and digital outputs. An optional capability of the Model 100AS is for generation 

of internal zero and span mixtures, using an SO2 permeation tube. Table 3-3 shows the 

specifications of the Model 100AS. 

Note: The Model 100AS is not API’s “true high sensitivity” analyzer, and the Model 100EU high 

sensitivity analyzer is expected to be commercially available this year. 
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Table 3-3. Teledyne API Model 100AS SO2 analyzer specifications. 

Performance 

Parameters 

Teledyne API Model 100AS SO2 Analyzer 

Specifications 

Precision 0.5% of reading 

Bias Not available 

Method Detection Limit Not available 

Lower Detectable Limit 100 ppt (0.1 ppb) (4 minute averaging time) 

Linearity 1% full scale 

Zero Drift < 0.2 ppb/24 hours 

Span Drift < 0.5% reading/24 hours 

NO Rejection Ratio 100:1 standard; 250:1 with optional filter 

3.3.4 Sampling Requirements

 Proper siting of the sampling equipment and sampling probes is necessary to ensure that 

the gas analyzers are obtaining representative samples of the ambient air. Likewise, proper 

environmental control of the analyzer and proper sampling are critical to ensuring that the 

analyzers are operating correctly and that the SO2 measurements are comparable to SO2

measurements recorded at other sites. 

Figure 3-4. Teledyne API Model 100AS SO2 analyzer (courtesy Teledyne API). 
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3.3.4.1 Analyzer Siting 

 Analyzer siting should follow the criteria in 40 CFR58, Appendix E. The installation of 

the precursor SO2 analyzer should allow for the sample manifold inlet to be located between 3 

and 15 meters above ground level, with at least one meter of vertical and horizontal separation 

from supporting structures. The probe should be positioned with at least 270 degrees of 

unrestricted airflow including the predominant wind direction. The probe should be separated 

from the drip line of nearby trees or structures by at least 20 meters, and should be positioned at 

least twice as far from of nearby obstacles as the height of the obstacles. 

3.3.4.2 Instrument Shelter 

 To help ensure proper performance, the precursor analyzers and supporting equipment 

should be installed and operated in a temperature controlled environment. An insulated 

instrument shelter should be used to protect the analyzer from precipitation and adverse weather 

conditions, maintain operating temperature within the analyzer’s temperature range 

requirements, and provide security and electrical power. The environmental control of the 

shelter should be sufficient to minimize fluctuations in shelter temperature. The recommended 

shelter temperature range is 20oC to 30oC, and daily changes in temperature should not exceed 

5oC over a 24-hour period. Condensation of moisture must be prevented, and it may be 

necessary to impose seasonal temperature ranges to assure remaining above the ambient 

dewpoint. 

3.3.4.3 Sample Inlet or Manifold 

 Sample air for a high sensitivity SO2 analyzer should be drawn directly to the analyzer 

through FEP or PTFE tubing (e.g., 1⁄4 inch outer diameter (OD)), equipped with a 1-micron 

Teflon® filter at the inlet to remove particles from the sample air. The filter should be changed 

weekly, or more often in excessively dirty conditions. In this configuration the SO2 analyzer 

does not share its inlet system with any other analyzer. 
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 Some existing air monitoring stations may provide air to multiple analyzers through a 

common manifold. In such a case it is recommended that manifolds for precursor SO2

measurements be made of glass. Since neither zero air nor sample air is totally particulate-free, 

over time sample manifolds will collect particulate matter on the internal walls. A transparent 

glass manifold can be inspected easily and cleaned readily by rinsing with distilled water and air 

drying. However, caution must be used with glass manifolds because of their fragility. 

 The SO2 analyzer should be located as close to the inlet manifold as possible, to minimize 

the length of sampling lines, and sampling lines should be of constructed of FEP or PTFE. The 

sample manifold must be of sufficient diameter that outside air is drawn into the manifold at as 

close to atmospheric pressure as possible. The manifold must also allow for excess gas to be 

exhausted in the event of over pressurization (i.e., during delivery of gases from high-pressure 

cylinders.) If the pressure in the manifold differs from atmospheric pressure, the SO2 readings 

obtained will not be representative. A manifold of 1 inch inner diameter should be sufficient to 

avoid pressure differences. A detailed description of sample manifold designs is presented in 

Appendix A.

3.4 Potential Problems and Solutions 

 This section describes several of the potential problems associated with precursor SO2

measurements, and discusses the practical solutions to these problems, many of which the SO2

analyzer vendors have already implemented in their analyzers. 

 The following sections describe several potential positive and negative sources of 

interference or bias. Section 3.4.1 describes the most common positive interferences (volatile 

aromatic and poly-nuclear aromatic hydrocarbons, and NO), and the most common source of 

positive bias (stray light). Section 3.4.2 describes the most common sources of negative bias 

(collisional quenching of SO2 and loss of SO2 in sampling lines). In each section recommended 

procedures to minimize these interferences or sources of bias are described. 
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 In addition to these potential problems, other problems may arise in the routine operation 

of precursor SO2 analyzers. Operators are encouraged to report any observations or anecdotal 

data that might add to the understanding or awareness of interferences or other anomalies in SO2

measurements with UV fluorescence analyzers in general. 

3.4.1 Sources of Positive Interference or Bias

 Positive interference in precursor SO2 monitoring can result from other gases in the 

sample that happen to fluoresce at the same wavelength as SO2. Perhaps the most prevalent 

sources of this type of interference are volatile aromatic (e.g., xylenes) and poly-nuclear aromatic 

(PNA) (e.g., naphthalene) hydrocarbons. Such compounds absorb UV photons and fluoresce in 

the region of the SO2 fluorescence. Consequently, any such aromatic hydrocarbons that are in 

the optical chamber can act as a positive interference. To remove this source of interference, the 

high sensitivity SO2 analyzers have hydrocarbon scrubbers or “kickers” to remove these 

compounds from the sample stream before the sample air enters the optical chamber. Another 

potential source of positive interference is nitric oxide (NO). NO fluoresces in a spectral region 

that is close to the SO2 fluorescence. However, in high sensitivity SO2 analyzers, the bandpass 

filter in front of the PMT is designed to prevent NO fluorescence from reaching the PMT and 

being detected. Care must be exercised when using multicomponent calibration gases containing 

both NO and SO2 that the NO rejection ratio of the SO2 analyzer is sufficient to prevent NO 

interference.

 The most common source of positive bias (as opposed to positive spectral interference) in 

high sensitivity SO2 monitoring is stray light reaching the optical chamber. Since SO2 can be 

excited by a broad range of UV wavelengths, any stray light with an appropriate wavelength that 

enters the optical chamber can excite SO2 in the sample and increase the fluorescence signal. 

Furthermore, stray light at the wavelength of the SO2 fluorescence that enters the optical 

chamber may impinge on the PMT and increase the fluorescence signal. The analyzer 

manufacturers incorporate several design features to minimize the stray light that enters the 
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chamber. These features include the use of light filters, dark surfaces, and opaque tubing to 

prevent light from entering the chamber. 

3.4.2 Sources of Negative Interference or Bias

 Non-radiative deactivation (quenching) of excited SO2 molecules can occur from 

collisions with common molecules in air, including nitrogen, oxygen, and water. During 

collisional quenching, the excited SO2 molecule transfers energy kinetically allowing the SO2

molecule to return to the original lower energy state without emitting a photon. Collisional 

quenching results in a decrease in the SO2 fluorescence and results in the underestimation of SO2

concentration in the air sample. The concentrations of nitrogen and oxygen are constant in the 

ambient air, so quenching from those species at a surface site is also constant, but the water 

vapor content of air can vary. Despite this variability, in routine ambient monitoring the effect of 

water vapor on SO2 fluorescence measurements is negligible. Only if high or highly variable 

water vapor concentrations were a concern (as in source sampling), should it be necessary to dry 

the sample air using optional equipment available from the analyzer vendors. Condensation of 

water vapor in sampling lines must be avoided, as it can absorb SO2 from the sample air. The 

simplest approach to avoid condensation is to heat sampling lines to a temperature above the 

expected dew point, and within a few degrees of the controlled optical bench temperature. An 

alternative approach would be to maintain all sampling lines at reduced pressure by locating the 

analyzer’s critical orifice at the sample inlet point. 

3.5 Supporting Equipment 

 In addition to the precursor gas analyzers, several pieces of supporting equipment should 

be maintained at each NCore site. At a minimum, this equipment includes a data acquisition 

device and calibration equipment.
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3.5.1 Data Acquisition Device

 Many types of equipment can be used to record the concentration measurements obtained 

from the analyzer. Recommended options for data acquisition are described in Section 6 of this 

TAD. 

3.5.2 Calibration Equipment

 The equipment required for calibration of a high sensitivity SO2 analyzer include a MFC 

calibrator unit, and a source of zero air. The following equipment is recommended for 

calibration of a high sensitivity SO2 analyzer. 

3.5.2.1 Calibration Standard and Standard Delivery System 

 The calibration standards used for the calibration of high sensitivity SO2 analyzers should 

be generated by dilution of a commercially-prepared and certified compressed gas SO2 standard 

using a MFC calibration unit. That commercially-prepared standard may contain only SO2 in an 

inert gas (e.g., N2), or may be a mixed component standard that also contains known 

concentrations of other precursor ambient gases (e.g., CO, NO). However, note the caution 

stated in Section 3.4.1 regarding potential NO interference in mixed standards containing SO2

and NO. 

 It is important when purchasing a MFC calibrator that it meets the 40 CFR 50 requirements 

of ±2 percent accuracy, and that the flow rates of both MFC channels are calibrated using a NIST 

traceable flow standard. 

 When the analyte concentration in the commercially-prepared standard cylinder is certified 

by reference to NIST standards, and the MFCs are calibrated to NIST-traceable standards, the 

resulting working gas concentration is considered to be NIST-traceable. 
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3.5.2.2 Zero Air Source/Generator 

 Zero air is required for the calibration of precursor SO2 instruments. This air must 

contain no detectable SO2 (i.e., SO2 content must be less than the LDL of the SO2 analyzer) and 

be free of particulate matter. Suitable zero air may be supplied from compressed gas cylinders of 

purified air. However, it may be expensive to maintain a sufficient supply of zero air cylinders 

to operate a precursor SO2 analyzer continuously. As an alternative, many commercially 

available zero air generation systems can supply suitably SO2-free air. 

 To ensure that the zero air used is free from contaminants, the SO2 analyzer should be 

independently supplied with zero air from different sources. If the analyzer responds differently 

to the different sources, generally the source with the lowest response is the highest quality 

source. Confirmation of zero air quality can be achieved using various additional scrubbing 

traps. For example, ambient air can be scrubbed of SO2 using 24 x 7 purged activated carbon. 

The carbon type used for scrubbing is important; Barnebey & Sutcliffe Corp. (formerly 

Barnebey-Cheney) type GI (www.bscarbon.com, Columbus, Ohio) has been shown to work well. 

As an alternative to using an activated carbon scrubber, a sodium carbonate coated denuder, such 

as the Sunset Laboratory Model #DN-315 stainless steel concentric denuder, can be used. 

Alternatively, a cartridge of soda lime attached to the outlet of the zero air system will last for 

extended periods (potentially over one year) and maintain SO2 at less than 0.05 ppb. 

Note: For zero-air sources based on removing SO2 by means of soda lime, 

charcoal, or a denuder as described above, the inlet air must be outside 

ambient air rather than instrument shelter air. Contaminant levels inside the 

shelter may greatly exceed those in outside air. Also to the extent possible, the 

components of the zero-air system should be free of materials that might outgas 

hydrocarbons. 
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3.6 Reagents and Standards 

 Routine operation of high sensitivity SO2 analyzers requires the use of calibration 

standards and zero air to conduct periodic calibrations and instrument checks. This section 

describes the requirements for these gases. 

3.6.1 Calibration Standards

 The primary SO2 standards used must be certified, commercially-prepared compressed 

gas standards, with a certified accuracy of no worse than ±2 percent. SO2 gas standards of 10 to 

20 ppm are conveniently diluted with a MFC calibrator down to working concentrations of 20 

ppb or less. The commercially-prepared standard may contain only SO2 in an inert gas (e.g., N2), 

or may be a mixed component standard that also contains known concentrations of other 

precursor ambient gases (e.g., CO, NO). The potential for NO interference must be kept in mind 

if a standard containing both SO2 and NO is used for SO2 calibration, as noted in Sections 3.4.1 

and 3.5.2.1. It is critical when placing an SO2 gas standard into service that the cylinder 

regulator be fully purged to avoid the effect of trace moisture on the delivered SO2 concentration. 

Evacuating the regulator by means of a vacuum line attached to the regulator outlet, before 

purging for a few minutes with the cylinder gas, is an effective procedure to dry and condition 

the regulator. 

 Every gas standard used in precursor gas monitoring must be accompanied by a 

certificate of calibration from the vendor stating the concentration of the standard, the 

uncertainty of that certification, and the expiration date of the certification. Standards traceable 

to NIST are preferred. Certification documents for all standards must be retained in a common 

location and reviewed periodically so that standards for which the vendor’s certification has 

expired may be removed from service and replaced. 
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3.6.2 Zero Air

 Zero air used as dilution gas for calibration purposes should have an SO2 concentration 

below the LDL of the SO2 analyzer. Multiple zero air sources should be checked, and soda lime, 

charcoal, or sodium carbonate scrubbers may be necessary to achieve adequate zero air quality, 

as noted in Section 3.5.2.2. A canister of soda lime followed by a particle filter on the outlet of 

the zero air source will remove SO2 for extended periods. Breakthrough can be tested by 

temporarily adding a carbonate denuder and observing zero gas readings. 

3.7 Quality Control 

3.7.1 Site Visit Checklists and Remote Diagnostic Checks

 To determine whether the SO2 analyzer is working properly, field operators should 

conduct routine checks of instrument diagnostics and performance every time they visit the 

monitoring station. Each agency needs to develop diagnostic or maintenance checklists or 

electronic spreadsheets to document that all required checks have been made. Such lists and 

sheets should be useful both for collecting diagnostic information and for assessing the quality of 

the monitoring data. To the extent possible, diagnostic checks can be done remotely, provided 

the data acquisition system allows remote access to instrument diagnostic information (see 

Section 6). 

3.7.2 Multipoint Calibrations

 A multipoint calibration includes a minimum of four points (three spaced over the 

expected range and a zero point), generated by the calibration system. Although more points 

may be preferable, current high sensitivity SO2 analyzers provide inherently linear response over 

their entire operating range; therefore, four points should be sufficient. Multipoint calibrations 

must be done prior to the precursor SO2 analyzer being put into service and at least every 

six months thereafter. An analyzer should be calibrated (or recalibrated) if any of the following 

conditions occur: 
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• Upon initial installation; 

• The Level 1 span check or precision check difference exceeds 15 percent; 

• After repairs or service is conducted that may affect the calibration; 

• Following physical relocation or an interruption in operation of more than a few days; 

• Upon any indication that the analyzer has malfunctioned or a there has been a change 

in calibration; or 

• The measured concentration values during challenges with performance test samples 

(Section 5.4.1) differ from the certified standard values by ±15 percent. 

The analyzers should be calibrated in-situ without disturbing the normal sampling inlet system to 

the degree possible. 

3.7.3 Level 1 Zero/Span Checks 

 Level 1 zero and span calibrations are simplified, two-point calibrations used when 

adjustments may be made to the analyzer. When no adjustments are made to the analyzer, the 

Level 1 calibration may also be called a zero/span “check” and must not be confused with a level 

2 zero and span check. Level 1 zero and span checks should be conducted nightly if the 

calibration system and SO2 analyzers used can be programmed to automatically perform these. 

They are used to assess if the analyzers are operating properly and to assess if any drift in 

instrument response has occurred. They are conducted by challenging the analyzer with zero air 

and a test atmosphere containing SO2 at a concentration of between 70 percent and 90 percent of 

the full measurement range in which the analyzer is operating. The challenge gas should be 

sampled through as much of the sampling inlet system as practical to mimic the actual sampling 
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of ambient air. The results of the Level 1 zero/span check should be plotted on control charts to 

graphically illustrate the trends in the response of the analyzer to the challenge gases. The span 

check should not exceed ±15 percent and the zero drift should not exceed ±0.5 percent of full 

scale. If the measured concentrations fall outside of the control limits, the accuracy of the MFC 

calibration system should be checked with a NIST-traceable flow standard. If the MFC flow 

accuracy is confirmed, the data recorded since the last successful Level 1 check should be 

flagged and the analyzer should be recalibrated using the multipoint calibration procedures 

described in Section 3.7.2. 

State-of-the-art calibration equipment now exists that is fully automated. These "new 

generation" calibration units are fully integrated with computers, mass flow calibrators, and the 

associated hardware and software where they can create test atmospheres manually or 

automatically. For the precursor gas program, it is recommended that the NCore sites have fully 

automated calibration capability. Below are a number of reasons why this is advantageous: 

• By performing the calibrations or checks automatically, agencies no longer spend the 

manpower needed to perform them. 

• Automated calibrations or checks can be triggered internally or by a DAS. Since newer 

DASs allow remote access, this allows a remote user to challenge the analyzers without 

actually being present. 

• High sensitivity precursor gas analyzers are expected to have more zero and span drift than 

less sensitive analyzers; therefore, it is important that a zero and Level I check be performed 

daily. 

• New generation DASs can record calibration data and allow remote users to track daily Level 

I check and zero drift. This is important for data validation, verification and troubleshooting. 
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3.7.4 Precision Checks

 At least once every two weeks a precision check should be conducted by challenging the 

SO2 analyzer with a known low SO2 concentration to assess the performance of the analyzer. 

The precision checks should be conducted by challenging the SO2 analyzer with a standard gas 

of known concentration between 10 and 50 ppb. After completion of the precision check, the 

operator should calculate the percent difference between the measured value and the standard 

value. Precision should be calculated quarterly, using the calculated percent differences from the 

precision checks, according to the equations provided in section 3.3.1.1. For acceptable 

precision to be maintained, it is recommended that the calibration system’s gas flows be verified 

frequently against a NIST flow standard, and adjusted if necessary before making any 

adjustments to the analyzer. 

3.8 Preventive Maintenance and Troubleshooting 

 Long-term operation of continuous high sensitivity precursor gas analyzers requires a 

preventive maintenance program to avoid instrument down-time and data loss. Despite active 

preventive maintenance, occasional problems may arise with the precursor SO2 analyzers. This 

section briefly describes several key items that might be included in the preventive maintenance 

program established for precursor SO2 analyzers deployed at NCore sites, as well as some of the 

troubleshooting activities that may be useful in resolving unexpected problems with these 

analyzers. This discussion is not meant to be exhaustive or comprehensive in detail. More 

thorough discussions can be found in the analyzer operation manuals, and should be included in 

SOPs developed for these analyzers. Example SOP’s prepared by EPA are included as 

Appendix B of this TAD. 
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3.8.1 Preventive Maintenance

 Routine preventive maintenance procedures should be in place to prevent down-time and 

data loss. Management and field operators should jointly develop their preventive maintenance 

program. A program designed by persons unfamiliar with analyzer operations may include 

unnecessary items or omit mandatory ones. Several factors linked to shelter and sampling 

manifold design can contribute to data loss. SO2 values can be low if the sample probe, 

manifold, and lines are dirty, cracked, or leaky. The sample probe and manifold should be 

cleaned at least every six months. Sampling lines should be replaced every two years. Teflon® 

filters used in the sampling train to remove fine particles may need to be replaced as often as 

every week, depending on the condition of the filter and the particulate loading around the 

monitoring site. 

 Table 3-4 illustrates items that monitoring agencies should include in their preventive 

maintenance program for high sensitivity SO2 monitoring. 

Table 3-4. Example of a preventive maintenance schedule for high sensitivity SO2

analyzers. 

Item Schedule

Replace particle filter Weekly 

Replace internal span permeation tube (if applicable) Annually 

Perform pneumatic system leak check At least quarterly 

Inspect internal, external tubing; replace if necessary At least quarterly 

Rebuild or replace pump Annually 

Replace UV lamp As needed 

Clean optic bench As needed 

Replace PMT As needed 

 In addition to a schedule, the preventive maintenance plan should also include more 

detailed task descriptions, such as illustrated below: 
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• Because the analyzer pneumatic system requires so much preventive maintenance, the 

tubing, solenoids, and pump should be inspected regularly. Cracked tubing or loose 

fittings can cause the instrument to analyze room air rather than ambient air and lead 

to invalid data. A faulty pump can also cause problems with pneumatic systems. 

When oscillations in the flow rate force the operator to adjust the flow continually, 

the pump is failing and should be either repaired or replaced. The pump should be 

rebuilt or replaced when it is unable to maintain a vacuum of at least 25 inches of Hg. 

• Check the instrument for vibration. When pumps get old, they sometimes will vibrate 

more than is normal. If this occurs, it can cause cracks if the tubing is touching 

another surface. 

• Consult the analyzer operations manual for complete details on operation and 

maintenance. 

3.8.2 Troubleshooting

 High sensitivity SO2 analyzers are subject to many factors that can cause inaccurate 

measurements or down-time. Table 3-5 summarizes common problems seen with high 

sensitivity SO2 analyzers, their possible causes, and possible solutions. More specific 

information can be found in the manufacturer’s operations manual. 

 When troubleshooting, an operator must constantly be aware of environmental factors 

that may affect the instruments. Environmental factors can also cause sporadic problems that 

can be difficult to diagnose. Examples of factors that may affect the performance of the high 

sensitivity SO2 analyzers are: 

• Variable shelter temperature (fluctuations greater than several degrees) 

• Excessive vibration from other equipment 
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• Voltage instability; fluctuations in the 110 VAC line voltage 

• Air conditioning system blowing on the instrument 

• Frequent opening of the door of the shelter.

Table 3-5. Instrument troubleshooting for precursor SO2 analyzers. 

Problem Possible Cause Possible Solution 

Defective DC power supply Replace power supply

Noisy output Dirty optics Clean optics bench

PMT failure Replace PMT 

Defective bandpass filter Replace filter High positive zero drift PMT failure Replace PMT 

UV source is defective Replace UV lamp 

No response to span gas UV power supply defective Replace UV power supply 

PMT failure Replace PMT 

Pump failure Check pump 

UV lamp failure Replace UV lamp 

UV power supply defective Replace power supply Zero output at ambient levels 

PMT failure Replace PMT 

No flow through analyzer Pump failure Replace/ rebuild pump head 

3.9 References 

1. Rhodes, R.C., Guidelines on the Meaning and Use of Precision and Accuracy Data 

Required by 40CFR Part 58, Appendices A and B, EPA60014-83-023, U.S. 

Environmental Protection Agency, Research Triangle Park, NC, June 1983. 

2. Ecotech Pty Ltd. (2004). “EC9850T Trace SO2 Analyzer Product Specification Sheet.” 

Accessed September, 2004. Available at http://www.ecotech.com.au/brochures_new/

EC9850T.pdf. 

3. Thermo Electron Corporation (2004a). “Instruction Manual, Model 43C Precursor SO2

Analyzer.” Accessed September, 2004. Available at https://www.thermo.com/

eThermo/CMA/PDFs/Various/File_20810.pdf. 
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4. Teledyne Advanced Pollution Instrumentation (2004a). “Model 100AS Ultra Sensitivity 

SO2 Analyzer Data Sheet.” Accessed September, 2004. Available at 

http://www.teledyne-api.com/products/Model.100AS.pdf. 

5. Teledyne Advanced Pollution Instrumentation (2004b). “Instruction Manual, 

Model 100E UV Fluorescence SO2 Analyzer.” Accessed September, 2004. 

Available at http://www.teledyne-api.com/manuals/04515B2.M100E.Manual.pdf. 
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4.0 HIGH SENSITIVITY TOTAL REACTIVE NITROGEN OXIDES MEASUREMENTS 

4.1 Introduction 

 Measurement of ambient nitrogen oxides differs from measurement of CO or SO2 in that 

the target air pollutant is not a single chemical but a group of chemicals of differing properties, 

and is not a criteria air pollutant. Nitrogen oxides released from emission sources are primarily 

nitric oxide (NO) with lesser amounts of nitrogen dioxide (NO2), which collectively are termed 

NOx (i.e., NOx = NO + NO2). These primary emitted species are converted by atmospheric 

processes to numerous other inorganic and organic nitrogen oxides, which collectively are called 

NOz, and the total of all reactive gaseous nitrogen species present in ambient air is called NOy 

(i.e., NOy = NOx + NOz). 

 Precursor gas monitoring in the NCore network builds upon capabilities of EPA’s 

Photochemical Assessment Measurement Stations (PAMS) network and Southern Oxidants 

Study to measure ozone precursors, including total reactive oxides of nitrogen (NOy). Measuring 

NOy is a valuable adjunct to NO and NOx monitoring because the individual species comprising 

NOz include numerous organic and inorganic nitrogen oxide compounds, that are difficult to 

measure individually, but collectively contribute to a more complete and conservative measure 

of nitrogen oxides. Determining NOy concentrations is useful in establishing nitrogen oxide 

emission patterns and temporal trends, and in assessing the photochemical age and reactivity of 

air masses.(e.g., 1-4) NOy measurements are a critical tool in accounting for progress in large-scale 

nitrogen emission reduction programs, providing input for a variety of source apportionment and 

observation based models, and assisting in the evaluation of air quality models.[e.g., 1, 5, 6 ]

4.1.1 Properties of NOy

 NOy includes all of the nitrogen oxide compounds that react or are formed in the lower 

atmosphere and that contribute to the photochemical formation of O3 and the transport and 

ultimate fate of nitrogen oxides.[1-4] NOy compounds include NOx (NO + NO2) and NOz, which 

include nitrogen acids [nitric acid (HNO3) and nitrous acid (HONO)], organic nitrates 
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[e.g., peroxyl acetyl nitrate (PAN), methyl peroxyl acetyl nitrate (MPAN), and peroxyl propionyl 

nitrate (PPN)], other organic nitrogen oxides, particulate nitrates, nitrate radical (NO3), nitrogen 

trioxide (N2O3), nitrogen pentoxide (N2O5) and halogen-nitrogen species (e.g., ClONO2 and 

BrONO2). In typical urban environments, the principal NOy compounds include NO, NO2, 

HNO3, and PAN, and in some cases particulate nitrate. 

 In terms of precursor monitoring in NCore, a key factor is that the numerous species 

making up the total NOy differ widely in their physical properties and chemical reactivity. For 

example, some species, such as NO2 and HONO, are readily photolyzed, whereas others, such as 

PAN, decompose rapidly at moderate temperatures. NO and NO2 are chemically reactive but 

have relatively low solubility in water, whereas the key product species HNO3 is highly soluble 

and relatively unreactive. Consequently, physical removal of HNO3 from the atmosphere is a 

key removal process for NOy. Organic nitrogen oxides can vary widely in volatility and 

stability, and HNO3 is known to be highly “sticky”; that is, adsorptive on surfaces. In addition, 

particulate ammonium nitrate (NH4NO3) is volatile under certain ambient conditions, and can 

decompose to release HNO3 and ammonia (NH3) into the gas phase. These factors make 

accurate sampling and measurement of atmospheric NOy much more challenging than 

determination of CO or SO2. A discussion of sampling and measurement issues that must be 

addressed in order to make more useful measurements of NOy is provided in Section 4.3.2. 

4.1.2 Sources of NOy

 Nitrogen oxides are emitted to the atmosphere principally as NO and NO2, by both 

natural and man-made sources. Important natural sources include lightning and natural fires. 

The major man-made emissions result from transportation and combustion of fossil fuels for 

energy production. Once released into the atmosphere, NO and NO2 are oxidized by 

photochemical processes to a wide variety of products. Oxidation of NO to NO2 can occur by 

reaction with atmospheric oxygen (only at high NO concentrations that may exist very near the 

emissions source), or by reaction with atmospheric ozone (O3) and free radical species. When 

NOx is mixed with hydrocarbon air pollutants and exposed to sunlight, a complex set of reactions 
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occurs that constitutes the phenomenon known as photochemical smog. This photochemical 

process involves free radicals generated by photolysis and maintained through chain reactions, 

and results in the production of large amounts of ozone. Depending on the nature of copollutants, this process can also produce fine particulate matter containing nitrate, sulfate, and 

organic material, and the more complex nitrogen oxide species that make up NOz (and, in turn, 

NOy). The extent of conversion of NOx species to NOy species is a measure of the 

“photochemical age” of an air mass; i.e., a measure of the time of transport and the reactivity of 

the mix of pollutants in that air mass.(2-4)

4.1.3 Historical Overview of NOy Measurement Method

 Ambient NOy must be measured in a practical, standardized manner, as it is not possible 

to measure individually all the compounds that comprise NOy. Instruments used to measure NOy

must be sensitive enough to measure the low concentrations typically encountered in rural 

locations as well as the higher concentrations encountered in urban smog. The standard 

reference method for the determination of NO and NOx at ambient levels is chemiluminescence 

(40 CFR Part 53), with several manufacturers offering EPA-approved instruments. 

Instrumentation designated as Reference or Equivalent methods for measuring ambient 

concentrations of NO2 is listed in 40 CFR Part 53.[7] Instruments designated as Reference 

methods for NO2 are also approved for measuring NO. It must be noted that the designated 

instruments may not truly measure NOx (i.e., NO plus NO2) in urban areas where photochemical 

processes have occurred, but NOx plus some poorly defined fraction of NOz. 

 For NOy, a standard reference method has not yet been designated; however, EPA has 

suggested a modification of the NOx chemiluminescence monitoring approach that uses a heated 

converter to reduce all reactive nitrogen species to NO, followed by detection of that NO by its 

chemiluminescence reaction with an excess of O3. The original ambient NO is measured by 

bypassing the converter. This procedure is similar to the current methodology used to monitor 

NOx except that, in the NOy methodology, the converter has been moved to the sample inlet to 
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avoid line losses of adsorbent NOy species like HNO3, and additional calibration procedures 

recommended for adequate measurement of the various NOz species. 

4.2 Summary of NOy Measurement by Chemiluminescence Method 

 NOy concentrations are determined by photometrically measuring the light intensity at 

wavelengths greater than 600 nm from the chemiluminescent reaction of NO with O3.

(8) This 

principle is identical to that on which the measurement of NO and NOx is based, which is 

designated by EPA as the Reference method for determining NO2 in ambient air.[9] 

 The chemiluminescence approach is based on the gas-phase reaction of NO and O3, 

which produces a characteristic near-infrared luminescence (broad-band radiation from 500 

to 3,000 nm, with a maximum intensity at approximately 1,100 nm) with an intensity that is 

proportional to the concentration of NO. Specifically, 

NO + O NO + O 3 22 → (Eq. 4-1a) 

or NO * + O → 2 2 (Eq. 4-1b) 

NO * NO 2

M

⎯ →⎯ 2 (Eq. 4-2a) 

or NO + h → 2 ν (Eq. 4-2b) 

where: 

 NO2* = an electronically excited NO2 molecule 

 hν = E, the emitted photon energy (where h is Planck’s constant, and ν is the 

frequency of the emitted photon) 

 M = inert molecules, predominantly N2 and O2 in air. 

 The reaction of NO with O3 produces predominantly ground state NO2 molecules, as in 

reaction (4-1a), but in a small fraction of the reactions, the NO2 produced is in an excited state, 
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as in reaction (4-1b). The resulting excited NO2 molecules lose their excess energy either 

through collisions with other inert molecules (M), as in reaction (4-2a), or by releasing a photon 

of light, as in reaction (4-2b). Monitoring instruments based on chemiluminescence are designed 

to enhance the emission and detection of the light produced in reaction (4-2b). For example, to 

minimize the unproductive pathway in reaction (4-2a), the concentration of other molecules (M) 

is kept low by carrying out the NO/O3 reaction at low pressure. 

 To determine the concentration of NO by chemiluminescence, the sample gas flow is 

mixed with O3 in a reaction chamber causing reactions (4-1) and (4-2) to occur. The 

chemiluminescence that results from the reaction is monitored by an optically filtered 

high-sensitivity photomultiplier, that responds to NO2 chemiluminescence emission at 

wavelengths longer than 600 nm. The electronic signal produced in the photomultiplier is 

proportional to the NO concentration in the sample air. 

 To measure NOy, sample air is passed through a chemical reductant (molybdenum) 

converter placed at the extreme sample air inlet point, and the nitrogen oxide compounds present 

are reduced to NO.[10] The NO resulting from the reduction of these nitrogen oxide compounds, 

plus any native NO, is reacted with O3, and the resulting chemiluminescent light is measured as 

an indication of the total NOy concentration. To measure NO separately and specifically, sample 

air is by-passed around the chemical reductant converter so that no reduction of the other 

nitrogen oxide compounds to NO occurs. The NO (i.e., native NO only) is reacted with O3, and 

the resulting chemiluminescent light intensity is proportional to the NO concentration. 

 The primary differences between this method, as implemented for NOy monitoring and as 

implemented for conventional NOx monitoring, are in the location of the molybdenum (Mo) 

converter and in the calibration procedures required. The converter location at the extreme inlet 

of the sampling system is designed to convert all NOy species to NO immediately upon entry of 

sample air into the sampling system. This approach minimizes loss of NOy constituents such as 

HNO3 in sampling, and help to assure complete capture of the total NOy. Calibration procedures 
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for NOy monitoring go beyond those used for NOx monitoring, in that more stringent tests of 

converter efficiency are required (see Section 4.4.2 for a discussion of converter efficiency). 

 Figure 4-1 shows a schematic illustration of a typical NOy instrument. Sample air is 

drawn either from the ambient air or from calibration sources (i.e., zero/span gas), using a 

three-way solenoid valve (not shown). At the sample inlet, the sample flow is either directed 

through a heated molybdenum converter to reduce the reactive oxides of nitrogen to NO, or 

directed around the converter to allow detection of only NO. The sample air flow then passes 

through a filter to remove particulate matter and then through a flow control capillary to another 

three-way valve. This three-way valve directs the sample flow either directly to the reaction 

chamber (RX) where it is mixed with O3 and the resultant chemiluminescence is measured, or 

the sample is directed to a prereactor vessel where it is mixed with O3 before passage into the 

reaction chamber. The use of the prereactor allows the NO/O3 chemiluminescence to occur out 

of view of the PMT, providing for an accurate measurement of background chemiluminescence 

resulting from reactions other than the NO/O3 reaction (e.g., reactions of hydrocarbons and O3). 

The PMT is housed in a thermoelectric (TE) cooler to minimize thermal noise. 

 As shown in Figure 4-1, separate sample transfer lines downstream of the sample inlet 

point are used for the NOy and NO measurement channels, and a third transfer line is used to 

deliver calibration and converter efficiency assessment standards from the gas phase titration 

(GPT) calibration system to the sample inlet. Because of the remote location of the converter 

relative to the analyzer itself, these transfer lines may be of considerable length (i.e., up to 20 m). 

The length of the sample transfer line presents no problem in the NOy measurement mode of the 

NOy instrument, since all NOy species are converted to NO in the heated converter, and since 

that same converter destroys any ozone present in the sample air. However, in the instrument’s 

NO mode, the ambient air drawn down the sample transfer line contains both ambient NO and 

ambient O3. These two species can react [by reactions 4-1a and b] to decrease the NO reaching 

the chemiluminescence detector, resulting in an under-estimation of the ambient NO level. This 
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Figure 4-1. General schematic of a typical chemiluminescence NOy instrument. 

effect can be substantial: assuming 100 ppbv of O3, loss of 10 percent of the NO can occur 

within a few seconds. One way to counteract this effect, is for sample air to be drawn rapidly 

through the sample transfer line. For example, at a sample flow rate of 6 L/min, a sampling line 

with an inner diameter of 4 mm and a length of 15 m (50 feet) would result in a residence time of 

less than 2 seconds. Rapid transport of the sample can best be accomplished using an auxiliary 

sampling pump (not shown in Figure 4-1) to draw sample down the transfer line to a “T” fitting 

at the back panel of the NOy analyzer. The sample flow to the chemiluminescence detector is 

then drawn from that “T” by the analyzer’s internal sample pump. If implemented, it is 

recommended that this approach be implemented on both the NO and NOy sample lines, to 

achieve consistent residence times in the two lines. However, implementing rapid sample 

transport through the Mo converter in this way may reduce converter efficiency and/or lifetime. 

Consequently, a preferable approach may be to reduce sample transport time in both the NO and 

NOy flow paths by reducing the gas pressure. 
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4.3 Recommendations for NCore 

 Since the high sensitivity analyzers deployed at NCore sites are intended to monitor low 

ambient NOy concentrations, it is important that they meet a variety of performance criteria as 

described below. Many of these performance criteria for high sensitivity NOy analyzers are 

more stringent than those for routine NOx analyzers; consequently, there are a number of 

recommended features that the NOy analyzers should have in order to achieve the performance 

criteria. This section describes the recommended performance criteria and the analyzer features 

that are recommended in order to achieve the performance criteria, and provides examples of 

commercial high sensitivity NOy analyzers that are available for deployment at the NCore sites. 

Additionally, this section discusses some important sampling requirements that should be 

considered during the installation of the analyzers. 

4.3.1 Recommended Method Performance Criteria

 The U.S. EPA has recently assessed the measurement quality objectives needed for high 

sensitivity precursor gas monitoring in NCore, relative to the long-established statistics stated in 

40 CFR 58.[11] In particular, EPA recommends that measurement quality objectives for bias and 

precision be based on upper confidence limits at the monitoring site level, to provide a higher 

probability of reaching appropriate conclusions (e.g., in comparisons to NAAQS). The intent of 

this recommendation is to move S/L/T agencies to a performance-based quality system i.e., 

allowing organizations that show tight control of precision and bias to reduce the frequency of 

certain QC checks, and to focus their quality system efforts where most needed. 

 The U.S. EPA recommends that the high sensitivity NOy analyzers that are deployed at 

NCore sites meet the following method performance criteria. It is to be expected that these 

criteria may be more difficult to meet for NOy than for NO. 
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4.3.1.1 Precision 

 Precision is defined as the measure of agreement among individual measurements of the 

same property taken under the same conditions. Precision is assessed from checks that are 

performed at least once every two weeks (see Sections 4.7.4 and 5.3.3). Calculations to assess 

precision are given below and should be used to assess precision on a quarterly basis. It is 

recommended that high sensitivity NOy analyzers have a 95 percent probability limit for 

precision of ±15 percent or less. 

 Calculation of precision starts with the comparison of the known challenge concentration 

used in the precision checks to the corresponding measured concentrations reported by the 

analyzer. The resulting percent differences are then used as described below. For each single 

point precision check, calculate the percent difference, di, as follows: 

Equation 1

 

where reported is the concentration indicated by the high sensitivity NOy analyzer and challenge

is the concentration of the standard used in the precision check. The precision estimator is then 

calculated as the coefficient of variation (CV) upper bound, using Equation 2 as follows: 

Equation 2

 

 

where n is the number of data points (i.e., precision check comparisons), the di values are the 

resulting percent differences, and X 0.1,n-1 is the 10th percentile of a chi-squared distribution with 

n-1 degrees of freedom. 

d reported challenge

challenge i = − ⋅100

( ) CV

nd d

n n

n

X

i

i

n

i

i

n

n

=

⋅ −

⎛

⎝

⎜

⎜

⎞

⎠

⎟

⎟

− ⋅ = = −

−

∑ ∑ 2

1 1

2

2

01 1 1

1

. ,
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4.3.1.2 Bias 

 Bias is defined as a systematic or persistent distortion of a measurement process that 

causes errors in one direction. Bias is assessed from the degree of agreement between a 

measured value and the true, expected, or accepted value. Analyzer bias is calculated using 

comparisons of known challenge concentrations to the corresponding measured concentrations 

reported by the analyzer. The challenge comparisons used to assess bias should be the same as 

those used to assess precision (see Section 4.3.1.1 above). The bias estimator is an upper bound 

on the mean absolute value of the percent differences as described in Equation 3 as follows: 

Equation 3

where n is the number of challenge comparisons being aggregated; t0.95,n-1 is the 95th quantile of 

a t-distribution with n-1 degrees of freedom; the quantity AB is the mean of the absolute values 

of the individual di’s and is calculated using Equation 4 as follows: 

Equation 4

 

and the quantity AS is the standard deviation of the absolute value of the di’s and is calculated 

using Equation 5 as follows: 

Equation 5

 

 

bias AB t

AS

n

=+ ⋅ 0. , 95 n −1

AB

n

d i

i

n

= ⋅

=

∑1

1

( ) AS

nd d

n n

i

i

n

i

i

n

=

⋅ −⎛

⎝

⎜

⎜

⎞

⎠

⎟

⎟

−

= =

∑ ∑ 2

1 1

2

1
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Since the bias statistic as calculated in Equation 3 uses absolute values, it does not have a 

direction or sign (negative or positive) associated with it. The sign of the calculated bias is to be 

determined by rank ordering the percent differences of the QC check samples from a given 

analyzer for a particular assessment interval. Calculate the 25th and 75th percentiles of the 

percent differences for each analyzer. The absolute bias upper bound should be flagged as 

positive if both the 25th and 75th percentiles are positive, and as negative if both these percentiles 

are negative. The absolute bias upper bound would not be flagged if the 25th and 75th percentiles 

are of different signs. It is recommended that high sensitivity NOy analyzers have an upper 

bound for the average bias of ± 15 percent or less. 

4.3.1.3 Representativeness 

 Representativeness refers to whether the data collected accurately reflect the conditions 

being measured. It is the data quality indicator most difficult to quantify. Unless the samples are 

truly representative, the other indicators are meaningless. Representativeness for monitoring of 

low ambient levels of NOy in NCore is different than for routine monitoring, since the objectives 

of the monitoring are much different. Representativeness can only be assured in terms of the 

appropriate selection of the sampling site, proper implementation of ambient air sampling, and 

reasonable coverage of the sampling schedule (i.e., continuous). 

4.3.1.4 Completeness 

 Completeness is defined as the amount of data collected relative to the total expected 

amount. Ideally, 100 percent of the expected amount of data would always be collected; in 

practice, completeness will be less for many reasons, ranging from calibration time and site 

relocation to power outages and equipment failure. For monitoring of ambient NOy 

concentrations in NCore, EPA requires a minimum data completeness of 75 percent. In practice 

typical completeness values can often approach 90 to 95 percent. 
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4.3.1.5 Comparability 

 Comparability is defined as the process of collecting data under conditions that are 

consistent with those used for other data sets of the same pollutant. The goal is to ensure that 

instruments purchased and operated by different states and local agencies produce comparable 

data. To promote comparability, this TAD describes the recommended characteristics of high 

sensitivity NOy analyzers and the procedures for their installation and use. For example, all 

monitoring agencies should purchase instruments that minimally have the features described in 

Section 4.3.2, and should adhere to the sampling requirements described in Section 4.3.3. 

