Performance of the Proposed 

New Federal Reference 

Method for Measuring Ozone 

Concentrations in Ambient Air

Technical Report

EPA/600/R-14/432 | October, 2014 | www.epa.gov/ord

Office of Research and Development

National Exposure Research Laboratory

EPA/600/R-14/432 | October, 2014 | www.epa.gov/ord

Office of Research and Development

National Exposure Research Laboratory

Performance of the Proposed 

New Federal Reference 

Method for Measuring Ozone 

Concentrations in Ambient Air

Technical Report
ii 

Russell Long, Eric S. Hall, Melinda Beaver, Rachelle M. Duvall, and Surender Kaushik

National Exposure Research Laboratory

Office of Research and Development

U.S. Environmental Protection Agency

Research Triangle Park, NC, USA 27709

Keith Kronmiller, Michael Wheeler, Samuel Garvey, Zora Drake

Alion Science and Technology

Research Triangle Park, NC, USA 27709

Frank McElroy, Consultant

The McConnell Group

Rockville, MD, USA 20850

Process Modeling Research Branch

Human Exposure and Atmospheric Sciences Division

National Exposure Research Laboratory

U.S. EPA Office of Research and Development

October 2014

Disclaimer/Notice

The information in this document has been funded wholly by the U.S. Environmental Protection Agency. It has been 

subjected to the Agency’s peer and administrative review and has been approved for publication as an EPA document. 

Mention of products or trade names does not indicate endorsement or recommendation for use by the Agency.

Acknowledgments

The U.S. Environmental Protection Agency (EPA) wishes to thank the following collaborating institutions and their 

staff members for their contribution to the success of this research. The National Aeronautics and Space Administration 

Langley Research Center, the National Oceanic and Atmospheric Administration, the Maryland Department of the 

Environment, the Texas Commission on Environmental Quality, the Colorado Department of Public Health and the 

Environment, and Alion Science and Technology are acknowledged for their contributions in supporting EPA in 

the execution of complex laboratory and ambient data collections and analyses. Jim Szykman, Jonathan Krug, Lew 

Weinstock, Joann Rice, Tim Buckley, Roy Fortmann, Lindsay Stanek, Tim Watkins, Jennifer Orme-Zavaleta, and 

Dan Costa (EPA) are acknowledged for their efforts to ensure the success of the research effort reported here. EPA 

would also like to thank the members of the Clean Air Scientific Advisory Committee’s (CASAC) Air Monitoring and 

Methods Subcommittee (AMMS) and Ed Hanlon (Designated Federal Officer for CASAC/AMMS, EPA) for their 

substantial effort in reviewing EPA’s proposed adoption of the new nitric oxide-chemiluminescence Federal Reference 

Method for ozone in ambient air.
 iii

The current Federal Reference Method (FRM) for measuring 

concentrations of ozone in ambient air, described in EPA 

regulations at 40 CFR Part 50, Appendix D, is based on 

the dry, gas-phase, chemiluminescence reaction between 

ethylene and any ozone that may be present in air samples. 

This methodology is technically sound and has well served 

its role in ozone monitoring and as an FRM for many years 

since its establishment in 1971. However, the method 

now no longer meets the full needs of an FRM because no 

manufacturer of ozone-monitoring instruments currently 

offers an FRM analyzer for sale. Existing FRM analyzers 

are largely obsolete and poorly supported (if supported at 

all) by their manufacturers, and, consequently, all current 

ozone monitoring is carried out with other types of monitors 

(equivalent methods). A new FRM for ozone is needed to 

meet the needs that the existing FRM can no longer fulfill.

Executive Summary

A rather similar measurement method, based on the dry, 

gas-phase, chemiluminescence reaction between nitric oxide 

(NO) and any ozone present in ambient samples has been 

subjected to extensive laboratory and field testing (along with 

an FRM and other Federal Equivalent Methods [FEMs]) to 

determine its performance and other attributes relative to 

those of the existing FRM. This report describes the nature 

and results of this testing and documents the conclusion 

that this alternative nitric oxide-chemiluminescence 

(NO-CL) method has performance as good as or better 

than the existing FRM. Further, at least two NO-CL ozonemonitoring analyzers are commercially available (from 

one manufacturer) and have been designated by the U.S. 

Environmental Protection Agency as FEMs for use in ozonemonitoring networks. Therefore, this alternative method is 

shown to be well suited as a supplemental FRM for ozone 

to serve in the FRM role as a practical reference standard 

for candidate FEMs and for quality assurance of ozonemonitoring data.
iv 
 v

List of Tables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi

List of Figures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii

Acronyms/Abbreviations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix

1.0 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

2.0 Issues of Concern Regarding the Ozone FRM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

3.0 Ozone Monitor/Analyzer Types. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

3.1 Ethylene-Chemiluminescence Ozone Analyzers (FRM). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

3.1.1. Theory of Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

3.1.2. Advantages. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

3.1.3. Disadvantages. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

3.1.4. Interferences. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

3.1.5. Current Status. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

3.2 NO-CL Ozone Analyzers (FEM). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

3.2.1. Theory of Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

3.2.2. Advantages. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

3.2.3. Disadvantages. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

3.2.4 Interferences. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

3.2.5. Current Status. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

3.3. UV Photometric Ozone Analyzers (FEM). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

3.3.1. Theory of Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

3.3.2. Advantages. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

3.3.3. Disadvantages. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

3.3.4. Interferences. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

3.3.5. Current Status. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

3.4 Other Ozone Measurement Methodologies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

3.4.1 Open-Path Ozone Monitors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

3.4.2 Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

4.0 Performance Tests of the NO-CL Method. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

4.1 Test Analyzer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

4.2 Manufacturer Tests. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

4.3 EPA Tests. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

4.3.1 Background. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

4.3.2 Approach. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

4.3.2.1 Laboratory Tests. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

4.3.2.2 Ambient Evaluations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

4.3.2.3 Quality Assurance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

4.3.3 Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

4.3.3.1 Laboratory Test Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

4.3.3.2 Ambient Evaluation Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

5.0 Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

6.0 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Table of Contents
vi 

Table 1. Comparison of Model T265 and Model 211 Ozone Analyzer’s Manufacturer’s Performance Specifications with the 

Existing and Proposed Performance Requirements for Ozone FRM and FEM Analyzers. . . . . . . . . . . . . . . . . . . . . . . . 9

Table 2. FRMs and FEMs for Ozone Used in the Evaluation Study. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Table 3. Ozone Analyzer Inventory Deployed During Each Field Study1Used for calibration and nightly zero and 

span checks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Table 4. Comparison of EPA Laboratory Test Results to Existing and Proposed Revised FRM and FEM Performance 

Requirements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Table 5. Comparison of 1-h EPA Ozone Analyzer Results Collected During the Various Field Deployments. . . . . . . . . . . . . . . 13

Table 6. Comparison of Maximum Daily 8-h-Average Ozone Analyzer Results Collected During the Various Field 