4.3.1.6 Method Detection Limit 

 The MDL refers to the lowest concentration of a substance that can be reliably 

determined by a given procedure. The MDL is typically not provided by the vendor. Based on 

the objectives of the Precursor Gas Program, it is expected that most sites will be measuring 

pollutant concentrations at lower ranges than the typical SLAMS/NAMS network. Therefore, 

the ability to quantify concentrations at these lower levels will be very important. The use of a 

vendors advertised LDL is sufficient to make intelligent purchasing decisions. Vendors quantify 

LDLs under ideal conditions and therefore one might consider this value as the best possible 

detection that can be achieved. As these monitors are deployed into monitoring networks, where 

both environmental conditions, equipment (calibration, dilution devices, sampling lines, gaseous 

standards) and operator activities can vary, it is important to estimate what pollutant 

concentrations can truly be detected, above background noise (the potential conditions 

mentioned above). The site specific MDL establishes an estimate based on the routine operation 

(and conditions) of that instrument in the network and provides a more meaningful evaluation of 

data as it is aggregated across the precursor gas network. By establishing site specific MDLs, 

values less than the MDL can be flagged which would allow data users a more informed decision 

on the use of that data. 
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 To perform the MDL test, run zero air through the analyzer and establish an acceptable 

zero; dilute pollutant gas to the targeted concentration (one to five times the estimated MDL) and 

collect 20 to 25 one minute observations. Repeat this seven times over the course of 5 to 14 

days. Average the concentration from the 20-25 readings; calculate the standard deviation (S) of 

the average readings and compute the MDL. The MDL is then calculated as the standard 

deviation of the response values times the Student’s t-value for the number of test measurements 

(40 CFR Part 136, Appendix B). The MDL for high sensitivity NOy analyzers should be 

established prior to putting the analyzers into service, and should be 0.20 ppb or lower over an 

averaging time of no more than 5 minutes. 

4.3.1.7 Lower Detectable Limit 

 The LDL is the minimum pollutant concentration that produces a signal of twice the 

noise level. To estimate the LDL, zero air is sampled and the noise level of the readings is 

determined according to 40 CFR 53.23(b). The vendor-specified LDL for the most sensitive 

range of high sensitivity NOy analyzers should be 0.10 ppb or lower, over an averaging time of 

no more than 5 minutes. 

4.3.1.8 Linear Range 

 The linear range of each high sensitivity NOy analyzer should extend from approximately 

0.10 ppb to at least 200 ppb. Users should determine if their range should exceed 200 ppb and 

adjust accordingly. A range of 200 ppb may not be sufficient in all areas and situations. Note 

that some high sensitivity NOy analyzers can operate simultaneously on a number of ranges, with 

each range recorded on a separate data logger channel with its own calibration curve. Although 

requiring slightly more effort to calibrate and maintain, recording of multiple ranges would allow 

capture of a wide range of NOy concentrations. 
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4.3.1.9 Zero/Span Drift 

 Zero drift is defined as the change in response to zero pollutant concentration, over 

12- and 24-hour periods of continuous unadjusted operation. Span drift is defined as the percent 

change in response to an upscale pollutant concentration over a 24-hour period of continuous 

unadjusted operation. Zero and span drift should be obtained from the vendor prior to putting a 

high sensitivity NOy analyzer into service. Such NOy analyzers should have 12- and 24-hour 

zero drift less than 0.10 ppb, and should have a span drift of less than ±1 percent of the full scale 

measurement range of the analyzer per 24 hours. Zero tests should be performed with the 

internal zero prereactor engaged. 

4.3.2 Recommended Features for High Sensitivity Ambient NOy Measurements

 Continuous chemiluminescence NOy analyzers are commercially available from a 

number of vendors. The design of these analyzers is similar among vendors with some slight 

variations. A diagram of the typical chemiluminescence analyzer is described in Section 4.2, and 

examples of specific instruments are provided below in Section 4.3.3. In general, each of the 

analyzers contains the following systems: 

• Pneumatic System: This portion of the analyzer consists of a sample inlet 

incorporating a heated converter, sample inlet line, particulate filter, gas phase 

titration calibration unit, ozone generator, prereactor, flow meter, and pump, all 

used to bring ambient air samples to the analyzer inlet. 

• Analytical System: This portion of the analyzer consists of the reaction chamber, 

photomultiplier, and bandpass filters. 

• Electronic Hardware: This portion of the analyzer consists of the electronic 

components that control the analyzer and process the signals. This part of the 

analyzer generally requires little or no maintenance. If the instrument is operated 
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outside the manufacturer’s recommended temperature range, however, individual 

integrated chips can fail and cause problems with operation, data storage, or 

retrieval. 

 In operation of these systems, the following recommendations should be followed with 

precursor NOy analyzers to allow them to measure NOy at levels well below 1 ppb. 

• Locate the sample inlet at 10 meters to avoid the physical removal of HNO3. The 

inlet should face the prevailing wind direction, be as short as possible, and be 

constructed of PFA Teflon®. Half of a Teflon® filter holder with the filter 

support used as a “bug screen” should have a negligible effect on NOy 

measurements, and provides a practical solution to ward off larger insects. 

• Locate the site in an area that is not obstructed by nearby trees and obstacles (see 

Section 4.3.4.1) 

 

• Ensure that the sample residence time in the NO sample transfer line is less than 2 

seconds to address the O3/NO reaction and subsequent loss of NO in the line, and 

protect the sample transfer lines from light through the use of opaque conduit 

normally provided by the vendor. 

• A heated molybdenum converter rather than a heated gold/reactant converter is 

recommended, since the latter requires a supply of either a toxic reductant gas (CO) 

or a flammable reductant gas (H2), and provides no clear advantage in determining 

total NOy in urban and suburban air.[10]

• The temperature of the molybdenum converter should be maintained at 350 °C. 

Higher temperatures than recommended may result in converting significant 

amounts of non-NOy species such as ammonia, organic amines, or particulate 
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ammonium. If a manufacturer recommends a converter temperature above 350 °C, 

he should show evidence that such non-NOy species are not converted. It is equally 

important that the converter not be operated below 350 °C to ensure optimal 

conversion of NOy species. 

• Automatic over-range capabilities are used to track the rapid changes that may 

occur in ambient NOy levels. High sensitivity analyzers often have an analog 

output range limited to 200 ppb full scale; digital ranges of up to 400 ppb may be 

needed to track peak concentrations in urban areas. 

It is recommended that the NOy analyzers deployed in NCore include these additional siting and 

operational features in order to ensure useful measurements. 

4.3.3 Commercial Chemiluminescent NOy Monitors

 Vendors of commercial NOy analyzers typically supply instruments for both routine 

ambient and high sensitivity monitoring. In this case, only analyzers with an LDL of 0.1 ppb or 

less for NO are considered to have high sensitivity. (Note that the LDL for NO may be lower 

than that for NOy.) Analyzers from Thermo Electron Corporation, Teledyne Advanced Pollution 

Instrumentation (API), Ecotech, and ECO PHYSICS are described here as examples (no 

endorsement should be inferred), though not all have both the requisite detection limit and NOy

measurement capabilities. A summary of each monitor follows. The descriptions provided for 

these instruments, and the performance claimed for them, are based solely on information 

provided by the respective vendors, and confirmation by EPA should not be inferred. 

4.3.3.1 Thermo Electron Corporation Model 42C-Y

 The Model 42C-Y NOy analyzer[12, 13] shown in Figure 4-2 is based on the Model 42C 

NO-NO2-NOx analyzer, and employs an external molybdenum converter that is typically 

operated at 325 °C. The Model 42C-Y NOy analyzer has a lower detection limit of 0.05 ppb, and 
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has adjustable range settings from 0 to 5 ppb up to 0 to 200 ppb. The recommended operating 

temperature range is between 15 °C and 35 °C. The Model 42C-Y NOy analyzer uses increased 

pumping speed to minimize residence time and enhance chemiluminescent detection, and has 

increased ozone production capabilities. 

 Table 4-1 shows the vendor specifications of the Model 42C-Y NOy analyzer. 

Table 4-1. Thermo Electron Model 42C-Y NOy Analyzer Specifications. 

Performance 

Parameters Model 42C-Y NOy Analyzer Specifications

Precision Not available

Bias Not available

Method Detection Limit Not available

Lower Detectable Limit 50 ppt (0.05 ppb) (120 second average time)

Linearity ± 1% of full scale

Zero Drift Negligible (24-hour)

Span Drift ± 1% of full scale (24-hour)

Figure 4-2. Thermo Electron Model 42C-Y NOy analyzer (courtesy Thermo Electron). 
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4.3.3.2 API Model 200AU with Model 501Y Converter

 The API Model 200AU high sensitivity analyzer[14-16] shown in Figure 4-3 is based on the 

Model 200A NO/NO2/NOx analyzer, and uses the optional Model 501Y molybdenum NOy

converter that places the converter at the sample inlet point. 

The Model 200AU has operating ranges from 0 to 5 ppb up to 0 to 2,000 ppb (2 ppm), 

with a lower detectable limit of 0.05 ppb, and may be safely operated in the temperature range of 

5 °C to 35 °C. Table 4-2 shows the vendor specifications for the Model 200AU/501 NOy 

Analyzer. 

Table 4-2. API Model 200AU/501 NOy Analyzer Specifications. 

Performance Parameters API Model 200AU/501NOy Analyzer Specifications 

Precision 0.5% of reading 

Bias Not available

Method Detection Limit Not available

Lower Detectable Limit 50 ppt (0.05 ppb); 120 second averaging time

Linearity 1% full scale

Zero Drift <0.1 ppb/24 hours, <0.2 ppb/7 days 

Span Drift <0.5% full scale/7 days or 50 ppt/7 days, whichever is greater 

Figure 4-3. API Model 200AU/501Y NOy analyzer (courtesy Teledyne API).
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4.3.3.3 Ecotech Model EC9841

 High sensitivity NOy capabilities are only partly established in the Ecotech line of 

analyzers. Although an Ecotech high sensitivity nitrogen oxides analyzer exists, it is not yet 

available in an NOy configuration. 

 The high sensitivity Ecotech analyzer is the Model EC9841T Trace Nitrogen Oxides 

Analyzer, which has a LDL of 0.05 ppb, and a maximum full scale reading of 200 ppb. 

However, at this time the Model EC9841T is not available in a configuration consistent with the 

NOy requirements illustrated in Figure 4-1. On the other hand, Ecotech’s Model EC9841-NOy

does incorporate the needed NOy configuration, but has an LDL of 0.5 ppb. On the assumption 

that Ecotech may later adapt the high sensitivity EC9841T analyzer for NOy detection, the 

capabilities of both the EC9841-T and the EC9841-NOy are summarized below. 

The EC9841-NOy analyzer[17, 18] shown in Figure 4-4 has a lower detection limit of 

500 ppt (0.5 ppb). It uses a programmable temperature-controlled molybdenum (Mo) converter 

that is typically operated at 350 °C and is mounted directly onto the system’s sample manifold 

(external to the analyzer). The sample manifold and inlet lines are heated to ensure there is no 

condensation as the sample gas is transported from the converter to the analyzer. The EC9841-

NOy analyzer also uses a high-vacuum pump to minimize residence time, and to decrease 

reaction cell pressure and thus increase the sensitivity of the chemiluminescent detection. 

Interferences are minimized in the EC9841-NOy through the use in the converter of Mo chips 

that have a greater gas contact area than solid Mo granules to provide greater converter 

efficiency with low flow restriction at atmospheric pressure. Under typical operating conditions, 

the converter has less than a 5 percent conversion efficiency for ammonia, cyanides, and amines, 

thereby limiting interference from these non-NOy species. The analyzer has automatically 

selected range settings up to 20 ppm full scale, and has a recommended operating temperature 

range of 20 °C to 30 °C, but may be operated between 15 °C and 35 °C. The Model EC9841T 

differs from the EC9841-NOy primarily in its higher sensitivity and lower zero and span drift. 

Table 4-3 shows the vendor specifications of both analyzers. 
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Table 4-3. Ecotech EC9841-NOy Analyzer Specifications. 

Performance 

Parameters EC9841-NOy EC9841T 

Precision ± 2% of reading ± 2% of reading

Bias Not available Not available

Method Detection 

Limit Not available Not available

Lower Detectable 

Limit

500 ppt (0.5 ppb) (with Kalman or 

300 sec filter active)

50 ppt (0.05 ppb) (with Kalman or 

300 sec filter active)

Linearity Not available Not available

Zero Drift

Temperature dependence, 0.1% per 

degree C changes.

24 hours; less than 1 ppb

Temperature dependence, 0.1% per 

degree C changes.

24 hours; less than 50 ppt (0.05 ppb)

Span Drift

Temperature dependence, 0.1 % per 

degree C changes.

24 hours less than 1.0% of reading 

30 days less than 1.0% of reading

Temperature dependence, 0.05 % per 

degree C changes.

24 hours less than 0.5% of reading 

30 days less than 1.0% of reading

4.3.3.4 ECO PHYSICS Models CLD 88 p or CLD 780 TR with CON 765 NOy Converter

ECO PHYSICS produces two different chemiluminescent analyzers with the requisite 

high sensitivity for trace level measurements.[19] The ECO PHYSICS Model CLD 88 p analyzer 

has a lower detection limit of 50 ppt (0.05 ppb), and the CLD 780 TR is a research grade NO 

instrument capable of a lower detection limit of 10 ppt (0.01 ppb) with a 60 second integration 

Figure 4-4. Ecotech EC9841-NOy analyzer (courtesy of Ecotech).
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time. The CLD 88 p has four selectable operating ranges from 5 to 5,000 ppb (5 ppm) and may 

be safely operated in the temperature range of 5 °C to 40 °C. The CLD 780 TR has five 

selectable operating ranges from 5 to 500 ppb, and may be safely operated in the temperature 

range of 5 °C to 50 °C. However, at this time these analyzers are not available in a configuration 

consistent with the NOy requirements illustrated in Figure 4-1. On the assumption that the 

manufacturer may adapt one or both analyzers to the required configuration, the capabilities of 

both the CLD 88 p and the CLD 780 TR are summarized below. 

The limitation of the ECO PHYSICS analyzers lies in the ECO PHYSICS CON 765 NOy

converter, which is designed to be used with either of the CLD 88 p or CLD 780 TR NO 

analyzers.[19] The CON 765 reduces NOy species to NO by chemical reaction with CO on a gold 

surface maintained at 315 °C. This converter has a reported NOy conversion efficiency that 

exceeds 95%, and due to the nature of the reduction process the presence of water vapor in the 

sample air is said to keep interference from NH3 and HCN to a negligible level. Despite these 

attractive features, the CON 765 is not the type of NOy converter recommended for use in 

precursor gas monitoring in NCore. The need for a constant supply of highly toxic high purity 

CO is a serious disadvantage of this converter, especially since the gold converter offers 

essentially the same NOy conversion efficiency as the molybdenum converter recommended for 

use in NCore. 

Figure 4-5 shows the Model CLD 88 p with the CON 765 converter. Table 4-4 shows the 

information available on the specifications of both the CLD 88 p and CLD 780 TR NO 

analyzers. 
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Table 4-4. ECO PHYSICS CLD 88 p and CLD 780 TR Analyzer Specifications.

Performance 

Parameters CLD 88 p CLD 780 TR 

Precision Not available Not available

Bias Not available Not available

Method Detection Limit Not available Not available

Lower Detectable Limit 50 ppt (0.05 ppb) 10 ppt (0.01 ppb) w. 60 sec response

Linearity 1% of full scale 1% of full scale

Zero Drift 0.05% of full scale (24 hours) None (i.e., zero) 

Span Drift 1% of full scale (24 hours) Not available

4.3.4 Sampling Requirements

 Proper siting of the sampling equipment and sampling probes is necessary to ensure that 

the gas analyzers are obtaining representative samples of the ambient air. Likewise, proper 

environmental control of the analyzer and proper sampling are critical to ensuring that the 

analyzers are operating correctly and that the NOy measurements are comparable to NOy

measurements recorded at other sites. 

Figure 4-5. ECO PHYSICS Model CLD 88 p and CON 765 NOy Converter
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4.3.4.1 Analyzer Siting

 Analyzer siting should follow the criteria in 40 CFR 58, Apendix E. The installation of 

the precursor NOy analyzer should allow for the sample probe inlet to be approximately 10 

meters above ground level with the inlet facing the prevailing wind direction. The probe should 

be positioned with at least 270 degrees of unrestricted airflow including the predominant wind 

direction. The probe should be separated from the drip line of nearby trees or structures by at 

least 20 meters, and should be positioned at least twice as far from of nearby obstacles as the 

height of the obstacles. 

4.3.4.2 Instrument Shelter

 To help ensure proper performance, the precursor analyzers and supporting equipment 

should be installed and operated in a temperature controlled environment. An insulated 

instrument shelter should be used to protect the analyzer from precipitation and adverse weather 

conditions, maintain operating temperature within the analyzer’s temperature range 

requirements, and provide security and electrical power. The environmental control of the 

shelter should be sufficient to minimize fluctuations in shelter temperature. The recommended 

shelter temperature range is 20 °C to 30 °C, and daily changes in temperature should not exceed 

5 °C over a 24-hour period. Condensation of moisture must be avoided and it may be necessary 

to impose seasonal temperature ranges to assure remaining above the ambient dewpoint. 

4.3.4.3 Sampling Issues

 Studies of NOy sampling inlet issues have focused primarily on airborne NOy

measurements, where it is not feasible to locate the converter directly at the sample inlet 

point.[20-22] The purpose of these studies was to identify the material that causes the least 

adsorptive loss of NOy components during sampling. Nitric acid, as both a key component of 

NOy and a strongly adsorbed species, has generally been the target compound in these studies. 

Adsorption of NO and NO2 is of much less concern. Numerous tubing materials, including TFE, 
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PFA, and FEP Teflon®, have been investigated for use in sampling inlets.[20] In testing these 

materials for HNO3 adsorption, less than 5 percent of the HNO3 was lost with Teflon® tubing, 

while greater than 70 percent was lost with tubing made of stainless steel, glass, fused silica, 

aluminum, nylon, silica-steel, and silane-coated steel. HNO3 transmission through aluminum, 

steel, and nylon tubes did not increase in over 1 hour of HNO3 exposure. HNO3 loss on 

aluminum and steel tubes heated to 50 °C was irreversible. However, HNO3 adsorption on glass 

decreased over time, so that over a period of several hours of continuous HNO3 exposure, glass 

will be passivated to HNO3 adsorption. Furthermore, heated glass tubing passivates faster than 

room temperature tubing, and larger diameter glass tubing takes longer than smaller diameter 

glass tubing to passivate with HNO3. PFA Teflon® causes the least adsorption of HNO3, and so 

is recommended for sampling inlets. 

 Although PFA Teflon® is far superior to other materials in minimizing HNO3 adsorption, 

it has the disadvantage that any previously adsorbed HNO3 can be released back into the air 

stream by changes in temperature and/or relative humidity.[20] Thus, the best approach to NOy

monitoring is to expose the incoming sample air to as little surface area as possible upstream of 

the heated converter. Therefore, the best approach is to minimize the length of PFA tubing at the 

inlet. 

 The inlet system must also be configured to allow calibration through the same inlet 

plumbing used in monitoring. As shown in Figure 4-1, this is easily accomplished by means of a 

PFA cross fitting on the inlet of the converter, with one arm of the cross connected to the GPT 

calibration system. 

4.4 Potential Problems and Solutions 

 In addition to the potential problems with sampling described above, there are other 

potential problems with the high sensitivity measurement of NOy in ambient air. 
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4.4.1 Interferences

 Interferences in NOy measurements are of two types. One potential interference is the 

presence of nitrogen-containing species in ambient air that are not components of NOy, but that 

can potentially be converted to NO by the heated converters used to achieve NOy measurement. 

The primary examples of such an interferent are ammonia (NH3), and particulate ammonium 

(NH4

+

), but other amines and even cyanide compounds (e.g., hydrogen cyanide, HCN) could be 

present. This type of interference is addressed in the discussion of converter efficiency in 

Section 4.4.2. 

 The other type of potential interferent consists of non-NOy species that can react with O3

to produce chemiluminescence in the relevant wavelength region, thereby artificially increasing 

the apparent signal from NO in the sample air. The most important such interferents in ambient 

air are unsaturated hydrocarbons (e.g., ethylene, propylene, and naturally emitted species such as 

terpenes). Interference from such compounds in ambient NOy monitoring is minimized by the 

use of a prereactor vessel in the NOy monitor (see Figure 4-1). The prereactor is a part of the 

normal flow path of ozone to the reaction chamber in the monitor. When the sample air flow is 

diverted into the prereactor, the NO/O3 reaction occurs rapidly and the resulting NO2

chemiluminescent emission occurs entirely within the prereactor, where it cannot be detected by 

the photomultiplier. However, the O3 reactions with unsaturated hydrocarbons occur more 

slowly, so light emission from these reactions is not completed within the prereactor volume. As 

the sample/O3 mixture flows from the prereactor into the reaction chamber, the photomultiplier 

detects the background chemiluminescence from the hydrocarbon interferents, without emission 

from the NO/O3 reaction. Commercial high sensitivity NOy analyzers typically determine their 

background readings automatically using this prereactor mode and, thus, this type of interference 

is automatically accounted for by the analyzer software through subtraction of the background 

readings. 
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4.4.2 Converter Efficiency

4.4.2.1 Overview

 The heated molybdenum converters used in commercial high sensitivity NOy analyzers 

have undergone extensive testing and intercomparison in both laboratory and field studies to 

confirm the wide variety of species that can be converted to NO and measured as part of the NOy

total.[e.g., 10, 23] These studies indicate that the molybdenum converters can provide accurate 

measurements of NOy. The goal with such converters is to achieve 100 percent conversion 

efficiency of NOy species to NO, while approaching zero percent conversion of other non-NOy

nitrogen-containing species. Note that, as used in commercial high sensitivity NOy monitors, the 

molybdenum converters are designed to convert particulate nitrate compounds, as well as the 

numerous gaseous components of NOy, to NO for detection.[10]

 As noted in Section 4.4.1, non-NOy species such as ammonia, particulate ammonium, or 

hydrogen cyanide can also be oxidized to NO, although this conversion can be minimized (to a 

few percent conversion or less) by maintaining the converter temperature at 350 °C. At sub-ppb 

NOy concentrations, interference from such compounds can be substantial, and even at higher 

levels the potential for interferences must be kept in mind. Sampling near a large source of 

ammonia, for example, could produce erroneously high NOy readings, even though the 

conversion efficiency for ammonia is much less than that for NO2 or the various NOz

compounds. In general, the efficiency of a converter system at sub-ppb levels may vary 

depending on the mix of NOy species present, the age and condition of the converter, the 

converter temperature, ambient humidity, or ozone levels and cannot be entirely predicted even 

from the behavior of a similar system. For these reasons, converter efficiency must be evaluated. 
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4.4.2.2 Challenge Species for Converter Efficiency Checks

 Studies of converter efficiencies have established that among NOy species, NO2 is 

relatively easily reduced to NO. As a result calibration with NO and NO2, as described in 

Section 4.7.2, is a necessary but not entirely sufficient approach to characterizing an NOy

monitoring system. A more stringent approach is to also calibrate with an NOy species that is 

both more difficult to convert to NO and relatively easy to prepare in known concentrations. The 

most common choice for such an additional compound to determine NOy converter efficiency is 

n-propyl nitrate (NPN). This organic nitrate is used in the form of compressed gas standards that 

are readily diluted to near-ambient NOy levels. Diluted NPN mixtures (Scott-Marrin, Inc., 

Riverside, CA; www.scottmarrin.com) are supplied to the monitor through the calibration line to 

the monitor’s inlet (Figure 4-1), and provide a more challenging test of the conversion efficiency 

than testing with NO2 alone. 

 Conversion efficiency testing with NPN is in addition to, not in place of, routine 

calibration with NO and NO2. Changes in pollutant levels and meteorological conditions over 

time can significantly alter the instrument’s conversion efficiency. Thus, NOy monitoring 

requires routine NPN converter efficiency checks and consistent procedures to maintain or repair 

the converter when its efficiency falls below acceptable levels. A single-point conversion 

efficiency check with NPN is recommended every month in continuous NOy monitoring. An 

NPN conversion efficiency of 95 percent or greater is considered acceptable for NOy monitoring, 

converters falling below 95 percent efficiency should be replaced. Note that a new converter 

should be allowed to “burn in” over one to three days of use before performance of an NPN test. 

Also, the NPN standard may not be certified to better than ±5%, so it is recommended to track 

conversion over time and use 95% of the original efficiency as the performance cutoff. 

 The most rigorous way to perform NO or NO2 calibrations and NPN conversion 

efficiency checks would be by standard addition (i.e., by adding known concentrations of these 

species to the ambient air sampled by the monitor). This approach would provide the most 

accurate and realistic calibration because it includes the effects of water vapor and other 
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constituents in the sample air. However, this procedure may not fit well into the routine data 

acquisition used at many monitoring sites. Often, data acquisition is keyed to recording one-hour 

average data. Over that period, the ambient air background NO and NOy levels are not likely to 

remain constant enough for an accurate standard addition calibration or efficiency check. As a 

result, it is recommended to perform calibrations and conversion efficiency checks by diluting 

appropriate standards with high purity air using a MFC dilution system. Personnel at NOy

monitoring sites are advised to consider the calibration approaches that fit best within their 

programs. 

 Although HNO3 is a key component of NOz and in turn of NOy, and is known to be 

especially difficult to sample, it is not advisable to attempt routine calibration checks with HNO3

in the field. The complexities of maintaining an HNO3 source and delivering accurate HNO3

levels to the sample inlet outweigh the potential benefits. The best way to assure adequate 

sampling of HNO3 and other NOy species is to use a properly configured NOy monitor, as 

described in Section 4.3.2 and 4.3.4. However, an annual or more frequent challenge of the 

monitor with multiple compounds may be a valuable test of instrument performance. If 

performed, such a challenge should involve several different tests, i.e., calibrations with NO and 

NO2, a converter efficiency check with NPN, and perhaps a test of the conversion efficiency for 

NH3 (the most likely gas-phase interferent) using a certified permeation source of NH3. An NPN 

conversion efficiency of at least 95 percent, and a simultaneous ammonia conversion efficiency 

of at most 5 percent, should be the target performance criteria for such a challenge. 

4.5 Equipment and Supplies 

4.5.1 Data Acquisition Device

 Many types of equipment can be used to record the concentration measurements obtained 

from the analyzer. Recommended options for data acquisition are described in Section 6 of this 

TAD. 
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4.5.2 Calibration Equipment

 The equipment required for calibration of a precursor NOy analyzer include a MFC 

calibrator unit as described in Section 2.5.2, with gas phase titration capability, and a source of 

zero air. The following equipment is recommended for calibration of a high sensitivity NOy

analyzer. 

4.5.2.1 Calibration Standard and Standard Delivery System 

 The calibration standards used for the calibration of precursor NOy analyzers should be 

generated by dilution of a commercially-prepared and certified compressed gas NO standard 

using a MFC calibration unit. It is important when purchasing a MFC calibrator that it meet the 

40 CFR 50 requirements of ±2 percent accuracy, and that the flow rates of both MFC channels 

be calibrated using a NIST-traceable flow standard. 

 When the analyte concentration in the commercially-prepared standard cylinder is vendorcertified by reference to NIST standards, and the MFCs are calibrated to NIST-traceable 

standards, the resulting working gas concentration is considered to be NIST-traceable. 

4.5.2.2 Zero Air Source/Generator 

 Zero air is required for the calibration of high sensitivity NOy instruments. This air must 

contain no detectable NOy species (i.e., NOy content must be less than the LDL of the analyzer) 

and must be free of particulate matter. Suitable zero air may be supplied from compressed gas 

cylinders, with additional scrubbing by passage through a soda lime trap, sodium carbonate trap, 

or carbonate coated denuder. However, it is likely too expensive and impractical to maintain a 

sufficient supply of zero air cylinders to operate a high sensitivity NOy analyzer continuously. 

As an alternative, many commercially-available zero-air generation systems can supply suitably 

NOy-free air, provided additional external scrubbing is provided as noted above. 
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4.6 Reagents and Standards 

 Routine operation of precursor NOy analyzers requires the use of calibration standards 

and zero air to conduct periodic calibrations and instrument checks. This section describes the 

requirements for these gases. 

4.6.1 Calibration Standards

 The primary NO standards must be certified commercially-prepared compressed gas 

standards of NO in N2, with a certified accuracy of no worse than ±2 percent. NO gas standards 

of 5 to 20 ppm (with less than 1 ppm NO2) are conveniently diluted with a MFC calibrator down 

to working concentrations of 10 ppb or less. The commercially-prepared standard may contain 

only NO, or may be a mixed component standard that also contains known concentrations of 

other non-reactive precursor gases (e.g., CO, SO2). This standard must be traceable to a NIST 

NO in N2 Standard Reference Material (SRM 1683 or SRM 1684), NIST NO2 Standard 

Reference Material (SRM 1629), or a NIST/EPA-approved commercially available Certified 

Reference Material (CRM). Section 2.0.7 of EPA’s Quality Assurance Handbook[24] gives a 

recommended protocol for certifying NO gas cylinders against either a NO SRM or CRM. 

Procedures for certifying a NO gas cylinder against a NIST NO2 SRM and for determining the 

amount of NO2 impurity in a NO cylinder are presented by Ellis.[25] Commercial gas standards 

for NO2 and NPN should be obtained with a certified accuracy no worse than ±2 percent, and ±5 

percent, respectively. 

 Every gas standard used in precursor gas monitoring must be accompanied by a 

certificate of calibration from the vendor stating the type of traceability, concentration of the 

standard, the uncertainty of that certification, and the expiration date of the certification. 

Standards traceable to NIST are preferred. Certification documents for all standards must be 

retained in a common location and reviewed periodically so that standards for which the 

vendor’s certification has expired may be removed from service and replaced. 
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4.6.2 Zero Air

 Zero air used as dilution gas for calibration purposes should have an NOy concentration 

below the LDL of the NOy monitor. Commercial grades of zero air may be suitable as a starting 

point, provided additional cleanup is employed as noted in Section 4.5.2.2. Commercial zero air 

further scrubbed of NOy may be used to crosscheck the purity of air provided by a commercial 

continuous air purification system, or a rapid check of the purity of a zero air source can be made 

by intercomparison of zero air readings when sampled directly vs. through the prereactor mode 

of the NOy analyzer. 

4.7 Quality Control 

4.7.1 Site Visit Checklists and Remote Diagnostic Checks

 To determine whether the high sensitivity NOy analyzer is working properly, field 

operators conduct many routine checks of instrument diagnostics and performance every time 

they visit the monitoring station. Each agency needs to develop maintenance checklists or 

electronic spreadsheets to document that all required checks have been made. The lists and 

sheets should be useful both for collecting data and for assessing the quality of that data. 

Management must review them regularly and change them if necessary. To the extent possible, 

diagnostic checks can be done remotely, provided the data acquisition system allows remote 

access to instrument diagnostic information (see Section 6). 

4.7.2 Multipoint Calibrations

 Calibration procedures for high sensitivity NOy analyzers are more complicated than for 

other high sensitivity precursor gas analyzers (i.e., for CO and SO2), in that they include 

calibration with NO and NO2,

[9] as well as checks of the converter efficiency for NOz species and 

potential interferents. A basic requirement is for a multipoint NO calibration that includes a 

minimum of four points (three spaced over the expected range and a zero point), generated by 

the calibration system. Although more points may be preferable, current high sensitivity 
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analyzers typically provide linear response over their entire operating range; therefore, four 

points should be sufficient. Multipoint calibrations must be done prior to the high sensitivity 

NOy analyzer being put into service and at least quarterly thereafter. An analyzer should be 

calibrated (or recalibrated) if any of the following conditions occur: 

• Upon initial installation; 

• The Level 1 span check or precision check difference exceeds 15 percent; 

• After repairs or service is conducted that may affect the calibration; 

• Following physical relocation or an interruption in operation of more than a few days; 

• Upon any indication that the analyzer has malfunctioned or a there has been a change 

in calibration; or 

• The measured concentration values during challenges with performance test samples 

(Section 5.4.1) differ from the certified standard values by ±15 percent. 

The analyzers should be calibrated in-situ without disturbing the normal sampling inlet system to 

the degree possible. 

 A second requirement is for multipoint calibration with NO2, as a check of the conversion 

efficiency of the molybdenum converter for NO2. This calibration is conducted by gas phase 

titration of NO with O3. MFC calibration systems in common use at ambient monitoring sites 

have GPT capability. The multipoint NO2 calibration should be done at approximately the same 

three concentration levels as the NO calibration noted above. The major equipment/components 

required for the GPT NO2 calibration are: a stable O3 generator, a data acquisition and display 

device, and the NO concentration standard used for the multipoint NO calibration. The principle 
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of this calibration technique is the rapid gas phase reaction of NO with O3 to produce equal 

stoichiometric quantities of NO2 in accordance with the following equation: 

NO + O3 → NO2 + O2

This is the same overall reaction detailed in reactions (4-1a and b) and (4-2a and b) above. For 

calibration purposes, ozone is added to a stable and excess concentration of NO in a dynamic 

calibration system, and the NO reading of the chemiluminescence NOy instrument is used as an 

indicator of changes in NO concentration. The NO standard is diluted sufficiently to produce an 

upscale NO reading on the measurement range of interest, and upon addition of O3 the decrease 

in NO reading observed is equivalent to the concentration of NO2 produced. The amount of NO2

generated may be varied by adding variable amounts of O3 from a stable O3 generator, which is a 

component of the GPT system of the calibrator. Comparison of the NO and NOy responses of 

the analyzer then allows determination of the ratio of NO2 response to NO2 generated, which 

indicates the converter efficiency for NO2. Maintenance or replacement of the converter should 

be undertaken whenever the NO2 conversion efficiency falls below 96 percent. 

4.7.3 Level 1 Zero/Span Checks

 Level 1 zero and span calibrations are simplified, two-point calibrations used when 

adjustments may be made to the analyzer. When no adjustments are made to the analyzer, the 

Level 1 calibration may also be called a zero/span “check” and must not be confused with a level 

2 zero and span check. Level 1 zero and span checks should be conducted nightly if the 

calibration system and NOy analyzers used can be programmed to automatically perform these. 

They are used to assess if the analyzers are operating properly and to assess if any drift in 

instrument response has occurred. The level 1 span check should not exceed ±15 percent. They 

are conducted by challenging the analyzer with zero air and a test atmosphere containing NOy at 

a concentration of between 70 percent and 90 percent of the full measurement range in which the 

analyzer is operating. The challenge gas should be sampled through as much of the sampling 

inlet system as practical to mimic the actual sampling of ambient air. The results of the Level 1 
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zero/span check should be plotted on control charts to graphically illustrate the trends in the 

response of the analyzer to the challenge gases. If the measured concentrations fall outside of 

the control limits, the accuracy of the MFC calibration system should be checked with a NISTtraceable flow standard. If the MFC flow accuracy is confirmed, the data recorded since the last 

successful Level 1 check should be flagged and the analyzer should be recalibrated using the 

multipoint calibration procedures described in Section 4.7.2. 

State-of-the-art calibration equipment now exists that is fully automated. These "new 

generation" calibration units are fully integrated with computers, mass flow calibrators, and the 

associated hardware and software where they can create test atmospheres manually or 

automatically. For the precursor gas program, it is recommended that the NCore sites have fully 

automated calibration capability. Below are a number of reasons why this is advantageous: 

• By performing the calibrations or checks automatically, agencies no longer spend the 

manpower needed to perform them. 

• Automated calibrations or checks can be triggered internally or by a DAS. Since newer 

DASs allow remote access, this allows a remote user to challenge the analyzers without 

actually being present. 

• High sensitivity precursor gas analyzers are expected to have more zero and span drift than 

less sensitive analyzers; therefore, it is important that a zero and Level I check be performed 

daily. 

• New generation DASs can record calibration or check data and allow remote users to track 

daily Level I check and zero drift. This is important for data validation, verification and 

troubleshooting. 
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4.7.4 Precision Checks

 At least once every two weeks a precision check should be conducted by challenging the 

NOy analyzer with a known low NO concentration to assess the performance of the analyzer. 

The precision checks should be conducted by challenging the precursor NOy analyzer with a 

calibration mixture of a known NO concentration near 20 ppb. After completion of the precision 

check, the operator should calculate the percent difference between the measured value and the 

standard value. Precision should be calculated quarterly, using the calculated percent differences 

from the precision checks, according to the equations provided in Section 4.3.1.1. For 

acceptable precision to be maintained, it is recommended that the calibration system’s gas flows 

be verified frequently against a NIST flow standard, and adjusted if necessary before making any 

adjustments to the analyzer. 

4.8 Preventive Maintenance and Troubleshooting 

 Long-term operation of continuous gas analyzers requires a preventive maintenance 

program to avoid instrument down-time and data loss. Despite active preventive maintenance, 

occasional problems may arise with the high sensitivity NOy analyzers. This section briefly 

describes several key items that might be included in the preventive maintenance program 

established for high sensitivity NOy analyzers deployed at NCore sites, as well as some of the 

troubleshooting activities that may be useful in resolving unexpected problems with these 

analyzers. This discussion is not meant to be exhaustive or comprehensive in detail. More 

thorough discussions should be included in the analyzer operation manuals and SOPs developed 

for these analyzers. Example SOP’s prepared by EPA are included as Appendix B of this TAD. 

4.8.1 Preventive Maintenance

 Routine preventive maintenance procedures should be in place to prevent down-time and 

data loss. Management and field operators should jointly develop their preventive maintenance 

program. A program designed by persons unfamiliar with analyzer operations may include 

unnecessary items or omit mandatory ones. 
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 NOy values can be erroneous if the sample inlet and lines become dirty, cracked, or leaky. 

PFA lines should be inspected at least quarterly and replaced as needed, but at least every two 

years. Teflon® filters used in the sampling train to remove fine particles may need to be 

replaced as often as every week, depending on the condition of the filter and the particulate 

loading around the monitoring site. The NOy inlet should be inspected every time the NOy filter 

is changed. 

 Table 4-5 illustrates items that monitoring agencies should include in their preventive 

maintenance program for high sensitivity NOy monitoring. 

Table 4-5. Example of a preventive maintenance schedule for NOy monitoring. 

Item Schedule

Maintain air dryer As needed 

Replace particle filter Weekly 

Perform pneumatic system leak check At least quarterly 

Inspect internal, external tubing; replace if necessary Inlet, weekly; other, 

quarterly 

Clean optical bench As needed 

Replace PMT As needed 

Monitor NO2 conversion efficiency At least every 6 months 

Monitor NPN conversion efficiency At least every month 

4.8.2 Troubleshooting

 Table 4-6 summarizes common problems seen with precursor NOy analyzers, possible 

causes, and possible solutions. More specific information can be found in the manufacturer’s 

operations manuals. When troubleshooting, an operator must constantly be aware of 

environmental factors that may affect the instruments. Environmental factors can also cause 

sporadic problems that can be difficult to diagnose. Examples of factors that may affect the 

performance of the precursor NOy analyzers are: 
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• Variable shelter temperature (fluctuations greater than several degrees) 

• Excessive vibration from other equipment 

• Voltage instability; fluctuations in the 110 VAC line voltage 

• Air conditioning system blowing on the instrument 

• Frequent opening of the door of the shelter. 

• Leaks 

Table 4-6. Instrument troubleshooting for high sensitivity NOy analyzers 

Problem Possible Cause Possible Solution 

Defective DC power supply Replace power supply

Noisy output Dirty reaction cell Clean cell

PMT failure Replace PMT 

Defective bandpass filter Replace filter High positive zero drift PMT failure Replace PMT 

High Prereactor zero reading Moisture in PMT housing Allow PMT housing to warm up; 

purge with dry gas, reassemble 

PMT failure Replace PMT 

No response to span gas Voltage failure Replace high voltage source 

No O3 supply Clean or replace O3 generator 

Low or declining response to O3 source failing Clean or replace O3 generator 

span gas Dirty reaction cell window Clean window 

Pump failure Check pump Zero output at ambient levels PMT failure Replace PMT 

Low NO2 or NPN efficiency Aging or dirty converter Replace converter 

No flow through analyzer Pump failure Replace/ rebuild pump head 
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4.9 References 

1. U.S. Environmental Protection Agency. Code of Federal Regulations. Title 40, Part 58, 

Subpart E. “Enhanced O3 Monitoring Regulations.” Office of the Federal Register, 

February, 1993. 

2. Parrish, D.D., et al., “The Total Reactive Oxidized Nitrogen Levels and the Partitioning 

Between the Individual Species at Six Rural Sites in Eastern North America”, J. 

Geophys. Research, 98; 2927-2939. 1993. 

3. Trainer, M., et al., “Correlation of Ozone with NOy in Photochemically Aged Air”, J. 

Geophys. Research, 98; 2917-2925. 1993. 

4. Kleinman, L.I., et al., “Photochemical Age Determinations in the Phoenix Metropolitan 

Area”, J. Geophys. Research, 108(D3); 4096. 2003. 

5. Arnold, J.R., R.L. Dennis, and G.S. Tonnesen, “Diagnostic Evaluation of Numerical Air 

Quality Models with Specialized Ambient Observations: Testing the Community 

Multiscale Air Quality Modeling System (CMAQ) at Selected SOS 95 Ground Sites”, 

Atmos. Environ., 37; 1185-1198. 2003. 

6. Li, Q., D.L. Jacob, J.W. Munger, R. M. Yantosca, and D.D. Parrish, “Export of NOy 

from the North American Boundary Layer: Reconciling Aircraft Observations and Global 

Model Budgets”, J. Geophys. Research, 109(D2); D02313. 2004. 

7. U.S. Environmental Protection Agency. Code of Federal Regulations. Title 40, Part 53, 

Office of the Federal Register, July 1, 1987.

8. Fontijn, A., A.J. Sabadell, and R.J. Ronco, “Homogeneous Chemiluminescent 

Measurement of Nitric Oxide with Ozone”, Anal. Chem., 42; 575-579. 1970.

9. 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 

Federal Register, December 1, 1976. 

10. Williams, E.J., et al., “Intercomparison of Ground-Based NOy Measurement 

Techniques.” J. Geophys. Research, 103:22; 261-280. 1998. 

11. Rhodes, R.C., Guidelines on the Meaning and Use of Precision and Accuracy Data 

Required by 40CFR Part 58, Appendices A and B, EPA60014-83-023, U.S. 

Environmental Protection Agency, Research Triangle Park, NC, June 1983. 
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12. Thermo Electron Corporation (2004). “Product Specifications, Model 42C-Y NOy

Analyzer.” Accessed December, 2004. Available at http://www.thermo.com/eThermo/

CMA/PDFs/Product/productPDF_24533.pdf. 

13. Personal Communication with Thermo representative, Michael Nemergut. 

November 2004. 

14. Teledyne Advanced Pollution Instrumentation (2004). “M200AU NOy Converter 

Option.” Manual Addendum. 

15 Teledyne Advanced Pollution Instrumentation (1999). “Model 200AU Nitrogen Oxides 

Analyzer (1999).” Instruction Manual. 

16. Teledyne Advanced Pollution Instrumentation. “Model 200AU Ultra Sensitivity 

NO/NO2/NOx Analyzer Data Sheet.” Accessed November 2004. Available at 

http://www.teledyne-api.com/products/model_200au.asp. 

17. Ecotech Pty Ltd. (2004). “EC9841-NOy Analyzer Product Specification Sheet.” 

Accessed December, 2004. Available at http://www.ecotech.com.au/brochures_new/

EC9841A-NOy.pdf. 

18. Personal Communication with Ecotech representative, Andy Tolley. September 2004. 

19. Information on ECO PHYSICS CLD 88 p and CLD 780 TR NO analyzers, and on CON 

765 NOy converter, provided by ECO PHYSICS AG, Duernten, Switzerland and Ann 

Arbor, Michigan, at www.ecophysics.com and www.ecophysics-us.com. 

20. Neuman, J.A., L.G. Huey, T.B. Ryerson, and D.W. Fahey. “Study of Inlet Materials for 

Sampling Atmospheric Nitric Acid.” Environ. Sci. Technol., 33:7; 1,133-1,136. 1999. 

21. Ryerson, T.B., L.G. Huey, K. Knapp, J.A. Neuman, D.D. Parrish, D.T. Sueper, and 

F.C. Fehsenfeld. “Design and Initial Characterization of an Inlet for Gas-Phase NOy

Measurements from Aircraft.” J. Geophys. Research, 104; 5,483-5,492. 1999. 

22. Kondo, Y., S. Kawakami, M. Koike, D.W. Fahey, H. Nakajima, Y. Zhao, N. Toriyama, 

M. Kanada, G.W. Sachse, and G.L. Gregory. “Performance of an Aircraft Instrument for 

the Measurement of NOy.” J. Geophys. Research, 102; 28,663-28,671. 1997. 

23. Dahv, A.V., B.C. Daube, J.D. Burley, and S.C. Wofsy. “Laboratory Investigation of the 

Catalytic Reduction Technique for Measurement of Atmospheric NOy.” J. Geophys. 

Research, 102; 10,759-10,776. 1997. 
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24. 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. 

25. 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. 
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5.0 QUALITY ASSURANCE/QUALITY CONTROL (QA/QC) PROCEDURES 

5.1 Introduction 

 One of the primary objectives of the NAAMS is to accurately measure CO, SO2, and NOy

at low concentrations.[1] Therefore, a rigorous quality assurance (QA) program, with appropriate 

quality control (QC) activities, must be maintained to ensure that the precursor monitoring data 

collected in the NCore network are of suitable quality to meet the objectives of the program. 

Quality assurance is defined by EPA as “an integrated system of management activities 

involving planning, implementation, assessment reporting and quality improvement to ensure 

that a process, item or service is of the type and quality needed and the client expects.”[2] QA is 

an overall process, described in a management plan, to guarantee the integrity of the data, and 

QA activities ensure that the process is appropriately defined and implemented. Quality control 

(QC) is defined as “the overall system of technical activities that measures the attributes and 

performance of a process, item or service against defined standards to verify that they meet the 

stated requirements established by the customer.”[2] QC activities are a series of analytical 

measurements taken throughout the air monitoring process that are used to assess the quality of 

the monitoring data. This section of the NCore TAD describes the QA/QC activities that should 

be implemented for precursor gas monitoring in NCore. 

5.2 QA/QC Management 

 The overall QA/QC program should be defined in a Quality Assurance Project Plan 

(QAPP). Each State or Local monitoring agency should develop a QAPP in accordance with the 

guidance document prepared by EPA.[3] The primary purpose of the QAPP is to “provide an 

overview of the project, describe the need for the measurements, and define QA/QC activities to 

be applied to the project, all within a single document. The QAPP should be detailed enough to 

provide a clear description of every aspect of the project and include information for every 

member of the project staff, including samplers, lab staff, and data reviewers.”[4] 
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5.3 Network Calibration and Instrument Check Procedures 

 The following sections describe the instrument calibration and routine instrument check 

procedures for precursor analyzers that should be implemented within NCore. In general, these 

procedures may be followed for all the precursor pollutant monitors (i.e., CO, SO2, NOy) unless 

noted. 

5.3.1 Multipoint Calibrations

 A multipoint calibration includes a minimum of four points (three spaced over the 

expected range and a zero point), generated by the calibration system. Although more points 

may be preferable, current high sensitivity analyzers typically provide linear response over the 

entire operating range; therefore, four points should be sufficient. Multipoint calibrations must 

be done prior to the high sensitivity analyzer being put into service and should be repeated at 

least quarterly thereafter. An analyzer should be calibrated (or recalibrated) if any of the 

following conditions occur: 

• Upon initial installation; 

• The Level 1 span check or precision check difference exceeds 15 percent; 

• After repairs or service is conducted that may affect the calibration; 

• Following physical relocation or an interruption in operation of more than a few days; 

• Upon any indication that the analyzer has malfunctioned or a there has been a change 

in calibration; or 

• The measured concentration values during challenges with performance test samples 

(Section 5.4.1) differ from the certified standard values by ±15 percent. 
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The analyzers should be calibrated in-situ without disturbing the normal sampling inlet system to 

the degree possible. 

5.3.1.1 Precautions 

 A primary precaution is to check the calibration of the mass flow controllers in the 

calibration system before calibration of the precursor gas analyzers, rather than relying solely on 

the vendor-supplied calibration. This check should be conducted by comparison of readings over 

the full range of each flow controller, using an independent and NIST-traceable flow 

measurement device, such as an electronically timed bubble or piston-type flow meter. 

Commonly used MFC calibrators allow the input of regression data from such comparisons, so 

that corrections to the flow readings are made automatically by the calibration system. 

Once the calibration system has been inspected, tested, and NIST traceability established, the 

precursor analyzers can be calibrated in a field situation. The following additional precautions 

should be observed. 

• FEP or PTFE is the recommended material for all components and lines throughout 

the calibration system, and all tubing and connection from the gas standard cylinders. 

It is also preferred for any surfaces contacting the gas flows in solenoid valves in the 

calibration system. 

• When connecting cylinders to a MFC, make sure that the cylinder regulator is purged. 

Fill and vent the regulator at least three successive times before connecting the 

regulator to the delivery tubing. If a cylinder is changed, regulator purging is needed, 

and the resulting calibration should be monitored very closely. If the response of the 

analyzer is lower than before the cylinder change, then it can most likely be traced to 

improper regulator purging. Purging and drying of a regulator can be aided by the 

application of vacuum, as described in Section 3.6.1. 
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• It is recommended that stainless steel regulators with internal diaphragms that are 

coated with Teflon® or other inert material be used with all calibration and audit 

cylinders. 

5.3.1.2 Calibration Procedures 

 Analyzer-specific SOPs should be developed based on the manufacturer’s recommended 

calibration procedures. Example SOP’s prepared by EPA are included in Appendix B of this 

TAD. However, the following steps outline the multipoint calibration procedure for the 

precursor gas analyzers. If appropriate, a NIST-traceable multicomponent gas mixture (i.e., CO, 

SO2, NO in N2) may be used to calibrate multiple precursor gas analyzers. 

1. Allow both the calibration system and the analyzer to warm up properly. Consult the 

manufacturer’s instruction manual for specific details. 

2. Record the normal QC check information. Especially note the zero and span 

dial/readout values before starting the calibration. 

3. Start introduction of zero air to the sampling manifold or the NOy inlet, and flag this 

event in the data. With the zero air supplied at a constant flow rate, allow the 

analyzer readings to stabilize on zero air. When stability is satisfactory, record the 

response of the analyzer. 

4. Set the MFC calibration unit to allow diluted calibration gas to flood the manifold or 

NOy inlet at a concentration that is 80 to 90 percent of full scale of the analyzer 

measurement range. 

5. Allow the analyzer readings to stabilize at the working concentration. Record the 

response from the analyzer. 
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6. Lower the concentration of the diluted calibration standard to 40 to 50 percent of the 

analyzer’s full scale. Repeat the previous step. 

7. Lower the concentration of the diluted calibration standard to 15 to 20 percent of the 

analyzer’s full scale. Repeat Step 5. 

8. Once three concentration levels are tested and all values recorded, allow the analyzer 

to sample zero air again (Step 3), and again record the reading. Once the calibration 

is completed, return the instrument to its normal ambient operational status. 

 The responses of the precursor analyzer should be analyzed by linear regression to assess 

the results of the calibration. Acceptance criteria for the linear regressions are left to the 

discretion of the monitoring agency, but the following are suggested: slope, 1 ± 0.10; intercept, 

zero ± 1 × analyzer LDL or ±1% of the tested range (whichever is greater); and correlation 

coefficient (r), > 0.995, where the ± values represent 95% confidence intervals. Regardless of 

what criteria are selected, the instrument still must also pass audit tests, which require an 

absolute difference between the analyzer reading and the standard gas concentration of no more 

than 15 percent. 

5.3.2 Level 1 Zero/Span Checks

 Level 1 zero and span calibrations are simplified, two-point calibrations used when 

adjustments may be made to the analyzer. When no adjustments are made to the analyzer, the 

Level 1 calibration may also be called a zero/span “check” and must not be confused with a level 

2 zero and span check. Level 1 zero and span checks should be conducted nightly. They are used 

to assess if the analyzers are operating properly and to assess if any drift in instrument response 

has occurred. The level 1 check should not exceed ±15 percent. If zero drift is internally 

adjusted by the analyzer, the zero check is used to verify that the internal zero is working 

properly. Zero checks are conducted by challenging the analyzer with zero air and a test 
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atmosphere containing concentrations between 70 percent and 90 percent of the full 

measurement range in which the analyzer is operating. The challenge gas should be sampled 

through as much of the sampling inlet system as practical to mimic the actual sampling of 

ambient air. The results of the Level 1 zero/span check should be plotted on control charts to 

graphically illustrate the trends in the response of the analyzer to the challenge gases. If the 

measured concentrations fall outside of the control limits, the accuracy of the MFC calibration 

system should be checked with a NIST-traceable flow standard. If the MFC flow accuracy is 

confirmed, the data recorded since the last successful Level 1 check should be flagged and the 

analyzer should be recalibrated using the multipoint calibration procedures described in Section 

5.3.1. 

State-of-the-art calibration equipment now exists that is fully automated. These "new 

generation" calibration units are fully integrated with computers, mass flow calibrators, and the 

associated hardware and software where they can create test atmospheres manually or 

automatically. For the precursor gas program, it is recommended that the NCore sites have fully 

automated calibration capability. Below are a number of reasons why this is advantageous: 

• By performing the calibrations or checks automatically, agencies no longer spend the 

manpower needed to perform them. 

• Automated calibrations or checks can be triggered internally or by a DAS. Since newer 

DASs allow remote access, this allows a remote user to challenge the analyzers without 

actually being present. 

• High sensitivity precursor gas analyzers are expected to have more zero and span drift than 

less sensitive analyzers; therefore, it is important that a zero and Level I check be performed 

daily. 
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• New generation DASs can record calibration data and allow remote users to track daily Level 

I check and zero drift. This is important for data validation, verification and troubleshooting. 

5.3.3 Precision Checks

 At least once every two weeks a precision check should be conducted by challenging 

each precursor analyzer with a known concentration of a standard gas mixture to assess the 

ability of the analyzers to measure a gas under reproducible conditions. The precision checks 

should be conducted by challenging the precursor analyzer with a standard gas of known 

concentration in the ranges shown in Table 5-1. The gas must be supplied through all filters, 

scrubbers, and other conditioners and should be supplied through as much of the sample inlet 

system as possible. After completion of the precision check, the actual concentration of the 

working standard and the measured concentration indicated by the analyzer should be reported 

along with the percent difference between these values. Precision should be calculated at the end 

of each calendar quarter as described in Section 2.3.1.1, 3.3.1.1, or 4.3.1.1. 

Table 5-1. Concentration levels for biweekly precision checks. 

Target Concentration Range 

CO 250 to 500 ppb 

SO2 10 to 50 ppb 

NOy Approx. 20 ppb 

5.4 Independent Audits and Assessments 

 The effectiveness of the QA/QC procedures in place at each site should be evaluated 

routinely through a series of independent audits and assessments. These assessments should 

include: 

• Proficiency test samples; 

• Technical systems audits; and 
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• Audits of data quality. 

5.4.1 Proficiency Test Samples

 Proficiency test (PT) samples are used to ensure the performance of the precursor gas 

analyzers used to collect the monitoring data. PT samples are challenges of the gas analyzers 

with standards of known concentration that are independent of those standards used to calibrate 

the analyzers. Generally this challenge is conducted as a blind audit, such that the site operator 

is not aware of the gas standard concentrations delivered to the analyzers. Clearly, the 

appropriate concentration values to be used for PT samples will be different for the different 

precursor gases (CO, SO2, and NOy). In addition, for any one of these gases, the appropriate PT 

concentrations may vary with the analyzer operating range, which is selected based on the 

characteristics of the monitoring site. Consequently, the recommended concentration ranges for 

PT samples are given in Table 5-2 relative to the full scale range of the analyzer, rather than in 

concentration units. At least one PT sample of known concentration is to be delivered to the 

analyzer from each of the applicable ranges shown in Table 5-2. The indicated ranges are 

consistent with the requirements of 40 CFR 58 Appendix A, Section 3.2.1. 

Table 5-2. Concentration ranges for PT samples. 

Audit Point Percent of Full Scale Rangea

1 3 to 8 

2 15 to 20 

3 35 to 45 

4 80 to 90 

 a: Applies to operating range of CO, SO2, or NOy analyzer. 

 PT sample challenges should be conducted at least annually on each analyzer, and can be 

conducted (a) by a person outside of the agency, or an independent QA group within the agency, 

or (b) by having an independent audit device, such as used in the National Performance Audit 

Program (NPAP), sent to the monitoring station. In the former case, an independent audit system 
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or standard is brought to the monitoring station and used to produce working standards of the 

target gases that are supplied to the analyzers by the auditor. In the latter case, the audit device 

provided to the monitoring agency produces working standards of the calibration gases that are 

supplied to the analyzers. The operators and auditor do not know the concentrations of the 

standards that are produced by the audit equipment. Responses of the precursor analyzers are 

recorded and provided to the agency that supplied the audit device. That agency compares the 

responses of the analyzers to the calculated concentrations from the audit device and provides an 

audit report to the monitoring agency. In both cases, the PT sample audit should be conducted 

by supplying the analyzer with the PT sample gas in its normal sampling mode such that the 

audit gas passes through all sample inlet components used during normal ambient sampling. 

 Both the actual concentration of the PT sample gases and the concentration measured by 

the analyzer being audited should be reported, along with the percent differences between these 

concentrations for each audit point. The calculated percent differences are used to confirm the 

analyzer precision and bias estimates obtained from routine checks. 

 The PT audit should also include an independent check of the gas flow controllers in the 

calibration system, using a NIST-traceable flow standard. 

5.4.2 Technical Systems Audit

 A technical systems audit (TSA) is an on-site review and inspection of the operation of 

an air monitoring station to assess its compliance with established QA/QC procedures and any 

applicable regulations. TSAs assess whether all procedures for the monitoring program are 

being followed and documented. A TSA should be conducted immediately before or shortly 

after the start of monitoring and should be repeated at least every three years. TSAs should be 

performed by a regional auditor who is knowledgeable of the monitoring program but 

independent of routine operations. 
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5.4.3 Audits of Data Quality

 An audit of data quality (ADQ) process is an examination of data after they have been 

collected and verified. ADQs are conducted to determine how well the measurement system 

performed with respect to goals specified in the Quality Assurance Project Plan (QAPP) and 

whether the date were accumulated, transferred, calculated, summarized, and reported correctly. 

The ADQ documents and evaluates the methods by which decisions were made during the data 

treatment process. 

5.5 References 

1. “National Ambient Air Monitoring Strategy,” U.S. Environmental Protection Agency, 

Office of Air Quality Planning and Standards, Research Triangle Park, NC 27711, 

April 2004, Final Draft. 

2. EPA Order 5360.1 A2, “Policy and Program Requirements for the Mandatory Quality 

Assurance Program,” U.S. Environmental Protection Agency, Washington, D.C., 

May 2000. 

3. “EPA Requirements for Quality Assurance Project Plans,” EPA/QA R-5, 

U.S. Environmental Protection Agency, Office of Environmental Information, 

Washington, D.C., 20460, March 2001. 

4. “Quality Assurance Handbook for Air Pollution Measurement Systems, Volume II: 

Part 1,” EPA-454/R-98-004, U. S. Environmental Protection Agency, Office of Air 

Quality Planning and Standards, Research Triangle Park, NC, 27711, August 1998. 

5. “Volume 1: A Field Guide to Environmental Quality Assurance,” EPA/600/R-94/038a, 

U.S. Environmental Protection Agency, Office of Research and Development, 

Washington, D.C. 20460, April 1994. 
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6.0 DATA ACQUISITION AND MANAGEMENT 

6.1 Introduction 

 The ambient pollutant data generated by the high sensitivity precursor gas analyzers in 

the NCore network must be captured, organized, and verified in order to be useful. The process 

of capturing the precursor gas data is known as data acquisition, whereas the organization of the 

data is known as data management. Within both of these areas, quality assurance efforts and 

data reviews must be carried out to verify the quality of the ambient data. This chapter of the 

NCore TAD provides guidance in these areas, including identification of advanced equipment 

and procedures that are recommended for implementation in NCore. The recommended 

procedures rely on digital communication by the data acquisition system to collect a wider 

variety of information from the precursor gas analyzers, to control instrument calibrations, and to 

allow for more routine, automated, and thorough data quality efforts. 

6.2 Data Acquisition and Analysis 

 Many S/L/T agencies currently perform precursor gas data acquisition by recording an 

analog output from each precursor gas analyzer, using an electronic data logger. The analog 

readings are converted and stored in digital memory in the data logger, for subsequent automatic 

retrieval by a remote data management system. This approach can reliably capture the 

monitoring data, but does not allow complete control of monitoring operations, and the recorded 

analog signals are subject to noise that limits the detection of low concentrations. Furthermore, 

with this data acquisition approach, the data review process is typically labor-intensive and not 

highly automated. For these reasons, EPA discourages this approach, and instead strongly 

recommends adoption of digital data acquisition methods. In that regard, the common analog 

data acquisition approach often does not fully utilize the capabilities of the electronic data 

logger. For example, a data logger used by many agencies for analog data acquisition is the ESC 

Model 8816 Data Logger/Controller (Environmental Systems Corporation, 

Knoxville, Tennessee). This and similar data loggers have the capability to acquire data in 
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digital form, and to control some aspects of calibrations and analyzer operation, but these 

capabilities are not exercised in typical analog data acquisition approaches. 

 The recommended data acquisition approach for precursor gas monitoring in NCore is a 

system that records analyzer readings and diagnostic information in digital form, and allows 

direct digital communication between the data system and the precursor analyzers and calibration 

systems, at one or more monitoring sites. Digital data acquisition reduces noise in the recording 

of precursor gas monitoring data, thereby improving sensitivity, and also allows recording and 

control of the instrument settings, internal diagnostics, and programmed activities of monitoring 

and calibration equipment. Such data acquisition systems (DAS) also typically provide 

automated data quality assessment as part of the data acquisition process. 

It may be cost-effective for S/L/T agencies to adopt digital data acquisition and 

calibration control simply by more fully exploiting the capabilities of their existing electronic 

data loggers, such as the ESC 8816 noted above. For example, many high sensitivity gas 

analyzers are capable of being calibrated under remote control. The opportunity to reduce travel 

and personnel costs through automated calibrations is a strong motivator for S/L/T agencies to 

make greater use of the capabilities of their existing data acquisition systems. Alternatively, 

Section 6.2.1 presents one example of a new commercial data logger that is capable of 

performing the recommended digital data acquisition. Also, Section 6.2.2 presents an example 

of a highly sophisticated environmental data system capable of performing such digital data 

acquisition and equipment control at multiple monitoring sites. Section 6.2.3 summarizes the 

process by which precursor gas data is transferred from the high sensitivity analyzers to ultimate 

use in public data systems such as EPA’s Air Quality System (AQS).[1]

6.2.1 Example Data Logger: ESC 8832 Data System Controller

 The ESC Model 8832 Data System Controller[2, 3] (Environmental Systems Corporation, 

Knoxville, Tennessee), shown in Figure 6-1, is an example of a digital data logger suitable for 
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Figure 6-1. ESC 8832 data system controller. 

use in NCore precursor gas monitoring. The ESC 8832 is the most recent version in a line of 

ESC digital data loggers that have been used in ambient monitoring, such as the ESC 8816, 

which has been widely used by S/L/T agencies for recording analog monitoring data. Relative to 

the Model 8816, the Model 8832 uses a 32-bit rather than 16-bit processor, provides more 

memory capacity and somewhat faster data transfer, and allows comma-delimited parsing of 

serial data. The ESC 8832 uses a 32-bit 50 MHz processor, and is designed for acquisition or 

calculation of up to 99 data channels, with the capability of updating each channel once per 

second. “Calculated” data channels include vector wind speed and direction and sigma theta. In 

the standard configuration, the ESC 8832 can store over 100,000 data records and, with an 

optional memory expansion card, can store over 300,000 data records. The ESC 8832 

incorporates high-speed serial ports for data polling, and for downloads of configuration and 

software upgrades without changing the data logger’s EPROM. The ESC 8832 can record 

internal diagnostic parameters of precursor gas analyzers, and program the performance of 

zeroing and calibration procedures. Digital output relays can control valve switching or other 

devices, with up to 32 events programmable. Up to 64 programmable alarms can be used to flag 

recorded data values, and up to 32 calibrations can be applied to recorded data. The ESC 8832 

can record analog inputs with 14-bit resolution over voltage ranges from ±100 mV to ±10 V full 
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scale. An Ethernet port and VGA analyzer output port are also available. The ESC 8832 is 

capable of network communication with analyzers that have network ports installed (e.g., 

Thermo Environmental and API analyzers can provide this feature). Once configured as a 

network client, the data logger can gather data from the instrument as if via a serial port. 

 Obtaining the maximum benefit from using a digital data logger, as exemplified by the 

ESC 8832, requires using suitable software to manage the collected data. This requirement 

especially applies when operating multiple ambient monitoring sites. To continue this example, 

the E-DAS/ATX Ambient software developed by ESC is capable of polling one or more data 

loggers at widely dispersed sites to process, edit, archive, and report the ambient data. The 

Windows-based software can be used to perform data retrieval with error checking, automatic 

time synchronization for multiple sites, graphical display of data, data storage and archiving, data 

editing, and reporting of data in specified formats such as for EPA’s AQS.[1]

6.2.2 Example Environmental Data System: ENVIDAS System

 An example of the type of data system recommended for precursor gas monitoring at 

NCore sites is the ENVIDAS environmental data acquisition system[4] (Envitech Ltd., 

Ramat Gan, Israel). The ENVIDAS system uses non-proprietary desktop or industrial personal 

computer (PC) hardware to run flexible, Windows-based data acquisition software. A wide 

variety of data acquisition cards may be installed for use with the ENVIDAS system. Typically, 

the ENVIDAS system can accept up to 64 inputs, either analog or digital, with analog ranges 

from ±1.25 V to ±10 V, and supports up to eight RS232C serial communication channels. Data 

sampling rates (1, 2, 5, or 10 seconds) and averaging periods (e.g., 1, 5, 6, 15, or 60 minutes) are 

user-selectable. Data storage includes calculated parameters such as vector wind speed and 

direction and sigma theta. The multi-tasking software assures that data are not lost during data 

polling or user interaction with the software. Data can be averaged, archived, displayed, and 

reported in various formats including wind roses, pollution roses, histograms, and time series 

plots. 
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 The advantage of systems such as ENVIDAS, relative to data logging systems, is that 

ENVIDAS is designed to communicate with and control a variety of precursor analyzers and 

dilution calibrators at multiple monitoring sites. Thus, ENVIDAS facilitates remote control of 

analyzer and calibrator operations at a monitoring site, as well as data acquisition. This 

communication is achieved by means of RS232C protocols specific to each manufacturer’s 

analyzer or calibrator. For example, ENVIDAS supports RS232C protocols for analyzers made 

by Thermo Environmental, API, Environnement S.A., and Monitor Labs, and for calibrators 

made by Thermo Environmental, API, Horiba, Sabio, and Environics. Digital communication 

and data acquisition means that the ENVIDAS system can access the internal software of an 

analyzer or calibrator, and control the device’s internal settings and parameters. Control of such 

a device can be accomplished as fully through the ENVIDAS system as by an operator through 

the front panel push buttons of the analyzer or calibrator itself. Basic analyzer settings, such as 

the time and date, measurement range, units of concentration, time constant or averaging time, 

and zero and calibration factors, can be controlled by the ENVIDAS system. 

As in the data loggers exemplified in Section 6.2.1, a key feature for precursor 

monitoring is recording of internal diagnostic information from the analyzers, to document the 

status of the analyzer or diagnose data quality problems. For example, Table 6-1 lists several 

internal status parameters for a typical CO, SO2, and NOy analyzer that could be recorded and 

controlled through the ENVIDAS (or a digital data logging) system. 

 EPA recommends that a high-performance data acquisition system such as ENVIDAS, or 

a system such as the ESC 8832 data logger with digital data transfer and suitable software, be 

used for precursor gas monitoring at NCore sites. Implementation of such a system offers a 

monitoring agency the most up-to-date capabilities in instrument control, data acquisition, and 

data analysis, especially when multiple monitoring sites are in operation. 
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Table 6-1. Example Internal Diagnostic Parameters of High Sensitivity Precursor Gas 

Analyzers Accessible to a Digital Data Acquisition System. 

CO Analyzer SO2 Analyzer NOy Analyzer 

Optical chamber temperature Optical chamber temperature Reaction chamber temperature 

Optical chamber pressure Optical chamber pressure Reaction chamber pressure 

Temperature correction Temperature correction P/T correction 

Pressure correction Pressure correction Converter temperature 

Sample flow rate Sample flow rate PMT cooler temperature 

Power supply voltage Power supply voltage Sample flow rate 

Sample/reference intensity ratio Flash lamp voltage Power supply voltage 

Auto gain control frequency PMT high voltage Alarms and max/min settings 

Chopper motor speed Alarms and max/min settings Prereactor zero reading 

Alarms and max/min settings Internal temperature 

6.2.3 Summary Data Acquisition Process

 Figure 6-2 illustrates the recommended digital data acquisition approach, in the form of a 

schematic of the data flow from NCore precursor gas monitors through a local digital data 

acquisition system, to final reporting of the data in various public databases. This schematic 

shows several of the key capabilities of the recommended approach. A basic capability is the 

acquisition of digital data from multiple analyzers and other devices, thereby reducing noise and 

minimizing the effort needed in data processing. Another capability is two-way communication, 

so that the data acquisition system can interrogate and/or control the local analyzers, calibration 

systems, and even sample inlet systems, as well as receive data from the analyzers. Data transfer 

to a central location is also illustrated, with several possible means of that transfer shown. S/L/T 

agencies are urged to take advantage of the state of the art in this part of the process, as even 

sophisticated technologies such as satellite data communication are now well established, 

commercially available, and inexpensive to implement for monitoring operations. Finally, it is 

important that data are reported in formats of immediate use in public data bases such as AQS, 

and air quality index sites such as the multi-agency AIRNow site.[5] An advantage of software 

such as the ESC E-DAX/ATS or ENVIDAS systems introduced above is their ability to facilitate 

the assembly, formatting, and reporting of monitoring data to these data databases. 
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Station Desktop 

CO System

PM

(continuous or FRM)

SO2

NOy

Calibrator

Zero Air Supply

RS-232 Multi-drop

(within manufacturer)

MET

RS 232 connections Digital I/O

Dial-up/DSL

Cable

Satellite Wireless

Status

Relay control

Measurements

Diagnostics

Data pushed or pulled 

from multiple stations

Database

Server

Public reporting

AQS

S/L/T validation

(optional)

Manifold/external valves

Figure 6-2. Flow of data from precursor gas analyzers to final reporting. 

6.3 Data Acquisition System Quality Assurance 

 The use of a data acquisition system such as those described above is strongly 

encouraged for the NCore precursor gas monitoring community. However, several practices 

should be followed to ensure the quality of the data that are collected. 

6.3.1 Personnel

 Each organization conducting precursor gas monitoring should identify one or more 

persons within the organization to implement and oversee the data acquisition and management 

system. These personnel must have adequate education, training, and experience to perform 
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these functions, and must recognize the performance of these functions as a key (if not primary) 

component of their responsibilities. These personnel contribute to quality assurance of the data 

acquisition system through reviews and audits of the DAS and the collected data. 

6.3.2 Security

 The data acquisition system must be safeguarded against accidental or deliberate actions 

that could result in the following potential problems: 

Modification, destruction, or unwanted disclosure of data. The integrity of the data 

should be maintained by (e.g.) implementing password protection and user authorization for 

setup of the DAS, control of monitoring and calibration equipment, data acquisition and editing, 

and data reporting. 

Unavailability of the DAS or collected data. Protection against data loss may be avoided 

by redundant data storage, and assurance of DAS operation may require hardware maintenance 

or upgrades, surge protection, or backup systems. 

6.3.3 Data Entry and Formatting

 Electronic data acquisition systems such as those described above can record, average, 

and compile the monitoring data in a variety of reporting formats. The personnel responsible for 

the DAS should assure that the reported data are in the formats required for reporting to 

databases such as AQS. Information on AQS requirements is available in the AQS Users 

Guide[1] (Volume II, Air Quality Data Coding, and Volume III, Air Quality Data Storage). 

Precursor gas monitoring data from NCore sites are to be reported to AQS as hourly 

average values. However, it is suggested that S/L/T agencies also consider recording and 

archiving data with shorter time resolution, e.g., as five minute averages. Such data can easily be 

used to compute averages over longer time periods, and are valuable for diverse data analyses 

beyond the purposes of AQS. For example, short time period data can be used to assess the 
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variability and uncertainty in hourly or longer time period data, and to evaluate temporal trends, 

source impacts, and special research topics. The availability of high time resolution data will be 

valuable to the data user community, and is likely to foster analyses of air quality that could not 

be attempted with hourly or longer data periods. 

6.3.4 Data Review

 The review of collected data is the most important means to assure data quality in 

ambient monitoring. The review process has multiple stages, beginning with observations in the 

field, continuing through the analysis of electronic data, and ending with the reporting of final 

data. Data review should be the subject of an SOP that defines the criteria an agency will apply 

in processing and reporting the monitoring data. 

 Data review in the field should involve the observations and records of site operators on 

topics such as the operational status of precursor analyzers, the need for maintenance or repair, 

the occurrence of unexpected or unexplained readings, the existence of difficult or unusual 

meteorological conditions, and the observation of ambient data outside the normal range for the 

site. At a minimum, such observations must be recorded in a site notebook or other document. 

Preferably, such observations should be recorded by electronic word processor, and ideally such 

records are associated with the ambient data through the data acquisition system. Data review in 

the field is the first step in flagging suspect data for subsequent review. 

 Data review is a key component of the data analysis process. Electronic data acquisition 

systems allow automatic flagging of data based on the status (i.e., alarms, internal diagnostics, 

calibration results) of the precursor analyzer, or based on other criteria such as expected data 

ranges. However, review of the data by experienced personnel is still necessary. This review 

should be carried out promptly after data collection and should take into account any field 

observations such as those noted above. The aim of this review is to identify and remove suspect 

data, and to identify and retain valid data based on the variety of information recorded. Software 

associated with an electronic data acquisition system can be used to automatically compare 
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various types of data to flag or confirm the validity of the ambient measurements. This 

capability should be exploited in data review for NCore. 

 The final step of data review is conducted in appropriately averaging and formatting data 

to be reported. The usefulness of the AQS database, or other such publicly accessible data 

repositories, is dependent on the consistency and accuracy of the processed data submitted to it. 

Careful review of the data should take place to assure submission of complete and correctly 

formatted data sets. 

6.3.5 Calibrations and Audits

 Quality assurance of the DAS is based on the system being operated within some range 

of performance; i.e., that the data collected on the DAS and reported to the central database is the 

same as that generated by the monitoring equipment. Among the practices used to document 

DAS performance are routine calibration checks of the data acquisition system itself, data trail 

audits, and performance audits. 

6.3.5.1 DAS Calibration 

 In the case where analog signals from monitoring equipment are recorded by the DAS, 

the calibration of a DAS is similar to the approach used for calibration of a strip chart recorder. 

To calibrate the DAS, known voltages are supplied to each of the input channels and the 

corresponding measured response of the DAS is recorded. Specific calibration procedures in the 

DAS owner’s manual should be followed when performing such DAS calibrations. The DAS 

should be calibrated at least once per year. 

 In addition, precursor gas analyzers typically have an option to set output voltages to full 

scale, or to ramp the analog output voltages supplied by the analyzer over the full output range. 

Such a function can be used to check the analog recording process from the analyzer through the 

DAS. 
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6.3.5.2 Data Trail Audit 

 A data trail audit consists of following one or more data values from the analyzer through 

collection by the DAS, and through data processing to reporting to the central data repository. 

This audit should be conducted by those personnel assigned to manage the data acquisition 

hardware and software, and should be conducted at least annually. The procedure to be followed 

is that one or more data points or data averages reported from the analyzer (e.g., hourly values) 

should be collected by the DAS and checked on the DAS storage medium, and, in the final 

format, reported to the data repository. The same values must be traceable through all steps of 

the data acquisition and reporting process. 

6.4 Data and Records Management 

 All raw data, averaged or processed data, operator documentation, correspondence on 

data recording or processing issues, and other records should be retained for an appropriate 

period of time after data have been collected, processed, and reported in the required format. 

The following sections summarize specific data management recommendations for key types of 

records. 

6.4.1 Calibration Data

 Calibration data should be recorded in the same manner as all other precursor gas 

analyzer data, but appropriately flagged to distinguish it from routine ambient data. Any hard 

copy records associated with calibration data must be linked or cross-referenced to the electronic 

data, and the personnel who prepared the hard copy data must be fully identified. Calibration 

data should be sequestered from ambient data in the data review process, and the appropriate 

calibration results accurately applied to the relevant time periods of ambient monitoring. 

 Digital data acquisition systems such as those exemplified in Sections 6.2.1 and 6.2.2 

offer a great advantage over analog systems in the tracking of calibration data, because of their 
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ability to control and record the internal readings of gas analyzers and calibration systems. That 

is, a digital data acquisition system not only can record the analyzer’s output readings, but can 

schedule and direct the performance of analyzer calibrations, and record calibrator settings and 

status. Thus flagging of calibration data to distinguish them from ambient monitoring data is 

conducted automatically during data acquisition, with no additional effort or post-analysis. 

These capabilities greatly reduce the time and effort needed to organize and quantify calibration 

results. 

6.4.2 Electronic Data Files

 Electronic data files from different stages of the data collection and reporting process 

should be retained for an appropriate period of time. The files to be retained should at first 

include raw data files, intermediate files (e.g., edited to remove calibration or suspect data), and 

the final data files submitted to the data repository. Any supporting information (including hard 

copy records) should also be retained. Subsequent to final reporting of the data, a judgment may 

be made to reduce the extent of the files retained. However, any data files that directly support 

decisions made in the date review and editing process should be retained. In storing the 

electronic data files, use should be made of file compression methods that reduce the size of files 

for storage. 

6.4.3 Hard Copies

 As is evident from the discussion above, hard copy records are discouraged for precursor 

gas monitoring in NCore, in favor of electronic data acquisition systems. However, some hard 

copy records may be unavoidable; e.g., a site operator’s personal laboratory notebook. There are 

two key requirements for hard copy records. First, these records must be carefully reviewed by 

the staff who recorded them and the personnel who oversee the electronic data acquisition to 

assure that relevant information from the hard copy records is recognized and used in the data 

analysis process. Second, in storing hard copy records, care must be taken to properly and 

completely identify the records, and link them with the corresponding electronic data records. 
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6.5 References 

1. “AQS User Guide: Air Quality System”, U.S. Environmental Protection Agency, Office of 

Air Quality Planning and Standards, Research Triangle Park, NC 27711, November 15, 

2004; available at http://www.epa.gov/ttnairs1/airsaqs/manuals/AQSUserGuide.pdf. 

2. Information on ESC Model 8832 data system controller, Environmental Systems 

Corporation, Knoxville, Tennessee, available at http://www.escdas.com/cem/cem_8832.html. 

 

3. Information on ESC EDAS data software, Environmental Systems Corporation, Knoxville, 

Tennessee, available at http://www.escdas.com/ambient/atx.html. 

4. Information on ENVIDAS data acquisition system, Envitech Ltd., Givataim, Israel, available 

at http://www.envitech.co.il/EnvidasFW.aspx. 

5. AIRNow Web site, developed by the U.S. Environmental Protection Agency, 

State/Local/Tribal Agencies, National Park Service, and National Oceanic and Atmospheric 

Administration, with international and media partners. (http://www.epa.gov/airnow) 
APPENDIX A 

SAMPLE MANIFOLD DESIGN FOR PRECURSOR

GAS MONITORING
A-1 

Sample Manifold Design for Precursor Gas Monitoring 

Many important variables affect sampling manifold design for ambient precursor gas monitoring: 

residence time of sample gases, materials of construction, diameter, length, flow rate, and 

pressure drop. Considerations for these parameters are discussed below. 

Residence Time Determination: The residence time of air pollutants within the sampling system 

(defined as extending from the entrance of the sample inlet above the instrument shelter to the 

bulkhead of the precursor gas analyzer) is critical. Residence time is defined as the amount of 

time that it takes for a sample of air to travel through the sampling system. This issue is 

discussed in detail for NOy monitoring in Section 4.2, and recommendations in Section 4 for the 

arrangement of the molybdenum converter and inlet system should be followed. However, 

residence time is also an issue for other precursor gases, and should be considered in designing 

sample manifolds for those species. For example, Code of Federal Regulations (CFR), Title 40 

Part 58, Appendix E.9 states, “Ozone in the presence of NO will show significant losses even in 

the most inert probe material when the residence time exceeds 20 seconds. Other studies indicate 

that 10-second or less residence time is easily achievable.”1

 Although 20-second residence time 

is the maximum allowed as specified in 40 CFR 58, Appendix E, it is recommended that the 

residence time within the sampling system be less than 10 seconds. If the volume of the 

sampling system does not allow this to occur, then a blower motor or other device (such as a 

vacuum pump) can be used to increase flow rate and decrease the residence time. The residence 

time for a sample manifold system is determined in the following way. First the total volume of 

the cane (inlet), manifold, and sample lines must be determined using the following equation: 

Total Volume = Cv + Mv + Lv Equation 1 

Where: 

Cv = Volume of the sample cane or inlet and extensions 

Mv = Volume of the sample manifold and moisture trap 

Lv = Volume of the instrument lines from the manifold to the instrument bulkhead 
A-2 

The volume of each component of the sampling system must be measured individually. To 

measure the volume of the components (assuming they are cylindrical in shape), use the 

following equation: 

V = π * (d/2)2

 * L Equation 2 

Where: 

V = volume of the component, cm3

π = 3.14 

L = Length of the component, cm 

d = inside diameter of the component, cm 

Once the total volume is determined, divide the total volume by the total sample flow rate of all 

instruments to calculate the residence time in the inlet. If the residence time is greater than 20 

seconds, attach a blower or vacuum pump to increase the flow rate and decrease the residence 

time. 

Laminar Flow Manifolds: In the past, vertical laminar flow manifolds were a popular design. 

By the proper selection of a large diameter vertical inlet probe and by maintaining a laminar flow 

throughout, it was assumed that the sample air would not react with the walls of the probe. 

Numerous materials such as glass, plastic, galvanized steel, and stainless steel were used for 

constructing the probe. Removable sample lines constructed of FEP or PTFE were placed to 

protrude into the manifold to provide each instrument with sample air. A laminar flow manifold 

could have a flow rate as high as 150 L/min, in order to minimize any losses, and large diameter 

tubing was used to minimize pressure drops. However, vertical laminar flow manifolds have 

many disadvantages which are listed below: 

• Since the flow rates are so high, it is difficult to supply enough audit gas to provide an 

adequate independent assessment for the entire sampling system; 

• Long laminar flow manifolds may be difficult to clean due to size and length; 

• Temperature differentials may exist that could change the characteristics of the gases, e.g., if 

a laminar manifold’s inlet is on top of a building, the temperature at the bottom of the 

building may be much lower, thereby dropping the dew point and condensing water. 
A-3 

For these technical reasons, EPA strongly discourages the use of laminar flow manifolds in the 

national air monitoring network. It is recommended that agencies that utilize laminar manifolds 

migrate to conventional manifold designs that are described below. 

Sampling Lines as Inlet and Manifold: Often air monitoring agencies will place individual 

sample lines outside of their shelter for each instrument. If the sample lines are manufactured 

out of Polytetrafluoroethylene (PTFE) or Fluoroethylpropylene (FEP) Teflon®, this is 

acceptable to the EPA. The advantages to using single sample lines are: no breakage and ease 

of external auditing. However, please note the following caveats: 

1. PTFE and FEP lines can deteriorate when exposed to atmospheric conditions, particularly 

ultraviolet radiation from the sun. Therefore, it is recommended that sample lines be 

inspected and replaced regularly. 

2. Small insects and particles can accumulate inside of the tubing. It has been reported that 

small spiders build their webs inside of tubing. This can cause blockage and affect the 

response of the instruments. In addition, particles can collect inside the tubing, especially at 

the entrance, thus affecting precursor gas concentrations. Check the sampling lines and 

replace or clean the tubing on a regular basis. 

3. Since there is no central manifold, these configurations sometimes have a “three-way” tee, 

i.e., one flow path for supplying calibration mixtures and the other for the sampling of 

ambient air. If the three-way tee is not placed near the outermost limit of the sample inlet 

tubing, then the entire sampling system is not challenged by the provision of calibration gas. 

It is strongly recommended that at least on a periodic basis calibration gas be supplied so 

that it floods the entire sample line. This is best done by placing the three-way tee just 

below the sample inlet, so that calibration gas supplied there is drawn through the entire 

sampling line. 

4. The calibration gas must be delivered to the analyzers at near ambient pressure. Some 

instruments are very sensitive to pressure changes. If the calibration gas flow is excessive, 

the analyzer may sample the gas under pressure. If a pressure effect on calibration gas 

response is suspected, it is recommended that the gas be introduced at more than one place 

in the sampling line (by placement of the tee, as described in item #3 above). If the response 
A-4 

to the calibration gas is the same regardless of delivery point, then there is likely no pressure 

effect. 

Conventional Manifold Design - A number of “conventional” manifold systems exist today. 

However, one manifold feature must be consistent: the probe and manifold must be constructed 

of borosilicate glass or Teflon® (PFA or PTFE). These are the only materials proven to be inert 

to gases. EPA will accept manifolds or inlets that are made from other materials, such as steel or 

aluminum, that are lined or coated with borosilicate glass or the Teflon® materials named above. 