Deployments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

List of Tables
 vii

List of Figures

Figure 1. Apparatus for performing laboratory-based evaluations of FRM/FEM analyzers.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Figure 2. Comparison of the 1-h-average Bendix 8002 (FRM) and T265 (NO-CL) ozone results in ambient air at Houston, TX, 

during September 2013 (left) and at Denver, CO, during July and August 2014 (right).. . . . . . . . . . . . . . . . . . . . . . . . 13

Figure 3. Comparison of the 1-h-average Model 211 (SL-UV) and T265 (NO-CL) ozone results in ambient air at Houston 

(LaPorte), TX, during September 2013 (top) and at Denver, CO, during July and August 2014 (bottom). . . . . . . . . . 14

Figure 4. Comparison of the 1-h-average EC9810 and T265 (NO-CL) ozone results in ambient air at Padonia, MD, during July 

2011 (top) and comparison of the 1-h-average Model 205 and T265 (NO-CL) ozone results in ambient air at RTP, NC, 

during June and July 2012 (bottom). Both the EC9810 and the Model 205 employ the UV photometric method and 

contain sample conditioning systems to remove water from the sample stream.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Figure 5. Comparison of the 1-h-average 49i and T265 (NO-CL) ozone results in ambient air at RTP, NC, during June and July 

2012 (top) and at Houston (LaPorte), TX, during September 2013 (bottom). The 49i employs the UV photometric 

method but does not contain a sample conditioning system to remove water from the sample stream.. . . . . . . . . . . . . 15

Figure 6. Comparison of the maximum daily 8-h-average (MDA8) ozone results in ambient air at Houston (LaPorte), TX, 

during September 2013 (top) and at Denver, CO, during July and August 2014 (bottom).. . . . . . . . . . . . . . . . . . . . . . 15

 ix

AIRS Ambient Air Innovative Research Site

API Advanced Pollution Instrumentation

AQS Air Quality System

C2H4 ethylene

CFR Code of Federal Regulations

Cal/Dil calibration/dillution

Cl2 chlorine

CO carbon monoxide

CO2 carbon dioxide

DC direct current

DISCOVER-AQ Deriving Information on Surface 

Conditions from Column and Vertically 

Resolved Observations Relevant to Air 

Quality

DOAS differential optical absorption 

spectroscopy

EPA U.S. Environmental Protection Agency

FEM Federal Equivalent Method

FR Federal Register

FRM Federal Reference Method

H2O water

H2S hydrogen sulfide

Hg mercury

hv photon

IE interference equivalent

Acronyms/Abbreviations

MDA8 maximum daily 8-h average

MFC mass flow controller

NAAQS National Ambient Air Quality Standards

NIST National Institute of Standards and 

Technology

NO nitric oxide

NO2 nitrogen dioxide

NO-CL nitric oxide-chemiluminescence

O2 oxygen

O3 ozone

OD outer diameter

Pb lead

PM particulate matter

PMT photomultiplier tube

R2 coefficient of determination

RH relative humidity

RMS root mean square

RTP Research Triangle Park, NC

SLAMS State and Local Air Monitoring Station

SL-UV scrubberless ultraviolet

SO2 sulfur dioxide

T temperature

URL upper range limit

UV ultraviolet

V volts

VOC volatile organic compound

x linear regression independent variable

y linear regression dependent variable

ZAG zero air generator

 1

Under the Clean Air Act, the U.S. Environmental Protection 

Agency (EPA) has established National Ambient Air Quality 

Standards (NAAQS) (i.e., concentration limits) for six air 

pollutants, known as the criteria air pollutants: (1) carbon 

monoxide (CO), (2) lead (Pb), (3) nitrogen dioxide (NO2), 

(4) sulfur dioxide (SO2), (5) ozone (O3), and (6) particulate 

matter (PM). These NAAQS are set forth in Title 40, Part 

50 of the Code of Federal Regulations (40 CFR Part 50). 

EPA and the States are jointly responsible for monitoring the 

ambient air for these six criteria pollutants. This monitoring 

is carried out as part of a national network of approximately 

4000 monitoring sites, called the State and Local Air 

Monitoring Stations (SLAMS). The air quality data obtained 

from these sites are collected in EPA’s Air Quality System 

(AQS) database, along with other information, and are used 

for 

• determining compliance with the NAAQS, 

• assessing effectiveness of State Implementation Plans 

in addressing NAAQS nonattainment areas, 

• characterizing local, State, and national air quality 

status and trends, and 

• associating health and environmental damage with air 

quality levels and concentrations.

To assure the accuracy, integrity, and uniformity of the 

SLAMS air quality monitoring data collected, EPA has 

established one or more Federal Reference Methods 

(FRMs) for measuring each criteria pollutant. These FRMs 

are set forth in several appendixes to 40 CFR Part 50 and 

typically specify a particular measurement technique to 

be implemented in a commercially produced monitoring 

instrument. These monitoring instruments must be shown to 

meet specific performance and other requirements detailed 

in the EPA regulations at 40 CFR Part 53, in which case the 

instrument may be designated by EPA as an FRM analyzer.

Also, to encourage innovation and development of new air 

quality monitoring methods, EPA has provided for Federal 

Equivalent Methods (FEMs). An FEM is not constrained 

to the particular measurement technique specified in the 

corresponding FRM. However, an FEM must meet the same 

or similar performance requirements as specified for the 

corresponding FRM, and in addition, it must show a high 

degree of comparative agreement with collocated FRM 

measurements at one or more field testing sites. These FEM 

requirements also are detailed in 40 CFR Part 53, and a 

monitor that is shown to meet all applicable requirements 

may be designated by EPA as an FEM monitor.

Section 2.1 of Appendix C to 40 CFR Part 58 mandates the 

use of either FRMs or FEMs for SLAMS monitoring to 

determine compliance with the NAAQS. In addition, FRMs 

are used in assessing the quality of the SLAMS monitoring 

data and as reference standards of comparison for designation 

of FEM monitors. The current listing of all designated FRMs 

and FEMs can be found at http://www.epa.gov/ttnamti1/files/

ambient/criteria/reference-equivalent-methods-list.pdf.

1.0

Introduction

 3

The current FRM for measuring concentrations of ozone 

in ambient air, described in EPA regulations at 40 CFR 

Part 50, Appendix D,1,2 is based on the dry, gas-phase, 

chemiluminescence reaction between ethylene (C2H4) and 

any ozone that may be present in air samples. This method 

was established in 1971, and, at that time and for many 

years after, it was widely used for monitoring ozone, as 

implemented in a variety of ozone analyzers manufactured by 

several instrument manufacturers. These analyzers proved to 

provide accurate and reliable monitoring data in the SLAMS 

for many years. This FRM is specific for ozone and has no 

significant interferences. It served its role well as an FRM 

and remains a technically sound method today.