However, all of the linings, joints and connectors that could possibly come into contact with the 

sample gases must be of glass or Teflon®. It is recommended that probes and manifolds be 

constructed in modular sections to enable frequent cleaning. It has been demonstrated that there 

are no significant losses of reactive gas concentrations in conventional 13 mm inside diameter 

(ID) sampling lines of glass or Teflon® if the sample residence time is 10 seconds or less. This is 

true even in sample lines up to 38 m in length. However, when the sample residence time 

exceeds 20 seconds, loss is detectable, and at 60 seconds the loss can be nearly complete. 

Therefore, EPA requires that residence times must be 20 seconds or less (except for NOy). 

Please note that for particulate matter (PM) monitoring instruments, such as nephelometers, 

Tapered Element Oscillating Microbalance (TEOM) instruments, or Beta Gauges, the ambient 

precursor gas manifold is not recommended. Particle monitoring instruments should have 

separate intake probes that are as short and as straight as possible to avoid particulate losses due 

to impaction on the walls of the probe. 

T-Type Design: The most popular gas sampling system in use today consists of a vertical 

"candy cane" protruding through the roof of the shelter with a horizontal sampling manifold 

connected by a tee fitting to the vertical section (Figure 1). This type of manifold is 

commercially available. At the bottom of the tee is a bottle for collecting particles and moisture 

that cannot make the bend; this is known as the “drop out” or moisture trap bottle. Please note 

that a small blower at the exhaust end of the system (optional) is used to provide flow through 

the sampling system. There are several issues that must be mitigated with this design: 

• The probe and manifold may have a volume such that the total draw of the precursor gas 

analyzers cannot keep the residence time less than 20 seconds (except NOy), thereby 

requiring a blower motor. However, a blower motor may prevent calibration and audit 
A-5 

gases from being supplied in sufficient quantity, because of the high flow rate in the 

manifold. To remedy this, the blower motor must be turned off for calibration. 

However, this may affect the response of the instruments since they are usually operated 

with the blower on. 

• Horizontal manifolds have been known to collect water, especially in humid climates. 

Standing water in the manifold can be pulled into the instrument lines. Since most 

monitoring shelters are maintained at 20-30 o

C, condensation can occur when warm 

humid outside air enters the manifold and is cooled. Station operators must be aware of 

this issue and mitigate this situation if it occurs. Tilting the horizontal manifold slightly 

and possibly heating the manifold have been used to mitigate the condensation problem. 

Water traps should be emptied whenever there is standing water. 

Sample Cane

Blower Motor

Teflon Connectors -

 Bushing

Modular Manifold

Moisture Trap

roof line

Screw Type Opening 

"T" 

adaptor

 

Figure 1. Conventional T-Type Glass Manifold System 

California Air Resources Board “Octopus” Style: Another type of manifold that is being 

widely used is known as the California Air Resources Board (CARB) style or “Octopus” 

manifold, illustrated in Figure 2. This manifold has a reduced profile, i.e., there is less volume in 

the cane and manifold; therefore, there is less need for a blower motor. If the combined flow 

rates of the gas analyzers are high enough, then an additional blower is not required. 
A-6 

roof line

Screw Type Opening 

Moisture Trap

Sample Cane

Teflon Connectors -

 Bushing

8-port "Octopus" 

 Manifold

Figure 2. CARB or “Octopus” Style Manifold 

Placement of Tubing on the Manifold: If the manifold employed at the station has multiple 

ports (as in Figure 2) then the position of the instrument lines relative to the calibration input line 

can be crucial. If a CARB “Octopus” or similar manifold is used, it is suggested that sample 

connections for analyzers requiring lower flows be placed towards the bottom of the manifold. 
A-7 

Also, the general rule of thumb states that the calibration gas delivery line (if used) should be in 

a location so that the calibration gas flows past the analyzer inlet points before the gas is 

evacuated out of the manifold. Figure 3 illustrates two potential locations for introduction of the 

calibration gas. One is located at the ports on the “Octopus” manifold, and the other is upstream 

near the air inlet point, using an audit or probe inlet stub. This stub is a tee fitting placed so that 

“Through-the-Probe” audit line or sampling system tests and calibrations can be conducted. 

Figure 3. Placement of Lines on the Manifold 

roof line

Sample Cane

Audit and probe 

inlet stub

Instrument 

inlet lines

Calibration 

outlet line

Instrument 

inlet lines
A-8 

3

14

2

8

1

4

15

13

12 12

9

11

7

6

16

5

Measurements and Features

1. Knurled Connector

2. O-ring

3. Threaded opening 

4. Top extension - 56 mm

5. Overall Length - 304 mm

6. Outside diameter - 24 mm

7. Top and bottom shoulder - 50 mm

8. Length of inlet tube - 30 mm

9. Distancebetween inlet tubes - 16 mm

10. Length of internal tube - 145 mm

11. Width of inlet tube OD - 6 mm

12. Distance from inner tube to wall - 18 mm

13. Inside width of outer tube 60 mm

14. Down tube length 76 mm

15. Width Down tube OD - 24 mm

16 Overall Width ~ 124 mm

10

7

Figure 4. Specifications for an ‘Octopus” Style Manifold 

Figure 4 illustrates the specifications of an Octopus style manifold. Please note that EPAOAQPS has used this style of manifold in its precursor gas analyzer testing program. This type 

of manifold is commercially available. 
A-9 

Vertical Manifold Design: Figure 5 shows a schematic of the vertical manifold design. 

Commercially available vertical manifolds have been on the market for some time. The issues 

with this type of manifold are the same with other conventional manifolds, i.e., when sample air 

moves from a warm humid atmosphere into an air-conditioned shelter, condensation of moisture 

can occur on the walls of the manifold. Commercially available vertical manifolds have the 

option for heated insulation to mitigate this problem. Whether the manifold tubing is made of 

glass or Teflon®, the heated insulation prevents viewing of the tubing, so the interior must be 

inspected often. The same issues apply to this manifold style as with horizontal or “Octopus” 

style manifolds: additional blower motors should not be used if the residence time is less than 20 

seconds, and the calibration gas inlet should be placed upstream so that the calibration gas flows 

past the analyzer inlets before it exits the manifold. 

roof line

Support Pipe

Glass Manifold

Sample Ports

Blower Motor

Insulation

Heater Power Cord

Manifold Support

Exhaust Hose

Floor

"T" Connector

Figure 5. Example of Vertical Design Manifold 
A-10 

Manifold/Instrument Line Interface: A sampling system is an integral part of a monitoring 

station, however, it is only one part of the whole monitoring process. With the continuing 

integration of advanced electronics into monitoring stations, manifold design must be taken into 

consideration. Data Acquisition Systems (DASs) are able not only to collect serial and analog 

data from the analyzers, but also to control Mass Flow Calibration (MFC) equipment and solid 

state solenoid switches, communicate via modem or Ethernet, and monitor conditions such as 

shelter temperature and manifold pressure. As described in Chapter 6, commercially available 

DASs may implement these features in an electronic data logger, or via software installed on a 

personal computer. Utilization of these features allows the DAS and support equipment to 

perform automated calibrations (Autocals). In addition to performing these tasks, the DAS can 

flag data during calibration periods and allow the data to be stored in separate files that can be 

reviewed remotely. 

Figure 6 shows a schematic of the integrated monitoring system at EPA’s Burden Creek NCore 

monitoring station. Note that a series of solenoid switches are positioned between the ambient 

air inlet manifold and an additional “calibration” manifold. This configuration allows the DAS 

to control the route from which the analyzers draw their sample. At the beginning of an Autocal, 

the DAS signals the MFC unit to come out of standby mode and start producing zero or 

calibration gas. Once the MFC has stabilized, the DAS switches the analyzers’ inlet flow (via 

solenoids) from the ambient air manifold to the calibration manifold. The calibration gas is 

routed to the instruments, and the DAS monitors and averages the response, flagging the data 

appropriately as calibration data. When the Autocal has terminated, the DAS switches the 

analyzers’ inlet flow from the calibration manifold back to the ambient manifold, and the data 

system resets the data flag to the normal ambient mode. 

The integration of DAS, solenoid switches, and MFC into an automated configuration can bring 

an additional level of complexity to the monitoring station. Operators must be aware that this 

additional complexity can create situations where leaks can occur. For instance, if a solenoid 

switch fails to open, then the inlet flow of an analyzer may not be switched back to the ambient 

manifold, but instead will be sampling interior room air. When the calibrations occur, the 

instrument will span correctly, but will not return to ambient air sampling. In this case, the data 

collected must be invalidated. These problems are usually not discovered until there is an 
A-11 

Figure 6. Example of a Manifold/Instrument Interface 

external “Through-the Probe” audit, but by then extensive data could be lost. It is recommended 

that the operator remove the calibration line from the calibration manifold on a routine basis and 

challenge the sampling system from the inlet probe. This test will discover any leak or switching 

problems within the entire sampling system. 

Figure 7 shows a close up of an ambient/calibration manifold, illustrating the calibration 

manifold – ambient manifold interface. This is the same interface used at EPA’s Burden’s Creek 

monitoring station. The interface consists of three distinct portions: the ambient manifold, the 

solenoid switching system and the calibration manifold. In this instance, the ambient manifold is 

a T-type design that is being utilized with a blower fan at the terminal. Teflon® tubing connects 

the manifold to the solenoid switching system. Two-way solenoids have two configurations. 

Either the solenoid is in its passive state, at which time the ports that are connected are the 

normally open (NO) and the common (COM). In the other state, when it is energized, the ports 

that are connected are the normally closed (NC) and the COM ports. Depending on whether the 

Burden's Creek Sampling Station - OAQPS/MQAG

Environics

9100 Cal Sys

TECO 42CY TL

NOx

TECO 43CTL

SO2

TECO 48CTL

CO

P

V V S

S S S

F

V

Other Monitor

(O3 etc)

C

C C C

NC

NC NC NC

NO

NO NO NO

External Moly

Sampling Cane Converter

Manifold Fan

Charcoal

Scrubber

4-ft

Notes:

S - Teflon 3-way Solenoid

P - Pump

F - Manifold Fan/Blower

V - Vent - Particulate Filter

Sample tubing lengths < 3-ft

Cal Standard

(triblend)

Temp/

Pressure/RH

Calibration Manifold

Ambient Sampling Manifold

UPS Power

Supply

Zero Air

Source

Cal

NOy

NO

Sample In

EnviDAS Data 

Acquisition System

Analog Inputs -

To Analyzers/

Sensors

Control Outputs

- To Environics

Cal Sys

Control Out- To Solenoids

Modem

Desktop System
A-12 

solenoid is ‘active’ or not, the solenoid routes the air from the calibration or ambient manifold to 

the instrument inlets. There are two configurations that can be instituted with this system. 

1. Ambient Mode: In this mode the solenoids are in “passive” state. The flow of air (under 

vacuum) is routed from the NO port through the solenoid to the COM port. 

2. Calibration Mode: In this mode, the solenoids are in the “active” state. An external 

switching device, usually the DAS, must supply direct current to the solenoid. This 

causes the solenoid to be energized so that the NO port is shut and the NC port is now 

connected to the COM port. As in all cases, the COM port is always selected. The 

switching of the solenoid is done in conjunction with the MFC unit becoming active; 

generally, the MFC is controlled by the DAS. When the calibration sequences have 

finished, the DAS stops the direct current from being sent to the solenoid and switches 

automatically back to the NO to COM (inactive) port configuration. This allows the air 

to flow through the NO to COM port and the instrument is now back on ambient mode. 

Air Flow to the Analyzers

N O

N C

N O N O

N C N C

COM

Calibration 

Gas from the Mass 

Flow Calibrator Exhaust

Air Flow Air Flow

Air Flow 

to 

Exhaust 

Fan

Air Flow Air Flow Air Flow

Figure 7. Ambient – Calibration Manifold Interface 
A-13 

Reference 

1. Code of Federal Regulations, Title 40, Part 58, Appendix E.9 
APPENDIX B 

STANDARD OPERATING PROCEDURES FOR

SELECTED TRACE LEVEL PRECURSOR GAS

MONITORING AND CALIBRATION EQUIPMENT

SOP’s also available at: http://www.epa.gov/ttn/amtic/precursop.html
STANDARD OPERATING PROCEDURES 

THERMO ELECTRON CORPORATION MODEL 48C-TLE 

TRACE LEVEL CO INSTRUMENT 

Version 2 

 

 
 Section 1.1 Acknowledgments 

This Standard Operating Procedure (SOP) for Carbon Monoxide – Trace Level is the product of EPA’s 

Office of Air Quality, Planning and Standards. The following individuals are acknowledged for their 

contributions. 

Principal Author 

Dennis K. Mikel, OAQPS-EMAD, Research Triangle Park, NC 27711 

Reviewers 

 

Joann Rice, Trace Gas Team Lead, OAQPS-EMAD, Research Triangle Park, NC 27711 

Anna Kelly, OAQPS-EMAD, Research Triangle Park, NC 27711 

Keith Kronmiller, Mantech, Inc. Research Triangle Park, NC 27711 

Comments and questions can be directed to: 

Joann Rice 

EPA-OAQPS 

Emission, Analysis and Monitoring Division 

Mail Drop D243-02 

Research Triangle Park, NC 27711 

Email: rice.joann@epa.gov 

Phone: (919)-541-3372 
Section 2.0 Table of Contents

Section Page 

1.0 Title Page 1 

1.1 Acknowledgements 2 

 2.0 Table of Contents 3 

 2.1 List of Tables and Figures 4 

3.0 Procedures 5 

 3.1 Scope and Applicability 5 

 3.2 Summary of Method 5 

 3.3 Definitions 7 

 3.4 Health and Safety Warnings 7 

 3.5 Cautions 7 

 3.6 Interferences 8 

 3.7 Personal Qualifications 8 

 3.8 Equipment and Supplies 8 

 3.9 Procedure 10 

 3.9.1 Sample Collection 10 

 3.9.2 Sample Handling and Preservation 10 

 3.9.3 Instrument Operation, Start up and Maintenance 10 

 3.9.3.1 Start up 10 

 3.9.3.2 Operation and Range Setting 11 

 3.9.9.3 Diagnostic Checks/Manual Checks 11 

 3.9.3.4 Preventive Maintenance 13 

 3.9.3.5 Instrument Troubleshooting 14 

 3.9.4 Calibration and Standardization 14 

 3.9.4.1 Adjustment to Zero Air 14 

 3.9.4.2 Adjustment to Calibration Gas 14 

 3.10 Data Analysis and Calculations 15 

 4.0 Quality Control and Quality Assurance 15 

 4.1 Precision 15 

 4.2 Bias 15 

 4.3 Representativeness 16 

 4.4 Completeness 16 

 4.5 Comparability 16 

 4.6 Method Detection Limit 16 

 5.0 References 17 
List of Tables 

Table Name and Number Page 

 3-1 Definition of Key Terms 7 

 3-2 Diagnostic Checks 13 

 3-3 Preventive Maintenance Schedule for the TECO 48C-TLE 13 

 4-1 Measurement Quality Assurance Objectives 16 

 4-2 Operating Parameters for the TECO 48C-TLE Trace Gas Instrument 17 

List of Figures 

Figure Name and Number Page 

 3-1 Schema of the TECO 48C-TLE 9 

 3-2 Menu Tree Schema 12 

 A-1 Monthly Quality Control and Maintenance Record 18 
TECO 48C-TLE CO SOP 

Version No. 2 

2/3/2005 

Page 5 of 18 

STANDARD OPERATING PROCEDURES 

THERMO 48C-TLE TRACE-LEVEL CO INSTRUMENT 

3.0 PROCEDURES 

3.1 Scope and Applicability 

Carbon Monoxide (CO), a colorless, odorless, tasteless, highly poisonous gas has detrimental effects on 

human health. CO originates from the partial oxidation of hydrocarbon fuels, coal and coke1

. CO affects 

the oxygen carrying capacity of the blood. CO can diffuse through the alveolar walls of the lungs and 

compete with oxygen for one of the four iron sites in the hemoglobin molecule. The affinity of the iron 

site for CO is approximately 210 times greater than oxygen2

. Low levels of CO can cause a number of 

symptoms including headache, mental dullness, dizziness, weakness, nausea, vomiting and loss of 

muscular control. In extreme cases, collapse, unconsciousness and death can occur. 

The Thermo Electron Corporation (TECO) model 48C-TLE is a state of the science instrument for the determination 

of trace levels of CO by Non-Dispersive Infrared Spectrophotometry (NDIR) using Gas Filter Correlation (GFC). 

This SOP will detail the operation, preventive maintenance, cautions and health warnings. 

The Detection Limit (DL) for non-trace levels of CO is 1.0 parts per million (ppm) (Code of Federal 

Regulations, Volume 40, Part 53.23c, or, in the shortened format used hereafter, 40 CFR 53.23c)3

. 

However, the 48C-TLE has a DL to 20 parts per billion (ppb), which is accomplished by modifications to 

the Federal Reference Method (FRM) instruments. This document will discuss the Trace Level (TL) 

operating procedures in detail. 

3.2 Summary of Method 

The analytical principle is based on absorption of IR light by the CO molecule. NDIR-GFC analyzers 

operate on the principle that CO has a sufficiently characteristic IR absorption spectrum such that the 

absorption of IR by the CO molecule can be used as a measure of CO concentration in the presence of 

other gases. CO absorbs IR maximally at 2.3 and 4.6 um. Since NDIR is a spectrophotometric method, it 

is based upon the Beer-Lambert Law. The degree of reduction depends on the length of the sample cell, 

the absorption coefficient, and CO concentration introduced into the sample cell, as expressed by the 

Beer-Lambert law shown below: 

T = I/Io = e(-axC) (equation 1) 

where: 

T = Transmittance of light through the gas to the detector 

I = light intensity after absorption by CO 

Io = light intensity at zero CO concentration 

a = specific CO molar absorption coefficient 

x = path length, and 

C = CO concentration 
TECO 48C-TLE CO SOP 

Version No. 2 

2/3/2005 

Page 6 of 18 

For Gas Filter Correlation, there is only one sample cell. This cell acts as the sample and reference cell. 

The broad band of IR radiation is emitted from an IR source. The IR light passes through a very narrow 

band pass filter which screens out most wavelengths and allows only the light that CO absorbs to enter 

the sample cell. The GFC analyzer has a chopper wheel with two pure gases: Nitrogen and CO. As the 

chopper wheel rotates and allows the IR energy to enter “CO side” of the wheel, all IR energy that could 

be absorbed by CO in the sample stream is absorbed by the CO in the wheel. This technique effectively 

“scrubs out” any light that could possibly be attenuated. The single detector records the light level (Io). 

As the wheel spins, the “N2 side” of the wheel reaches the IR energy beam. This side of the wheel allows 

all IR light to pass through the wheel and be absorbed by any CO that might be in the sample gas. This 

light level is CO sensitive (I). The detector records the attenuation of this light, compares the two light 

levels (I/Io) and sends a signal to the electrometer board that calculates the concentration. The voltage is 

related to the CO concentration according to the Beer-Lambert law in equation 1 shown above. Thus, 

TECO 48C-TLE can be measured continuously. The 48C-TLE version has four distinct features that 

allow it to measure CO at ppb levels: 

 Required sample stream dried using permeation dryer; 

 Analyzer baseline determined and corrected using heated Carolite catalytic converter; 

 Frequent auto-zero, at a minimum once per hour, through the catyalytic converter; 

 The instrument has an ultra-sensitive or “hot” detector. 

The 48C-TLE instrument operates in the following fashion:

1. In sample mode, ambient air is allowed to enter through the rear bulkhead sample port. Solenoid #1 

is in its Normally Open (NO) mode. The ambient air flows through the solenoid to the permeation 

dryer, which removes the moisture and water from the air stream. 

2. The sample stream then passes through a sample filter, which removes particles that can build up on 

the mirror and sample chamber and attenuate the IR beam. 

3. The sample then enters the sample cell. A major difference between a non-TL and TL instrument is 

the detector. The TL instrument has a detector that is more sensitive to the light emitted and 

absorbed in the sample cell. This detector must be more sensitive because the amount of attenuation 

by the CO gas in the sample stream is much lower. Therefore, the detector must be sensitive at lower 

ambient levels. Temperature of the sample cell is also critical. The sample cell and detector must be 

maintained at a constant temperature in order for the detector to keep a stable background. 

Fluctuations of more than 1o Centigrade can cause the baseline to drift, giving false readings at low 

levels. 

4. The detector sends the signal to the demodulator which interprets the signal. The demodulator sends 

a digital value to the Central Processor Unit (CPU).

5. At the end of the hour, the CPU sends a voltage signal to the Solenoid #1 and switches it to the 

“Normally Closed” (NC) position. This allows room air to be drawn into the instrument and to pass 

through the catalytic converter. The catalytic converter uses a Carolite bed heated to 50o Centrigrade 

to convert all CO to Carbon Dioxide (2CO + O2 —> 2CO2). This effectively “scrubs” all CO from 

the sample stream. The CO “free” air flows through the sample cell and the CPU interprets the 

signal from the demodulator as the “background” or “baseline” value. The baseline is then adjusted 

at that time. The baseline adjustment takes 10 minutes.

6. The CPU then switches Solenoid #1 to its NO position and ambient air then drawn into the analyzer. 
TECO 48C-TLE CO SOP 

Version No. 2 

2/3/2005 

Page 7 of 18 

3.3 Definitions

Here are some key terms for this method. 

Table 3-1 Definitions of Key Terms 

Term Definition 

DAS Data acquisition system. Used for automatic collection and 

recording of CO concentrations. 

Interferences Physical or chemical entities that cause CO measurements to be 

higher (positive) or lower (negative) than they would be without the 

entity. (See Section 3.6). 

3.4 Health and Safety Warnings 

To prevent personal injury, please heed these warnings concerning the 48C-TLE. 

1. CO is a poisonous gas. Vent any CO or calibration span gas to the atmosphere rather than into the 

shelter or other sampling area. If this is impossible, limit exposure to CO by getting fresh air every 

5 to 10 minutes. If the operator experiences light headedness, headache or dizziness, leave the area 

immediately. 

2. The IR source is a filament resistor that has an electrical current running through it. The IR source 

can become very hot. When troubleshooting, allow the instrument to cool off especially if you 

suspect the IR source as the cause of trouble. 

3. Always use a third ground wire on all instruments. 

4. Always unplug the analyzer when servicing or replacing parts. 

5. If it is mandatory to work inside an analyzer while it is in operation, use extreme caution to avoid 

contact with high voltages. The analyzer has a 110 volt Volts Alternating Current (VAC) power 

supply. Refer to the manufacturer's instruction manual and know the precise locations of the VAC 

components before working on the instrument. 

6. Avoid electrical contact with jewelry. Remove rings, watches, bracelets, and necklaces to prevent 

electrical bums. 

3.5 Cautions 

To prevent damage to the 48C-TLE, all cautions should immediately precede the applicable step in this 

SOP. The following precautions should be taken:

1. Normally, if TeflonTM filters are used in the sample train, cleaning the optical bench will not be 

required. However, in the event that the bench is cleaned, be careful to avoid damaging the interior of 

the sample chamber. In addition, some GFC instruments have a series of mirrors that deflect the light 

in order to increase the path length. The mirrors are aligned at the factory. If the mirrors become 

misaligned, the IR light beam will not be directed to the detector. Use extreme caution when cleaning 

or servicing the sample chamber(s). In addition the mirrors are very fragile Avoid dropping the 

instrument. This may damage, misalign or crack the mirrors and cause expensive repairs. 

2. Keep the interior of the analyzer clean. 

3. Inspect the system regularly for structural integrity. 
TECO 48C-TLE CO SOP 

Version No. 2 

2/3/2005 

Page 8 of 18 

4. To prevent major problems with leaks, make sure that all sampling lines are reconnected after 

required checks and before leaving the site. 

5. Inspect tubing for cracks and leaks. The permeation dryer may rest upon parts that vibrate, such as the 

air pump. Check the areas of the permeation dryer where they come into contact with other parts. 

6. It is recommended that the analyzer be leak checked after replacement of any pneumatic parts. 

7. If cylinders are used in tandem with Mass Flow Control (MFC) calibrators, use and transport of 

cylinders are a major concern. Gas cylinders can sometimes contain pressures as high as 2000 

pounds per square inch. Handling of cylinders must be done in a safe manner. If a cylinder is 

accidentally dropped and valve breaks off, the cylinder can become explosive or a projectile. 

8. Transportation of cylinders is regulated by the Department of Transportation (DOT). It is strongly 

recommended that all agencies contact the DOT or Highway Patrol to learn the most recent 

regulations concerning transport of cylinders. 

9. CO is a highly poisonous gas. Long term exposure can cause problems with motor coordination and 

mental acuity. It is strongly recommended that all agencies have Material Safety Data Sheets 

(MSDS) at all locations where CO cylinders are stored or used. MSDS can be obtained from the 

DOT or from your vendor. 

10. It is possible (and practical) to blend other compounds with CO. If this is the case, it is recommended 

that MSDS for all compounds be made available to all staff that use and handle the cylinders or 

permeation tubes. 

11. Shipping of cylinders is governed by the DOT. Contact the DOT or your local courier about the 

proper procedures and materials needed to ship high-pressure cylinders. 

3.6 Interferences

Water Vapor: Studies have shown conclusively that NDIR analyzers have interference from water 

vapor. Water absorbs very strongly across several bands of IR spectra. Water vapor interference occurs 

because water vapor absorption of light in the region of 3.1, 5.0 -5.5 and 7.1 -10.0 um in the IR region. 

Since water vapor absorbs light in this region, this has a quenching effect on the reaction of CO. The 

TECO 48C-TLE is equipped with a permeation drier, which effectively scrubs all water and water vapor. 

No maintenance is required on the dryer. 

Carbon Dioxide: CO2 absorbs in the IR spectrum at 2.7, 5.2, and 8.0 to 12.0 um. This is very close to 

the regions that CO absorbs within as well. However, since atmospheric carbon dioxide is much higher in 

concentration than CO, this UV spectral range must be avoided. To prevent light in this spectral region, 

the TECO 48C-TLE analyzer has a band pass filter that blocks these wavelengths. 

3.7 Personal Qualifications 

The person(s) chosen to operate the TECO 48C-TLE should have a minimum of qualifications. The 

understanding of basic chemistry and electronics are a must. The understanding of digital circuitry is 

helpful, but not required. Also, courses in data processing and validation are also welcome. 

3.8 Equipment and Supplies 

Monitoring Apparatus: The design of the 48C-TLE is identical to the 48C, with several major 

variations. A diagram of the TECO 48C-TLE instrument is described in Figure 3-1. The three main 

components are: 

 Pneumatic System: Consists of sample inlet line, particulate filter, filter holder, permeation dryer, 

reaction chamber, flowmeter, and pump, all used to bring ambient air samples to the analyzer inlet. 
TECO 48C-TLE CO SOP 

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 Analytical System: This portion of the instrument consists of the IR source, the correlation wheel, 

motor, mirrors, detector and band pass filter. 

 Electronic Hardware: The part of the analyzer that generally requires little or no maintenance. The 

brain of the 48C series is the CPU. It monitors and regulates motor speed, temperatures, flows and 

pressure. It also monitors and stores diagnostic information. If the 48C-TLE is operated above the 

manufacturer's recommended temperature limit, however, individual integrated chips can fail and 

cause problems with data storage or retrieval. 

Other apparatus and equipment includes the following. 

Instrument Shelter: A shelter is required to protect the analyzer from precipitation and adverse weather 

conditions, maintain operating temperature within the analyzer's temperature range requirements, and 

provide security and electrical power. The recommended shelter temperature range is 20-30o

C. 

Spare Parts and Incidental Supplies: See the TECO 48C-TLE operating manual, Section 5-1for 

specific maintenance and replacement requirements. 

Calibration System: A system that creates concentrations of CO of known quality is necessary for 

establishing traceability. This is described in detail in the “Environics 9100 SOP.” Please reference this 

document. 

DAS: A data acquisition system is necessary for storage of ambient and ancillary data collected by the 

48C-TLE. 

Figure 3-1 Schema of the TECO 48C-TLE 
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Wiring, Tubing and Fittings: TeflonTM and borosilicate glass are inert materials that should be used 

exclusively throughout the intake system. It is recommended that Polytetrafluoroethylene (PTFE) or 

Fluoroethylpropylene (FEP) TeflonTM tubing be used. PTFE and FEP are the best choice for the 

connection between the intake manifold and the 48C-TLE bulkhead fitting. Examine and discard if 

particulate matter collects in the inlet tubing. All fittings and ferrules should be made of TeflonTM or 

stainless steel. Connection wiring to the DAS should shielded two strand wire or RS-232 cables for 

digital connections. 

Reagents and Standard: The TECO 48C-TLE does not require any reagents since the instrument uses 

photometry to analyze for CO. All standards for the CO method can be obtained in compressed cylinders 

and must be NIST traceable. Please see the “Calibration of Trace Gas Analyzers” SOP. 

3.9 Procedure 

3.9.1 Sample Collection: Sampling for Trace Level CO is performed by drawing ambient air through a 

sample manifold directly into the analyzer continuously via a vacuum pump. All inlet materials must be 

constructed from TeflonTM or borosilicate glass as detailed in 40 CFR 58. The siting criteria for CO 

Trace Level instruments in detailed in 40 CFR 58, appendix A4 . 

3.9.2 Sample Handling and Preservation: CO samples receive no special preparation prior to analysis. 

Therefore this SOP does not need a section on Sample Handling and Preservation.

3.9.3 Instrument Operation, Startup and Maintenance 

This section discusses startup, operation and maintenance of the 48C-TLE. The TECO 48C-TLE series 

instrument has a digital front panel screen with selection switches below. This allows the user to check 

functions, switch operating parameters, adjust zero and span and read warnings messages. It is 

extremely important that the users familiarize themselves with the menus available. Inadvertently 

changing parameters within the analyzer can damage the instrument and possibly invalidate data 

as well. Please reference the TECO 48C-TLE owner’s manual and read it carefully before 

adjusting any parameters that are set by the factory. 

3.9.3.1 Start up 

The following text is taken from the TECO 48C-TL manual. It is the identical for the 48C-TLE model. 

The Model 48C Trace Level is shipped complete in one container. If, upon receipt of the analyzer, there is 

obvious damage to the shipping container, notify the carrier immediately and hold for inspection. The 

carrier, and not Thermo Environmental Instruments Inc., is responsible for any damage incurred during 

shipment. Follow the procedure below to unpack and inspect the instrument. 

1. Remove the instrument from the shipping container and set on a table or bench that allows easy 

access to both the front and rear of the instrument. 

2. Remove the instrument cover to expose the internal components and remove any packing material. 

3. Check for possible damage during shipment and check that all connectors and printed circuit boards 

are firmly attached. 

4. Re-install the instrument cover. 

5. Connect the sample line to the sample bulkhead on the rear panel. Ensure that the sample line is not 

contaminated by dirty, wet or incompatible materials. All tubing should be constructed of TeflonTM or 

borosilicate glass with an OD of 1⁄4” and a minimum ID of 1/8”. 
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6. The length of the tubing should be less than 10 feet. 

7. All gas must be delivered to the instrument at atmospheric pressure. It may be necessary to employ an 

atmospheric bypass plumbing arrangement or attach the instrument inlet line to a manifold that is 

vented to the atmosphere. 

8. Connect the exhaust bulkhead to a suitable vent. The exhaust line should be 1⁄4” OD (outside 

diameter) with a minimum ID of 1/8” ΟD. The length of the exhaust line should be less than 10 feet. 

Verify that there is no restriction in this line. 

9. Connect a suitable recording device to the rear panel terminals. The EPA recommends, but does not 

require, recording of the data digitally. The TECO 48C-TLE has this option. Please refer to the “Data 

Acquisition and Management” SOP. If the DAS system that you have does not have the RS-232 

capabilities, then proceed to the next section, Diagnostic Checks/Manual Checks. If you have 

connected the 48C-TLE to a computer or DAS, review the Diagnostic Check from your computer 

screen. TECO offers TECO communication software, a computer program that allows the operator to 

log the diagnostic data that is collected by the 48C-TLE CPU. Several DAS manufacturers offer this 

type of software as well. 

10. Plug the instrument into an outlet of the appropriate voltage and frequency. The Model 48C Trace 

Level is supplied with a three-wire grounding cord. Under no circumstances should this grounding 

system be defeated. 

11. Turn the power on. 

3.9.3.2 Operation and Range Setting 

1. The exhaust fan will start and the display will come on. The Central Processing Unit (CPU) will boot 

the system and load the firmware. 

2. The display has a 4 line by 20 character alphanumeric display that shows the sample concentration, 

instrument parameters, instrument controls and help/warning messages. The menus for access (as 

described in sections 3.9.3.4 and 3.9.3.5 of this SOP) are performed using the display and the 6 pushbuttons just below the display. 

3. Once the instrument loads the firmware, the display will display “CO PPM XX.XX, below this 

value is the time and “REMOTE.” This is the “RUN” menu and should always be left in the “RUN” 

menu when it is collecting ambient data. 

4. To access the Main Menu, press the “Menu.” This will put you into the Main Menu. 

5. From the Main Menu, Use the ↑ and ↓ pushbuttons move the cursor down so that the arrow is next to 

“Range” selection. Press “Enter.” 

6. The Range menu contains the gas units, CO ranges, and the custom ranges. In the upper right corner 

of the display, the words “SINGLE, DUAL, or AUTO” is displayed to indicate the active mode. The 

“Range” menu in the dual and auto-range modes appear the same except for the word DUAL or 

AUTO, displayed in the upper right corner. For more information about the SINGLE, DUAL, or 

AUTO-range modes, see page 3-6 of the owner’s manual. The default is set to single range. 

7. To set the upper scale range, use the ↑ and ↓ pushbuttons to move the cursor down so that the arrow is 

next to “CO Range” selection. Press “Enter.” 

8. Use the “ÇÈÆÅ” buttons on the front panel to enter in the desired concentration, this should be 

“5.” Press “Enter.” 

9. Press “Menu” and then press “Run.” The full scale range has now been set to 5.00 ppm. The default 

for the units is “ppm.” It is recommended that this not be changed. 

10. In single range mode, there is one range, one averaging time, and one span coefficient. The two CO 

analog outputs are arranged on the rear panel terminal strip as shown in Figure 3-3 of the owner’s 

manual. To use the single range mode, set option switches 4 and 5 off. For more information about 
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setting the internal option switches, see .Internal Option Switches, on page 3-7. 

3.9.3.3 Diagnostic Checks/Manual Checks 

To determine whether the 48C-TLE is working properly, the field operators should perform the 

Diagnostic Checks every time they visit the monitoring station. It is good practice for the operator to 

check these Diagnostic Checks either by the computer or manually. Figure 3-2 of this SOP has the menu 

“tree” that was taken from the TECO 48 C-TL manual. By pressing the “menu” button and following the 

tree, an operator can easily get to the location needed. 

Figure 3-2 Menu Tree Schema 

Below are instructions on how to perform the diagnostic checks manually. Please note that the TECO 

48C-TLE has set upper and lower ranges for some of these Diagnostic checks. Please reference the 

owner’s manual for these ranges. Please use the following instructions to access the Diagnostic data. 

1. While in the “Run” menu, press the “Menu” button. This will put you into the Main Menu. 

2. From the Main Menu, Use the ↑ and ↓ pushbuttons move the cursor down so that the arrow is next to 

“Diagnostics” selection. Press “Enter.” 

3. In the Diagnostics Menu, the operator can toggle the arrow using the ↑ and ↓ pushbuttons to align the 

arrow to the selection. Once the operator has toggled the arrow to the diagnostic check desired, press 

“Enter.” This will allow you to see the desired information. Record this information on your field 

work sheet. Please see Table 3-2 for a list of Diagnostic Checks and a brief explanation. Please 

check the Owners Manual for the manufacturer’s recommended ranges. 
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4. Once the operator has reviewed all of the diagnostic information, return to the Main Menu by 

pressing “Menu” followed by “Run.” 

Table 3-2 Diagnostic Checks 

Check Explanation 

Program Number The current software version used by the instrument 

Voltages There are four voltages that should be recorded. 

Temperatures There are two temperatures that should be recorded: internal and chamber. 

Reference Page 3-47 for details. 

Pressure This is the pressure inside of the optics bench. 

Flow This is the actual flow rate through the optics bench. Reference page 3-53 for 

specifications. 

S/R Ratio Sample/Reference Ratio. This is the ratio of the intensities of the light source 

through the sample side and the reference side of the correlation wheel. Please 

See page 3-38 for the optimal values. 

AGC Intensity Automatic Gain Control. The AGC displays the intensity (in Hertz) of the 

reference channel. The AGC circuit optimizes the noise and resolution level of 

the analyzer. Please see page 3-39 for details. 

Motor Speed This displays, in percentage, the status of the chopper motor. This value should 

be 100%. 

Once the Diagnostic checks have been established and recorded for the 48C-TLE, it is time to calibrate 

the instrument. Please refer to section 3.9.4 of this SOP. 

3.9.3.4 Preventive Maintenance

Preventive maintenance should prevent down-time and data loss. Table 3.3 lists the preventive 

maintenance items that are should be performed. Please see section 5-1 of the owner’s manual. Section 

5-1 also has a list of the spare parts that the operator should keep in stock. 

Table 3-3 Preventive Maintenance Schedule the TECO 48C-TLE

Item Schedule

 Replace particle filter Weekly 

 Diagnostics Checks Weekly 

 Perform Level I calibration Daily 

 Replace IR source As needed 

 Leak Check and Pump Check Out Annually 

 Inspect Pneumatic Lines Semi-annually 

 Clean inside of Chassis As needed 
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 Rebuild or replace pump As needed 

 Clean optic bench As needed 

 Replace wheel motor As needed 

 Replace gases in correlation wheel As needed 

3.9.3.5 Instrument Troubleshooting

The TECO 48C-TLE manual has an excellent troubleshooting guide in Section 6-1 of the manual. For 

details on using the Test Functions for predicting failures, please reference this section. 

3.9.4 Calibration and Standardization 

The calibration of the TECO 48C-TLE is performed by comparing the digital or analog output of the 

instrument against standardized gases of known quality. Generation of these gases is detailed in the 

“Calibration of Trace Gas Analyzers” SOP. The recommended ranges for the calibration are detailed in 

Table 4-2. This section will detail how to adjust the 48C-TLE to the standardized gases. Once the 

calibration has been performed, compare the response of your DAS to the calculated “source” value. If 

this is outside of +/-10%, then adjust the instrument response as detailed in the next sections of this SOP. 

3.9.4.1 Adjustment to Zero Air 

In order to adjust the output of the 48C-TLE to zero air, perform the following: 

1. Allow the instrument to sample zero air from a manifold that is at near atmospheric pressure for a 

minimum of 15 minutes. 

2. On the front panel press the “Menu” button. This will bring up the main menu. Using the È

arrow until the cursor is on the “Calibration” selection. Press “Enter.” 

3. This next screen is the “Calibration” screen. In this screen press the ÇÈ buttons until you align 

the cursor at the “Calibrate Zero” selection. Press “Enter.” 

4. The next screen will show a “CO PPM X.X above the words “SET TO ZERO?” If the 

analyzer has stabilized to zero air, press “Enter.” Then Press “Menu” and then press “Run.” This 

will adjust the baseline to the zero air. If you decide to adjust the higher range response, 

continue on to Section 3.9.4.2. 

3.9.4.2 Adjustment to Calibration Gas 

In order to adjust the output of the 48C-TLE to NIST traceable calibration gas, perform the following: 

1. Switch the calibration unit to generate a known concentration of CO. Allow the instrument to sample 

calibration gas from a manifold that is at near atmospheric pressure for a minimum of 15 minutes. 

2. On the front panel press the “Menu” button. This will bring up the main menu. Using the È arrow 

until the cursor is on the “Calibration” selection. Press “Enter.” 

3. This next screen is the “Calibration” screen. In this screen press the ÇÈ buttons until you align the 

cursor at the “Calibrate CO” selection. Press “Enter.” 

4. The first line of the display shows the current CO concentration reading. The second line shows the 

instrument range and the third line states, “SET TO...... XX.XX.” The next line shows “ÇÈ

INC/DEC.” The cursor should be under one of the digits in the third line. Use the “ÇÈÆÅ” 

buttons on the front panel to enter in the desired concentration, that is being generated by the 

calibration system. Press “Enter.” 
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5. Then Press “Menu” and then press “Run.” This will adjust the response of the instrument to the 

calibration gas concentration. The instrument is now calibrated. 

 

3.10 Data Analysis and Calculations 

Data analysis for this analyzer is detailed in “Data Acquisition and Management” SOP. For the TECO 

48C-TLE, there is one design detail of which the operator must be aware; the auto-zero function. As 

detailed in Section 3.1 of this SOP, the TECO 48C-TLE has an auto-zero sequence that occurs at the end 

of the hour (default). During this period, the 48C-TLE analog output will be at or close to zero, since the 

detector is sampling air with the CO “scrubbed out.” While this occurs the display will illustrate “ZERO.” 

If the operator records the data during this sequence via the analog output, then the operator must be 

aware and flag this data in the DAS. The digital output via the RS-232 is flagged; therefore, no other 

flagging is required. The auto-zero function can be modified from once per hour to any increment up to 

once per day. It is recommended that the factory default not be changed from once per hour at this time. 

 

4.0 QUALITY CONTROL AND QUALITY ASSURANCE

 

The following section has brief definitions of the QA/QC indicators. Table 4-1 has the Measurement 

Quality Objectives (MQOs) of the TECO 48C-TLE. Please note that this section details primarily with 

the QA indicators. Quality Control for continuous electronic instruments, such as the TECO 48C-TLE 

consists of performing the diagnostic checks, maintenance and calibrations. These procedures are 

detailed in sections 3.9.3 and 3.9.4: Instrument Operation, Startup and Maintenance and Calibration and 

Standardization. Appendix A has an example of a Quality Control and Maintenance Record developed by 

the EPA for this instrument. In addition, please review Table 4-2, which has the recommended 

operation parameters for the TECO 48C-TLE. The operation parameters include recommended operating 

full scale range, calibration ranges and recommended cylinder concentrations. 

4.1 Precision 

Precision is defined as the measure of agreement among individual measurements of the same property 

taken under the same conditions. For CO, this refers to testing the CO analyzer in the field at 

concentrations between 0.250 and 0.500 ppm. The test must be performed, at a minimum, once every two 

weeks. Calculations for Precision can be found in Reference 4. 

4.2 Bias 

Bias is defined as the degree of agreement between a measured value and the true, expected, or accepted 

value. Quantitative comparisons are made between the measured value and the true, standard value 

during audits. Generally, three upscale points and a zero point are compared. Two audit types commonly 

used for CO, direct comparison and blind, are discussed below. The SOP should discuss plans for each 

type of audit. 

 Direct Comparison Audits: An independent audit system is brought to the monitoring location and 

produces gas concentrations that are assayed by the monitoring station's CO analyzer. In most cases, 

a person outside of the agency or part of an independent QA group within the agency performs the 

audit. The responses of the on-site analyzer are then compared against the calculated concentration 

from the independent audit system and a linear regression is generated 

 Blind Audits: In blind audits (also called performance evaluation audits) State or Local agency staff 

are sent an audit device, such as the National Performance Evaluation Program (NPEP). The agency 
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staff does not know the CO concentrations produced by the audit equipment. Responses of the onsite analyzer are then compared against those of the generator and a linear regression is calculated. 

4.3 Representativeness 

Representativeness refers to whether the data collected accurately reflect the conditions being measured. 

It is the data quality indicator most difficult to quantify. Unless the samples are truly representative, the 

other indicators are meaningless. Since the NCORE Level I and II siting criteria are urban and regional, 

the CO Trace Level criteria are the same. Please reference the National Monitoring Strategy5 for a 

discussion of NCORE Level II CO monitoring scale. 

4.4 Completeness 

Completeness is defined as the amount of data collected compared to a pre-specified target amount. For 

CO, EPA requires a minimum completeness of 75% (40 CFR 50, App.H.3). Typical completeness with 

the TECO 48C-TLE values can approach 90-93%. 

4.5 Comparability 

Comparability is defined as the process of collecting data under conditions that are consistent with those 

used for other data sets of the same pollutant. The TECO 48C-TLE meets the MQOs for a Trace Level 

CO instrument. Please see Table 4-1. 

4.6 Method Detection Limit 

The method detection limit (MDL) or detectability refers to the lowest concentration of a substance that 

can be determined by a given procedure. The TECO 48C-TLE must be able to detect a minimum value of 

0.040 ppm of CO. 

Table 4-1 Measurement Quality Assurance Objectives 

Requirement Frequency Acceptance Criteria Reference Information or Action 

Bias NCORE, 

once per 

year 

To be Determined from Data 

Quality Objectives 

40 CFR Pt.58 Use of NIST generated gas 

concentrations with Mass 

Flow Calibration unit that is 

NIST traceable 

Precision 1 every 2 

weeks 

Concentration: 0.250 -0.500 ppm, 

Coefficient of Variance: To be 

determined 

40 CFR Pt.58 

Appendix A 

To be determined 

Completeness Quarterly, 

Annually 

NCORE, 75% National 

Monitoring 

Strategy. 

If under 75%, institute 

Quality Control Measures 

Representativeness N/A Neighborhood, Urban or Regional 

Scale 

40 CFR 58 N/A 

Comparability N/A Must be a Trace Level instrument. 

See Sections 3.1 and 3.2 of this 

document. 

National 

Monitoring 

Strategy. 

N/A 

Method Detection 

Limit 

NA 0.040 ppm National 

Monitoring 

Strategy 

Testing is performed at the 

factory. 
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Table 4-2 Operating Parameters for the TECO 48C-TLE Trace Gas Instrument 

Item Range Comments 

Full Scale Range 0 to 5.000 ppm Suggested Range. Reduce to 1.000 ppm if rural site 

Units Part per million (ppm) Recommended 

Compressed Gas 

Cylinder 

200 – 250 ppm NIST Traceable Protocol #1 cylinder with CO 

concentration between 200 – 250 ppm. 

Calibration Ranges 

a. zero 0 – 0.010 ppm There are a number of commercially available vendors. 

b. Level I Span 4.000 – 5.000 ppm NIST Traceable Protocol #1 cylinder with CO 

concentration between 200 – 250 ppm. Recommended 

gas flow range 75 – 90 cc/min. Zero air flow 4.80 – 

5.00 liters/min. 

c. Mid Point Span 2.000 – 2.500 ppm NIST Traceable Protocol #1 cylinder with CO 

concentration between 200 – 250 ppm. Recommended 

gas flow range 75 – 90 cc/min. Zero air flow 8.00 

10.00 liters/min. 

d. Precision Level 0.250 – 0.500 ppm NIST Traceable Protocol #1 cylinder with CO 

concentration between 200 – 250 ppm. Recommended 

gas flow range 20 - 35 cc/min. Zero air flow 18.00 – 

20.00 liters/min. 

5.0 REFERENCES 

1. Merck Index, twelfth edition 1996, page 296 

2. Seinfeld,, John H., Atmospheric Chemistry and Physics of Air Pollution, 1986, page 54 

3. Code of Federal Regulations, Title 40, Part 53.23c 

4. Code of Federal Regulation, Title 40, Part 58, Appendix A 

5. The National Air Monitoring Strategy, Final Draft, 4/29/04, 

http://www.epa.gov/ttn/amtic/monstratdoc.html
TECO 48C-TLE CO SOP 

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 Appendix A

Environmental Protection Agency 

Monthly Quality Control and Maintenance Records 

TECO 48C-TLE CO Analyzer 

Site Name/Location ________________________ 

 

Technician________________ 

Month/Year_______________ 

Serial Number Range______________ 

 

Parameter Date Date Date Acceptance Criteria 

Program Number 48 TR007 00 

Communications 

48LTR007 00 

Bias Voltage -105-115V 

+5 volt supply NA 

+15 volt supply NA 

-15 volt supply NA 

Battery NA 

Internal Temp 8.0 – 47 deg. C 

Chamber Temp 48.0 – 52.0 deg. C 

Pressure 250 – 1000 mm Hg 

Flow 0.35 - 2.5 LPM 

S/R Ratio 1.14 – 1.18 

AGC Intensity 200,000 – 300,000 Hz 

Motor Speed 100% 

Test Analog 

Outputs* 

 See note below 

Option 

Switches** 

 See note below 

* When the operator needs to set the analog output against the DAS, this function should be 

utilized. Please refer to page 3-41 to 3-44 of the owner’s manual to initiate this feature. 

* *The option switches are set at the factory. Please reference owner’s manual, Page 3-62 

“Service Mode Menu” on changing these options switches. 

 

Date Comments and Notes 

 

Figure A-1 TECO 48C-TLE Quality Control and Maintenance Record 
STANDARD OPERATING PROCEDURES 

TELEDYNE - ADVANCED POLLUTION INSTRUMENTS 

MODEL 300EU TRACE LEVEL 

 CARBON MONOXIDE INSTRUMENT 

Version 2 

 
Section 1.1 Acknowledgments 

This Standard Operating Procedure (SOP) for Carbon Monoxide – Trace Level is the product of EPA’s 

Office of Air Quality, Planning and Standards. The following individuals are acknowledged for their 

contributions. 

Principal Author 

Dennis K. Mikel, OAQPS-EMAD, Research Triangle Park, NC 27711 

Reviewers 

Office of Air Quality, Planning and Standards 

Joann Rice, Trace Gas Team Lead, OAQPS-EMAD, Research Triangle Park, NC 27711 

Anna Kelly, OAQPS-EMAD, Research Triangle Park, NC 27711 

Keith Kronmiller, Mantech, Inc. Research Triangle Park, NC 27711 

Comments and questions can be directed to: 

Joann Rice 

EPA-OAQPS 

Emission, Analysis and Monitoring Division 

Mail Drop D243-02 

Research Triangle Park, NC 27711 

Email: rice.joann@epa.gov 

Phone: (919)-541-3372 
Section 2.0 Table of Contents

Section Page 

1.0 Title Page 1 

1.2 Acknowledgements 2 

 2.0 Table of Contents 3 

 2.1 List of Tables and Figures 4 

3.0 Procedures 5 

 3.1 Scope and Applicability 5 

 3.2 Summary of Method 5 

 3.3 Definitions 7 

 3.4 Health and Safety Warnings 7 

 3.5 Cautions 7 

 3.6 Interferences 8 

 3.7 Personal Qualifications 8 

 3.8 Equipment and Supplies 8 

 3.9 Procedure 10 

 3.9.1 Sample Collection 10 

 3.9.2 Sample Handling and Preservation 10 

 3.9.3 Instrument Operation, Start up and Maintenance 10 

 3.9.3.1 Start up 10 

 3.9.3.2 Operation and Range Setting 10 

 3.9.9.3 Diagnostic Checks/Manual Checks 11 

 3.9.3.4 Preventive Maintenance 13 

 3.9.3.5 Instrument Troubleshooting 13 

 3.9.4 Calibration and Standardization 13 

 3.9.4.1 Adjustment to Zero Air 13 

 3.9.4.2 Adjustment to Calibration Gas 14 

 3.10 Data Analysis and Calculations 14 

 4.0 Quality Control and Quality Assurance 14 

 4.1 Precision 14 

 4.2 Bias 15 

 4.3 Representativeness 15 

 4.4 Completeness 15 

 4.5 Comparability 15 

 4.6 Method Detection Limit 15 

 5.0 References 17 
List of Tables 

Table Name and Number Page 

 3-1 Definition of Key Terms 7 

 3-2 Diagnostic Checks 12 

 3-3 Preventive Maintenance Schedule for the TAPI 300EU 13 

 4-1 Measurement Quality Assurance Objectives 16 

 4-2 Operating Parameters for the TAPI 300EU Trace Gas Instrument 17 

List of Figures 

Figure Name and Number Page 

 3-1 Schema of the Teledyne API 300EU 9 

 A-1 Teledyne API Quality Control and Maintenance Record 18 
Teledyne API CO SOP 

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STANDARD OPERATING PROCEDURES 

TELEDYNE - ADVANCED POLLUTION INSTRUMENTS 

MODEL 300EU TRACE LEVEL CARBON MONOXIDE INSTRUMENT 

3.0 PROCEDURES 

3.1 Scope and Applicability 

Carbon Monoxide (CO), a colorless, odorless, tasteless, highly poisonous gas has detrimental effects on 

human health. Carbon Monoxide originates from the partial oxidation of hydrocarbon fuels, coal and 

coke1

. Carbon Monoxide affects the oxygen carrying capacity of the blood. Carbon Monoxide can 

diffuse through the alveolar walls of the lungs and compete with oxygen for one of the four iron sites in 

the hemoglobin molecule. The affinity of the iron site for CO is approximately 210 times greater than 

oxygen2

. Low levels of CO can cause a number of symptoms including headache, mental dullness, 

dizziness, weakness, nausea, vomiting and loss of muscular control. In extreme cases, collapse, 

unconsciousness and death can occur. 

The Teledyne – Advanced Pollution Instruments (TAPI) model 300EU is a state of the science instrument 

for the determination of trace levels of Carbon Monoxide by Non-Dispersive Infrared Spectrophotometry 

(NDIR) using Gas Filter Correlation (GFC). This SOP will detail the operation, preventive maintenance, 

cautions and health warnings. 

The Detection Limit (DL) for non-trace levels of CO is 1.0 parts per million (ppm) (Code of Federal 

Regulations, Volume 40, Part 53.23c, or, in the shortened format used hereafter, 40 CFR 53.23c)3

. 

However, the 300EU has a DL to 20 parts per billion (ppb), which is accomplished by modifications to 

the Federal Reference Method (FRM) instruments. This document will discuss the Trace Level (TL) 

operating procedures in detail. 

3.2 Summary of Method 

The analytical principle is based on absorption of IR light by the CO molecule. NDIR-GFC analyzers 

operate on the principle that CO has a sufficiently characteristic IR absorption spectrum such that the 

absorption of IR by the CO molecule can be used as a measure of CO concentration in the presence of 

other gases. Carbon Monoxide absorbs IR maximally at 2.3 and 4.6 um. Since NDIR is a 

spectrophotometric method, it is based upon the Beer-Lambert Law. The degree of reduction depends on 

the length of the sample cell, the absorption coefficient, and CO concentration introduced into the sample 

cell, as expressed by the Beer-Lambert law shown below: 

T = I/Io = e(-axC) (equation 1) 

where: 

T = Transmittance of light through the gas to the detector 

I = light intensity after absorption by Carbon Monoxide 

Io = light intensity at zero Carbon Monoxide concentration 

a = specific Carbon Monoxide molar absorption coefficient 

x = path length, and 

C = Carbon Monoxide concentration 
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For Gas Filter Correlation, there is only one sample cell. This cell acts as the sample and reference cell. 

The broad band of IR radiation is emitted from an IR source. The IR light passes through a very narrow 

band pass filter which screens out most wavelengths and allows only the wavelength of light that CO 

absorbs to enter the sample cell. The GFC analyzer has a chopper wheel with two pure gases: Nitrogen 

and Carbon Monoxide. As the chopper wheel rotates and allows the IR energy to enter “CO side” of the 

wheel, all IR energy that could be absorbed by CO in the sample stream is absorbed by the CO in the 

wheel. This technique effectively “scrubs out” any light that could possibly be attenuated. The single 

detector records the light level (Io). As the wheel spins, the “N2 side” of the wheel reaches the IR energy 

beam. This side of the wheel allows all IR light to pass through the wheel and be absorbed by any CO 

that might be in the sample gas. This light level is CO sensitive (I). The detector records the attenuation 

of this light, compares the two light levels (I/Io) and sends a signal to the electrometer board that 

calculates the concentration. The voltage is related to the CO concentration according to the BeerLambert law in equation 1 shown above. Thus, TAPI 300EU can measure CO continuously. The 300EU 

version has four distinct features that allow it to measure CO at ppb levels: 

 The sample stream is dried using permeation or NafionTM Dryer; 

 The analyzer baseline is determined and corrected using heated palladium catalytic converter; 

 The baseline is frequently auto-zeroed, at a minimum once per hour, through the palladium converter; 

 The instrument has an ultra-sensitive or “hot” detector. 

The 300 EU instrument operates in the following fashion:

1. In sample mode, ambient air is allowed to enter through the rear bulkhead sample port. Solenoid #1 

is in its Normally Open (NO) mode. The ambient air flows through the solenoid to the permeation 

dryer, which removes the moisture and water from the sample air stream. 

2. The sample stream then passes through a sample filter, which removes particles that can build up on 

the mirror and sample chamber and attenuate the IR beam. 

3. The sample then enters the sample cell. A major difference between a non-TL and TL instrument is 

the detector. The TL instrument has a detector that is more sensitive to the light emitted and 

absorbed in the sample cell. This detector must be more sensitive because the amount of attenuation 

by the CO gas in the sample stream is much lower. Therefore, the detector must be sensitive at lower 

ambient levels. Temperature of the sample cell is also critical. The sample cell and detector must be 

maintained at a constant temperature in order for the detector to keep a stable background. 

Fluctuations of more than 1o Centigrade can cause the baseline to drift, giving false readings at low 

levels. 

4. The detector sends the signal to the demodulator which interprets the signal. The demodulator sends a 

digital value to the Central Processor Unit (CPU).

5. At the end of the hour, the CPU sends a voltage signal to the Solenoid #1 and switches it to the 

“Normally Closed” (NC) position. This allows room air to be drawn into the instrument and to pass 

through the catalytic converter. The catalytic converter uses a palladium bed heated to 50o

Centrigrade to convert all Carbon Monoxide to Carbon Dioxide (2CO + O2 —> 2CO2). This 

effectively “scrubs” all CO from the sample stream. The CO “free” air flows through the sample cell 

and the CPU interprets the signal from the demodulator as the “background” or “baseline” value. 

The baseline is then adjusted at that time. The baseline adjustment usually takes between 7-10 

minutes.

6. The CPU then switches Solenoid #1 to its NO position and ambient air then drawn into the analyzer. 
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3.3 Definitions

Here are some key terms for this method. 

Table 3-1, Definitions of Key Terms 

Term Definition 

DAS Data acquisition system. Used for automatic collection and 

recording of CO concentrations. 

Interferences Physical or chemical entities that cause CO measurements to be 

higher (positive) or lower (negative) than they would be without the 

entity. (See Section 3.6). 

 

3.4 Health and Safety Warnings 

To prevent personal injury, please heed these warnings concerning the 300EU. 

1. Carbon Monoxide is a poisonous gas. Vent any CO or calibration span gas to the atmosphere 

rather than into the shelter or other sampling area. If this is impossible, limit exposure to CO by 

getting fresh air every 5 to 10 minutes. If the operator experiences light headedness, headache or 

dizziness, leave the area immediately. 

2. The IR source is a filament resistor that has an electrical current running through it. The IR source 

can become very hot. When troubleshooting, allow the instrument to cool off especially if you 

suspect the IR source as the cause of trouble. 

3. Always use a third ground wire on all instruments. 

4. Always unplug the analyzer when servicing or replacing parts. 

5. If it is mandatory to work inside an analyzer while it is in operation, use extreme caution to avoid 

contact with high voltages. The analyzer has a 110 volt Volts Alternating Current (VAC) power 

supply. Refer to the manufacturer's instruction manual and know the precise locations of the VAC 

components before working on the instrument. 

6. Avoid electrical contact with jewelry. Remove rings, watches, bracelets, and necklaces to prevent 

electrical bums. 

3.5 Cautions 

To prevent damage to the 300EU, all cautions should immediately precede the applicable step in 

this SOP. The following precautions should be taken:

1. Normally, if TeflonTM filters are used in the sample train, cleaning the optical bench will not be 

required. However, in the event that the bench is cleaned, be careful to avoid damaging the interior of 

the sample chamber. In addition, some GFC instruments have a series of mirrors that deflect the light 

in order to increase the path length. The mirrors are aligned at the factory. If the mirrors become 

misaligned, the IR light beam will not be directed to the detector. Use extreme caution when cleaning 

or servicing the sample chamber(s). In addition the mirrors are very fragile. Avoid dropping the 

instrument. This may damage, misalign or crack the mirrors and cause expensive repairs. 

2. Keep the interior of the analyzer clean. 

3. Inspect the system regularly for structural integrity. 

4. To prevent major problems with leaks, make sure that all sampling lines are reconnected after 

required checks and before leaving the site. 
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5. Inspect tubing for cracks and leaks. 

6. It is recommended that the analyzer be leak checked after replacement of any pneumatic parts. 

7. If cylinders are used in tandem with Mass Flow Control (MFC) calibrators, use and transport is a 

major concern. Gas cylinders can sometimes contain pressures as high as 2000 pounds per square 

inch (psi). Handling of cylinders must be done in a safe manner. If a cylinder is accidentally dropped 

and valve breaks off, the cylinder can become explosive or a projectile. 

8. Transportation of cylinders is regulated by the Department of Transportation (DOT). It is strongly 

recommended that all agencies contact the DOT or Highway Patrol to learn the most recent 

regulations concerning transport of cylinders. 

9. Carbon Monoxide is a highly poisonous gas. Long term exposure can cause problems with motor 

coordination and mental acuity. It is strongly recommended that all agencies have Material Safety 

Data Sheets (MSDS) at all locations where CO cylinders are stored or used. MSDS can be obtained 

from the DOT or from your vendor. 

10. It is possible (and practical) to blend other compounds with CO. If this is the case, it is recommended 

that MSDS for all compounds be made available to all staff that use and handle the cylinders or 

permeation tubes. 

11. Shipping of cylinders is governed by the DOT. Contact the DOT or your local courier about the 

proper procedures and materials needed to ship high-pressure cylinders. 

3.6 Interferences

Water Vapor: Studies have shown conclusively that NDIR analyzers have interference from water 

vapor. Water absorbs very strongly across several bands of IR spectra. Water vapor interference occurs 

because water vapor absorption of light in the region of 3.1, 5.0 5.5 and 7.1 -10.0 um in the IR region. 

Since water vapor absorbs light in this region, this has a quenching effect on the reaction of CO. The 

TAPI 3000EU is equipped with a NafionTM drier, which effectively scrubs all water and water vapor. No 

maintenance is required on the dryer. 

Carbon Dioxide: Carbon dioxide absorbs in the IR spectrum at 2.7, 5.2, and 8.0 to 12.0 um. This is very 

close to the regions that CO absorbs within as well. However, since atmospheric CO2 is much higher in 

concentration than CO, this UV spectral range must be avoided. To prevent light in this spectral region, 

the TAPI 300EU analyzer has a band pass filter that blocks these wavelengths. 

3.7 Personal Qualifications 

The person(s) chosen to operate the TAPI 300EU should have a minimum of qualifications. The 

understanding of basic chemistry and electronics are a must. The understanding of digital circuitry is 

helpful, but not required. Also, courses in data processing and validation are also welcome. 

3.8 Equipment and Supplies 

Monitoring Apparatus: The design of the 300EU is identical to the 300E with several major variations. 

A diagram of the TAPI 300EU instrument is described in Figure 3-1. The three main components are: 

 Pneumatic System: Consists of sample inlet line, particulate filter, permeation dryer, reaction 

chamber, flowmeter, and pump, all used to bring ambient air samples to the analyzer inlet. 

 Analytical System: This portion of the instrument consists of the IR source, the correlation wheel, 

motor, mirrors, detector and band pass filter. 
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 Electronic Hardware: The part of the analyzer that generally requires little or no maintenance. If the 

300EU is operated above the manufacturer's recommended temperature limit, however, individual 

integrated chips can fail and cause problems with data storage or retrieval. 

Other apparatus and equipment includes the following. 

Instrument Shelter: A shelter is required to protect the analyzer from precipitation and adverse weather 

conditions, maintain operating temperature within the analyzer's temperature range requirements, and 

provide security and electrical power. The recommended shelter temperature range is 20-30o

C. 

Spare Parts and Incidental Supplies: See the TAPI 300EU operating manual, Appendix B for specific 

maintenance and replacement requirements. 

Calibration System: A system that creates concentrations of CO of known quality is necessary for 

establishing traceability. This is described in detail in the “Environics 9100 SOP.” Please reference this 

document. 

DAS: A data acquisition system is necessary for storage of ambient and ancillary data collected by the 

300EU. 

 

Figure 3-1 Schema of the Teledyne API 300EU 

Wiring, Tubing and Fittings: TeflonTM and borosilicate glass are inert materials that should be used 

exclusively throughout the intake system. It is recommended that Polytetrafluoroethylene (PTFE) or 

Fluoroethylpropylene (FEP) TeflonTM tubing be used. PTFE and FEP are the best choice for the 

connection between the intake manifold and the 300EU bulkhead inlet. Examine and discard if 

particulate matter collects in the tubing. All fittings and ferrules should be made of TeflonTM or stainless 
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steel. Connection wiring to the DAS should shielded two strand wire or RS-232 cables for digital 

connections. 

Reagents and Standard: The TAPI 300EU does not require any reagents since the instrument uses 

photometry to analyze for CO. All standards for the CO method can be obtained in compressed cylinders 

and must be NIST traceable. Please see the “Calibration of Trace Gas Analyzers” SOP. 

3.9 Procedure 

3.9.1 Sample Collection: Sampling for Trace Level CO is performed by continuously drawing ambient 

air through a sample manifold directly into the analyzer via a vacuum pump. All inlet materials must be 

constructed from TeflonTM or borosilicate glass as detailed in 40 CFR 58. The siting criteria for CO 

Trace Level instruments in detailed in 40 CFR 58, Appendix A4 . 

3.9.2 Sample Handling and Preservation: Carbon Monoxide samples receive no special preparation 

prior to analysis. Therefore this SOP does not have a section on Sample Handling and Preservation.

3.9.3 Instrument Operation, Startup and Maintenance 

This section discusses startup, operation and maintenance of the 300EU. The TAPI 300EU series 

instrument has a digital front panel screen with toggle switches below. This allows the user to check 

functions, switch operating parameters, adjust zero and span and read warnings messages. It is 

extremely important that the user familiarize themselves with the menus available. Inadvertently 

changing parameters within the analyzer can damage the instrument and possibly invalidate data 

as well. Please reference the TAPI 300EU owner’s manual and read it carefully before adjusting 

any parameters that are set by the factory. 

3.9.3.1 Start up 

Before the instrument is operated, inspect the instrument for any damage. If damage is observed to the 

shipping box or the instrument, contact your shipping personnel. 

Carefully remove the cover and check for internal damage. Please see Section 3.1 of the TAPI 300EU 

manual. 

Remove the 6 red shipping screws that hold down the internal bench and parts. See Section 3.1 of the 

TAPI 300EU manual. 

Once you have removed the shipping screws and performed your inspection, replace the cover. 

Plug the instrument into a grounded power strip that has surge protection. It is also advisable to purchase 

an Uninterrupted Power Supply (UPS). An UPS will protect the 300EU from power surges and keep 

the unit operating until an operator can shut it down. 

Check to see that the 300EU has enough clearance so that it gets proper ventilation. Check the TAPI 

300EU manual Section 3.1. 

Connect the output of the analog to a DAS via shielded two wire cable. Please see EPA SOP on “Data 

Management” for details. 

Connect the digital RS-232 port to an appropriate cable and connect it to the DAS. Please see EPA SOP 

on “Data Management” for further details. 

Connect the sample inlet port to the station intake manifold. 

Press the power rocker switch to “ON.” 
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3.9.3.2 Operation and Range Setting 

1. The exhaust fan will start and the display will come on. The Central Processing Unit (CPU) will boot 

the system and load the firmware. You will see in the upper right hand corner that the fault warning 

light will be flashing red. This is letting you know that the analyzer has been off. 

2. To clear the fault warning, press the “CLR” button below the display. This will clear the warning and 

the sample green light will flash. If the red fault light continues to flash, and clearing it does not 

change this condition, then reference section 6.2.1 of the TAPI 300EU manual for instruction. 

3. Once the red fault light is cleared, the operator will see the main menu. At this time, the time of day 

and date must be verified and reset if necessary. 

4. From main menu press the toggle button under the “SETUP” label. 

5. In this menu, you will see “8 1 8” on the bottom of the display. This is the default password. In 

addition, you will see on the top of the display the words “ENTER SETUP PASS:818.” 

6. At this time, press the toggle under “ENTR.” 

7. This will bring up the “PRIMARY SETUP MENU” screen. 

8. In this menu, press the toggle button under “CLK.” 

9. In the next menu, press the “TIME” toggle switch. 

10. In the next menu, you will see the time above 3 or 4 toggle switches. Adjust these toggles so that the 

time is correct. Press the “ENTR” toggle switch. 

11. This returns you to the “TIME OF DAY CLOCK” menu. Press the toggle switch under “DATE.” 

12. This will put you in the date menu. You should see the day (digits), month and year (digits) above 5 

toggle switches. Adjust these toggles until the correct date is obtained. Press the “ENTR” toggle 

switch. Press the “EXIT” toggle switch twice. This returns you to the main menu. 

13. The range should be illustrated in the top middle of the main menu. This value should be set to 5000 

ppb. If it is not set to this range, then it must be reset. 

14. To change the range of the instrument, press the toggle under “SETUP.” If the password is correct, 

then press “ENTR.” 

15. In this menu, you will see “8 1 8” on the bottom of the display. This is the default password. In 

addition, you will see on the top of the display the words “ENTER SETUP PASS:818.” 

16. At this time, press the toggle under “ENTR.” 

17. This will bring up the “PRIMARY SETUP MENU” screen. 

18. Press the toggle switch under the “RNGE.” 

19. This is the “RANGE CONTROL MENU.” Press the toggle switch under the “UNIT.” 

20. This display will show the range options. Press the toggle under the “PPB.” Press the toggle under 

the “ENTR.” 

21. This will put you into the “RANGE CONTROL MENU.” Press the toggle switch under the “SET.” 

22. This display will show the full scale range value. Press the toggles under the digits to adjust the 

instrument to the full scale value desired. Press the toggle under the “ENTR.” 

23. Press the “EXIT” toggle switch twice. 

24. The instrument is now set with the appropriate time, date and full scale range. 

25. It is recommended that you allow the 300EU 24 hours before you attempt function checks or 

calibration. 

26. If the DAS system that you have does not have the RS-232 capabilities, then proceed to the next 

section, Diagnostic Checks/Manual Checks. If you have connected the 300EU to a computer or DAS, 

review the Diagnostic Check from your computer screen. TAPI offers API.COM, a computer 

program that allows the operator to log the diagnostic data that is collected by the 300EU CPU. 

Several DAS manufacturers offer this type of software as well. 
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3.9.3.3 Diagnostic Checks/Manual Checks 

To determine whether the 300EU is working properly, the field operators should perform the Diagnostic 

Checks every time they visit the monitoring station. It is good practice for the operator to check these 

Diagnostic Checks either by the computer or manually. Below are instructions on how to perform this 

manually. Please note that the TAPI 300EU has set upper and lower ranges for some of these Diagnostic 

checks. Please reference the owner’s manual for these ranges. 

1. If you observe the display, it should show “Sample” in the left hand corner, “Range” in the middle of 

the display and “CO= XX.XX.” Below this line there should be one line that read “<TST”, “TST>”, 

“CAL” and “SETUP.” 

2. There is a series of toggle switches/ buttons below the display. These correspond to the bottom row 

of the display. 

3. If you press the button below the left hand “<TST,” you will toggle the display into function check 

tree in one direction. The button under the “TST>,” will allow you to access the function check tree 

in the opposite direction. 

4. Toggle through the function check tree. The following table illustrates the functions that should be 

recorded. Please see section 6.2.2 of the TAPI 300EU manual for more details. A manual check list 

on maintenance check sheet is attached in Appendix A of this SOP. 

Table 3-2 Diagnostic Checks 

Check Explanation 

Range The full scale range of the instrument 

Stabil The standard deviation of CO concentrations for the last 25 readings 

CO Meas The demodulated peak of the IR detector output on the measure side of the wheel 

CO Ref The demodulated peak of the IR detector on the reference side of the wheel 

MR ratio The result of the CO meas/CO Ref 

Azero ratio The result of the CO meas/CO Ref during the Azero cycle 

Sample Pres The absolute pressure of the sample gas in the sample chamber 

Sample FL Mass flow rate of sample air 

Sample Temp The temperature of the gas inside the sample chamber 

Bench Temp Optical bench temperature 

Wheel Temp Filter wheel temperature 

Box Temp The temperature inside the instrument chassis. 

PHT Drive The voltage needed to the thermoelectric coolers of the IR detector board 

Slope The sensitivity of the instrument as calculated during the last calibration. 

Offset The overall offset of the instrument calculated during the last calibration 

Time Displays current time. 

Once the Diagnostic checks have been established and recorded for the 300EU, it is time to calibrate the 

instrument. Please refer to section 3.9.4 of this SOP. 

3.9.3.4 Preventive Maintenance

Preventive maintenance should prevent down-time and data loss. Table 3.3 lists the preventive 

maintenance items that are listed in the Model 300EU manual, section 9.1. 
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Table 3-3 Preventive Maintenance Schedule the TAPI 300EU

Item Schedule

 Replace particle filter Weekly 

 Verify Test Function Weekly 

 Perform Level I calibration Daily 

 Pump Diaphragm Bi-annually 

 Perform Leak Check Annually 

 Inspect Pneumatic Lines Annually 

 Clean inside of Chassis As needed 

 Rebuild or replace pump As needed 

 Replace IR source As needed 

 Clean optic bench As needed 

 Replace wheel motor As needed 

 Replace gases in correlation wheel As needed 

3.9.3.5 Instrument Troubleshooting

The TAPI 300EU manual has an excellent troubleshooting guide in Section 9.2. Please reference page 

143 of the manual for details on using the Test Functions for predicting failures. 

3.9.4 Calibration and Standardization 

The calibration of the TAPI 300EU is performed by comparing the output of the instrument against 

standardized gases of known quality. Generation of these gases is detailed in the “Calibration of Trace 

Gas Analyzers” SOP. This section will detail how to adjust the 300EU to the standardized gases. Once 

the calibration has been performed, compare the response of your DAS to the calculated “source” value. 

If this is outside of +/-10%, then adjust the instrument response as detailed in the next sections. 

3.9.4.1 Adjustment to Zero Air 

In order to adjust the output of the 300EU to zero air, perform the following: 

1. Allow the instrument to sample zero air from a manifold that is at near atmospheric pressure for a 

minimum of 15 minutes. 

2. On the bottom of the front panel screen there is a toggle switch/ button that is beneath the “CAL” 

label. Press this button. 

3. This next screen is the “M-P CAL” screen. In this screen press the button below the “ZERO” 

label. 

4. The next screen will show an “ENTR, SPAN and CONC” above the toggle switches on the 

bottom of the panel. Press the button below the “ENTR” label. This operation changes the 

calculation equation and zeros the instrument. 

5. Press the button below the “EXIT” label. This returns the operator to the main “SETUP” menu. 

3.9.4.2 Adjustment to Calibration Gas 

In order to adjust the output of the 300EU to NIST traceable calibration gas, perform the following: 
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1. Switch the calibration unit to generate a known concentration of CO. Allow the instrument to 

sample calibration gas from a manifold that is at near atmospheric pressure for a minimum of 

15 minutes. 

2. On the bottom of the front panel screen of the main menu there is a button that is beneath the 

“CAL” label. Press this button. 

3. This next screen is the “M-P CAL” screen. The next screen will show an “ENTR, SPAN and 

CONC” above the toggle switches on the bottom of the panel. Press the button below the 

“CONC” label. On the bottom line, there will be digits below each toggle button. In order to 

change the concentration, toggle each digit before and after the decimal place to get the 

concentration that is being generated in the manifold by the calibrator. At this time, press the 

“ENTR.” 

4. At this time, press the toggle below the “SPAN” switch. 

5. This operation changes the calculation equation and adjusts the slope of the instrument. 

6. Press the button below the “EXIT” label. This returns the operator to the main “SETUP” 

menu. 

3.10 Data Analysis and Calculations 

Data analysis for this analyzer is detailed in the “Data Acquisition and Management” SOP. For the TAPI 

300EU, there is one design detail of which the operator must be aware; the auto-zero (Azero) function. 

As detailed in Section 3.1, the TAPI 300EU has an Azero sequence that occurs at the end of the hour. 

During this period, the 300EU “freezes” the output to the CPU at the last value calculated by the CPU and 

the display will illustrate “AZERO.” During the auto-zero sequence, the display and analog output are 

“frozen” on one value. If the operator records the data via the analog output, then the operator must be 

aware of this sequence and flag this data in the DAS. The digital output via the RS-232 is flagged; 

therefore, no other flagging is required. The Azero function can be modified from once per hour to any 

increment up to once per day. It is recommended that the factory default not be changed from once per 

hour at this time. 

 

4.0 QUALITY CONTROL AND QUALITY ASSURANCE

 

The following section has brief definitions of the QA/QC indicators. Table 4-1 has the Measurement 

Quality Objectives (MQOs) of the TAPI 300EU. Please note that this section deals primarily with the 

data quality indicators. Quality Control for continuous electronic instruments, such as the TAPI 300EU 

consists of performing the diagnostic checks, maintenance and calibrations. These procedures are 

detailed in sections 3.9.3 and 3.9.4: Instrument Operation, Startup and Maintenance and Calibration and 

Standardization. Appendix A has an example of a Quality Control and Maintenance Record developed by 

the EPA for this instrument. 

4.1 Precision 

Precision is defined as the measure of agreement among individual measurements of the same property 

taken under the same conditions. For CO, this refers to testing the CO analyzer in the field at 

concentrations between 0.250 and 0.500 ppm (250 – 500 ppb). The test must be performed, at a 

minimum, once every two weeks. Calculations for Precision can be found in Reference 4. 
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4.2 Bias 

Bias is defined as the degree of agreement between a measured value and the true, expected, or accepted 

value. Quantitative comparisons are made between the measured value and the true, standard value 

during audits. Generally, three upscale points and a zero point are compared. Two audit types commonly 

used for CO, direct comparison and blind, are discussed below. The SOP should discuss plans for each 

type of audit. 

 Direct Comparison Audits: An independent audit system is brought to the monitoring location and 

produces gas concentrations that are assayed by the monitoring station's CO analyzer. In most cases, 

a person outside of the agency or part of an independent QA group within the agency performs the 

audit. The responses of the on-site analyzer are then compared against the calculated concentration 

from the independent audit system and a linear regression is generated 

 Blind Audits: In blind audits (also called performance evaluation audits), State or Local Agency 

staff are sent an audit device, such as done in the National Performance Audit Program (NPAP). The 

agency staff does not know the CO concentrations produced by the audit equipment. Responses of 

the on-site analyzer are then compared against those of the audit device and a linear regression is 

calculated. 

4.3 Representativeness 

Representativeness refers to whether the data collected accurately reflect the conditions being measured. 

It is the data quality indicator most difficult to quantify. Unless the samples are truly representative, the 

other indicators are meaningless. Since the NCORE Level I and II siting criteria are urban and regional, 

the TL-CO criteria are the same. Please reference the National Monitoring Strategy5 for a discussion of 

NCORE Level II CO monitoring scale. 

4.4 Completeness 

Completeness is defined as the amount of data collected compared to a pre-specified target amount. For 

CO, EPA requires a minimum completeness of 75% (40 CFR 50, App.H.3). Typical completeness with 

the TAPI 300EU values can approach 90-93%. 

4.5 Comparability 

Comparability is defined as the process of collecting data under conditions that are consistent with those 

used for other data sets of the same pollutant. The TAPI 300EU meets the MQOs for a TL-CO 

instrument. Please see Table 4-1. 

4.6 Method Detection Limit 

The method detection limit (MDL) or detectability refers to the lowest concentration of a substance that 

can be determined by a given procedure. The TAPI 300EU must be able to detect a minimum value of 

0.020 ppm of CO. 
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Table 4-1 Measurement Quality Assurance Objectives 

Requirement Frequency Acceptance Criteria Reference Information or Action 

Bias NCORE, 

once per 

year 

To be Determined from 

Data Quality Objectives 

40 CFR Pt.58 Use of NIST generated 

gas concentrations with 

Mass Flow Calibration 

unit that is NIST 

traceable 

Precision 1 every 2 

weeks 

Concentration: 0.250 -

0.500 ppm, Coefficient of 

Variance: To be 

determined 

40 CFR Pt.58 

Appendix A 

To be determined 

Completeness Quarterly, 

Annually 

NCORE, 75% National 

Monitoring 

Strategy. 

If under 75%, institute 

Quality Control 

Measures 

Representativene

ss 

N/A Neighborhood, Urban or 

Regional Scale 

40 CFR 58 N/A 

Comparability N/A Must be a Trace Level 

instrument. See Sections 

3.1 and 3.2 of this 

document. 

National 

Monitoring 

Strategy. 

N/A 

Method 

Detection Limit 

NA 0.020 ppm National 

Monitoring 

Strategy 

Testing is performed at 

the factory. 
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Table 4-2 Operating Parameters for the TAPI 300EU Trace Gas Instrument 

Item Range Comments 

Full Scale Range 0 to 5000 ppb Suggested Range. Reduce to 1000 ppb if rural site 

Units Part per billion (ppb) Recommended 

Compressed Gas 

Cylinder 

200 – 250 ppm NIST Traceable Protocol #1 cylinder with CO 

concentration between 200 – 250 ppm. 

Calibration Ranges 

a. zero 0 – 10 ppb There are a number of commercially available vendors. 

b. Level I Span 4000 – 5000 ppb NIST Traceable Protocol #1 cylinder with CO 

concentration between 200 – 250 ppm. Recommended 

gas flow range 75 – 90 cc/min. Zero air flow 4.80 – 

5.00 liters/min. 

c. Mid Point Span 2000 – 2500 ppb NIST Traceable Protocol #1 cylinder with CO 

concentration between 200 – 250 ppm. Recommended 

gas flow range 75 – 90 cc/min. Zero air flow 8.00 

10.00 liters/min. 

d. Precision Level 250 – 500 ppb NIST Traceable Protocol #1 cylinder with CO 

concentration between 200 – 250 ppm. Recommended 

gas flow range 20 – 35 cc/min. Zero air flow 18.00 – 

20.00 liters/min. 

5.0 REFERENCES 

1. Merck Index, twelfth edition 1996, page 296 

2. Seinfeld,, John H., Atmospheric Chemistry and Physics of Air Pollution, 1986, page 54 

3. Code of Federal Regulations, Title 40, Part 53.23c 

4. Code of Federal Regulation, Title 40, Part 58, Appendix A 

5. The National Air Monitoring Strategy, Final Draft, 4/29/04, 

http://www.epa.gov/ttn/amtic/monstratdoc.html
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 Appendix A

Environmental Protection Agency 

Monthly Quality Control and Maintenance Records 

Teledyne API 300EU CO Analyzer 

Site Name/Location ________________________ 

 

Technician________________ 

Month/Year_______________ 

Serial Number Range______________ 

 

Parameter Date Date Date Acceptance 

Criteria 

Offset 

Slope 

PHT Drive 

Box Temp 

Wheel Temp 

Bench Temp 

Sample Temp 

Sample Flow 

Sample Pressure 

A-zero Ratio 

MR Ratio 

CO Reference 

CO Measured 

Stability 

Range 

Other Tests 

Dark Current 

 

 

Date Comments and Notes 

 

Figure A-1 Teledyne API 300 EU Quality Control and Maintenance Record 
STANDARD OPERATING PROCEDURES 

TELEDYNE – ADVANCED POLLUTION INSTRUMENTATION 

MODEL 100AS TRACE LEVEL 

 SULFUR DIOXIDE INSTRUMENT 

Version 2 

 

 
 Section 1.1 Acknowledgments 

This Standard Operating Procedure (SOP) for Sulfur Dioxide – Trace Level is the product of EPA’s 

Office of Air Quality, Planning and Standards. The following individuals are acknowledged for their 

contributions. 