Unfortunately, the method requires a constant supply of 

ethylene for continuous operation. Ethylene is a gas that 

is stored in high-pressure gas cylinders and is flammable 

and explosive. A large gas cylinder is required for extended 

operation, and the use of such gas cylinders often is restricted 

to an outdoor location or entirely precluded at some potential 

monitoring sites, rendering use of the FRM analyzers 

inconvenient, if not problematic, at least at many potential 

monitoring sites. Ozone analyzers utilizing an ultraviolet 

(UV) photometric measurement technique, which became 

available in the 1980s, do not require a supply of gas or any 

other reagent and are much more convenient to install and 

operate. Several UV photometric analyzer models have been 

designated by EPA as FEMs, and such monitors (along with 

a few other types of FEMs) have completely replaced the use 

of FRM analyzers in SLAMS monitoring. With no demand 

for FRM analyzers for SLAMS monitoring, instrument 

manufacturers have stopped producing them. The last ozone 

FRM analyzer was designated by EPA in 1979.

Although FEMs can fill the need for routing monitoring, 

FRM analyzers are required for other important purposes, 

such as quality assurance of monitoring data and for 

reference measurements for the required FEM comparability 

qualification. With no manufacturer of ozone-monitoring 

instruments currently offering an FRM analyzer for sale, 

the existing FRM can no longer fulfill the needs of an FRM. 

Previously manufactured FRM analyzers are largely obsolete, 

poorly supported (if supported at all) by their manufacturers, 

and likely now to be well beyond their expected operational 

lifetime. Because of the lack of availability and poor support, 

they are entirely inadequate for FRM-specific applications. 

For these reasons, a new FRM is needed.

A similar measurement technique based on the dry, gas-phase 

chemiluminescence reaction of nitric oxide (NO) with 

ozone in sampled air has been identified as a potential 

and advantageous candidate for a new ozone FRM. This 

report documents the extensive laboratory and field testing 

and analyses that have been carried out to examine the 

viability of this nitric oxide-chemiluminescence (NO-CL) 

method as a proposed new FRM for ozone. In addition, this 

report documents laboratory and field testing and analysis 

of additional methodologies that were also evaluated as 

potential FRMs. The results of this examination support the 

conclusion that the NO-CL method has the performance 

characteristics and other attributes necessary and appropriate 

for a new FRM for ozone.

2.0

Issues of Concern Regarding the Ozone FRM

 5

Various types of methods have been developed to monitor 

ozone concentrations in ambient air, and analyzers using 

several different methodologies have been designated by EPA 

as either FRM or FEM monitors. The current ozone FRM is 

the ethylene-chemiluminescence method, based on the dry, 

gas-phase reaction between ethylene and ozone as described 

in 40 CFR Part 50, Appendix D.

Because of the significant limitations of the current ethylenechemiluminescence type FRM analyzers, other types of 

ozone-measurement technologies have been examined as 

possible candidates for a new ozone FRM. The types of 

ozone methods that have achieved FRM or FEM status are 

described briefly below, with consideration of the FEMs as 

possible candidates for a new FRM.

3.1 Ethylene-Chemiluminescence Ozone 

Analyzers (FRM)

3.1.1. Theory of Operation

These analyzers implement the measurement principle 

specified for FRM analyzers, described in Appendix D of 40 

CFR Part 50. Ethylene-chemiluminescence ozone analyzers 

measure ozone concentrations by using the dry, gas-phase 

chemiluminescence reaction of ethylene with ozone in a 

flowing air sample. The overall reaction mechanism for 

ethylene-chemiluminescence generally proceeds as follows:

C2H4 + O3 à CO2 + H2CO* + CHO- + *OH.

The reaction generates electronically activated formaldehyde 

that luminesces (which is indicated by an asterisk) in the high 

UV to visible portion of the spectrum (380 nm to 550 nm) 

and vibrationally activated hydroxide ions that luminesce 

in the visible light to low infrared portion of the spectrum 

(550 nm to 800 nm). The number of photons emitted during 

the reaction is directly proportional to the amount of ozone 

present. When air without ozone (zero air) or an air sample 

containing ozone is introduced into the analyzer mixing 

chamber/reaction cell, the emitted photons (if any) are 

counted by a photomultiplier tube (PMT), with its response 

centered at 440 nm, then the count is converted to ozone 

concentration by a software-driven algorithm.3 Measurements 

are referenced to certified ozone concentration standards 

according to the calibration procedure specified as part of the 

FRM.

3.1.2. Advantages

The method is largely free of measurement interferences. It 

has been implemented successfully by several instrument 

manufacturers in various ozone analyzer models, which (in 

years past) have proved to provide stable and reliable ozone 

measurements in monitoring network operation. This method 

is not impacted by the known interferents (hydrogen sulfide 

[H2S], carbon dioxide [CO2], NO, water [H2O], meta-xylene, 

volatile organic compounds [VOCs], mercury [Hg], NO2, 

SO2, and chlorine [Cl2]), which are found in ambient air and 

can reduce the operational performance and reliability of the 

UV-based ozone analyzers. The resulting chemiluminescence 

from the reaction between ethylene and ozone is specific to 

ozone (i.e., there are no other atmospheric substances that 

react with ethylene resulting in chemiluminescence at or near 

the 440-nm wavelength). The reaction between ethylene and 

ozone is a flameless one.

3.1.3. Disadvantages

The method requires a constant supply of ethylene, which 

is a dangerous, flammable, and potentially explosive gas 

typically stored in high-pressure gas cylinders. The use of 

such gas cylinders may be inconvenient and is often restricted 

by building fire codes or other monitoring site limitations. 

Following the development and availability of other types of 

ozone monitors (such as those utilizing the UV absorption 

method) that do not require a supply of reagent gas, use of 

such alternative methods in ozone-monitoring networks 

completely supplanted the use of FRM analyzers in virtually 

all current ozone-monitoring networks. With little or no 

demand for FRM analyzers, manufacturers no longer produce 

them. There are no ethylene-chemiluminescence FRM 

analyzers currently used in EPA’s SLAMS network.

3.1.4. Interferences

The chemiluminescence from the reaction between ethylene 

and ozone is specific to ozone, thus the method is not 

impacted significantly by typical concentrations of potential 

interferents (such as H2S, CO2, NO, meta-xylene, VOCs, 

Hg, NO2, SO2, and Cl2) that may occur in ambient air. 

There are no other atmospheric substances that react with 

ethylene resulting in chemiluminescence near 440 nm. Some 

sensitivity to variations in water vapor concentration (because 

of quenching of the chemiluminescence reaction) generally 

does not present a significant measurement problem.

3.1.5. Current Status

There are no ethylene-chemiluminescence analyzers currently 

in EPA’s SLAMS network.

3.0

Ozone Monitor/Analyzer Types
6 

3.2 NO-CL Ozone Analyzers (FEM)

3.2.1. Theory of Operation

This method is quite similar to that of the ethylenechemiluminescence FRM. NO-CL ozone analyzers measure 

ozone concentrations by using the fact that the dry, gas-phase 

reaction between nitric oxide and ozone generates nitrogen 

dioxide in an activated state (NO2

*

), and oxygen (O2).4,5 As 

each unstable NO2

*

 returns to a lower energy state (NO2), it 

emits a photon (hv). The reaction causes luminescence in a 

broadband spectrum ranging from visible light to infrared 

light (approximately 590 nm to 2800 nm). The two-step 

gas-phase reaction proceeds as follows:

NO + O3 à NO2

*

 + O2,

then

NO2

* à NO2

 + hv.