Principal Author 

Solomon Ricks, OAQPS-EMAD, Research Triangle Park, NC 27711 

Reviewers 

Office of Air Quality, Planning and Standards 

Joann Rice, Trace Gas Team Lead, OAQPS-EMAD, Research Triangle Park, NC 27711 

Anna Kelly, OAQPS-EMAD, Research Triangle Park, NC 27711 

Keith Kronmiller, Mantech, Inc. Research Triangle Park, NC 27711 

Comments and questions can be directed to: 

Solomon Ricks 

EPA-OAQPS 

Emission, Analysis and Monitoring Division 

Mail Drop D339-02 

Research Triangle Park, NC 27711 

Email: ricks.solomon@epa.gov

Phone: (919)-541-5242 
Section 2.0 Table of Contents

Section Page 

1.0 Title Page 1 

1.3 Acknowledgements 2 

 2.0 Table of Contents 3 

 2.1 List of Tables and Figures 4 

3.0 Procedures 5 

 3.1 Scope and Applicability 5 

 3.2 Summary of Method 5 

 3.3 Definitions 6 

 3.4 Health and Safety Warnings 6 

 3.5 Cautions 7 

 3.6 Interferences 7 

 3.7 Personal Qualifications 8 

 3.8 Equipment and Supplies 8 

 3.9 Procedure 9 

 3.9.1 Sample Collection 9 

 3.9.2 Sample Handling and Preservation 9 

 3.9.3 Instrument Operation, Start up and Maintenance 9 

 3.9.3.1 Start up 10 

 3.9.3.2 Operation and Range Setting 10 

 3.9.9.3 Diagnostic Checks/Manual Checks 11 

 3.9.3.4 Preventive Maintenance 12 

 3.9.3.5 Instrument Troubleshooting 13 

 3.9.4 Calibration and Standardization 13 

 3.9.4.1 Adjustment to Zero Air 13 

 3.9.4.2 Adjustment to Calibration Gas 13 

 3.10 Data Analysis and Calculations 14 

 4.0 Quality Control and Quality Assurance 14 

 4.1 Precision 14 

 4.2 Bias 14 

 4.3 Representativeness 15 

 4.4 Completeness 15 

 4.5 Comparability 15 

 4.6 Method Detection Limit 15 

 5.0 References 16 
List of Tables 

Table Name and Number Page 

 3-1 Definition of Key Terms 6 

 3-2 Diagnostic Checks 12 

 3-3 Preventive Maintenance Schedule for the T-API 100AS 13 

 4-1 Measurement Quality Assurance Objectives 16 

List of Figures 

Figure Name and Number Page 

 3-1 T-API Model 100AS Flow Diagram 9 

 A-1 T-API Model 100AS Quality Control and Maintenance Record 17 

 
Teledyne-API SO2 SOP 

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STANDARD OPERATING PROCEDURES 

TELEDYNE – ADVANCED POLLUTION INSTRUMENTATION 

MODEL 100AS TRACE LEVEL SULFUR DIOXIDE INSTRUMENT 

3.0 PROCEDURES 

3.1 Scope and Applicability 

Sulfur Dioxide (SO2) is a colorless, nonflammable gas that has a strong suffocating odor. SO2 originates 

from fuel containing sulfur (mainly coal and oil) burned at power plants and during metal smelting and 

other industrial processes. High levels of SO2 can result in temporary breathing impairment for asthmatic 

children and adults who are active outdoors. Long-term exposure to high levels of SO2, in the presence of 

high levels of particulate matter, may aggravate existing cardiovascular disease and respiratory illness. 

The Teledyne-Advanced Pollution Instrumentation (T-API) model 100AS combines proven detection technology for 

the determination of trace levels of SO2. This SOP will detail the operation, preventive maintenance, cautions and 

health warnings. 

The Detection Limit (DL) for a non-trace level SO2 analyzer is 10 parts per billion (ppb) (Code of Federal 

Regulations, Volume 40, Part 53.23c, or, in the shortened format used hereafter, 40 CFR 53.23c)3

. 

However, the T-API model 100AS has an estimated DL of 100 parts per trillion (ppt), which is 

accomplished by an increased detector sensitivity, as well as increasing the length of the standard 

instrument’s optics bench. This document will discuss the Trace Level (TL) operating procedures in 

detail. 

3.2 Summary of Method 

The Model 100AS Trace Level operating principle is based on measuring the emitted fluorescence of SO2

produced by the absorption of ultraviolet (UV) light. The UV lamp emits ultraviolet radiation which 

passes through a 214 nm band pass filter, excites the SO2 molecules, producing fluorescence which is 

measured by a photomultiplier tube (PMT) with a second UV band pass filter. SO2 absorbs in the 190 nm 

– 230 nm region free of quenching by air and relatively free of other interferences. The equations 

describing the above reactions are as follows: 

 SO2 + hν1

Ia → SO2* 

The excitation ultraviolet light at any point in the system is given by: 

 Ia =I0[1-exp(-ax(SO2))] 

 where: 

 I0 = UV light intensity, 

 a = the absorption coefficient of SO2

 x = the path length 

 SO2 = concentration of SO2
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The excited SO2 decays back to the ground state emitting a characteristic fluorescence: 

 SO2* kF→ SO2 + hν2

When the SO2 concentration is relatively low, the path length of exciting light is short and the background 

is air, the above expression reduces to: 

 F = k(SO2) 

 where: 

 F = amount of fluorescent light given off 

 k = rate at which SO2* decays into SO2

The 100AS instrument operates in the following fashion: 

1. In sample mode, the sample is drawn into the analyzer through the SAMPLE bulkhead. The sample 

flows through a hydrocarbon “kicker,” which operates on a selective permeation principle, allowing 

only hydrocarbon molecules to pass through the tube wall. The driving force for the hydrocarbon 

removal is the differential partial pressure across the wall. This differential pressure is produced 

within the instrument by passing the sample gas through a capillary tube to reduce its pressure and 

feeding it into the shell side of the hydrocarbon kicker. The SO2 molecules pass through the 

hydrocarbon “kicker” unaffected.

2. The sample flows into the fluorescence chamber, where UV light is focused through a narrow 214 nm 

band pass filter into the reaction chamber, exciting the SO2 molecules; the molecules then give off 

their characteristic decay radiation. A second filter allows only the decay radiation to fall on the 

PMT. The PMT transfers the light energy into the electrical signal which is directly proportional to 

the light energy in the sample stream being analyzed. The preamp board converts this signal into a 

voltage which is further conditioned by the signal processing electronics.

3. The UV light source is measured by a UV detector. Software calculates the ratio of the PMT output 

and the UV detector in order to compensate for variations in the UV light energy. Stray light is the 

background light produced with zero ppb SO2. Once this background light is subtracted, the CPU 

will convert this electrical signal into the SO2 concentration which is directly proportional to the 

number of SO2 molecules.

3.3 Definitions

Here are some key terms for this method. 

Table 3-1 Definitions of Key Terms 

Term Definition 

DAS Data acquisition system. Used for automatic collection and 

recording of Sulfur Dioxide concentrations. 

Interferences Physical or chemical entities that cause Sulfur Dioxide 

measurements to be higher (positive) or lower (negative) than they 

would be without the entity. (See Section 3.6). 
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3.4 Health and Safety Warnings 

To prevent personal injury, please heed these warnings concerning the T-API 100AS. 

1. Always use a third ground wire on all instruments. 

2. Always unplug the analyzer when servicing or replacing parts. 

3. If it is mandatory to work inside an analyzer while it is in operation, use extreme caution to avoid 

contact with high voltages. The analyzer has a 110 volt Volts Alternating Current (VAC) power 

supply. Refer to the manufacturer's instruction manual and know the precise locations of the VAC 

components before working on the instrument. 

4. Avoid electrical contact with jewelry. Remove rings, watches, bracelets, and necklaces to prevent 

electrical bums. 

3.5 Safety Precautions 

To avoid damaging internal components of the T-API 100AS, the following precautions should be taken:

1. Wear an anti-static wrist strap that is properly connected to earth ground (note that when the analyzer 

is unplugged, the chassis is not at earth ground); 

2. If an anti-static wrist strap is not available, be sure to touch a grounded metal object before touching 

any internal components; 

3. Handle all printed circuit boards by the edge; 

4. Carefully observe the instructions in each procedure specified in Section 8 of the manual; 

5. Normally, if TeflonTM filters are used in the sample train, cleaning the optical bench will not be 

required. However, in the event that the bench is cleaned, be careful to avoid damaging the interior of 

the sample chamber. Use extreme caution when cleaning or servicing the sample chamber(s). In 

addition the mirrors are very fragile; avoid dropping the instrument. This may damage, misalign or 

crack the mirrors and cause expensive repairs; 

6. Keep the interior of the analyzer clean; 

7. Inspect the system regularly for structural integrity; 

8. To prevent major problems with leaks, make sure that all sampling lines are reconnected after 

required checks and before leaving the site; 

9. Inspect tubing for cracks and leaks; 

10. It is recommended that the analyzer be leak checked after replacement of any pneumatic parts; 

11. If cylinders are used in tandem with Mass Flow Control (MFC) calibrators, use and transport is a 

major concern. Gas cylinders can sometimes contain pressures as high as 2000 pounds per square 

inch (psi). Handling of cylinders must be done in a safe manner. If a cylinder is accidentally dropped 

and valve breaks off, the cylinder can become explosive or a projectile; 

12. Transportation of cylinders is regulated by the Department of Transportation (DOT). It is strongly 

recommended that all agencies contact the DOT or Highway Patrol to learn the most recent 

regulations concerning transport of cylinders; 

13. It is possible (and practical) to blend other compounds with SO2. If this is the case, it is 

recommended that MSDS for all compounds be made available to all staff that use and handle the 

cylinders or permeation tubes; and 

14. Shipping of cylinders is governed by the DOT. Contact the DOT or your local courier about the 

proper procedures and materials needed to ship high-pressure cylinders. 
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3.6 Interferences

The most common source of interference is from other gases that fluoresce in a similar fashion to SO2

when exposed to UV light. The most significant of these is a class of hydrocarbons called polynuclear 

aromatic hydrocarbons (PAH); of which naphthalene is a prominent example. Xylene is another 

hydrocarbon that can cause interference. These hydrocarbons are removed via the hydrocarbon “kicker” 

(see section 3.2 for explanation on the hydrocarbon “kicker”). 

Nitrogen oxide (NO) fluoresces in a spectral range close to SO2. Interference from NO is addressed by 

the presence of the band pass filter, which allows only the wavelengths emitted by the excited SO 

molecules to reach the PMT. 

3.7 Personnel Qualifications 

The person(s) chosen to operate the T-API 100AS should have a minimum of qualifications. The 

understanding of basic chemistry and electronics are a must. The understanding of digital circuitry is 

helpful, but not required. Also, courses in data processing and validation are also welcome. 

3.8 Equipment and Supplies 

Monitoring Apparatus: The T-API 100AS combines proven detection technology with advanced 

diagnostics for greater flexibility and reliability. A diagram of the T-API 100AS instrument is described 

in Figure 3-1. The three main components are: 

 Pneumatic System: Consists of sample inlet line, particulate filter, reaction chamber, flowmeter, and 

pump, all used to bring ambient air samples to the analyzer inlet. 

 Analytical System: This portion of the instrument consists of the UV lamp, mirrors, photo-detector 

and band pass filter. 

 Electronic Hardware: The part of the analyzer that generally requires little or no maintenance. If the 

T-API 100AS is operated above the manufacturer's recommended temperature limit, however, 

individual integrated chips can fail and cause problems with data storage or retrieval. 

Other apparatus and equipment includes the following. 

Instrument Shelter: A shelter is required to protect the analyzer from precipitation and adverse weather 

conditions, maintain operating temperature within the analyzer's temperature range requirements, and 

provide security and electrical power. The recommended shelter temperature range is 20-30o

C. 

Spare Parts and Incidental Supplies: See the T-API 100AS manual, Section 10, for a list of 

recommended spare parts. 

Calibration System: A system that creates concentrations of SO2 of known quality is necessary for 

establishing traceability. This is described in detail in the Environics Series 9100 Computerized Ambient 

Monitoring Calibration System SOP. Please reference this document. 

DAS: A data acquisition system is necessary for storage of ambient and ancillary data collected by the TAPI 100AS. 
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 Figure 3-1 T-API Model 100AS Flow Diagram 

Wiring, Tubing and Fittings: TeflonTM, stainless steel, and borosilicate glass are inert materials that 

should be used exclusively throughout the intake system. Stainless steel tubing should be avoided 

because it is expensive, hard to clean, and can develop micro-cracks that are difficult to detect. TeflonTM 

tubing is the best choice for the connection between the intake manifold and the T-API 100AS inlet. 

Examine and discard if particulate matter collects in the tubing. All fittings and ferrules should be made 

of TeflonTM or stainless steel. Connection wiring to the DAS should shielded two strand wire or RS-232 

cables for digital connections. 

Reagents and Standard: The T-API 100AS does not require any reagents since the instrument uses 

photometry to analyze for sulfur dioxide. All standards for the SO2 method can be obtained in 

compressed cylinders and must be NIST traceable. Please see the Environics Series 9100 Computerized 

Ambient Monitoring Calibration System SOP. 

3.9 Procedure 

3.9.1 Sample Collection: Sampling for trace level SO2 is performed by drawing ambient air through a 

sample manifold directly into the analyzer continuously via a vacuum pump. All inlet materials must be 

constructed from TeflonTM, or borosilicate glass. The siting criteria for SO2 Trace Level instruments in 

detailed in 40 CFR 58, appendix A4 . 

3.9.2 Sample Handling and Preservation: SO2 samples receive no special preparation prior to analysis. 

Therefore this SOP does not need a section on Sample Handling and Preservation.

3.9.3 Instrument Operation , Startup and Maintenance 

This section discusses startup, operation and maintenance of the T-API 100AS. The T-API 100AS has a 

digital front panel screen with pushbuttons below. This allows the user to check functions, switch 

operating parameters, and adjust zero and span. Recommend at start-up of instrument and after a warmup period for the instrument, run through the menu items and record the current settings. It is extremely 

important that the user familiarize themselves with the menus available. Inadvertently changing 

parameters within the analyzer can damage the instrument and possibly invalidate data as well. 
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Please reference the T-API 100AS owner’s manual and read it carefully before adjusting any 

parameters that are set by the factory. 

3.9.3.1 Start up

Before the instrument is operated, inspect the instrument for any damage. If damage is observed to the 

shipping box or the instrument, contact your shipping personnel. 

Carefully remove the cover and check for internal damage. Please see Section 2 of the T-API 100AS 

manual. 

Remove the red shipping screws that hold down the internal bench and parts. See Section 2 of the T-API 

100AS manual. 

Once you have removed the shipping screws and performed your inspection, replace the cover. 

Plug the instrument into a grounded power strip that has surge protection. It is also advisable to purchase 

an Uninterrupted Power Supply (UPS). An UPS will protect the T-API 100AS from power surges and 

keep the unit operating until an operator can shut it down. 

Check to see that the 100AS has enough clearance so that it gets proper ventilation. Check the T-API 

100AS manual, Section 2. 

Connect the output of the analog to a DAS via shielded two wire cable. Please see EPA SOP on “Data 

Management” for details. 

Connect the digital RS-232 port to an appropriate cable and connect it to the DAS. Please see EPA SOP 

on “Data Management” for further details. 

Connect the sample inlet port to the station intake manifold. 

Press the power rocker switch to “ON.” 

3.9.3.2 Operation and Range Setting 

1. The exhaust fan will start and the display will come on. The Central Processing Unit (CPU) will boot 

the system and load the firmware. You will see in the upper right hand corner that the fault warning 

light will be flashing red. This is letting you know that the analyzer has been off. 

2. To clear the fault warning, press the “CLR” button below the display. This will clear the warning and 

the sample green light will flash. 

3. Once the red fault light is cleared, the operator will see the main menu. At this time, the time of day 

and date must be verified and reset if necessary. 

4. From main menu press the toggle button under the “SETUP” label. 

5. In this menu, you will see “8 1 8” on the bottom of the display. This is the default password. In 

addition, you will see on the top of the display the words “ENTER SETUP PASS: 818.” 

6. At this time, press the toggle under “ENTR.” 

7. This will bring up the “PRIMARY SETUP MENU” screen. 

8. In this menu, press the toggle button under “CLK.” 

9. In the next menu, press the “TIME” toggle switch. 

10. In the next menu, you will see the time above 3 or 4 toggle switches. Adjust these toggles so that the 

time is correct. Press the “ENTR” toggle switch. 

11. This returns you to the “TIME OF DAY CLOCK” menu. Press the toggle switch under “DATE.” 

12. This will put you in the date menu. You should see the day (digits), month and year (digits) above 5 

toggle switches. Adjust these toggles until the correct date is obtained. Press the “ENTR” toggle 

switch. Press the “EXIT” toggle switch twice. This returns you to the main menu. 

13. The range should be illustrated in the top middle of the main menu. This value should be set to 100 

ppb. If it is not set to this range, then it must be reset. 

14. To change the range of the instrument, press the toggle under “SETUP.” If the password is correct, 

then press “ENTR.” 
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15. In this menu, you will see “8 1 8” on the bottom of the display. This is the default password. In 

addition, you will see on the top of the display the words “ENTER SETUP PASS: 818.” 

16. At this time, press the toggle under “ENTR.” 

17. This will bring up the “PRIMARY SETUP MENU” screen. 

18. Press the toggle switch under the “RNGE.” 

19. This is the “RANGE CONTROL MENU.” Press the toggle switch under the “UNIT.” 

20. This display will show the range options. Press the toggle under the “PPB.” Press the toggle under 

the “ENTR.” 

21. This will put you into the “RANGE CONTROL MENU.” Press the toggle switch under the “SET.” 

22. This display will show the full scale range value. Press the toggles under the digits to adjust the 

instrument to the full scale value desired. Press the toggle under the “ENTR.” 

23. Press the “EXIT” toggle switch twice. 

24. The instrument is now set with the appropriate time, date and full scale range. 

25. It is recommended that you allow the T-API 100AS 24 hours before you attempt function checks or 

calibration. 

If your DAS does not have RS-232 capabilities, then proceed to the next section, Diagnostic 

Checks/Manual Checks. If you have connected the T-API 100AS to a computer or DAS, review the 

Diagnostic Check from your computer screen. T-API offers API.COM, a computer program that allows 

the operator to log the diagnostic data that is collected by the T-API 100AS CPU. Several DAS 

manufacturers offer this type of software as well. 

3.9.3.3 Diagnostic Checks/Manual Checks 

To determine whether the T-API 100AS is working properly, the field operators should perform the 

Diagnostic Checks every time they visit the monitoring station. It is good practice for the operator to 

check these Diagnostic Checks either by the computer or manually. Below are instructions on how to 

perform this manually. Please note that the T-API 100AS has set upper and lower ranges for some of 

these Diagnostic checks. Please reference the owner’s manual for these ranges. 

1. If you observe the display, it should show “Sample” in the left hand corner, “Range” in the middle of 

the display and “SO2= XX.X.” Below this line there should be one line that read “<TST”, “TST>”, 

“CAL” and “SETUP.” 

2. There is a series of toggle switches/ buttons below the display. These correspond to the bottom row 

of the display. 

3. If you press the button below the left hand “<TST,” you will toggle the display into function check 

tree in one direction. The button under the “TST>,” will allow you to access the function check tree 

in the opposite direction. 

4. Toggle through the function check tree. The following table illustrates the functions that should be 

recorded. Please see the T-API 100AS manual for more details. A maintenance checklist is attached 

in Appendix A of this SOP.
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Table 3-2 Diagnostic Checks 

Check Explanation 

Range The full scale limit at which the reporting range of the instrument’s analog outputs 

are currently set. 

Stability The standard deviation of SO2 concentrations for the last 25 readings. 

Pressure The current pressure of the sample gas as it enters the sample chamber. 

Sample flow The flow rate of the sample gas through the sample chamber. 

PMT The raw output voltage of the PMT. 

Norm PMT The output voltage of the PMT after normalization. 

UV lamp The output voltage of the UV reference detector. 

Lamp ratio The current output of the UV reference detector divided by the reading stored in 

the CPU’s memory from the last time a UV lamp calibration was performed. 

Stray light The offset due to stray light recorded by the CPU during the last zero-point 

calibration. 

Dark PMT The PMT output reading recorded the last time the UV source lamp shutter was 

closed. 

Dark lamp The UV reference detector output reading recorded the last time the UV source 

lamp shutter was closed. 

Slope The sensitivity of the instrument as calculated during the last calibration. 

Offset The overall offset of the instrument as calculated during the last calibration. 

HVPS The PMT high voltage power supply. 

DCPS The composite of the +5 and + 15 VDC supplies. 

RCell temp The current temperature of the sample chamber. 

Box temp The ambient temperature of the inside of the analyzer case. 

PMT temp The current temperature of the PMT. 

Once the Diagnostic checks have been established and recorded for the T-API100AS, it is time to 

calibrate the instrument. Please refer to section 3.9.4 of this SOP. 

3.9.3.4 Preventive Maintenance

Preventive maintenance should prevent down-time and data loss. Table 3.3 lists the preventive 

maintenance items that are listed in the T-API 100AS manual, Section 8. 

Table 3-3 Preventive Maintenance Schedule for the 100AS

Item Schedule

 Visual inspection and cleaning Bi-annually 

 Sample particulate filter inspection Weekly 

 TEST Functions Weekly 

 Perform Level I calibration Daily 

 Pneumatic sub-system Annually, or after repairs 

 PMT sensor hardware calibration On PMT or preamp changes 

 Sample chamber windows and filters As necessary 

 Leak check Annually 

 Pump diaphragm Change annually 

 Factory calibration Annually, or after repairs 
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3.9.3.5 Instrument Troubleshooting

The T-API 100AS manual has an excellent troubleshooting guide in Section 9. 

3.9.4 Calibration and Standardization 

The calibration of the T-API 100AS is performed by comparing the output of the instrument against 

standardized gases of known quality. Generation of these gases is detailed in the Environics Series 9100 

Computerized Ambient Monitoring Calibration System SOP. This section will detail how to adjust the 

T-API 100AS to the standardized gases. Once the calibration has been performed, compare the response 

of your DAS to the calculated “source” value. If this is outside of +/-10%, then adjust the instrument 

response as detailed in the next sections. 

3.9.4.1 Adjustment to Zero Air 

Before running the zero air through the T-API 100AS, ensure that the zero air is free from contaminants. 

One way to determine if the zero air is free from contaminants is through the use of multiple zero air 

sources, and determining which source produces the lowest response.5

To adjust the output of the T-API 100AS to zero air, perform the following: 

1. Allow the instrument to sample zero air from a manifold that is at or near atmospheric pressure 

for a minimum of 15 minutes. 

2. On the bottom of the front panel screen there is a toggle switch/ button that is beneath the “CAL” 

label. Press this button. 

3. This next screen is the “M-P CAL” screen. In this screen press the button below the “ZERO” 

label. 

4. The next screen will show an “ENTR, SPAN and CONC” above the toggle switches on the 

bottom of the panel. Press the button below the “ENTR” label. This operation changes the 

calculation equation and zeros the instrument. 

Press the button below the “EXIT” label. This returns the operator to the main “SETUP” menu. 

3.9.4.2 Adjustment to Calibration Gas 

It is desirable, but not essential, to calibrate the T-API 100AS at low SO2 levels (typically, less than 20 

ppb). However, fluorescence SO2 analyzers have been shown to be inherently linear over a wide dynamic 

range. If low concentration SO2 calibration cylinders (less than 50 ppm) are used, there is the potential 

for contamination by back diffusion from a poorly purged regulator. Contamination with even a small 

amount of moisture from back diffusion can cause the SO2 concentration to become unstable; the lower 

the cylinder concentration, the more susceptible it is to any contamination from “abuse” in the field5

. The 

best way to ensure low concentration cylinders are not contaminated by back diffusion is to make sure 

whenever the cylinder valve is open, there is gas flow out of the cylinder. 

To adjust the output of the T-API 100AS to NIST traceable calibration gas, perform the following: 

1. Switch the calibration unit to generate a known concentration of SO2. Allow the instrument to 

sample calibration gas from a manifold that is at near atmospheric pressure for a minimum of 15 

minutes. 
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2. On the bottom of the front panel screen of the main menu there is a button that is beneath the 

“CAL” label. Press this button. 

3. This next screen is the “M-P CAL” screen. The next screen will show an “ENTR, SPAN and 

CONC” above the toggle switches on the bottom of the panel. Press the button below the 

“CONC” label. On the bottom line, there will be digits below each toggle button. In order to 

change the concentration, toggle each digit before and after the decimal place to get the 

concentration that is being generated in the manifold by the calibrator. At this time, press the 

“ENTR.” 

4. At this time, press the toggle below the “SPAN” switch. 

5. This operation changes the calculation equation and adjusts the slope of the instrument. 

Press the button below the “EXIT” label. This returns the operator to the main “SETUP” menu. 

3.10 Data Analysis and Calculations 

Data analysis for this analyzer is detailed in the “Data Acquisition and Management SOP.” 

4.0 QUALITY CONTROL AND QUALITY ASSURANCE

 

The following section has brief definitions of the QA/QC indicators. Table 4-1 has the Measurement 

Quality Objectives (MQOs) of the T-API 100AS. Please note that this section details primarily with the 

QA indicators. Quality Control for continuous electronic instruments, such as the T-API 100AS consists 

of performing the diagnostic checks, maintenance and calibrations. These procedures are detailed in 

sections 3.9.3 and 3.9.4: Instrument Operation, Startup and Maintenance and Calibration and 

Standardization. Appendix A has an example of a Quality Control and Maintenance Record developed by 

the EPA for this instrument.

4.1 Precision 

Precision is defined as the measure of agreement among individual measurements of the same property 

taken under the same conditions. For SO2, this refers to testing the SO2 analyzer in the field at 

concentrations between 0.0003 and 0.005 ppm. The test must be performed, at a minimum, once every 

two weeks. Calculations for Precision can be found in Reference item 3. 

4.2 Bias 

Bias is defined as the degree of agreement between a measured value and the true, expected, or accepted 

value. Quantitative comparisons are made between the measured value and the true, standard value 

during audits. Generally, three upscale points and a zero point are compared. Two audit types commonly 

used for SO2, direct comparison and blind, are discussed below. The SOP should discuss plans for each 

type of audit. 

 Direct Comparison Audits: An independent audit system is brought to the monitoring location and 

produces gas concentrations that are assayed by the monitoring station's SO2 analyzer. In most cases, 

a person outside of the agency or part of an independent QA group within the agency performs the 

audit. The responses of the on-site analyzer are then compared against the calculated concentration 

from the independent audit system and a linear regression is generated 

 Blind Audits: In blind audits (also called performance evaluation audits); agency staff are sent an 

audit device, such as the National Performance Evaluation Program (NPEP). The agency staff does 
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not know the SO2 concentrations produced by the audit equipment. Responses of the on-site analyzer 

are then compared against those of the generator and a linear regression is calculated. 

4.3 Representativeness 

Representativeness refers to whether the data collected accurately reflect the conditions being measured. 

It is the data quality indicator most difficult to quantify. Unless the samples are truly representative, the 

other indicators are meaningless. Since the NCORE Level I and II siting criteria are urban and regional, 

the trace level SO2 criteria are the same. Please reference the National Monitoring Strategy5 for a 

discussion of NCORE Level II SO2 monitoring scale. 

4.4 Completeness 

Completeness is defined as the amount of data collected compared to a pre-specified target amount. For 

SO2, EPA requires a minimum completeness of 75% (40 CFR 50, App.H.3). Typical completeness with 

the T-API 100AS values can approach 90-93%. 

4.5 Comparability 

Comparability is defined as the process of collecting data under conditions that are consistent with those 

used for other data sets of the same pollutant. The MQOs for a trace level SO2 instrument are still to be 

determined. Please see Table 4-1. 

4.6 Method Detection Limit 

The method detection limit (MDL) or detectability refers to the lowest concentration of a substance that 

can be determined by a given procedure. The T-API 100AS must be able to detect a minimum value of 

300 ppt of SO2. 
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4/26/2005 

Page 16 of 17 

Table 4-1 Measurement Quality Assurance Objectives 

Requirement Frequency Acceptance Criteria Reference Information or 

Action 

Bias NCORE, 

once per 

year 

To be determined. 40 CFR 

Pt.58 

To be determined. 

Precision 1 every 2 

weeks 

Concentration: 0.0003 

-0.005 ppm, 

Coefficient of 

Variance: To be 

determined. 

40 CFR 

Pt.58 

Appendix 

A 

To be determined.

Completeness Quarterly, 

Annually 

NCORE, 75% National 

Monitoring 

Strategy. 

If under 75%, 

institute Quality 

Control Measures 

Representativen

ess 

N/A Neighborhood, Urban 

or Regional Scale 

40 CFR 58 N/A 

Comparability N/A Must be a Trace Level 

instrument. See 

Sections 3.1 and 3.2 of 

this document. 

National 

Monitoring 

Strategy. 

N/A 

Method 

Detection Limit 

N/A 300 ppt National 

Monitoring 

Strategy 

Testing is 

performed at the 

factory. 

5.0 REFERENCES 

1. Code of Federal Regulations, Title 40, Part 53.23c 

2. Code of Federal Regulation, Title 40, Part 58, Appendix A 

3. The National Air Monitoring Strategy, Final Draft, 4/29/04, 

http://www.epa.gov/ttn/amtic/monstratdoc.html

4. Instruction Manual, T-API Model 100AS Trace Level SO2 Analyzer. 

5. Trace SO2 Monitoring Guidance for the MANE-VU Regional Aerosol Intensive Network (RAIN) 

program, Draft (dated March 7, 2005). 
Teledyne-API SO2 SOP 

Version No. 2 

4/26/2005 

Page 17 of 17 

 Appendix A

Environmental Protection Agency 

Monthly Quality Control and Maintenance Records 

Teledyne – API 100AS Ultra-Sensitivity SO2 Analyzer 

Site Name/Location ______________ __________ 

 

Technician________________ 

Month/Year_______________ 

Serial Number Range______________ 

 

Date 

Time 

 Parameters 

Acceptance 

Criteria 

Range 

Stability 

Pressure 

Sample flow 

PMT 

Norm PMT 

UV lamp 

Lamp ratio 

Stray light 

Dark PMT 

Dark lamp 

Slope 

Offset 

HVPS 

DCPS 

RCell temp 

Box temp 

PMT temp 

Other Tests 

ETest 

OTest 

 

 

Date Comments and Notes 

 

Figure A-1. T-API 100AS Quality Control and Maintenance Record 
STANDARD OPERATING PROCEDURES 

THERMO ELECTRON CORPORATION 

MODEL 43C-TLE TRACE LEVEL 

 SULFUR DIOXIDE INSTRUMENT 

Version 3 

 
 Section 1.1 Acknowledgments 

This Standard Operating Procedure (SOP) for Sulfur Dioxide – Trace Level is the product of EPA’s 

Office of Air Quality, Planning and Standards. The following individuals are acknowledged for their 

contributions. 

Principal Author 

Solomon Ricks, OAQPS-EMAD, Research Triangle Park, NC 27711 

Reviewers 

Office of Air Quality, Planning and Standards 

Joann Rice, Trace Gas Team Lead, OAQPS-EMAD, Research Triangle Park, NC 27711 

Anna Kelly, OAQPS-EMAD, Research Triangle Park, NC 27711 

Keith Kronmiller, Mantech, Inc. Research Triangle Park, NC 27711 

Comments and questions can be directed to: 

Solomon Ricks 

EPA-OAQPS 

Emission, Analysis and Monitoring Division 

Mail Drop D339-02 

Research Triangle Park, NC 27711 

Email: ricks.solomon@epa.gov

Phone: (919)-541-5242 
Section 2.0 Table of Contents

Section Page 

1.0 Title Page 1 

1.4 Acknowledgements 2 

 2.0 Table of Contents 3 

 2.1 List of Tables and Figures 4 

3.0 Procedures 5 

 3.1 Scope and Applicability 5 

 3.2 Summary of Method 5 

 3.3 Definitions 6 

 3.4 Health and Safety Warnings 6 

 3.5 Cautions 6 

 3.6 Interferences 7 

 3.7 Personal Qualifications 7 

 3.8 Equipment and Supplies 8 

 3.9 Procedure 9 

 3.9.1 Sample Collection 9 

 3.9.2 Sample Handling and Preservation 9 

 3.9.3 Instrument Operation, Start up and Maintenance 9 

 3.9.3.1 Start up 9 

 3.9.3.2 Operation and Range Setting 9 

 3.9.9.3 Diagnostic Checks/Manual Checks 10 

 3.9.3.4 Preventive Maintenance 11 

 3.9.3.5 Instrument Troubleshooting 12 

 3.9.4 Calibration and Standardization 12 

 3.9.4.1 Adjustment to Zero Air 12 

 3.9.4.2 Adjustment to Calibration Gas 12 

 3.10 Data Analysis and Calculations 12 

 4.0 Quality Control and Quality Assurance 12 

 4.1 Precision 13 

 4.2 Bias 13 

 4.3 Representativeness 13 

 4.4 Completeness 13 

 4.5 Comparability 13 

 4.6 Method Detection Limit 14 

 5.0 References 15 
List of Tables 

Table Name and Number Page 

 3-1 Definition of Key Terms 6 

 3-2 Diagnostic Checks 11 

 3-3 Preventive Maintenance Schedule for the 43C-TLE 11 

 4-1 Measurement Quality Assurance Objectives 15 

List of Figures 

Figure Name and Number Page 

 3-1 Model 43C-TLE Flow Diagram 8 

 A-1 Model 43C-TLE Quality Control and Maintenance Record 16 

 
STANDARD OPERATING PROCEDURES 

THERMO ELECTRON CORPORATION 

MODEL 43C-TLE TRACE LEVEL SULFUR DIOXIDE INSTRUMENT 

3.0 PROCEDURES 

3.1 Scope and Applicability 

Sulfur Dioxide (SO2) is a colorless, nonflammable gas that has a strong suffocating odor. SO2 originates 

from fuel containing sulfur (mainly coal and oil) burned at power plants and during metal smelting and 

other industrial processes. High levels of SO2 can result in temporary breathing impairment for asthmatic 

children and adults who are active outdoors. Long-term exposure to high levels of SO2, in the presence of 

high levels of particulate matter, may aggravate existing cardiovascular disease and respiratory illness. 

The Thermo Electron Corporation model 43C-TLE combines proven detection technology and advanced diagnostics 

for the determination of trace levels of SO2. This SOP will detail the operation, preventive maintenance, cautions 

and health warnings. 

The Detection Limit (DL) for a non-trace level SO2 analyzer is 10 parts per billion (ppb) (Code of Federal 

Regulations, Volume 40, Part 53.23c, or, in the shortened format used hereafter, 40 CFR 53.23c)3

. 

However, the 43C-TLE has an estimated DL of 100 parts per trillion (ppt), which is accomplished by an 

increased detector sensitivity, as well as increasing the length of the standard instrument’s optics bench. 

This document will discuss the Trace Level (TL) operating procedures in detail. 

3.2 Summary of Method 

The Model 43C-TLE Trace Level operating principle is based on measuring the emitted fluorescence of 

SO2 produced by the absorption of ultraviolet (UV) light. Pulsating UV light is focused through a narrow 

band-pass filter mirror allowing only light wavelengths of 190 to 230 nm to pass into the fluorescent 

chamber. SO2 absorbs light in this region without any quenching by air or most other molecules found in 

polluted air. The SO2 molecules are excited by UV light and emit a characteristic decay radiation. A 

second filter allows only this decay radiation to contact a photomultiplier tube (PMT). Electronic signal 

processing transfers the light energy impinging on the PMT into a voltage which is directly analyzed. 

Specifically, 

 SO2 + hν1 → SO2* → SO2 + hν2

 where: 

 hν1 = incidence light, 

 hν2 = fluoresced light, and 

 SO2* = SO2 in its excited state 

The 43C-TLE instrument operates in the following fashion:
 

1. In sample mode, the sample is drawn into the analyzer through the SAMPLE bulkhead. The sample 

flows through a hydrocarbon “kicker,” which operates on a selective permeation principle, allowing 

only hydrocarbon molecules to pass through the tube wall. The driving force for the hydrocarbon 

removal is the differential partial pressure across the wall. This differential pressure is produced 

within the instrument by passing the sample gas through a capillary tube to reduce its pressure and 

feeding it into the shell side of the hydrocarbon kicker. The SO2 molecules pass through the 

hydrocarbon “kicker” unaffected. 

2. The sample flows into the fluorescence chamber, where pulsating UV light excites the SO2

molecules. The condensing lens focuses the pulsating UV light into the mirror assembly. The mirror 

assembly contains eight selective mirrors that reflect only the wavelengths which excite SO2

molecules. 

3. As the excited SO2 molecules decay to lower energy states they emit UV light that is proportional to 

the SO2 concentration. The band pass filter allows only the wavelengths emitted by the excited SO2

molecules to reach the PMT. The PMT detects the UV light emission from the decaying SO2

molecules. The photo detector, located at the back of the fluorescence chamber, continuously 

monitors the pulsating UV light source and is connected to a circuit that compensates for fluctuations 

in the UV light. 

4. The sample then flows through a flow sensor, a capillary, and the shell side of the hydrocarbon 

“kicker.” The model 43C-TLE trace level outputs the SO2 concentration to the front panel display 

and the analog or digital outputs. 

3.3 Definitions

Here are some key terms for this method. 

Table 3-1 Definitions of Key Terms 

Term Definition 

DAS Data acquisition system. Used for automatic collection and 

recording of Sulfur Dioxide concentrations. 

Interferences Physical or chemical entities that cause Sulfur Dioxide 

measurements to be higher (positive) or lower (negative) than they 

would be without the entity. (See Section 3.6). 

3.4 Health and Safety Warnings 

To prevent personal injury, please heed these warnings concerning the 43C-TLE. 

1. Always use a third ground wire on all instruments. 

2. Always unplug the analyzer when servicing or replacing parts. 

3. If it is mandatory to work inside an analyzer while it is in operation, use extreme caution to avoid 

contact with high voltages. The analyzer has a 110 volt Volts Alternating Current (VAC) power 

supply. Refer to the manufacturer's instruction manual and know the precise locations of the VAC 

components before working on the instrument. 

4. Avoid electrical contact with jewelry. Remove rings, watches, bracelets, and necklaces to prevent 

electrical bums. 

3.5 Safety Precautions 

To avoid damaging internal components of the 43C-TLE, the following precautions should be taken:
1. Wear an anti-static wrist strap that is properly connected to earth ground (note that when the analyzer 

is unplugged, the chassis is not at earth ground); 

2. If an anti-static wrist strap is not available, be sure to touch a grounded metal object before touching 

any internal components; 

3. Handle all printed circuit boards by the edge; 

4. Carefully observe the instructions in each procedure specified in Chapter 7 of the manual; 

5. Normally, if TeflonTM filters are used in the sample train, cleaning the optical bench will not be 

required. However, in the event that the bench is cleaned, be careful to avoid damaging the interior of 

the sample chamber. Use extreme caution when cleaning or servicing the sample chamber(s). In 

addition the mirrors are very fragile; avoid dropping the instrument. This may damage, misalign or 

crack the mirrors and cause expensive repairs; 

6. Keep the interior of the analyzer clean; 

7. Inspect the system regularly for structural integrity; 

8. To prevent major problems with leaks, make sure that all sampling lines are reconnected after 

required checks and before leaving the site; 

9. Inspect tubing for cracks and leaks; 

10. It is recommended that the analyzer be leak checked after replacement of any pneumatic parts; 

11. If cylinders are used in tandem with Mass Flow Control (MFC) calibrators, use and transport is a 

major concern. Gas cylinders can sometimes contain pressures as high as 2000 pounds per square 

inch (psi). Handling of cylinders must be done in a safe manner. If a cylinder is accidentally dropped 

and valve breaks off, the cylinder can become explosive or a projectile; 

12. Transportation of cylinders is regulated by the Department of Transportation (DOT). It is strongly 

recommended that all agencies contact the DOT or Highway Patrol to learn the most recent 

regulations concerning transport of cylinders; 

13. It is possible (and practical) to blend other compounds with SO2. If this is the case, it is 

recommended that MSDS for all compounds be made available to all staff that use and handle the 

cylinders or permeation tubes; and 

14. Shipping of cylinders is governed by the DOT. Contact the DOT or your local courier about the 

proper procedures and materials needed to ship high-pressure cylinders. 

3.6 Interferences

The most common source of interference is from other gases that fluoresce in a similar fashion to SO2

when exposed to UV light. The most significant of these is a class of hydrocarbons called polynuclear 

aromatic hydrocarbons (PAH); of which naphthalene is a prominent example. Xylene is another 

hydrocarbon that can cause interference. These hydrocarbons are removed via the hydrocarbon “kicker” 

(see section 3.2 for explanation on the hydrocarbon “kicker”). 

Nitrogen oxide (NO) fluoresces in a spectral range close to SO2. Interference from NO is addressed by 

the presence of the band pass filter, which allows only the wavelengths emitted by the excited SO 

molecules to reach the PMT. 
3.7 Personnel Qualifications 

The person(s) chosen to operate the Thermo 43C-TLE should have a minimum of qualifications. The 

understanding of basic chemistry and electronics are a must. The understanding of digital circuitry is 

helpful, but not required. Also, courses in data processing and validation are also welcome. 

3.8 Equipment and Supplies 

Monitoring Apparatus: The design of the 43C-TLE combines proven detection technology with 

advanced diagnostics for greater flexibility and reliability. A diagram of the 43C-TLE instrument is 

described in Figure 3-1. The three main components are: 

 Pneumatic System: Consists of sample inlet line, particulate filter, reaction chamber, flowmeter, and 

pump, all used to bring ambient air samples to the analyzer inlet. 

 Analytical System: This portion of the instrument consists of the UV lamp, mirrors, photo-detector 

and band pass filter. 

 Electronic Hardware: The part of the analyzer that generally requires little or no maintenance. If the 

43C-TLE is operated above the manufacturer's recommended temperature limit, however, individual 

integrated chips can fail and cause problems with data storage or retrieval. 

Other apparatus and equipment includes the following. 

Instrument Shelter: A shelter is required to protect the analyzer from precipitation and adverse weather 

conditions, maintain operating temperature within the analyzer's temperature range requirements, and 

provide security and electrical power. The recommended shelter temperature range is 20-30o

C. 

Spare Parts and Incidental Supplies: See the 43C-TLE manual, Chapter 5, for a list of recommended 

spare parts. 

Calibration System: A system that creates concentrations of SO2 of known quality is necessary for 

establishing traceability. This is described in detail in the Environics Series 9100 Computerized Ambient 

Monitoring Calibration System SOP. Please reference this document. 

DAS: A data acquisition system is necessary for storage of ambient and ancillary data collected by the 

43C-TLE. 
 Figure 3-1 Model 43C-TLE Flow Diagram 

Wiring, Tubing and Fittings: TeflonTM, stainless steel, and borosilicate glass are inert materials that 

should be used exclusively throughout the intake system. Stainless steel tubing should be avoided 

because it is expensive, hard to clean, and can develop micro-cracks that are difficult to detect. TeflonTM 

tubing is the best choice for the connection between the intake manifold and the 43C-TLE inlet. Examine 

and discard if particulate matter collects in the tubing. All fittings and ferrules should be made of 

TeflonTM or stainless steel. Connection wiring to the DAS should shielded two strand wire or RS-232 

cables for digital connections. 

Reagents and Standard: The 43C-TLE does not require any reagents since the instrument uses 

photometry to analyze for sulfur dioxide. All standards for the SO2 method can be obtained in 

compressed cylinders and must be NIST traceable. Please see the Environics Series 9100 Computerized 

Ambient Monitoring Calibration System SOP. 

3.9 Procedure 

3.9.1 Sample Collection: Sampling for trace level SO2 is performed by drawing ambient air through a 

sample manifold directly into the analyzer continuously via a vacuum pump. All inlet materials must be 

constructed from TeflonTM, or borosilicate glass. The siting criteria for SO2 Trace Level instruments in 

detailed in 40 CFR 58, appendix A4 . 

3.9.2 Sample Handling and Preservation: SO2 samples receive no special preparation prior to analysis. 

Therefore this SOP does not need a section on Sample Handling and Preservation.