The number of photons emitted during the reaction is directly 

proportional to the amount of ozone present, and the photons 

are counted by a PMT. The photon count is converted to 

ozone concentration by a software-driven algorithm.

3.2.2. Advantages

Similar to the FRM, the NO-CL method has no significant 

interferents. The method behaves in the same manner as 

the ethylene-chemiluminescence FRM when exposed to the 

same interferents listed in 40 CFR Part 53, Table B-3 (e.g., 

H2S, CO2, and H2O) that are found in ambient air, which 

may have an effect on the response of the widely-used 

UV-spectrophotometric ozone methods in certain situations.

The NO-CL method is designated as an FEM. It meets all 

of the same performance specifications (as specified in 

40 CFR Part 53) as the existing FRM and is comparable 

to the existing FRM from a measurement perspective. In 

addition, the NO-CL devices currently are in manufacturing 

production. The method has been implemented successfully 

by at least one instrument manufacturer, which offers two 

models that have been designated by EPA as FEMs.

In addition, extensive laboratory and field testing by EPA 

has shown that the NO-CL method exhibits performance that 

equals or exceeds that of FRM analyzers and is, thus, a fully 

qualified candidate for consideration as a proposed new FRM 

for ozone.

3.2.3. Disadvantages

The method requires a constant supply of nitric oxide 

gas (approximately 1% [w/w]), which is stored in a highpressure gas cylinder. Because nitric oxide is not flammable 

or explosive, monitoring site restrictions on the use of a 

high-pressure nitric oxide gas cylinder may be less than 

those for ethylene gas needed for FRM analyzers, but 

analyzer installation is still somewhat inconvenient. For 

use in nonmonitoring FRM applications, where shorter 

term operation is likely, the use of small, more convenient, 

compressed-gas cylinders (as opposed to the large cylinders 

required for long-term operation) is possible. High 

concentrations of nitric oxide such as those found in the nitric 

oxide cylinders are toxic (asphyxiant).

3.2.4 Interferences

The NO-CL method is not impacted significantly by typical 

concentrations of potential interferents (such as H2S, CO2, 

H2O, NO, meta-xylene, VOCs, Hg, NO2, SO2, and Cl2) 

that may occur in ambient air. Further testing by EPA has 

confirmed the lack of any significant interferences from 

compounds that might be encountered in ambient air 

monitoring.

3.2.5. Current Status

Currently, one commercial manufacturer has had an NO-CL 

instrument type (with two different model numbers) 

designated in 2011 as an FEM.

3.3. UV Photometric Ozone Analyzers (FEM)

3.3.1. Theory of Operation

UV photometric ozone analyzers determine ozone 

concentrations by quantitatively measuring the attenuation 

of light due to absorption by ozone present in an absorption 

cell at the specific wavelength of 254 nm.6,7 The ozone 

concentration generally is determined through a two-step 

process in which the light intensity passing through the 

sample air (I) is compared with the light intensity passing 

through similar sample air from which all ozone is first 

removed (I0). The ratio of these two light-intensity values 

(I/I0) provides the measure of the light absorbed at 254 nm, 

and the ozone concentration in the sample then is determined 

through the use of the Beer-Lambert Law as:

I/I0 = e-KLC(C = 1/KL ln [I/I0]),

where L is the length of the absorption cell (in centimeters), 

C is the ozone concentration (in parts per million), and 

K is the absorption cross section of ozone at 254 nm at 

standard atmospheric temperature and pressure conditions 

(308 atm-1 cm-1). Some systems have one absorption cell with 

I and I0 measured alternately, whereas other systems have two 

separate absorption cells with I and I0 measured concurrently. 

Photometric monitors for ozone generally use mercury lamps 

as the UV light source, with optical filters to attenuate lamp 

output at other than the 254 nm wavelength. Zero air for the 

reference measurement typically is obtained with manganese 

dioxide, heated silver wool, or nitric oxide gas to “scrub” 

ozone from the sample air while preserving other substances 

in the sample air that absorb at 254 nm, so that their effects 

are cancelled in the differential I/I0 measurement.
 7

3.3.2. Advantages

UV photometric ozone analyzers require no external gas 

supply or other reagents and are compact, easy to install, 

and convenient to operate. Various analyzer models from 

several instrument manufacturers have been shown to meet 

FEM performance requirements and have been designated 

as FEMs by EPA. These UV FEM analyzers currently 

represent the vast majority of analyzers used in State and 

local ozone monitoring networks. In general, UV photometric 

measurements compare very well with those obtained from 

FRM analyzers. UV ozone analyzers represent more recent 

measurement technology than the current FRM and would be 

advantageous for consideration as a new FRM because they 

currently are in manufacturing production, and their use is 

widespread.

3.3.3. Disadvantages

The integrity of the ozone zero air scrubber is critical and 

may enable measurement interferences if it does not perform 

adequately (see section 3.3.4 Interferences). Similarly, any 

tendency of the scrubber to fail to effectively remove all 

ozone from the reference sample will result in a measurement 

bias. The integrity of the scrubber has been shown to be 

affected to some extent by changes in sample air humidity. 

These shortcomings make the method an unlikely candidate 

for consideration as a new FRM for ozone. The UV 

photometric method is impacted by known interferences 

(see section 3.3.4 Interferences) that often are found in 

ambient air and may reduce the operational performance and 

reliability of this method.

3.3.4. Interferences

Various substances that may be present at some monitoring 

sites (including H2S, CO2, H2O, meta-xylene, Hg, and 

aromatic hydrocarbon compounds) have strong absorbance of 

light at 254 nm and may cause measurement interferences if 

the zero air ozone scrubber fails to pass any such substances 

unattenuated in the zero reference air.

3.3.5. Current Status

UV photometric analyzers are the most widely used methods 

for ozone compliance measurements. There were 1,367 UV 

photometric analyzers in EPA’s SLAMS network as of June 

2014. A newly introduced and recently designated (June 

18, 2014, 79 FR 34734) ozone FEM analyzer represents 

a variation of the UV photometric method, known as the 

“scrubberless” UV photometric method,4 that specifies 

removal of ozone from the sample air for the zero reference 

by a gas-phase reaction with nitric oxide rather than via 

a conventional solid chemical scrubber. The nitric oxide 

reacts with the ozone much faster than with other potential 

interfering compounds and is very effective at removing the 

ozone without affecting other compounds that may be present 

in the ambient air sample. The differential UV measurement 

then effectively can eliminate interferences to an insignificant 

level. EPA currently is evaluating this variation of the UV 

photometric method for future consideration as an ozone 

FRM.

3.4 Other Ozone Measurement Methodologies

3.4.1 Open-Path Ozone Monitors

EPA has designated two open-path air analyzers as FEMs. 

These analyzers operate on the principle of differential 

optical absorption spectroscopy (DOAS) over an open path 

of several meters up to 1 kilometer.7 The DOAS system 

analyzes the spectral absorption fingerprint of several 

ambient air pollutants over a range of visible or nearUV wavelengths. This technology was not evaluated as a 

potential candidate FRM for ozone because its open-path 

nature makes it difficult to assess in a laboratory setting.

3.4.2 Sensors

Sensors are small, relatively inexpensive monitoring devices 

that represent a new class of air pollution measurement 

devices. These gas-measurement sensors, such as those 

used to measure ozone, are based on electrochemical, metal 

oxide, and spectroscopic technologies. Some sensors have 

undergone preliminary testing in EPA’s Office of Research 

and Development laboratory in Research Triangle Park 

(RTP), NC.8 A number of sensors have been evaluated in 

the field in Houston (September 2013), and in Denver, CO 

(July and August 2014). EPA continues its laboratory and 

field analysis of ozone sensors. Preliminary results will be 

documented in future technical reports and peer-reviewed 

scientific journal articles.

 9

4.1 Test Analyzer

The NO-CL method—the proposed new FRM—is 

implemented in two ozone analyzers manufactured by 

Teledyne Advanced Pollution Instrumentation (API), Inc. 

(9480 Carroll Park Drive, San Diego, CA 92121-5201, 

858-657-9800, www.teledyne-api.com). Both Models 265E 

and T265 provide user-selectable ozone measurement ranges 

of 0 to 100 ppb to 0 to 2000 ppb (0 to 2 ppm) and identical 

performance, with the following manufacturer ratings.

Zero noise <0.15 ppb (root mean square [RMS])

Span noise <0.5% of reading (RMS) above 100 ppb

Lower detectable 

limit <0.3 ppb

Zero drift <0.5 ppb/24 h

Span drift <0.5% of full scale/24 h

Rise and fall time <20 s to 95% of final reading

Linearity <1% of full scale

Precision <0.5% of reading

Sample flow rate 500 cm3/min ±10%

The Model T265 features a more advanced user interface 

than the standard Model 265E.

4.2 Manufacturer Tests

Both analyzer models were designated by EPA as FEMs 

(identified as Equivalent Method No. EQOA-0611-199) 

on October 7, 2011 (76 FR 62402). This designation 

indicates that a representative Model 265 analyzer was 

tested in accordance with the FEM test and performance 

requirements specified in 40 CFR Part 53 and has, to EPA’s 

satisfaction, been shown to meet all such requirements. 

In laboratory FEM tests, the candidate FEM analyzer is 

required to show performance equal to or better than the 

FRM/FEM requirements given in Table B-1 of Part 53. 

These requirements are listed in Table 1, along with revised 

performance requirements that EPA intends to propose for 

new ozone FRM and FEM analyzers.

Table 1 compares the manufacturer’s claimed performance 

for the analyzer (taken from the manufacturer’s published 

specification sheet) with both the existing FRM and FEM 

performance requirements, as well as the revised and new 

requirements that EPA intends to propose for new FRM 

and FEM analyzers. The manufacturer’s performance 

specifications for some of performance parameters defined 

Table 1. Comparison of Model T265 and Model 211 Ozone Analyzer’s Manufacturer’s Performance Specifications with 

the Existing and Proposed Performance Requirements for Ozone FRM and FEM Analyzers

Performance Parameter

Model T265 Manufacturer’s 

Claimed Performance 

Specification1

Model 211 

Manufacturer’s 

Claimed Performance 

Specification1

FRM and FEM 

Performance Limit 

Specifications2

Proposed New FRM and FEM Performance Limit 

Specifications3

Standard Range Lower Range

1. Range 0-0.5 ppm (0-0.1 to 0-2.0 

available)

0.0005-2.0 ppm 0-0.5 ppm 0-0.5 ppm 0-<0.5 ppm

2. Noise <0.00015 ppm 0.005 ppm 0.001 ppm 0.0005 ppm

3. Lower detectable limit <0.0003 ppm 0.001 ppm 0.010 ppm 0.003 ppm 0.001 ppm

4. Interference equivalent

 Each interferent Not specified ±0.002 ppm ±0.02 ppm ±0.005 ppm ±0.005 ppm

 Total, all interferents Not specified ≤0.007 ppm 0.06 ppm — —

5. Zero drift, 12- and 24-h <0.0005 ppm <0.001 ppm ±0.02 ppm ±0.004 ppm ±0.002 ppm

6. Span drift, 80% of URL <0.5% (of 0.5 ppm URL) <0.8% ±5.0% ±3.0% ±3.0%

7. Lag time <10 s 1 min 20 min 2 min 2 min

8. Rise time <20 s 1 min 15 min 2 min 2 min

9. Fall time <20 s 1 min 15 min 2 min 2 min

10. Precision

 20% URL <0.5% of reading (0.001 ppm) <0.4% of reading 0.010 ppm 2%4 2%4

 80% URL <0.5% of reading (0.004 ppm) <1% of reading 0.010 ppm 2%4 2%4

1

The manufacturer may not specify performance for all of the performance parameters defined by the FRM/FEM requirements or may measure 

them differently. The manufacturers’ specification sheets for Model T265 and Model 211 can be found in references 12 and 13, respectively.

2

Current performance specifications taken from Table B-1 to Subpart B of Part 53—Performance Limit Specifications for Automated Methods

3

In conjunction with the proposal of a new FRM for O3, EPA intends to propose revised, more stringent performance specifications, along with 

new performance specifications applicable to optional lower ranges for O3 analyzers. 4

Standard deviation expressed as percent of the URL.

4.0

Performance Tests of the NO-CL Method
10 

for FRM and FEM analyzers are not given or may be 

described somewhat differently. As noted above, the 

designation of the analyzer as an FEM confirms that actual 

FEM tests of these performance parameters, as carried out 

by the manufacturer, were examined by EPA, and those test 

results were found to show that that the analyzer met all 

existing FEM requirements. (These manufacturer-conducted 

FEM test results are included in a confidential business 

information claim covering the entire FEM application and, 

therefore, cannot be presented here.) Table 1 also suggests a 

high probability that the analyzer would meet the proposed 

revised and new requirements, as well.

The FEM test requirements also include a field test to 

compare ozone measurements from the candidate method 

with concurrent measurements from an FRM analyzer 

at a suitable field test site (40 CFR Part 53, Subpart C).9

Agreement must be shown within 20 to 40 ppb, depending on 

the concentration level. Again, designation of the Model 265 

as an FEM by EPA indicates that such a test was performed 

by the manufacturer, and that the results were examined by 

EPA and were determined to meet the FEM test requirements 

for comparability. (Again, these test results cannot be 

presented here because they are included in the confidential 

business information claim for the FEM application.)