3.9.3 Instrument Operation , Startup and Maintenance 

This section discusses startup, operation and maintenance of the 43C-TLE. The 43C-TLE has a digital 

front panel screen with pushbuttons below. This allows the user to check functions, switch operating 

parameters, and adjust zero and span. Recommend at start-up of instrument and after a warm-up period 

for the instrument, run through the menu items and record the current settings. It is extremely important 

that the user familiarize themselves with the menus available. Inadvertently changing parameters 

within the analyzer can damage the instrument and possibly invalidate data as well. Please 

reference the Thermo 43C-TLE owner’s manual and read it carefully before adjusting any 

parameters that are set by the factory. 
3.9.3.1 Start up 

Before the instrument is operated, inspect the instrument for any damage. If damage is observed to the 

shipping box or the instrument, contact your shipping personnel. 

Carefully remove the cover and check for internal damage. Please see Chapter 2 of the 43C-TLE 

manual. 

Check that all connectors and printed circuit boards are firmly attached. 

Once you have removed any packing material and performed your inspection, replace the cover. 

Connect the sample line to the SAMPLE bulkhead on the rear panel of the instrument. See Chapter 2 of 

the 43C-TLE manual. 

Connect the EXHAUST bulkhead to a suitable vent. 

Connect a suitable recording device to the rear panel terminals. Please see EPA SOP on “Data 

Management” for details. 

Plug the instrument into a grounded power strip that has surge protection. It is also advisable to purchase 

an Uninterrupted Power Supply (UPS). An UPS will protect the 43C-TLE from power surges and 

keep the unit operating until an operator can shut it down. 

Press the power rocker switch to “ON.” 

3.9.3.2 Operation and Range Setting 

1. The exhaust fan will start and the Power-Up and Self-Test screens will be displayed. These screens 

are displayed each time the instrument is turned on, and will continue to be displayed till the 

instrument has completed its warm up and self-checks. You should allow 30 minutes for the 

instrument to stabilize. 

2. After the warm-up period the Run screen, the normal operating screen, is displayed. This screen is 

where the SO2 concentration is displayed. 

3. From the Run screen, the Main Menu, which contains a list of submenus, can be displayed by 

pressing the MENU pushbutton. If the instrument is in REMOTE mode, press ENTER and select 

LOCAL mode in order to be able to change parameters. 

4. Instrument parameters and features are divided into the submenus according to their function. Use 

the UP/DOWN ARROW pushbuttons to move the cursor to each submenu. Note: When the Main 

Menu is entered directly from the Run screen, the LEFT ARROW pushbutton may be used to jump 

to the most recently displayed submenu screen. 

5. To set the range for the instrument, press the DOWN ARROW pushbutton till the cursor is on 

“Range.” Press the ENTER pushbutton to display the Range Menu. 

6. In the upper right corner of the display, the word SINGLE, DUAL, or AUTO is displayed to indicate 

the active mode. For a detailed explanation about the SINGLE, DUAL, or AUTORANGE mode, see 

Chapter 3 (page 3-7) of the manual. This SOP addresses setting the range for a single range. 

7. Press the ENTER pushbutton for the Gas Units screen. Use the DOWN ARROW pushbutton to 

select “PPB” and press ENTER. Press MENU to return to the Range Menu. 

8. Use the DOWN ARROW pushbutton to display the Range screen and press ENTER. 

9. Use the UP/DOWN ARROW pushbuttons to scroll through the preset ranges. Select “100.0” and 

press ENTER. Press MENU to return to the Range Menu. 

10. Press RUN to return to the Run screen. 

11. To set the correct time and date on the instrument, press MENU to return to the Main Menu. Press 

the DOWN ARROW pushbutton till the cursor is on Instrument Controls. Press ENTER to display 

the Instrument Controls screen. 

12. Use the UP/DOWN ARROW pushbuttons to scroll through the choices. Select “Time” and press 

ENTER. 

13. Use the UP/DOWN ARROW pushbuttons to increase/decrease the hours and minutes; use the 

LEFT/RIGHT ARROW pushbuttons to move the cursor left and right. Set the appropriate time and 

press ENTER. Press MENU to return to the Instrument Controls screen. 
14. Select “Date” and press ENTER. 

15. Use the UP/DOWN ARROW pushbuttons to increase/decrease the month, day, and year; use the 

LEFT/RIGHT ARROW pushbuttons to move the cursor left and right. Set the appropriate date and 

press ENTER. Press RUN to return to the Run screen. 

16. The instrument is now set with the appropriate time, date, full scale range and units. 

17. It is recommended that you allow the 43C-TLE 24 hours before you attempt function checks or 

calibration. 

18. If your DAS does not have RS-232 capabilities, then proceed to the next section, Diagnostic 

Checks/Manual Checks. If you have connected the 43C-TLE to a computer or DAS, review the 

Diagnostic Check from your computer screen.

3.9.3.3 Diagnostic Checks/Manual Checks 

To determine whether the 43C-TLE is working properly, the field operators should perform the 

Diagnostic Checks every time they visit the monitoring station. It is good practice for the operator to 

check these Diagnostic Checks either by the computer or manually. Below are instructions on how to 

perform this manually. Please note that the 43C-TLE has set upper and lower ranges for some of these 

Diagnostic checks. Please reference the owner’s manual for these ranges. 

1. To display the Diagnostics menu, from the Run screen press the MENU pushbutton to display the 

Main Menu. Use the UP/DOWN ARROW pushbuttons to move the cursor to “Diagnostics.” Press 

ENTER for the Diagnostics screen. 

2. Use the UP/DOWN ARROW pushbuttons to toggle through the function check tree. The following 

table illustrates the functions that should be recorded. Please see Chapter 3 (page 3-34) 43C-TLE 

manual for more details. A maintenance check sheet is attached in Appendix A of this SOP. 

3. On the Program Number screen, the version numbers of the program installed are displayed. Prior to 

contacting the factory with any questions regarding the instrument, note the program numbers. 
Table 3-2 Diagnostic Checks 

Check Explanation 

Voltages The current DC power supply and PMT power supply voltages 

Temperatures The current internal instrument and chamber temperatures 

Pressure The current chamber pressure 

Flow The current sample flow rate 

Lamp intensity The current UV lamp intensity 

Optical Span Test A quick way of checking the optics and electronics for span drift 

Test Analog Outputs Enable analog outputs to be set to zero and full scale to adjust analog outputs to 

agree with the front panel display 

Once the Diagnostic checks have been established and recorded for the 43C-TLE, it is time to calibrate 

the instrument. Please refer to section 3.9.4 of this SOP. 

3.9.3.4 Preventive Maintenance

Preventive maintenance should prevent down-time and data loss. Table 3.3 lists the preventive 

maintenance items that are listed in the model 43C-TLE manual, Chapter 5. The maintenance procedures 

described in Chapter 5 of the manual should be performed every six months. 

Table 3-3 Preventive Maintenance Schedule for the 43C-TLE

Item Schedule

 Visual inspection and cleaning Bi-annually 

 Sample particulate filter inspection Weekly 

 Verify Test Function Weekly 

 Perform Level I calibration Daily 

 Capillary inspection and replacement Bi-annually 

 Perform flow check Bi-annually 

 Fan filter inspection and cleaning Bi-annually 

 Lamp voltage check Bi-annually 

3.9.3.5 Instrument Troubleshooting

The 43C-TLE manual has an excellent troubleshooting guide in Chapter 6. 

3.9.4 Calibration and Standardization 

The calibration of the 43C-TLE is performed by comparing the output of the instrument against 

standardized gases of known quality. Generation of these gases is detailed in the Environics Series 9100 

Computerized Ambient Monitoring Calibration System SOP. This section will detail how to adjust the 

43C-TLE to the standardized gases. Once the calibration has been performed, compare the response of 

your DAS to the calculated “source” value. If this is outside of +/-10%, then adjust the instrument 

response as detailed in the next sections. 

3.9.4.1 Adjustment to Zero Air 

Before running the zero air through the 43C-TLE, ensure that the zero air is free from contaminants. One 

way to determine if the zero air is free from contaminants is through the use of multiple zero air sources, 

and determining which source produces the lowest response5

. Appendix D of the 43C-TLE manual 

provides suggestions for generating trace-quality zero air. 
In order to adjust the output of the 43C-TLE to zero air, perform the following: 

1. Allow the instrument to sample zero air from a manifold that is at near atmospheric pressure for a 

minimum of 15 minutes. 

2. From the Main Menu select the Calibration menu; select the “Calibrate Zero” screen. 

3. Press ENTER to set the SO2 reading to zero. 

4. Press MENU to return to the Calibration menu. 

5. Press RUN to return to the Run screen. 

3.9.4.2 Adjustment to Calibration Gas

It is desirable, but not essential, to calibrate the 43C-TLE at low SO2 levels (typically, less than 20 ppb). 

However, fluorescence SO2 analyzers have been shown to be inherently linear over a wide dynamic 

range. If low concentration SO2 calibration cylinders (less than 50 ppm) are used, there is the potential 

for contamination by back diffusion from a poorly purged regulator. Contamination with even a small 

amount of moisture from back diffusion can cause the SO2 concentration to become unstable; the lower 

the cylinder concentration, the more susceptible it is to any contamination from “abuse” in the field5. The 

best way to ensure low concentration cylinders are not contaminated by back diffusion is to make sure 

whenever the cylinder valve is open, there is gas flow out of the cylinder. 

Appendix D of the 43C-TLE manual offers additional discussion on trace level calibration issues. 

In order to adjust the output of the 43C-TLE to NIST traceable calibration gas, perform the following: 

1. Switch the calibration unit to generate a known concentration of SO2. Allow the instrument to 

sample calibration gas from a manifold that is at near atmospheric pressure for a minimum of 15 

minutes. 

2. From the Main Menu select the Calibration menu; select the “Calibrate SO2” screen. 

3. On the bottom line, there will be individual digits with which the span value can be set. In order 

to change the concentration, use the UP/DOWN ARROW pushbuttons to increase/decrease 

each digit; use the LEFT/RIGHT ARROW pushbuttons to move the cursor left and right. 

4. Press ENTER to calibrate the SO2 reading to the SO2 calibration gas. 

5. This operation changes the calculation equation and adjusts the SO2 span coefficient of the 

instrument. 

6. Press MENU to return to the Calibration menu. 

7. Press RUN to return to the Run screen. 

3.10 Data Analysis and Calculations 

Data analysis for this analyzer is detailed in the “Data Acquisition and Management SOP.” 

4.0 QUALITY CONTROL AND QUALITY ASSURANCE

 

The following section has brief definitions of the QA/QC indicators. Table 4-1 has the Measurement 

Quality Objectives (MQOs) of the Thermo 43C-TLE. Please note that this section details primarily with 

the QA indicators. Quality Control for continuous electronic instruments, such as the 43C-TLE consists 

of performing the diagnostic checks, maintenance and calibrations. These procedures are detailed in 

sections 3.9.3 and 3.9.4: Instrument Operation, Startup and Maintenance and Calibration and 

Standardization. Appendix A has an example of a Quality Control and Maintenance Record developed by 

the EPA for this instrument. 
4.1 Precision 

Precision is defined as the measure of agreement among individual measurements of the same property 

taken under the same conditions. For SO2, this refers to testing the SO2 analyzer in the field at 

concentrations between 0.0003 and 0.005 ppm. The test must be performed, at a minimum, once every 

two weeks. Calculations for Precision can be found in Reference item 3. 

4.2 Bias 

Bias is defined as the degree of agreement between a measured value and the true, expected, or accepted 

value. Quantitative comparisons are made between the measured value and the true, standard value 

during audits. Generally, three upscale points and a zero point are compared. Two audit types commonly 

used for SO2, direct comparison and blind, are discussed below. The SOP should discuss plans for each 

type of audit. 

 Direct Comparison Audits: An independent audit system is brought to the monitoring location and 

produces gas concentrations that are assayed by the monitoring station's SO2 analyzer. In most cases, 

a person outside of the agency or part of an independent QA group within the agency performs the 

audit. The responses of the on-site analyzer are then compared against the calculated concentration 

from the independent audit system and a linear regression is generated 

 Blind Audits: In blind audits (also called performance evaluation audits); agency staff are sent an 

audit device, such as the National Performance Evaluation Program (NPEP). The agency staff does 

not know the SO2 concentrations produced by the audit equipment. Responses of the on-site analyzer 

are then compared against those of the generator and a linear regression is calculated. 

4.3 Representativeness 

Representativeness refers to whether the data collected accurately reflect the conditions being measured. 

It is the data quality indicator most difficult to quantify. Unless the samples are truly representative, the 

other indicators are meaningless. Since the NCORE Level I and II siting criteria are urban and regional, 

the trace level SO2 criteria are the same. Please reference the National Monitoring Strategy5 for a 

discussion of NCORE Level II SO2 monitoring scale. 

4.4 Completeness 

Completeness is defined as the amount of data collected compared to a pre-specified target amount. For 

SO2, EPA requires a minimum completeness of 75% (40 CFR 50, App.H.3). Typical completeness with 

the 43C-TLE values can approach 90-93%. 

4.5 Comparability 

Comparability is defined as the process of collecting data under conditions that are consistent with those 

used for other data sets of the same pollutant. The 43C-TLE meets the MQOs for a trace level SO2

instrument. Please see Table 4-1. 

4.6 Method Detection Limit 

The method detection limit (MDL) or detectability refers to the lowest concentration of a substance that 

can be determined by a given procedure. The 43C-TLE must be able to detect a minimum value of 300 

ppt of SO2. 
Table 4-1 Measurement Quality Assurance Objectives 

Requirement Frequency Acceptance Criteria Reference Information or 

Action 

Bias NCORE, 

once per 

year 

To be determined. 40 CFR 

Pt.58 

To be determined. 

Precision 1 every 2 

weeks 

Concentration: 0.0003 

-0.005 ppm, 

Coefficient of 

Variance: To be 

determined. 

40 CFR 

Pt.58 

Appendix 

A 

To be determined.

Completeness Quarterly, 

Annually 

NCORE, 75% National 

Monitoring 

Strategy. 

If under 75%, 

institute Quality 

Control Measures 

Representativen

ess 

N/A Neighborhood, Urban 

or Regional Scale 

40 CFR 58 N/A 

Comparability N/A Must be a Trace Level 

instrument. See 

Sections 3.1 and 3.2 of 

this document. 

National 

Monitoring 

Strategy. 

N/A 

Method 

Detection Limit 

N/A 300 ppt National 

Monitoring 

Strategy 

Testing is 

performed at the 

factory. 

5.0 REFERENCES 

1. Code of Federal Regulations, Title 40, Part 53.23c 

2. Code of Federal Regulation, Title 40, Part 58, Appendix A 

3. The National Air Monitoring Strategy, Final Draft, 4/29/04, 

http://www.epa.gov/ttn/amtic/monstratdoc.html

4. Instruction Manual, Model 43C Trace Level SO2 Analyzer 

5. Trace SO2 Monitoring Guidance for the MANE-VU Regional Aerosol Intensive Network (RAIN) 

program, Draft (dated March 7, 2005). 
 Appendix A

Environmental Protection Agency 

Monthly Quality Control and Maintenance Records 

Thermo 43C-TLE SO2 Analyzer 

Site Name/Location ________________________ 

 

Technician________________ 

Month/Year_______________ 

Serial Number Range______________ 

 

Parameter Date Date Date Acceptance 

Criteria 

DC Voltage 

PMT Voltage 

Internal Temp 

Chamber Temp 

Chamber 

Pressure 

 

Sample Flow 

UV Lamp 

Intensity 

 

 

Other Tests 

Optical Span 

Test 

 

 

 

Date Comments and Notes 

 

Figure A-1 Thermo 43C-TLE Quality Control and Maintenance Record 
STANDARD OPERATING PROCEDURES 

THERMO ENVIRONMENTAL INSTRUMENTS 

42CY NOy TRACE LEVEL 

 REACTIVE NITROGEN COMPOUNDS INSTRUMENT 

Version 3

 

 
 

Section 1.1 Acknowledgments 

This Standard Operating Procedure (SOP) for Trace Level Reactive Nitrogen Compounds is the product 

of EPA’s Office of Air Quality, Planning and Standards. The following individuals are acknowledged for 

their contributions. 

Principal Author 

Kevin A. Cavender, OAQPS-EMAD, Research Triangle Park, NC 27711 

Reviewers 

Office of Air Quality, Planning and Standards 

Joann Rice, Trace Gas Team Lead, OAQPS-EMAD, Research Triangle Park, NC 27711 

Anna Kelly, OAQPS-EMAD, Research Triangle Park, NC 27711 

Keith Kronmiller, Mantech, Inc. Research Triangle Park, NC 27711 

Comments and questions can be directed to: 

Kevin A. Cavender 

EPA-OAQPS 

Emission, Analysis and Monitoring Division 

Mail Drop C339-02 

Research Triangle Park, NC 27711 

Email: cavender.kevin@epa.gov

Phone: (919)-541-2364 
 

Section 2.0 Table of Contents

Section Page 

1.0 Title Page 1 

1.5 Acknowledgements 2 

 2.0 Table of Contents 3 

 2.1 List of Tables and Figures 4 

3.0 Procedures 5 

 3.1 Scope and Applicability 5 

 3.2 Summary of Method 5 

 3.3 Definitions 7 

 3.4 Health and Safety Warnings 7 

 3.5 Cautions 7 

 3.6 Interferences 8 

 3.7 Personal Qualifications 8 

 3.8 Equipment and Supplies 8 

 3.9 Procedure 10 

 3.9.1 Sample Collection 10 

 3.9.2 Sample Handling and Preservation 10 

 3.9.3 Instrument Operation, Start up and Maintenance 10 

 3.9.3.1 Start up 10 

 3.9.3.2 Operation and Range Setting 11 

 3.9.9.3 Diagnostic Checks/Manual Checks 12 

 3.9.3.4 Preventive Maintenance 13 

 3.9.3.5 Instrument Troubleshooting 13 

 3.9.4 Calibration and Standardization 13 

 3.9.4.1 Adjustment to Zero Air 14 

 3.9.4.2 Adjustment to Calibration Gas 14 

 3.10 Data Analysis and Calculations 15 

 4.0 Quality Control and Quality Assurance 15 

 4.1 Precision 15 

 4.2 Bias 15 

 4.3 Representativeness 16 

 4.4 Completeness 16 

 4.5 Comparability 16 

 4.6 Method Detection Limit 16 

 5.0 References 17 
 

List of Tables 

Table Name and Number Page 

 3-1 Definition of Key Terms 7 

 3-2 Diagnostic Checks 13 

 3-3 Preventive Maintenance Schedule for the 42CY 13 

 4-1 Measurement Quality Assurance Objectives 17 

List of Figures 

Figure Name and Number Page 

 3-1 Simplified Flow Diagram of 42CY Monitor 6 

 3-2 Schematic of plumbing and wiring for 42CY External Converter 11 
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STANDARD OPERATING PROCEDURES 

THERMO ENVIRONMENTAL INSTRUMENTS 

42CY NOy TRACE LEVEL 

REACTIVE NITROGEN COMPOUNDS INSTRUMENT 

3.0 PROCEDURES 

3.1 Scope and Applicability 

Reactive nitrogen compounds (NOy) have been identified as precursors for both ozone and fine particulate 

matter (PM2.5). Measurements of NOy constitute a valuable adjunct to current NO and NO2 monitoring 

because the individual species comprising NOy include not only NO and NO2 but also other organic 

nitroxyl compounds that have recently been shown to play a significant role in the photochemical O3

formation process. 

NOy consists of all oxides of nitrogen in which the oxidation state of the N atom is +2 or greater, ie, the 

sum of all reactive nitrogen oxides including NOx (NO + NO2) and other nitrogen oxides referred to as 

NOz. The major components of NOz include nitrous acids [nitric acid (HNO3), and nitrous acid 

(HONO)], organic nitrates [peroxyl acetyl nitrate (PAN), methyl peroxyl acetyl nitrate (MPAN), and 

peroxyl propionyl nitrate, (PPN)], and particulate nitrates. 

NO + NO2 + NOz = NOy

The Thermo Environmental Instruments (TECO) model 42CY is an instrument for the determination of trace levels 

of NOy by its chemiluminescent reaction with O3. This SOP will detail the operation, calibration, preventive 

maintenance, cautions and health warnings. 

3.2 Summary of Method 

The analytical principle is based on the chemiluminescent reaction of NO with an excess of O3. This 

reaction produces a characteristic near infrared luminescence with an intensity that is linearly proportional 

to the concentration of NO present. Specifically, 

 NO + O3 → NO2 + O2 + hν

where: 

 hν = emitted photon energy 

The reaction results in electronically excited NO2 molecules which revert to their ground state, 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 O3 reaction. The electronic signal produced in the 

photomultiplier is proportional to the NO concentration. 

To measure NOy, sample air is passed through a probe-mounted chemical reduction converter and the 

nitroxyl compounds present are reduced to NO. The sample is then blended with O3 and the 
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chemiluminescent response is proportional to the concentration of NOy entering the converter. The 

chemical reduction converter uses heated molybdenum to convert non-NO NOy species to NO. 

Specifically, 

 NO2/Z + Mo → NO + MoO3 

where: 

 Mo = heated molybdenum reductant 

The concentration of NO2 + NOz is calculated as the difference between a measured NOy value and a 

measured NO value representing approximately the same point in time. This procedure is similar to the 

current methodology used to measure NOx, however, the converter temperature is higher in order to 

enhance conversion of NOz species. In addition, the converter has been moved to the sample inlet to 

avoid line losses of “sticky” NOy species such as HNO3. 

A diagram of the 42CY instrument is presented in Figure 3-1. For the 42CY, ambient sample is first 

drawn through a short Teflon sample line and split into two parallel flow channels using a 1⁄2 inch PFT 

Teflon tee. Channel 1 passes through a Teflon filter and then directly to the monitor. Channel 2 first 

passes through a catalytic converter before going through a Teflon filter to the monitor. Flow from each 

channel is alternately fed to the reaction chamber to detect the NO. The converter is operated outside of 

the analyzer, close to the ambient sampling point. This allows for a short flow path upstream of the 

converter and minimizes the loss of species such as HNO3. In addition to alternating flows from Channel 

1 and Channel 2 to the reactor, the analyzer also alternates a flow of internal zero air, produced by prereacting the sample flow with a high concentration of ozone before reaching the chemiluminescent 

detector. The signal from this zero air stream is used to correct for analyzer drift, and allows the analyzer 

to achieve very low detection limits (0.05 ppb) compared with standard NOx analyzers. 

Figure 3-1. Simplified Flow Diagram of 42CY NOy Monitor 
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3.3 Definitions

Here are some key terms for this method. 

Table 3-1 Definitions of Key Terms 

Term Definition 

NOy Total reactive nitrogen including NO, NO2, HNO3, and other 

reactive organic nitrogen compounds. 

NOz Reactive nitrogen compounds other than NO and NO2. 

DAS Data acquisition system. Used for automatic collection and 

recording of Carbon Monoxide concentrations. 

Interferences Physical or chemical entities that cause NOy measurements to be 

higher (positive) or lower (negative) than they would be without the 

entity. (See Section 3.6). 

3.4 Health and Safety Warnings 

To prevent personal injury, please heed these warnings concerning the 42CY. 

1. Nitrogen oxides are a poisonous gas. Vent any nitrogen oxide or calibration span gas to the 

atmosphere rather than into the shelter or other sampling area. If this is impossible, limit exposure 

to nitrogen oxide by getting fresh air every 5 to 10 minutes. If the operator experiences light 

headedness, headache or dizziness, leave the area immediately. 

2. Always use a third ground wire on all instruments. 

3. Always unplug the analyzer when servicing or replacing parts. 

4. If it is mandatory to work inside an analyzer while it is in operation, use extreme caution to avoid 

contact with high voltages. The analyzer has a 110 volt Volts Alternating Current (VAC) power 

supply. Refer to the manufacturer's instruction manual and know the precise locations of the VAC 

components before working on the instrument. 

5. Avoid electrical contact with jewelry. Remove rings, watches, bracelets, and necklaces to prevent 

electrical bums. 

3.5 Cautions 

To prevent damage to the 42CY, all cautions should immediately precede the applicable step in this SOP. The following precautions 

should be taken:

1. Keep the interior of the analyzer clean. 

2. Inspect the system regularly for structural integrity. 

3. To prevent major problems with leaks, make sure that all sampling lines are reconnected after 

required checks and before leaving the site. 

4. Inspect tubing for cracks and leaks. 

5. It is recommended that the analyzer be leak checked after replacement of any pneumatic parts. 

6. If cylinders are used in tandem with Mass Flow Control (MFC) calibrators, use and transport is a 

major concern. Gas cylinders can sometimes contain pressures as high as 2000 pounds per square 

inch (psi). Handling of cylinders must be done in a safe manner. If a cylinder is accidentally dropped 

and valve breaks off, the cylinder can become explosive or a projectile. 
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7. Transportation of cylinders is regulated by the Department of Transportation (DOT). It is strongly 

recommended that all agencies contact the DOT or Highway Patrol to learn the most recent 

regulations concerning transport of cylinders. 

8. Low levels of nitrogen oxides in the air can irritate your eyes, nose, throat, and lungs, possibly 

causing you to cough and experience shortness of breath, tiredness, and nausea. Exposure to low 

levels can also result in fluid build-up in the lungs 1 or 2 days after exposure. Breathing high levels of 

nitrogen oxides can cause rapid burning, spasms, and swelling of tissues in the throat and upper 

respiratory tract, reduced oxygenation of body tissues, a build-up of fluid in your lungs, and death. 

9. It is possible (and practical) to blend other compounds with NO. If this is the case, it is recommended 

that MSDS for all compounds be made available to all staff that use and handle the cylinders or 

permeation tubes. 

10. Shipping of cylinders is governed by the DOT. Contact the DOT or your local courier about the 

proper procedures and materials needed to ship high-pressure cylinders. 

3.6 Interferences

Ammonia: Depending on the converter temperature, the converter may convert a small amount of 

ammonia (NH3) to NO, resulting in increased NO readings. However, under normal circumstances NH3

concentrations are low compared to NO and this positive interference is negligible. Nonetheless, care 

should be taken when siting the monitor to be sure that it is not located near significant NH3 sources 

which could cause elevated NH3 concentrations (e.g., concentrated animal feeding operations). 

3.7 Personal Qualifications 

The person(s) chosen to operate the 42CY should have a minimum of qualifications. The understanding 

of basic chemistry and electronics are a must. The understanding of digital circuitry is helpful, but not 

required. Also, courses in data processing and validation are also welcome. 

3.8 Equipment and Supplies 

Monitoring Apparatus: The design of the 42CY is similar to the 42C with several major variations. A 

diagram of the 42CY instrument is presented in Figure 3-1. The four main components are: 

 Remote Inlet and Converter: This component consists of a weather resistant enclosure that houses the 

molybdenum converter and supports the sample inlet. 

 Pneumatic System: Consists of sample inlet lines, sample bypass pump, particulate filters, reaction 

chamber, flowmeters, and vacuum pump, all used to bring ambient air samples to the analyzer. 

 Analytical System: This portion of the instrument consists of the ozone generator, pre-reaction 

chamber, reaction chamber, and photomultiplier tube. 

 Electronic Hardware: The part of the analyzer that generally requires little or no maintenance. If the 

42CY is operated above the manufacturer's recommended temperature limit, however, individual 

integrated chips can fail and cause problems with data storage or retrieval. 

Other apparatus and equipment includes the following. 

Instrument Shelter: A shelter is required to protect the analyzer from precipitation and adverse weather 

conditions, maintain operating temperature within the analyzer's temperature range requirements, and 

provide security and electrical power. The recommended shelter temperature range is 20-30o

C. 

 
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Spare Parts and Incidental Supplies:. See the 42CY operating manual, Chapter 5, for specific 

maintenance and replacement requirements. 

Calibration System: A system that creates concentrations of nitrogen oxide of known quality is 

necessary for establishing traceability. The calibration system must also include a high precision ozone 

generator in order to generate concentrations of nitrogen dioxide by gas phase titration with nitrogen 

oxide. This is described in detail in the “Environics 9100 SOP.” Please reference this document. 

DAS: A data acquisition system is necessary for storage of ambient and ancillary data collected by the 

42CY. The 42CY requires a minimum of two analog outputs, one each for NO and NOy outputs. A third 

output is also needed if the monitor is to be run in auto-ranging mode to capture the range information. 

Note, a digital DAS is preferred because diagnostic information can also be collected which will greatly 

help troubleshooting and validation of data. 

Wiring, Tubing and Fittings: PFT TeflonTM should be used exclusively throughout the intake system. 

Examine the tubing and discard if particulate matter is collects in the tubing. All fittings and ferrules 

should be made of TeflonTM or stainless steel. Connection wiring to the DAS should be shielded two 

strand wire or RS-232 cables for digital connections. 

Reagents and Standard: The 42CY does not require any reagents since the instrument uses photometry 

to analyze for NOy. All standards for the NOy method can be obtained in compressed cylinders and must 

be NIST traceable. Please see the “Calibration of Trace Gas Analyzers” SOP. 

3.9 Procedure 

3.9.1 Sample Collection: Ambient air is drawn through a sample inlet located on the remote 

inlet/converter. The sampling point should be located 3 to 5 meters above ground level, at least 1 meter 

from all obstructions, and at least 10 meters from obstructions over a range of at least 180 degrees. These 

requirements necessitate mounting the catalytic converter outside the shelter. The sample bypass lines 

from the converter to the instrument should not exceed 10 meters in length. 

3.9.2 Sample Handling and Preservation: NOy samples receive no special preparation prior to analysis. 

Therefore this SOP does not need a section on Sample Handling and Preservation.

3.9.3 Instrument Operation, Startup and Maintenance 

This section discusses startup, operation and maintenance of the 42C-NOY. The 42CY series instrument 

has a digital front panel screen with control buttons below. This allows the user to check functions, 

switch operating parameters, adjust zero and span and read warnings messages. It is extremely 

important that the user familiarize themselves with the menus available. Inadvertently changing 

parameters within the analyzer can damage the instrument and possibly invalidate data as well. 

Please reference the 42CY owner’s manual and read it carefully before adjusting any parameters 

that are set by the factory. 

3.9.3.1 Installation and Start up 

1. Before the instrument is operated, inspect the instrument for any damage. If damage is observed 

to the shipping box or the instrument, contact your shipping personnel. 

2. Remove the instrument from its shipping container and set on a table or bench that allows easy 

access to both the front and read or the instrument. 
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3. Carefully remove the instrument cover and remove any packing material. 

4. Check for possible internal damage. 

5. Check that all connectors and printed circuit boards are firmly attached. 

6. Once you have performed your inspection, replace the cover. 

7. Remove the remote inlet enclosure and place on a bench that allows easy access. 

8. Open the enclosure and check for internal damage. 

9. Using 1⁄4 inch PFT TeflonTM tubing, plumb the inlet as shown in Figure 3-2. 

10. Mount the enclosure at the desired sampling location being sure to meet the requirements detailed 

in 3.9.1, above. 

11. Determine the distance from the point where the sample tubing exits the converter enclosure to 

the point where the tubing will enter the monitoring station, including ample length to account for 

any curves or obstructions. Cut the two plastic conduits to this length. 

12. Run the two sample lines, calibration line, and thermocouple wire through one conduit, and the 

converter power cable through the second. 

13. Connect the two sample lines, calibration line, thermocouple wire, and power cable inside the 

converter enclosure as shown in Figure 3-2, and secure the conduits to the converter enclosure. 

14. Run the tubing, thermocouple wire, and power cable in to the monitoring station. 

15. Mount the 42CY in its rack being sure that the 42CY has enough clearance so that it gets proper 

ventilation. 

16. Connect the sample lines to the bypass pump, filters, and analyzer as shown in Figure 3-1. 

17. Connect the DryriteTM air dryer to the dry air bulkhead. 

18. Connect the intake of the vacuum pump to the exhaust bulkhead. 

19. Connect the charcoal container to the outlet of the vacuum pump. 

20. Connect the converter power cable and thermocouple wire to the back of the 42CY. 

21. Connect the power cable and plug the instrument, vacuum pump, and bypass pump into a 

grounded power strip that has surge protection. It is also advisable to purchase an Uninterrupted 

Power Supply (UPS). An UPS will protect the 42CY from power surges and keep the unit 

operating until an operator can shut it down. 

22. Connect the output of the analog to a DAS via shielded two wire cable. Please see EPA SOP on 

“Data Management” for details. 

23. Connect the digital RS-232 port to an appropriate cable and connect it to the DAS. Please see 

EPA SOP on “Data Management” for further details. 

24. Press the power rocker switch to “ON.” 

25. After an adequate warm-up period, run through the menu and record factory/start-up settings. 

Compare to recommended limits located in the manual and listed on the daily worksheet. 

26. Perform a leak check. Press the MENU pushbutton to display the Main Menu. Use the 

UP/DOWN ARROW pushbuttons to move the cursor to “Diagnostics.” Press ENTER for the 

Diagnostics screen. Use the UP/DOWN ARROW pushbuttons to select Flow. The sample flow 

rate should be approximately 1 lpm. Cap or otherwise plug the sample inlet on the remote 

converter. The sample flow rate should drop to less than 0.1 lpm with in 15 seconds. Slowly 

remove the cap. Do not leave the inlet capped for more than a minute as it can cause damage to 

the monitor. If the sample flow does not drop to below 0.1 lpm, tighten all connections and 

repeat leak test. 
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Figure 3-2. Schematic of plumbing and wiring for 42CY External Converter

3.9.3.2 Operation and Range Setting 

1. The exhaust fan will start and the Power-Up and Self-Test screens will be displayed. These screens 

are displayed each time the instrument is turned on, and will continue to be displayed till the 

instrument has completed its warm up and self-checks. You should allow 30 minutes for the 

instrument to stabilize. 

2. After the warm-up period the Run screen, the normal operating screen, is displayed. This screen is 

where the NO and NOy concentration is displayed. The display for the model that EPA is using 

currently mis-reports the data. The data reported as NOx is actually NOy. The data reported as NO2 is 

actually NO2 + NOz. Future versions should correct this, and are expected to report NO, NOy and 

“DIFF” which would represent NO2 + NOz. 

3. In the bottom right hand corner the word “LOCAL” or “REMOTE” will be displayed. The analyzer 

must be in local mode to adjust the configuration using the keys on the front panel. Press the ENTER

button until the analyzer is in local mode. 

4. From the Run screen, the Main Menu, which contains a list of submenus, can be displayed by 

pressing the MENU pushbutton. 

5. Instrument parameters and features are divided into the submenus according to their function. Use 

the UP/DOWN ARROW pushbuttons to move the cursor to each submenu. Note: When the Main 

Menu is entered directly from the Run screen, the LEFT ARROW pushbutton may be used to jump 

to the most recently displayed submenu screen. 

6. To set the range for the instrument, press the DOWN ARROW pushbutton till the cursor is on 

“Range.” Press the ENTER pushbutton to display the Range Menu. 

7. In the upper right corner of the display, the word single, dual, or auto is displayed to indicate the 

active mode. For a detailed explanation about the single, dual, or autorange mode, see Chapter 3 

(page 3-7) of the manual. This SOP addresses setting the range for a single range. 
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8. Press the ENTER pushbutton for the Gas Units screen. Use the DOWN ARROW pushbutton to 

select “PPB” and press ENTER. Press MENU to return to the Range Menu. 

9. Use the DOWN ARROW pushbutton to display the Range screen and press ENTER. 

10. Use the UP/DOWN ARROW pushbuttons to scroll through the preset ranges. Select “100.0” and 

press ENTER. Press MENU to return to the Range Menu. Note, a higher range may be required in 

areas with higher NOy concentrations. 

11. Press RUN to return to the Run screen. 

12. To set the averaging time, press the MENU button to return to the Main Menu. Press the DOWN 

ARROW pushbutton till the cursor is on Averaging Time. 

13. Press ENTER for the averaging time screen. Use the DOWN ARROW pushbutton to select the 

desired averaging time and press ENTER. Press RUN to return to the Range Menu. 

14. To set the correct time and date on the instrument, press MENU to return to the Main Menu. Press 

the DOWN ARROW pushbutton till the cursor is on Instrument Controls. Press ENTER to display 

the Instrument Controls screen. 

15. Use the UP/DOWN ARROW pushbuttons to scroll through the choices. Select “Time” and press 

ENTER. 

16. Use the UP/DOWN ARROW pushbuttons to increase/decrease the hours and minutes; use the 

LEFT/RIGHT ARROW pushbuttons to move the cursor left and right. Set the appropriate time and 

press ENTER. Press MENU to return to the Instrument Controls screen. 

17. Select “Date” and press ENTER. 

18. Use the UP/DOWN ARROW pushbuttons to increase/decrease the month, day, and year; use the 

LEFT/RIGHT ARROW pushbuttons to move the cursor left and right. Set the appropriate date and 

press ENTER. Press RUN to return to the Run screen. 

19. The instrument is now set with the appropriate time, date and full scale range. 

20. It is recommended that you allow the 42CY 24 hours before you attempt function checks or 

calibration. 

21. If the DAS system that you have does not have the RS-232 capabilities, then proceed to the next 

section, Diagnostic Checks/Manual Checks. If you have connected the 42CY to a computer or DAS, 

review the Diagnostic Check from your computer screen.

3.9.3.3 Diagnostic Checks/Manual Checks 

To determine whether the 42CY is working properly, the field operators should perform the Diagnostic 

Checks every time they visit the monitoring station. It is good practice for the operator to check these 

Diagnostic Checks either by the computer or manually. Below are instructions on how to perform this 

manually. Please note that the 42CY has set upper and lower ranges for some of these Diagnostic checks. 

Please reference the owner’s manual for these ranges. 

1. To display the Diagnostics menu, from the Run screen press the MENU pushbutton to display the 

Main Menu. Use the UP/DOWN ARROW pushbuttons to move the cursor to “Diagnostics.” Press 

ENTER for the Diagnostics screen. 

2. Use the UP/DOWN ARROW pushbuttons to toggle through the function check tree. The following 

table illustrates the functions that should be recorded. Please see Chapter 3 (page 3-36) 42CY manual 

for more details. A manual checklist on maintenance is attached in Appendix A of this SOP. 

3. On the Program Number screen, the version numbers of the program installed are displayed. Prior to 

contacting the factory with any questions regarding the instrument, note the program numbers. 
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Table 3-2 Diagnostic Checks 

Check Explanation 

Voltages The current DC power supply and PMT power supply voltages 

Temperatures The current internal instrument and chamber temperatures 

Pressure The current chamber pressure 

Flow The current ozonator and sample flow rate 

Test Analog Outputs Enable analog outputs to be set to zero and full scale to adjust analog outputs to 

agree with the front panel display 

Reference the owners manual or the worksheet in Appendix A of this SOP for 

acceptable limits. Once the Diagnostic checks have been established and recorded for 

the 42CY, it is time to calibrate the instrument. Please refer to section 3.9.4 of this 

SOP. 

3.9.3.4 Preventive Maintenance

Preventive maintenance should prevent down-time and data loss. Table 3.3 lists the preventive 

maintenance items that are listed in the 42CY manual, section 5. 

Table 3-3 Preventive Maintenance Schedule the TECO 42CY

Item Schedule

 Replace ozonator air feed drying column As needed 

 Inspect and replace sample filters Weekly 

 Inspect and replace capillaries Quarterly 

 Digital to analog converter test As needed 

 Inspect and clean cooler fins Semi-annually 

 Inspect and clean fan filters Semi-annually 

3.9.3.5 Instrument Troubleshooting

The 42CY manual has an excellent troubleshooting guide in Chapter 6. Please reference the manual for details on 

troubleshooting the 42CY analyzer. 

3.9.4 Calibration and Standardization 

The calibration of the 42CY is performed by comparing the output of the instrument against standardized 

gases of known quality. Generation of these gases is detailed in the “Calibration of Trace Gas Analyzers” 

SOP. This section will detail how to adjust the 42CY to the standardized gases. Once the calibration has 

been performed, compare the response of your DAS to the calculated “source” value. If this is outside of 

+/-10%, then adjust the instrument response as detailed in the next sections. 

3.9.4.1 Adjustment to Zero Air 

In order to adjust the output of the 42CY to zero air, perform the following: 

1. Connect the calibration line to a source of zero air. Supply a sufficient amount of zero air to 

supply the analyzer and to ensure that a small amount of excess zero air exits from the sample 

inlet. 
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2. Allow the analyzer to sample zero air for at least 15 minutes or until stable NO, NOy, and 

NO2+NOz readings are obtained. 

3. From the Main Menu, choose Calibration. From the calibration menu, choose Calibrate Zero. 

4. The Calibrate Zero screen displays the NO, NOy, and Prereactor readings. 

5. Press ENTER to set the NO, NOy, and Prereactor readings to zero. 

6. The message “Savings Parameters(s)” is briefly displayed to indicate that the background 

readings have been set to zero. 

7. Press MENU to return to the Calibration menu. 

8. Press RUN to return to the Run screen. 

3.9.4.2 Adjustment to Calibration Gas 

In order to adjust the output of the 42CY to NIST traceable calibration gas, perform the following: 

1. Switch the calibration unit to generate a known concentration of NO corresponding to 

approximately 80% of full scale. 

2. Supply a sufficient amount of calibration air to supply the analyzer and to ensure that a small 

amount of excess calibration air exits from the sample inlet. 

3. Allow the instrument to sample calibration gas for a minimum of 15 minutes, or until stable NO, 

NOy, and NO2+NOz readings are obtained. 

4. From the Main Menu select the Calibration menu; select the “Calibrate NO” screen. 

5. On the bottom line, there will be individual digits with which the span value can be set. In order 

to change the span value, use the UP/DOWN ARROW pushbuttons to increase/decrease each 

digit; use the LEFT/RIGHT ARROW pushbuttons to move the cursor left and right. 

6. Change the span value to reflect the known concentration of NO in the calibration gas being 

sampled. 

7. Press ENTER to calibrate the NO reading to the NO calibration gas. 

8. This operation changes the calculation equation and adjusts the NO span coefficient of the 

instrument. 

9. Press MENU to return to the Calibration menu. 

10. Select “Calibrate NOy”. 

11. Change the span value to reflect the known concentration of NO plus any known NO2 impurity 

in the calibration gas being sampled. 

12. Press ENTER to calibrate the NOy reading to the NO calibration gas. 

13. This operation changes the calculation equation and adjusts the NOy span coefficient of the 

instrument. 

14. Press MENU to return to the Calibration menu. 

15. Adjust the calibrator to add a known concentration of ozone to the calibration gas corresponding 

to approximately 60% of full scale. The ozone will react with the NO in the calibration gas to 

form NO2. 

16. Supply a sufficient amount of calibration air to supply the analyzer and to ensure that a small 

amount of excess calibration air exits from the sample inlet. 

17. Allow the instrument to sample calibration gas for a minimum of 15 minutes, or until stable NO, 

NOy, and NO2+NOz readings are obtained. 

18. Select “Calibrate NO2” from the Calibration menu. 

19. Change the span value to reflect the known concentration of ozone added to the calibration gas 

plus any known NO2 impurity in the calibration gas being sampled. 