4.3 EPA Tests

4.3.1 Background

EPA conducted extensive laboratory and ambient testing of 

the NO-CL method (Model T265 analyzer) (1) to verify that 

the method meets all existing requirements for FRM and 

FEM analyzers and its capability to serve the functions of 

a reference method and (2) to determine its ability to meet 

proposed revised and new requirements for FRM and FEM 

analyzers. The tests also evaluated the analyzer’s general 

performance relative to the FRM (Bendix Model 8002 

Ozone Analyzer; Reference Method No. RFOA-0176-007) 

and several other FEM ozone analyzers, namely Thermo 

Scientific Model 49i Photometric Ambient Ozone Analyzer 

(Equivalent Method No. EQOA-0880-047), Ecotech EC9810 

Ozone Analyzer (Equivalent Method No. EQOA-0193-

091) and 2B Technologies Model 205 (Equivalent Method 

No. EQOA-1410-190) and Model 211 (Equivalent Method 

No. EQOA-0514-215). The Bendix Model 8002 is a true 

ethylene-chemiluminescence FRM analyzer that has been 

refurbished to full operational status. These analyzers, 

operation principle, and designation information are 

summarized in Table 2.

4.3.2 Approach

4.3.2.1 Laboratory Tests

The laboratory-based tests were conducted in accordance 

with the test procedures detailed in Subpart B of 40 CFR 

Part 53.10 Prior to laboratory-based testing, all analyzers 

under evaluation were calibrated according to manufacturers’ 

operation manuals and in accordance with FRM requirements 

listed in 40 CFR 50, Appendix D. During laboratory testing, 

all analyzers were connected to a common sampling manifold 

(Ace Glassware) via 6.4-mm (0.25-in) outer diameter (OD), 

perfluoroalkoxy Teflon sampling lines. Particulate filters 

(5-μm pore size) were fitted to each analyzer’s inlet port. 

Air containing known concentrations of the test atmosphere 

(ozone) and/or interferent gas was provided to the manifold 

inlet as needed to conduct the test procedures. An exhaust 

line was attached to the manifold outlet and placed into the 

laboratory’s 6-in ceiling vent to allow a continuous flowthrough-design feature. All calibration gas concentrations and 

laboratory test atmospheres were established using a National 

Institute of Standards and Technology (NIST)-traceable and 

programmable dynamic dilution calibration system (Teledyne 

API Model T700U). Constituents were delivered to the 

system from either the T700U enclosed ozone generator 

(with NIST-traceable photometer) or EPA protocol (±2% 

accuracy) reference gas standards. Dilution air that had been 

scrubbed of all contaminants was delivered to the mixing 

system to meet test gas dilution needs. Relative humidity 

(RH) within the system was produced and controlled through 

the use of a deionized water bubbler. Temperature and RH 

were measured with a temperature/RH probe consisting of a 

precision thin-film platinum, 1000-Ω resistive temperature 

device that employs a linear resistance change with 

temperature converted to a 0- to 10-V DC output proportional 

to 0 to 100.0 °C. The sensor was calibrated using a NISTtraceable reference thermometer. The RH sensor consists 

of a HyCal, Inc., IH-3602-C monolithic integrated circuit 

capacitance sensor that produces a linear voltage proportional 

to RH (0- to 10-V DC output directly proportional to 0 to 

100% RH). The RH sensor was calibrated using saturated 

Table 2. FRMs and FEMs for Ozone Used in the Evaluation Study

Manufacturer and Model Operation Principle FRM/FEM Designation

Bendix Model 8002 (FRM) Ethylene-chemiluminescence Federal Register: Vol. 41, page 5145, 02/04/76

Teledyne API Model T265 (FEM) NO-CL Federal Register: Vol. 76, page 62402, 10/07/11

2B Technologies Model 211 (FEM) “Scrubberless” UV photometric (dual beam) Federal Register: Vol.79, pages 34734-34735, 06/18/2014

2B Technologies Model 205 (FEM) UV photometric (dual beam) Federal Register: Vol.75, pages 22126-22127, 04/27/10

Ecotech EC9810 (FEM) UV photometric Federal Register: Vol. 58, page 6964, 02/03/93

Thermo Scientific Model 49i (FEM) UV photometric Federal Register: Vol. 45, page 57168, 08/27/1980

Teledyne API Model T700U1 Dynamic dilution calibrator

Teledyne API Model 7011 Zero air generator

1

Used for calibration and nightly zero and span checks
 11

salt solutions that have known RH over headspace. The 

temperature and RH signal response were shown on a liquid 

crystal display and logged using an in-laboratory dataacquisition system (Envidas Ultimate). A schematic diagram 

of the apparatus used during the laboratory-based evaluations 

is given in Figure 1.

4.3.2.2 Ambient Evaluations

Ambient evaluations of the proposed FRM and the various 

FEM methods were conducted during field-intensive 

studies at the Ambient Air Innovative Research Site (AIRS) 

located on the EPA campus in RTP during the springs and 

summers of 2012 and 2014. Ambient evaluations also were 

performed as part of the National Aeronautics and Space 

Administration’s Deriving Information on Surface Conditions 

from Column and Vertically Resolved Observations 

Relevant to Air Quality (DISCOVER-AQ) project conducted 

during July 2011 near Baltimore, MD; September 2013 in 

Houston (La Porte); and July and August 2014 near Denver. 

During field-intensive studies, instruments were calibrated 

according to manufacturers’ operation manuals and in 

accordance with FRM requirements listed in 40 CFR 50, 

Appendix D. During the ambient evaluation campaigns, 

nightly automated zero and span checks were performed 

to monitor the validity of the calibration and to control for 

drifts or variations in the span or zero response. Both the 

calibration gas concentrations and the nightly zero and span 

gas concentrations were delivered using the T700U dynamic 

dilution calibration system described in section 4.3.2.1. The 

analyzers were contained within a temperature-controlled 

shelter during the sampling campaigns. A glass inlet with 

sampling height located approximately 5 m above ground 

Figure 1. Apparatus for performing laboratory-based evaluations of FRM/FEM analyzers.

Field Deployment 

(Date) Ozone Analyzer

Baltimore MD (July 

2011)

Teledyne API Model T265 (FEM)

Ecotech EC9810 (FEM)

Teledyne API Model T700U1

Teledyne API Model 7011

AIRS 2012 (June 

and July 2012)

Teledyne API Model T265 (FEM)

2B Technologies Model 205 (FEM)

Bendix Model 8002 (FRM)

Thermo Scientific Model 49i (FEM)

Teledyne API Model T700U1

Teledyne API Model 7011

Houston (LaPorte), 

TX (September 

2013)

Teledyne API Model T265 (FEM)

2B Technologies Model 211 (FEM)

Bendix Model 8002 (FRM)

Thermo Scientific Model 49i (FEM)

Teledyne API Model T700U1

Teledyne API Model 7011

Field Deployment 

(Date) Ozone Analyzer

AIRS 2014 (AprilJune 2014)

Teledyne API Model T265 (FEM)

2B Technologies Model 211 (FEM)

2B Technologies Model 205 (FEM)

Bendix Model 8002 (FRM)

Teledyne API Model T700U1

Teledyne API Model 7011

Denver, CO (July 

and August 2014)

Teledyne API Model T265 (FEM)

2B Technologies Model 211 (FEM)—2 analyzers collocated

Bendix Model 8002 (FRM)

Teledyne API Model T700U1

Teledyne API Model 7011

1

Used for calibration and nightly zero and span checks

Table 3. Ozone Analyzer Inventory Deployed During Each Field Study
12 

level and a subsequent sampling manifold were shared by 

all instruments. Table 3 summarizes the different ozone 

analyzers evaluated during each field deployment. 

4.3.2.3 Quality Assurance

As previously stated, the laboratory-based tests were 

conducted in accordance with the test procedures detailed in 

Subpart B of 40 CFR Part 53.10. Prior to both laboratorybased and ambient testing, all analyzers under evaluation 

were calibrated according to manufacturers’ operation 

manuals (per FEM designations) and in accordance with 

FRM requirements listed in 40 CFR 50, Appendix D. In 

addition, all research detailed in this report was conducted 

under the EPA approved QAPP-AB-12-02 – Quality 

Assurance Project Plan: Ambient Air Monitoring Methods 

Assessment and Development for Criteria Gas National 

Ambient Air Quality Standards.

4.3.3 Results

4.3.3.1 Laboratory Test Results

The average laboratory test results are summarized in Table 

4, which is presented in a format similar to that given in 

Table B-1 of Subpart B (Part 53). The result of each test 

trial is compared with the prescribed test limit requirement 

to determine whether the test result passes or fails. All test 

results must pass the test criteria to pass the test requirement 

for that performance parameter. Clearly, the test results 

reported in Table 4 show that the Model T265 met all existing 

and revised proposed performance requirements proposed 

for new ozone FRM and FEM analyzers for the standard 

measurement range (0 to 0.5 ppm). Even the test results for 

total interferents met the existing requirements for these 

parameters. (This requirement is proposed to be withdrawn in 

the revised performance requirements and is shown in Table 

1 but not in Table 4.)

The laboratory-based tests were carried out with the test 

analyzer operating with a 0- to 0.5-ppm measurement 

range, so the test results are not directly comparable with 

the proposed new, lower range performance requirements 

for noise, lower detectible limit, span drift, and precision. 

However, the results given in Table 4 clearly show that 

the T265 analyzer would meet the proposed lower range 

performance requirements as well.

In addition, the EPA-performed laboratory test results 

reported in Table 4 show that other methods, including the 

Model 211 and Model 49i, met all existing and revised 

performance requirements proposed for new ozone FRM and 

FEM analyzers for the standard measurement range (0 to 0.5 

ppm). Similar to those for the T265 analyzer, the laboratorybased tests for the other methods were carried out in the 

0- to 0.5-ppm analyzer measurement range. The results also 

clearly suggest that the Model 211 and Model 49i analyzer 

Table 4. Comparison of EPA Laboratory Test Results to Existing and Proposed Revised FRM and FEM Performance 

Requirements

Performance 

Parameter

Teledyne-API Model 

T265

2B Technologies 

Model 211 Thermo Model 49i

FRM and FEM 

Performance Limit 

Specifications1

Proposed New FRM and FEM Performance 

Limit Specifications2

Standard Range Lower Range

1. Range 0-0.1 ppm

0-1.0 ppm 0-2.0 ppm 0-0.5 ppm0-1.0 ppm 0-0.5 ppm 0-0.5 ppm 0-<0.5 ppm

2. Noise <0.0005 ppm <0.0005 ppm <0.0005 ppm 0.005 ppm 0.001 ppm 0.0005 ppm

3. Lower detectable 

 limit <0.0006 ppm <0.001 ppm <0.001 ppm 0.010 ppm 0.003 ppm 0.001 ppm

4. Interference 

 equivalent

 - Each 

 interferent

<0.0001 ppm <0.0002 ppm 

<0.0001 ppm

0.01 ppm for water 

vapor

±0.02 ppm ±0.005 ppm ±0.005ppm

5. Zero drift, 12- and 

24-h <0.0001 ppm <0.0001 ppm <0.0002 ppm ±0.02 ppm ±0.004 ppm ±0.002 ppm

6. Span drift, 80% 

of URL <0.5% <0.5% <0.5% ±5.0% ±3.0% ±3.0%

7. Lag time <1 min <1 min <1 min 20 min 2 min 2 min

8. Rise time <1 min <1 min <2 min 15 min 2 min 2 min

9. Fall time <1 min <1 min <2 min 15 min 2 min 2 min

10. Precision

20% URL <0.4% <0.5% <0.4% 0.010 ppm 2%3 2%3

80% URL <0.6% <0.5% <0.4% 0.010 ppm 2%3 2%3

1 Current performance specifications taken from Table B-1 to Subpart B of Part 53—Performance Limit Specifications for Automated Methods

2 In conjunction with the proposal of a new FRM for O3

, EPA intends to propose revised, more stringent performance specifications, along with 

new performance specifications applicable to optional lower ranges for O3 analyzers. 3 Standard deviation expressed as percent of the URL.

 
 13

likely would meet the proposed lower range performance 

requirements, with the exception of the water interference 

result for the Model 49i (see Table 4).

4.3.3.2 Ambient Evaluation Results

Table 5 gives comparisons (linear regressions) of 1-h EPA 

test results for the NO-CL ozone analyzer (Teledyne API 

Model T265) collected during the various field deployments. 

In ambient air evaluations in Houston and Denver, hourly 

average ozone results from the T265 compared very closely 

with those from the Bendix 8002 FRM, as shown in Figure 2. 

Linear regression results for comparison of the T265 with the 

Bendix 8002 FRM in Houston and Denver give slopes within 

2.5% of unity and sub-parts-per-billion intercepts (Table 

5, Figure 2). It should be noted that the Bendix 8002 FRM 

Table 5. Comparison of 1-h EPA Ozone Analyzer Results Collected During the Various Field Deployments

Comparison x vs. y n x Average (ppb) y Average (ppb) Linear Regression R2 Comments

Baltimore, MD: July 2011

T265 vs. EC9810 689 42.3 42.4 y=1.002x-0.046 0.997

AIRS, NC: June and July 2012

T265 vs. Bendix 8002 756 35.3 37.8 y=1.013x-0.817 0.983 Scatter in data attributed to Bendix 8002