20. Press ENTER to calibrate the NO2 reading to the NO calibration gas. 

21. This operation changes the calculation equation and adjusts the NO2 span coefficient of the 

instrument. 
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22. Press RUN to return to the Run screen. 

3.10 Data Analysis and Calculations 

Data analysis for this analyzer is detailed in “Data Acquisition and Management” SOP. 

4.0 QUALITY CONTROL AND QUALITY ASSURANCE

 

The following section has brief definitions of the QA/QC indicators. Table 4-1 has the Measurement 

Quality Objectives (MQOs) of the 42CY. Please note that this section details primarily with the data 

quality indicators. Quality Control for continuous electronic instruments, such as the 42CY consists of 

performing the diagnostic checks, maintenance and calibrations. These procedures are detailed in 

sections 3.9.3 and 3.9.4: Instrument Operation, Startup and Maintenance and Calibration and 

Standardization. Appendix A has an example of a Quality Control and Maintenance Record developed by 

the EPA for this instrument. 

4.1 Precision 

Precision is defined as the measure of agreement among individual measurements of the same property 

taken under the same conditions. For NOy, this refers to testing the NOy analyzer in the field at 

concentrations between 0.2 and 100 ppb (note, higher test levels may be required in areas with higher 

NOy concentrations). The test must be performed, at a minimum, once every two weeks. Calculations for 

Precision can be found in Reference 4. 

4.2 Bias 

Bias is defined as the degree of agreement between a measured value and the true, expected, or accepted 

value. Quantitative comparisons are made between the measured value and the true, standard value 

during audits. Generally, three upscale points and a zero point are compared. Two audit types commonly 

used for NOy, direct comparison and blind, are discussed below. The SOP should discuss plans for each 

type of audit. 

 Direct Comparison Audits: An independent audit system is brought to the monitoring location and 

produces gas concentrations that are assayed by the monitoring station's NOy analyzer. In most cases, 

a person outside of the agency or part of an independent QA group within the agency performs the 

audit. The responses of the on-site analyzer are then compared against the calculated concentration 

from the independent audit system and a linear regression is generated 

 Blind Audits: In blind audits (also called performance evaluation audits); agency staff are sent an 

audit device, such as the National Performance Evaluation Program (NPEP). The agency staff does 

not know the NOy concentrations produced by the audit equipment. Responses of the on-site analyzer 

are then compared against those of the generator and a linear regression is calculated. 

4.3 Representativeness 

Representativeness refers to whether the data collected accurately reflect the conditions being measured. 

It is the data quality indicator most difficult to quantify. Unless the samples are truly representative, the 

other indicators are meaningless. Since the NCORE Level I and II siting criteria are urban and regional, 

the TL-NOy criteria are the same. Please reference the National Monitoring Strategy5 for a discussion of 

NCORE Level II NOy monitoring scale. 
Thermo 42CY-NOy SOP 

Version No. 3 

9/28/2005 

Page 16 of 18 

4.4 Completeness 

Completeness is defined as the amount of data collected compared to a pre-specified target amount. The 

EPA does not have a minimum completeness requirement for NOy sampling. However, for NOx, EPA 

requires a minimum completeness of 75% (40 CFR 50, App.H.3). Typical completeness with the 42CY 

values can approach 90-93%. 

4.5 Comparability 

Comparability is defined as the process of collecting data under conditions that are consistent with those 

used for other data sets of the same pollutant. The 42CY meets the MQOs for a Trace Level NOy

instrument. Please see Table 4-1. 

4.6 Method Detection Limit 

The method detection limit (MDL) or detectability refers to the lowest concentration of a substance that 

can be determined by a given procedure. The 42CY must be able to detect a minimum value of 50 ppt of 

NOy. 

Table 4-1 Measurement Quality Assurance Objectives 

Requirement Frequency Acceptance Criteria Reference Information or 

Action 

Bias NCORE, 

once per 

year 

Slope: 1.00 +/- 0.15 

Intercept: +/- 3% of 

full scale 

Regression: <0.9950 

40 CFR 

Pt.58 

Use of NIST 

generated gas 

concentrations 

with Mass Flow 

Calibration unit 

that is NIST 

traceable 

Precision 1 every 2 

weeks 

Concentration: 0.2 -

600 ppb, Coefficient of 

Variance less than 

15%. 

40 CFR 

Pt.58 

Appendix A 

If CV is greater 

than 15%, institute 

Quality Control 

measures 

Completeness Quarterly, 

Annually 

NCORE, 75% National 

Monitoring 

Strategy. 

If under 75%, 

institute Quality 

Control Measures 

Representativ

eness 

N/A Neighborhood, Urban 

or Regional Scale 

40 CFR 58 N/A 

Comparability N/A Must be a Trace Level 

instrument. See 

Sections 3.1 and 3.2 of 

this document. 

National 

Monitoring 

Strategy. 

N/A 

Method 

Detection 

Limit 

NA 50 ppt National 

Monitoring 

Strategy 

Testing is 

performed at the 

factory. 
Thermo 42CY-NOy SOP 

Version No. 3 

9/28/2005 

Page 17 of 18 

5.0 REFERENCES 

2. Merck Index, twelfth edition 1996, page 296 

3. Seinfeld, John H., Atmospheric Chemistry and Physics of Air Pollution, 1986, page 54 

4. Code of Federal Regulations, Title 40, Part 53.23c 

4. Code of Federal Regulation, Title 40, Part 58, Appendix A 

5. The National Air Monitoring Strategy, Final Draft, 4/29/04, 

http://www.epa.gov/ttn/amtic/monstratdoc.html

 6. Model 42CY Instruction Manual, Thermo Environmental Instruments 
Thermo 42CY-NOy SOP 

Version No. 3 

9/28/2005 

Page 18 of 18 

 Appendix A

Environmental Protection Agency 

Monthly Quality Control and Maintenance Records 

Thermo 42C Trace Level NO/NOy Analyzer 

Site Name/Location: ____________________________________________________________ 

Technician: ___________________________ 

Date/Time: ___________________________ 

Instrument: ___________________________ 

Serial Number: ___________________________ 

Range: ___________________________ 

Date 

Time 

 Parameters Acceptance Range 

PMT voltage 

+5 volt supply 5 +/- 0.5 

+15 volt supply 15 +/- 1.5 

Internal temp 15-45 C 

Chamber temp 47-51 C 

Cooler temp -20 - -1 C 

Converter temp 300 - 350 C 

Chamber pressure 200 - 400 mm Hg 

Ozonator flow 0.05 - 0.15 lpm 

Sample flow 0.1-2 lpm 

 

Other Tests 

 
STANDARD OPERATING PROCEDURES 

ENVIRONICS SERIES 9100 

COMPUTERIZED AMBIENT MONITORING CALIBRATION 

SYSTEM 

Version 1 

 

 
Section 1.1 Acknowledgments 

This Standard Operating Procedure (SOP) for the Environics Series 9100 Computerized Ambient 

Monitoring Calibration System is the product of EPA’s Office of Air Quality, Planning and 

Standards. The following individuals are acknowledged for their contributions. 

Principal Author 

Anna Kelley, Hamilton County Department of Environmental Services, Cincinnati, OH 45219 

On an Intergovernmental Personnel Act (IPA) assignment with OAQPS-EMAD, Research 

Triangle Park, NC 27711

Reviewers 

Office of Air Quality, Planning and Standards 

Joann Rice, Precursor Gas Monitoring Team Lead, OAQPS-EMAD, Research Triangle Park, NC 

27711 

Michael Papp, QA Team Lead, OAQPS-EMAD, Research Triangle Park, NC 27711 

Keith Kronmiller, Mantech, Inc. Research Triangle Park, NC 27711 

Comments and questions can be directed to:

Joann Rice 

EPA-OAQPS 

Emissions, Monitoring, and Analysis Division 

Mail Drop D243-02 

Research Triangle Park, NC 27711 

Email: rice.joann@epa.gov

(919)541-3372 
2.0 Table of Contents 

Section Page 

1.0 Title Page 1 

 1.1 Acknowledgements 2 

2.0 Table of Contents 3 

 2.1 List of Figures 3 

3.0 Scope and Procedures 4 

 3.1 Scope and Applicability 4 

 3.2 Summary of Method 4 

 3.2.1 Summary of Specific Procedures 4 

 3.2.2 Summary of Analyzer Operation 4 

 3.3 Definitions 5 

 3.4 Health and Safety Warnings 6 

 3.5 Cautions 6 

 3.6 Interferences 7 

 3.7 Personnel Qualifications 7 

 3.8 Equipment and Supplies 7 

 3.9 Procedures 9 

 3.9.1 Start-up 9 

 3.9.1.1 Unpack the Instrument 9 

 3.9.1.2 Warm-up 10 

 3.9.1.3 Leak Check 10 

 3.9.1.4 Flow Verification 11 

 3.9.2 Identifying Calibrator Ports to Standards 12 

 3.9.3 Calibrations – Multi-point 13 

 3.9.3.1 Determination of Concentrations for Multi-Point Calibration 13 

 3.9.3.2 Performing the Multi-Point Calibration 15 

 3.9.4 Verifications – Zero, Span and One-point Quality Checks 16 

 3.9.4.1 Set-up a Sequence 16 

 3.9.4.2 Set-up Timer Control 17 

 3.9.4.3 Run a Timer Control 18 

 3.9.4.4 Zero, Span and One-Point Quality Checks 18 

 3.9.4.5 Calibrator Automation 18 

4.0 Quality Assurance and Quality Control 19 

5.0 References 19 

List of Figures 

Figure 1.0 Flow Diagram: Environics 9100 5 

Figure 2.0 Sampling System Set-up 7 

Figure 3.0 Calibration Graph of Environics 9100 Mass Flow Controller 12 

List of Tables 

Table 1.0 Proposed Audit Level Concentrations 15 

Table 2.0 MQO Table for Calibrator 19 
Environics 9100 SOP 

Version No. 1 

March 2, 2005 

Page 4 of 19 

3.0 Scope and Procedures 

3.1 Scope and Applicability

This Standard Operating Procedure (SOP) is applicable for the Environics Series 9100 

Computerized Ambient Monitoring Calibration System integrated with several ambient air 

monitoring analyzers. The SOP outlines the steps to run calibrations and verifications either 

automatically through programming sequences or through manual commands. 

3.2 Summary of Method

3.2.1 Summary of Specific Procedures 

This SOP will use the following methods to unpack, check and set-up, and execute a multi-point 

calibration, and daily zero, span and one point QC checks. 

3.9.1.1 Unpack the Instrument 

3.9.1.2 Warm up the Environics 

3.9.1.3 Leak check the Environics 

3.9.1.4 Flow Verification 

3.9.2 Assign the Calibrator Ports to the Gaseous Standards 

3.9.3 Multi-point Calibrations 

3.9.4 Verifications: Zero, Span and One Point Quality Checks 

3.9.4.1 Setting up a Sequence 

3.9.4.2 Setting up a Timer Control 

3.9.4.3 Running the Timer Control 

3.9.4.4 Zero, Span, and One-Point Quality Checks 

3.9.4.5 Calibrator Automation 

 3.2.2 Summary of Analyzer Operation Refer to the Flow Diagram, Figure 1. 

 In the Environics 9100 Calibrator, Port 1 is connected to mass flow controller (MFC) 1. 

 Port 1 is used for Zero Air. MFC 2 can choose any of the remaining available ports. 

 When nitrogen dioxide (NO2) is required pollutant, ozone flows into the reaction 

 chamber along with gases from the other ports except 1. It is here that ozone reacts with 

 the gas. The resultant gas is then sent to the Mixing Chamber and is diluted with zero air 

 from Port 1 before exiting the calibrator and sent to the appropriate analyzer. If diluting 

 gases for CO and SO2, this process is by-passed. 
Environics 9100 SOP 

Version No. 1 

March 2, 2005 

Page 5 of 19 

 Figure 1.0 Flow Diagram: Environics 9100

3.3 Definitions 

MFC Mass Flow Controller 

Sccm Standard Cubic Centimeter per minute 

DAS Digital Acquisition System 

Span Check a one point verification of the monitoring system challenging an 

 analyzer with a known concentration of gas and measuring the 

 analyzer response. Span checks are the highest concentration 

 test point approximately 80 to 90% of full scale range. 

One Point Quality Check a one point verification of the analyzer made by challenging the 

analyzer with a known concentration of gas and measuring the 

analyzer response. This concentration ideally should be in the 

range of daily observed acceptable quality. A response outside 

the limits initiates a series of actions to determine data quality. 
Environics 9100 SOP 

Version No. 1 

March 2, 2005 

Page 6 of 19 

3.4 Health and Safety Warnings 

1. Some gases can be explosive or otherwise reactive when blended. Users must check gas 

compatibility before blending. Please consult a gas handbook, a specialty gas manufacturer or 

other competent source for information about gas compatibility. Failure to observe these 

precautions may result in damage to the instrument, serious injury or death. 

2. Pressurized cylinders are extremely dangerous if improperly handled. Proper regulators, use 

of safety caps and proper restraints are mandatory. Avoid cross contamination when attaching 

regulators or making manifold connections. Always consult your gas supplier for proper 

safety procedures. Failure to observe these precautions may result in serious injury or death. 

3. Rules and regulations regarding the transportation of gas cylinders are governed by the 

Department of Transportation. Each agency should familiarize themselves with these 

regulations and follow them when involved in transporting gas cylinders. Failure to follow 

these precautions may result in serious injury or death. 

4. Secure Material Safety Data Sheets (MSDS) for all gases and keep in specially designated 

binder in any easily accessible location. 

5. Power to the unit should be disconnected before working on it to prevent injury or electrical 

shock. 

6. If it is necessary to work on the inside of the unit with power connected, extreme caution 

should be taken. Failure to do so can result in injury or electrical shock. 

7. Because the electronic circuit boards contain static sensitive components, always use static 

discharge equipment when working on the unit and handling circuit boards. 

8. A line should be run to the outside or a fume hood, whichever is more readily available, to 

vent the outflow of gases from the entire system: Environics 9100, the Zero Air Generator, 

and the analyzers. This should be done to prevent the possibility of a build-up of gases in a 

closed room/monitoring station and the potential for gaseous poisoning to the unaware station 

operator. 

3.5 Cautions 

1. The Environics 9100 operates at a line voltage between 100-120 VAC (optional 220-240 

VAC). Operating at an incorrect line voltage will damage the instrument and void the 

manufacturer’s warranty. 

2. Because the RS-232 ports and the parallel printer port are especially susceptible to damage if 

the unit is powered ON while any computer or printer equipment is being connected or 

disconnected, the unit must be powered OFF before connecting or disconnecting any cables, 

wiring harnesses or other sources of potential electrical impulses.
Environics 9100 SOP 

Version No. 1 

March 2, 2005 

Page 7 of 19 

3. If routine maintenance is performed, prior to putting the unit back into service check the 

following items: 

• Inspect the power cord and internal wiring 

• Check all fittings for tightness and leak check if possible 

• Clean circuit boards using a vacuum or air gun to remove dust 

• Check all tubing for splits, kinks, or cuts 

3.6 Interferences 

The calibrator as well as the zero air supply and any gaseous cylinders should be stored and 

operated in a temperature and humidity controlled shelter as extremes of either can effect the final 

concentration. Condensation of humidity in the sampling and associated lines can also dilute the 

concentration of gases delivered to the analyzers. 

3.7 Personnel Qualifications 

Persons setting up and operating this system should have an understanding of gaseous systems 

and/or a good background in chemistry, physics, and the scientific process. For someone 

unfamiliar with gaseous systems and/or setting up analyzers and related equipment at a 

monitoring site, an instructional course would be beneficial. Other sources of instruction include 

any US EPA guidance documents and training with other experienced personnel. 

3.8 Equipment and Supplies 

Zero Air Generator

Environics 9100

Calibrator

Pollutant Analyzer

Cal Standard #1 Cal Standard #2

Fan

Com NO

NC

Sampling Manifold

Vent

 Figure 2.0: Sampling System Set-up 
Environics 9100 SOP 

Version No. 1 

March 2, 2005 

Page 8 of 19 

Environics Series 9100: used to blend gases to desired concentration to run check calibration of 

ambient air analyzers through not only a calibration of each but also through the daily zero, span, 

and one point quality checks. 

Zero Air Source: For this study, an API Model 701 Zero Air Generator is used. Carbon monoxide 

and hydrocarbon scrubbers are available as an option when purchasing. For precursor gas 

applications, the CO scrubber is required. Please see the manual for a recommended maintenance 

schedule on the unit. The purpose of the zero air source is to dilute the gases to achieve the 

desired final concentration of gaseous pollutants in question. Zero Air should be filtered before 

entering the calibrator to ensure it is free of any particulate contaminants. A cylinder of zero air 

may also be used. However, the latter may not be cost effective or practical for monitoring 

organizations given the frequency of use of the zero air supply. It is also imperative for the 

monitoring organization to verify/recertify their zero air supply annually using an independent 

zero air source. The independent source should be of a higher quality than what is routinely used. 

Most high purity cylinder air sources are not of the quality needed as an independent source. 

High quality cylinders can be used, but they require external scrubbers for the precursor gases of 

interest. 

It is not recommended that the API 701 be used to generate air at a flow rate greater than 10 

LPM. The internal CO scrubber is not as efficient at the higher flow rates (e.g., 20 LPM); 

therefore, caution should be taken when exceeding 10 LPM. Decreased scrubber efficiency 

presents itself as an increased CO analyzer baseline. An external Hopcalite or Carulite scrubber 

can be added to the API 701 to remove any CO not eliminated by the scrubber at higher flow 

rates. CO scrubbers can fail. The manual recommends replacement on an annual schedule 

depending on CO levels in the source air. 

It is also recommended that ambient air, not air from the inside of the monitoring station, is used 

as a source for the API zero air generator. 

Reagents and Standards: Gas Cylinders are used as the source of the target pollutant 

concentration. Cylinders used should be of the highest purity available, specifically for multipoint calibrations and performance evaluations. All gases used should be either NIST traceable or 

EPA Protocol Gases having acceptance criteria of 2%. Three different gas cylinders were used in 

the initial testing project. The concentrations used to obtain the desired blend for the routine span 

and precision checks follow: 

Concentration of gases, cylinder one: 

• NO 50 ppm nominal in N2 balance @ 2000 psig Tolerance: ± 1% EPA 

• CO 5000 ppm nominal in N2 balance @ 2000 psig Tolerance: ± 1% EPA 

• NOx 50 ppm nominal in N2 balance @ 2000 psig 

• NO2 <0.2 ppm in N2 balance @ 2000 psig 

• SO2 50 ppm nominal in N2 balance @ 2000 psig Tolerance: ±1% EPA 

Concentration of gases used in cylinder two: 
Environics 9100 SOP 

Version No. 1 

March 2, 2005 

Page 9 of 19 

• CO 350 ppm nominal in N2 balance @ 2000 psig Tolerance ± 1% EPA 

• NO 10 ppm nominal in N2 balance @ 2000 psig Tolerance ± 1% EPA 

• NO2 <0.05 ppm in N2 balance @ 2000 psig 

• NOx 10 ppm nominal in N2 balance @ 2000 psig 

• SO2 10 ppm nominal in N2 balance @ 2000 psig Tolerance ± 1% EPA 

Cylinder three (span and precision checks) 

• CO 60 ppm nominal 

Targeted concentrations of the span and precision checks: 

Pollutant Range Span Precision Check 

CO 5000 ppb 4000 ppb 250-500 ppb 

SO2 100 ppb 80 ppb 20 ppb 

 NOy 100 ppb 80 ppb 20 ppb 

Data Acquisition, Storage and Communication Package: A data acquisition package is 

necessary to retrieve the data from a remote site and store it for further analysis. Two data 

acquisition systems were used in this project: Environmental Data Acquisition System (EDAS) 

for Windows both models 8816 and 8832, Environmental Services Corporation and Envidas, by 

Envotech. For further information, please refer to the Data Management SOP. 

3.9 Procedures 

3.9.1 Start-up 

3.9.1.1 Unpack the instrument

1. Remove the unit from the shipping container and inspect for damages. 

2. Note any damage to the shipping case and report to freight carrier immediately. 

3. Removing the screws on each side of the top removes the top cover. 

4. Inspect the interior of the calibrator for any loose parts or visible damage. 

5. Check for any loose circuit boards. If loose, press down to reseat them before connecting the 

power. 

6. Report any instrument damage to Environics or the local distributor. 

7. If no damage is found, replace the cover and screws. 

The above procedure should be done upon immediate receipt of the instrument or can be moved 

to the location the calibrator will be sited and then inspected for damage. However, do not wait 

too long to do the inspection to ensure validation of the warranty period. Please refer to inside the 

front cover of the manual for specifics on the warranty period and specific coverage. 
Environics 9100 SOP 

Version No. 1 

March 2, 2005 

Page 10 of 19 

3.9.1.2 Warm-up 

When bringing zero air supply and calibrator together for initial checks, suggested warm up time 

is 24 hours. If moving to sampling location after initial checks, suggested warm up time would be 

3-4 hours. 

1. Set-up Calibrator in place and connect zero air supply to Port 1. 

Note: Pressure of zero air supply should be between 30-35 PSI 

2. Secure the appropriate electrical power supply to the Environics and switch to the “ON” 

position 

3. Allow calibrator and zero air supply to warm-up and stabilize before proceeding. 

3.9.1.3 Leak Check Refer to Section 5.14 in the Environics Manual for further information on 

the Leak Check 

A leak check of the calibrator should be performed before beginning other work. A leak in the 

calibrator will result an incorrect dilution of gases delivered to analyzers yielding incorrect 

calibration and verifications of concentrations by the analyzer(s). It is strongly recommended to 

perform the leak check even if the calibrator is brand new. This ensures integrity of the system 

and prevents aggravation to the operator. 

1. Set the pressure of the zero air supply to 10 PSI 

2. At the READY screen, press the MORE key (F8) in the lower right hand corner of the 

screen. This will take you to the second screen. 

3. Once on the second screen, press the LEAK CHECK key (F7) 

4. Adjust the PSI reading on the external pressure gage on the front of the zero air supply source 

as necessary. 

Note: The PSI should NOT be above 13. A PSI over 13 will activate the pressure safety. 

5. Press the START key (F1) on the front panel. 

6. Allow the Environics to run through the leak test cycle. The factory acceptance criterion for a 

leak check is less than 3 sccm. 

 Automatic sequence of events during the LEAK CHECK cycle: 

 1. Acquire atmospheric pressure (approximately 59 seconds) 

 2. Pressurize system - calibrator and zero air supply (approximately 89 seconds) 

 3. Shut down solenoids in calibrator – actual leak check of the calibrator and zero 

air supply 

 Note: The test may be cancelled at any time by pressing any key. 

7. Once the LEAK CHECK is complete, the Environics will display the results. If less than 3 

sccm, the results are acceptable. 

8. Record results in appropriate lab notebook 

9. Press the EXIT (F8) key located in the lower right hand corner of the screen. 

10. Adjust the zero air supply to read 30 PSI on the external pressure gage 
Environics 9100 SOP 

Version No. 1 

March 2, 2005 

Page 11 of 19 

3.9.1.4 Flow Verification 

Although the mass flow controllers have been factory set, it is strongly recommended to verify 

the flows through the calibrator using a NIST traceable source. This ensures accuracy as the flow 

measurement standard must be more accurate than the specified flow accuracy of the MFC. For 

this study, a BIOS Dry-Cal device was used. Flow devices must be certified annually. Flow 

checks should be verified at the start-up of the sampling system. Additional verifications should 

be performed annually or when the gaseous pollutant flow is questioned. 

To complete flow verification of Port 1, zero air, and Port 2, cylinder gases, a BIOS Dry-Cal 

device was used. If another type of flow device is used, these procedures may differ. Consult the 

manual that accompanies that device for specific instructions. 

1. Attach the appropriate BIOS cell to the base of the dry-cal. 

2. Attach tubing to the exhaust end of the dry-cal. 

3. Attach the calibration output tubing to the dry-cal. Note: the tubing from the calibrator output 

may not be the correct size to connect to the input of the dry-cal. Therefore, it may be 

necessary to have a small adapter/connector between two different sizes of tubing. 

4. Turn on dry-cal 

5. From the READY screen on the front panel of the Environics calibrator, press the CONC 

MODE (F1) soft key 

6. When the Concentration Mode Screen appears, move cursor using the arrow keys on the soft 

key pad to Port 1. 

7. Enter Port 1 and the cursor will move to the Target Gas area 

8. Once in the Target Gas area, the concentration should be 0 for all gases. If not, change to 0 in 

those pollutant concentration fields as needed using the numeric key pad and the arrow keys. 

9. After work in Target Gas area is complete, cursor should be in Total Flow area. If not move 

cursor to that area and enter total flow desired: 5.0 SLPM. 

10. Move the cursor to another field using the arrow keys. This will update and confirm on the 

screen the current requested information. 

11. Press START (F1) on the soft key pad at the bottom of the screen. This initiates the calibrator 

to open the appropriate solenoids and start the air flow through the calibrator. 

12. Observing the display on the dry cal and the front of the calibrator, begin to record the actual 

readings from the dry cal when the flows are constant on both. It is recommended to record 

eight to ten readings. 

13. After the readings are completed for a specific flow, select STOP (F ) on the bottom of the 

front panel of the calibrator, repeat steps 9-12. Five or more Target Flows up to 20 LPM 

should be used to create a line. 

14. When completed with Port 1, EXIT (F8) to the READY screen and switch to the cell for 

flows on the dry cal device. The flow of Port 2 will now be verified. 

15. At the READY screen, select the FLOW MODE (F2) at the bottom of the screen. 

16. Cursor should appear at Port 1. Move to Target Flow area and enter 0 SLPM. 

17. Move cursor to Port 2 and enter desired SCCM: 90. 

18. Move the cursor to another field using the arrow keys. This will update and confirm on the 

screen the current requested information. 

19. Turn on dry-cal 
Environics 9100 SOP 

Version No. 1 

March 2, 2005 

Page 12 of 19 

20. Select the START key (F1) on the soft key pad at the bottom of the screen. This initiates the 

calibrator to open the appropriate solenoids and start the air flow through the calibrator. 

21. Observing the display on the dry cal and the front of the calibrator, begin to record the actual 

readings from the dry cal when the flows are constant on both. It is recommended to record 

eight to ten readings. 

22. After the readings are completed for a specific flow, select EXIT (F8) on the bottom of the 

front panel of the calibrator, repeat steps 17, 18, and 20. Five or more Target Flows down to 

10 SCCM should be used to create a line. 

23. When completed with Port 2, EXIT (F8) to the READY screen. 

24. Turn off dry-cal, disconnect tubing, and replace all tubing to original set-up as necessary. 

25. Average each of the flow points. 

26. Perform a linear regression analysis and plot the actual vs. target concentration flows. 

Environics M F C 1 ZA C alibrat io n 12 / 16 / 0 4

LPM ( less 2 0 lpm set point ) 

y = 0.9972x + 0.1758

R2

 = 0.9999

0

2

4

6

8

10

12

14

16

18

20

0 2 4 6 8 10 12 14 16 18 20

Target Set

 Figure 3: Calibration Graph of Environics 9100 Mass Flow 

Controller

3.9.2 IDENTIFYING THE CALIBRATOR PORTS TO THE GASEOUS STANDARDS 

Refer to Section 5.8 in the Environics Series 9100 Manual 

The purpose of this section is to assign gaseous cylinders to a specific port located on the rear of 

the Environics 9100 Calibrator. 

1. From the READY SCREEN, select MAINTAIN PORTS (F6) 

2. Using the soft number key pad on the right front screen, choose the desired gas port to be 

configured. Once a port number is selected, the cursor will appear in front of the word 

BALANCE 

3. Using the Right Arrow key, move to the Gas ID column. Lines 1 will be used to name the 

BALANCE of the gas in the cylinder. Lines 2-6 will be used to name the individual gases in 

that cylinder. 

4. Enter the first gas to be configured on line 2
Environics 9100 SOP 

Version No. 1 

March 2, 2005 

Page 13 of 19 

Note: If it is intended to use nitric oxide to perform a Gas Phase Titration, “NO” must be 

used as the GAS ID. The system will compute the NO2 while running. System recognizes 

NO only for this process. 

5. Use the “Exit” key to return to the CGC area or use the “Up and/or Down” keys to move to a 

different CGC field. 

6. Enter the CGC for each GAS ID 

Note: The cylinder concentration can either be entered as parts per million (ppm) 

 or percent (%).Percent of a concentration is more typically used for higher 

 blending higher concentration of gases. 

Note: Concentrations of up to five (5) gases may be added for one multi blend gas 

cylinder. Beneath the CGC, the first cell is labeled BALANCE. If using a multi blend gas 

and contains nitric oxide (NO), this must be the first gas entered. 

7. Repeat steps 2-4 for all gases to be entered for that cylinder 

8. Press CYL ID (F6), to move to cylinder ID field and enter a name for that cylinder. 

Suggestion: use the cylinder number listed on the cylinder tag 

9. After completing set-up for a desired port, press EXIT (F8) to select a different port. Press 

EXIT(F8) again to go to the Main Menu. 

3.9.3 CALIBRATIONS – Multi-point 

Running a multipoint calibration, a zero point and three separate concentrations are to be run to 

determine linearity of the instrument. The proposed audit ranges concentrations found in 40 CFR 

Part 58 Appendix A Section 3.2.2 combined with actual ambient concentrations observed would 

serve as a guideline of concentrations to choose for a multi-point calibration. The recommended 

sequence when performing the multi-point calibration is to perform a zero first, making any 

necessary adjustments to the zero, then move to the highest concentration working backwards 

ending with the low concentration and a final zero. Performing the points in this order more 

completely coats the exposed surfaces allowing for a more stable concentration. An added benefit 

to performing the concentration points in this sequence is the time savings element. 

3.9.3.1 Determination of Concentrations for the Multi-point Calibration

Before performing the actual multi-point calibration, calculate the desired concentration of each 

point based upon the gas cylinder concentrations and gas flow. A recommendation: calculate 

these values before purchasing your pollutant gas standards to ensure having the desired 

concentrations when ready to perform the multi-point calibration. 

Based on the flow verification of the mass flow controllers in the calibrator performed earlier, use 

the actual flow of the zero air and gases in the multi-blend cylinder to calculate what 

concentrations are needed for each pollutant for the multi-point calibration. Refer to Example #1 

as you follow the step by step process. 

 

1. Determine the range of the each pollutant, example CO is 0-5000 ppb
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2. Next, determine 10 and 90 percent of the range, 500 and 4500 ppb respectively. By solving 

for the minimum and maximum concentrations, you will be able to determine what 

concentration of pollutant gas cylinder(s) is needed. 

Note: It will be necessary to determine your total air flow needed through your system. 

 This will be based on the set-up of the entire sampling system including manifold. 

3. Using the following equation and referring to Example #1, Steps 2 & 3, determine what flow 

is needed to generate these concentrations. 

 Concentration of pollutant in cylinder x pollutant flow = desired concentration 

Total flow through system: pollutant flow + zero air flow 

4. In this example, make the pollutant flow, the unknown value and solve the equation for it. 

5. Once the 10 and 90 percent of range have been determined, solve for several more 

concentration values between those two. 

Example #1 – Calculations for actual one point quality checks

Actual flow of gases through the system: 

Zero air: 6.843 = 6.999.6 ccm; gaseous concentrations: 100 ccm = 98.05 ccm, 16.73 ccm = 13.63 

ccm 

Step 1: Zero air is run through the system to flush out any sample air before beginning the 

precision check 

Step 2: Zero air is mixed with a gas containing 

 X concentration of CO at a flow of 100 ccm: 

 10.07 ppm of CO resulting concentration of CO: 139.1 ppb 

 [10.07 ppm x 98.05/ (98.05 + 6999.6)] x 1000 = 139.1 ppb 

 

 X concentration of SO2 at a flow of 100 ccm: 

 

 13.13 ppm of SO2 resulting concentration of SO2: 181.4 ppb 

 [13.13 ppm x 98.05/ (98.05 + 6999.6)] x 1000 = 181.4 ppb - Over Range 

 X concentration of NO at a flow of 100 ccm: 

 10.26 ppm of NO resulting concentration of NO: 141.7 ppb 

 [10.26 x 98.05/ (98.05 + 6999.6)] x 1000 = 141.7 ppb - Over Range 

 

Step 3: Zero air is mixed with a gas containing 13.13 ppm SO2 , 10.26 ppm NO, and 10.07 ppm 

CO resulting in 25.5 ppb of SO2 , 19.9 ppb NO, and 19.6 ppb. 

 X concentration of CO at a flow of 16.73 ccm: 

 10.07 ppm of CO resulting concentration of CO: 19.6 ppb 

 [10.07 ppm x 13.63./ (13.63 + 6999.6)] x 1000 = 19.6 ppb - Under Range 

 X concentration of SO2 at a flow of 16.73 ccm
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 13.13 ppm of SO2 resulting concentration of SO2: 25.5 

 [13.13 ppm x 13.63/ (13.63)+ 6999.6)] x 1000 = 25.5 ppb 

 X concentration of NO at a flow of 16.73 ccm 

 10.26 ppm of NO resulting concentration of NO: 19.9 ppb 

 [10.26 ppm x 13.63/ (13.63)+ 6999.6)] x 1000 = 19.9 ppb 

Step 4: Zero air only is run through the system 

Audit Level Concentration Range, PPM

O3 SO2, NO2 CO

1............ 

2............ 

3............ 

4............ 

5............

0.02-0.05 

0.06-0.10 

0.11-0.20 

0.21-0.30 

0.31-0.90

0.0003-0.005 

0.006-0.01 

0.02-0.10 

0.11-0.40 

0.41-0.90

0.0002-0.002 

0.003-0.005 

0.006-0.10 

0.11-0.30 

0.31-0.60

0.08-0.10 

0.50-1.00 

1.50-4.00 

5-15 

20-50

 Table 1.0 Proposed Audit Levels, 40 CFR, Part 58 Appendix A, Section 3.2.2

 

Example concentrations used for Multipoint Calibration 

3.9.3.2 Performing the Multi-point Calibration 

1 From the READY screen, select Concentration Mode screen. This goes into the MANUAL 

Mode of Calibrations. Calibrations will occur for each analyzer and each point at a time. The 

cursor will appear at the first TARGET GAS concentration. 

2. Enter the desired gas concentration in the TARGET GAS area by moving the cursor using 

the arrows. 

3. Using the arrow keys, move to the TOTAL FLOW area and enter the flow, 10 LPM 

4. Using the arrow keys, cursor to the OZONE area and enter desired concentration if applicable 

for the pollutant needed for NO2 

5. Press START. This will initiate the blending of the gases to the analyzer. 

6. Allow the analyzer to stabilize. 

7. Once stable, wait ten minutes, record the reading for that concentration. 

8. Continue to the next concentration level repeating steps 1 through 5. 

CO SO2 NO/NOy

 

421 ppb 8.69 ppb 12.54 ppb 

855 ppb 18.57 ppb 28.6 ppb 

1078 ppb 40.56 ppb 50.04 ppb 

2660 ppb 59.98 ppb 71.3 ppb 

2990 ppb 82.5 ppb 92.28 ppb 

3534 ppb 93.0 ppb 

4081 ppb 
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9. The above steps can be automated by programming each step into a Sequence and assigning a 

designated time to Run. 

3.9.4 VERIFICATIONS – Zero, Span and One Point Quality Checks 

These steps will assess and confirm the upper range of the multi-point calibration, the zero base 

line and the ambient working range of the instrument. The one point quality checks will 

determine both precision and bias of the analyzers. 

 

This step may be either automated to occur as directed or manually. If performing a manual 

operation, follow the same procedure in Section 3.9.3.2 Performing the Multi-Point Calibrations. 

To operate in AUTOMATIC Mode, it is first necessary to program the Sequences and name the 

Programs.

 

3.9.4.1 SET-UP A SEQUENCE Refer to Section 5.6.1 in the Environics Series 9100 Manual 

In this step, the steps necessary to automate the zero and span check will be set up. Below 

is an automated Sequence used in the project. Refer to Example # 1 for a detailed 

explanation of each step. 

 Zero 

 Run Time Mode Port Air Flow (ccm) Gas (ccm) Total O3 Gas 

ID Conc.

1 10 (min) Conc. 2 6.843 0.0 6.843 0.0 NO 0.0 

2. 20 Conc. 2 6.843 100 6.943 0.0 NO 0.142 

3. 20 Conc. 2 6.843 16.73 6.8597 0.0 NO 0.025 

4. 10 Conc. 2 6.843 0.0 6.843 0.0 NO 0.0 

1. From the READY, select Program Mode (F4)

2. Once in Program Mode, select Sequence (F2)

3. At the blank screen, the cursor is in the RUNTIME column 

4. Enter the desired run time for the first step Refer to Row 1 - 10 minutes 

 Note: If “0” is entered, the step will be skipped and not displayed. 

 Valid run times are 1 to 60 minutes. 

 Twenty lines (20) are available for programming one SEQUENCE

5. Move the cursor to the MODE column. Using the function keys, choose the appropriate 

MODE 

Note: For zero, span, and precision checks use Concentration (CONC) Mode 

6. Move the cursor to the PORT column; enter the desired span gas port which has been 

established in section 3.9.2 (In this case, it is not necessary to use Port 1. Using Port 2 and 

telling it not to send any gas from port 2 serves the same purpose as using Port 1 only) 

7. Move to the Total Flow column and enter the desired flow. 

8. Move to the Gas ID column; when at this column, the GAS ID should default to those 

provided in section 3.9.2 

Note: Gas ID number refers to the order of gases entered in the 

MAINTAIN PORTS screen.
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9. Move to CONC column; enter desired concentration for that gas. Enter concentration in ppm. 

Note: Moving cursor from column to column initiates a check to 

 determine if the value entered is legal. If the value is not possible, an Error 

 message is displayed at the bottom of the screen. 

Note: When using the CONC MODE, the calibrator will automatically 

 calculate the amount of gas needed to produce the required concentration. It is 

considered Good Laboratory Practice to check to determine calculations are correct. This 

can be a random check on one or more of the calculations. 

10. Follow steps 3-9 for additional rows in the Sequence. Example 1 has four rows: zero, one 

quality check - CO; one point quality check – NO and SO2, and a zero. 

11. After entering all steps in a specific sequence, SAVE (F2) the Sequence in the Register. Use 

the function keys to type the name of the Sequence. We’ll call Example # 1 PC-1 and saved 

as sequence line number 01 

12. When the SAVE is complete, press EXIT (F8) to return to the Program Mode

13. Pressing EXIT again, returns to the READY screen. 

3.9.4.2 SET-UP TIMER CONTROL (TIMER CTL) Section 5.6.2 in the Environics Series 

9100 Manual

This is used to automate a number of sequences which allow for automating zero, span and onepoint quality checks. 

1. If this is the first set-up and no previous Timer CTL are stored in the register, the cursor will 

be in the Sequence line and it will be necessary to enter the desired sequence for the specific 

day(s) and time (s) the Timer CTL 

1. From the Main Menu, select Program Mode

2. From Program Mode, select TIMER CTL

3. Go to the day you want a specific Sequence to Run. 

4. Select the Sequence, 01, to be run. 

5. Enter the time to start the Sequence. Once the time is entered, the system will display the 

duration of the Sequence and calculate the end time. 

 

 Note: Time is based on a 24 hour clock with 12:00 being noon and 24:00 

 being midnight. Entering 0:00 will cause the Sequence to be skipped and 

 will not be displayed; therefore must enter time as low as 00:01 

 Note: Three sequences per day may be entered for each day of the week. 

6. Once the desired sequences are in the desired order, press the SAVE (F2) key. 

7. Enter the desired register number. A name may also be entered. 

8. Press EXIT (F8) 
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3.9.4.3 RUN TIMER CTL

1. If a program has been previously saved press the RECALL (F3) key to bring the program to 

the screen 

2. Press the START (F1) key. 

 

Note: The day and time of the next sequence will be displayed in the lower 

 right hand corner of the screen. 

3.9.4.4 Zero, Span, and One-Point Quality Checks 

1. At the Concentration Mode, Manual Operation screen, enter the TARGET GAS 

concentration for the desired gas. The system will determine the actual flows for each port to 

achieve the requested gas concentration(s). Remember: Port 1 is Zero Gas. 

2. Once the TARGET GAS concentrations have been set for the desired gas, press the START 

(F1) key, to begin the operation. 

Note: A similar process is to go to the FLOW MODE and enter the desired flow. The 

 Environics will calculate the actual concentration based on the flow. 

If the desire is to automate the zero, span and one point quality checks, set-up a Sequence and 

SAVE the sequence. Then to Run the Sequence, go to Timer Control and set the desired time to 

run your Sequence. Below is an example of a Sequence set-up for Precision Checks used in the 

testing program. Refer to previous sections 3.9.4.2 and 3.9.4.3. Note: A tri-blend standard was 

used in the testing process. An example of the gases used and the concentrations are found on 

pages 8 and 9. 

3.9.4.5 Calibrator Automation

A Data Acquisition System can control the running of a programmed sequence. To use this 

function, the Environics calibrator must have the optional status board. The INPUTS option 

provides the ability to trigger various actions within the system. The OUTPUTS option will 

signal external devices when certain operating conditions occur. In order for the data acquisition 

system to run the calibrator, the INPUTS option is needed. 

1. Using the key pad, press the STATUS SETUP – INPUT soft key at the Main Menu screen. 

2. At the INPUT screen add the desired function(s), Sequence, Timer Control, etc to be run in 

the Status Line. The desired function(s) can be chosen from the soft keys at the bottom of the 

screen. 

3. When the desired function(s) have been entered, select the EXIT soft key returning to the 

Main Menu and the READY mode. 

Note: the calibrator must be in the READY mode for the automation to occur 
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For further detailed information on communications between the data acquisition system, calibrator and 

analyzers, refer to the Data Acquisition SOP. 

4.0 Quality Control and Quality Assurance 

After confirming the flows through the calibrator, a multi-point calibration for each analyzer should be 

performed. A different certified gas cylinder should be used other than the cylinder used for span and 

precision check gas. 

 

Operating the MFC below 10% of its rated full-scale flow may result in flow inaccuracies. 

The system may produce gas blends that fall outside the accuracy specifications of the system if the gas 

pressures do not stay within the ranges specified for each gas port. 

The operator of the system should not be the same person who performs the multi-point calibrations, but 

in the case of the Trace Gas Analyzers, it could be. 

5.0 References

1. 40 CFR Part 58, Appendix A 

2. Environics Series 9100 Computerized Ambient Monitoring Calibration System, Operating Manual, 

Revision 6, October 1999 

MQO Table for Environics 9100 Calibrator 

Criteria Acceptable Range Minimum Frequency Reference 

 

Mass Flow Controllers 

Zero Air Source 
United States 

Environmental Protection Agency 

Office of Air Quality Planning and Standards 

Emissions, Monitoring and Analysis Division 

Research Triangle Park, NC 

Publicatio