AIRS, NC: June and July 2012

T265 vs. Model 205 756 35.3 35.6 y=1.006x+0.123 0.998

AIRS, NC: June and July 2012

T265 vs. 49i 735 35.3 35.4 y=1.019x+0.121 0.998

Houston (LaPorte), TX: September 2013

T265 vs. Bendix 8002 564 30.3 31.1 y=1.016x+0.346 0.998

Houston (LaPorte), TX: September 2013

T265 vs. Model 211 564 30.3 32.4 y=0.998x+2.192 0.999

Houston (LaPorte), TX: September 2013

T265 vs. Model 205 564 30.3 32.6 y=0.999x+2.574 0.999

Houston (LaPorte), TX: September 2013

T265 vs. 49i 564 30.3 32.9 y=0.974x+3.444 0.997

AIRS, NC: April-June 2014

T265 vs. Bendix 8002 924 35.3 36.6 y=1.027x+0.085 0.996

AIRS, NC: April-June 2014

T265 vs. Model 211 938 35.3 36.4 y=0.996x+1.090 0.999

AIRS, NC: April-June 2014

T265 vs. Model 205 729 36.1 35.5 y=0.973x-0.180 0.999

Denver, CO: July and August 2014

T265 vs. Bendix 8002 670 45.7 47.3 y=1.025x+0.424 0.993

Denver, CO: July and August 2014

T265 vs. Model 211#1 670 45.7 45.9 y=0.989x+0.652 0.999

Denver, CO: July and August 2014

T265 vs. Model 211#2 665 45.7 45.6 y=0.995x+0.075 0.999

Figure 2. Comparison of the 1-h-average Bendix 8002 (FRM) and T265 (NO-CL) ozone results in ambient air at 

Houston, TX, during September 2013 (left) and at Denver, CO, during July and August 2014 (right).

operated by EPA during the ambient evaluations was quite 

an old instrument, possibly not performing completely up to 

original factory specifications. This is evident in comparing 

the linear regression results of the T265 with the various 

other analyzers during each of the campaigns (Table 5). 

Generally, more scatter (lower R2 value) and deviations from 

a slope of 1.0 are observed when comparing the T265 with 

the Bendix 8002 (Table 5, Figure 2) than when comparing 

the T265 with other analyzer types (Table 5, Figures 3 and 

4). The exception to this is comparison of the 1-h T265 

results with those obtained from the 49i during both the RTP 

summer 2012 and Houston summer 2013 studies, as shown in 

Figure 5. The 49i analyzer is a conventional UV photometric 

method that does not employ a sample conditioning system to 
14 

Figure 3. Comparison of the 1-h-average Model 211 

(SL-UV) and T265 (NO-CL) ozone results in ambient 

air at Houston (LaPorte), TX, during September 2013 

(top) and at Denver, CO, during July and August 2014 

(bottom).

remove water (a known interferent in UV photometric ozone 

determination, see section 3.3.4) from the sample stream. 

During the RTP and Houston studies, RH values were high 

(>85%), possibly resulting in a measurement interference 

associated with the 49i. The closest agreement was obtained 

while comparing the T265 results with the Model 211 results 

during multiple field studies (Table 5, Figure 3). Linear 

regression results for comparison of the T265 with the Model 

211 in Houston, RTP (2014), and Denver give slopes within 

1% of unity (Table 5, Figure 3). A slightly elevated offset (~2 

Figure 4. Comparison of the 1-h-average EC9810 and 

T265 (NO-CL) ozone results in ambient air at Baltimore 

(Padonia), MD, during July 2011 (top) and comparison 

of the 1-h-average Model 205 and T265 (NO-CL) ozone 

results in ambient air at RTP, NC, during June and July 

2012 (bottom). Both the EC9810 and the Model 205 

employ the UV photometric method and contain sample 

conditioning systems to remove water from the sample 

stream.

ppb) was observed during the Houston study. Further analysis 

of the T265 and Model 211 and Bendix 8002 datasets 

indicates the offset is associated with the Model 211.

The current NAAQS for ozone is 0.075 ppm (75.0 ppb) in 

the form of the annual fourth-highest daily maximum 8-h 

concentration, averaged over 3 years. To enable evaluation of 

the T265 and other FRM and FEM analyzers’ performance 

with respect to monitoring for the ozone NAAQS, maximum 

daily 8-h-average (MDA8) ozone concentrations were 

calculated.11 Table 6 gives a comparison (linear regression) 

of MDA8 ozone analyzer results collected during the various 

field deployments. In ambient air evaluations in Houston and 
 15

Figure 5. Comparison of the 1-h-average 49i and T265 

(NO-CL) ozone results in ambient air at RTP, NC, during 

June and July 2012 (top) and at Houston (LaPorte), TX, 

during September 2013 (bottom). The 49i employs the 

UV photometric method but does not contain a sample 

conditioning system to remove water from the sample 

stream.

Figure 6. Comparison of the maximum daily 8-h-average 

(MDA8) ozone results in ambient air at Houston 

(LaPorte), TX, during September 2013 (top) and at 

Denver, CO, during July and August 2014 (bottom).

Denver, MDA8 ozone results from the T265 compared very 

closely with those from the Bendix 8002 FRM and Model 

211, as shown in Figure 6.

Clearly and as expected, ambient air measurement 

performance of the Model T265 is comparable with that of 

other FRM and FEM analyzers. Operation of the analyzer 

was very similar to that of the FRM analyzer, and it was 

straightforward to install, operate, and calibrate, particularly 

with the advanced user interface of the Model T265. No 

problems or user difficulties were encountered, and all 

operational observations indicated that the analyzer could 

serve well as an FRM analyzer if the proposed NO-CL ozone 

FRM were to be adopted. According to the manufacturer, 

Models T265 and 265E have the same specified performance. 

Therefore, the results of Model T265 testing should apply 

equally to the Model 265E, notwithstanding some differences 

in the user interface between the two models.
16 

Table 6. Comparison of Maximum Daily 8-h-Average Ozone Analyzer Results Collected During the Various Field 

Deployments

Comparison x vs. y n x Average (ppb) Average (ppb) Linear Regression R2 Comments

Baltimore, MD: July 2011 

T265 vs. EC9810 28 62.9 63.1 y=0.993x+0.657 0.984

AIRS, NC: June and July 2012

T265 vs. Bendix 8002 30 52.1 53.4 y=1.059-1.766 0.974 Scatter in data attributed to Bendix 8002

AIRS, NC: June and July 2012

T265 vs. Model 205 30 52.1 52.6 y=1.009x-0.001 0.997

AIRS, NC: June and July 2012

T265 vs. 49i 30 52.1 53.4 y=0.992x+1.695 0.983

Houston (LaPorte), TX: September 2013

T265 vs. Bendix 8002 24 42.9 43.4 y=0.998x+0.824 0.998

Houston (LaPorte), TX: September 2013

T265 vs. Model 211 24 42.9 44.8 y=0.996x+2.296 0.999

Houston (LaPorte), TX: September 2013

T265 vs. Model 205 24 42.9 44.8 y=1.004x+2.149 0.999

Houston (LaPorte), TX: September 2013

T265 vs. 49i 24 42.9 45.3 y=0.963x+4.131 0.998

AIRS, NC: April-June 2014

T265 vs. Bendix 8002 46 50.5 52.1 y=0.973x+2.927 0.976

AIRS, NC: April-June 2014

T265 vs. Model 211 46 50.5 51.4 y=0.977x+2.086 0.996

Denver CO: July and August 2014

T265 vs. Bendix 8002 29 58.2 60.2 y=0.979x-0.775 0.986

Denver, CO: July and August 2014

T265 vs. Model 211#1 29 58.2 58.2 y=0.978x+1.329 0.997
 17

5.0

Conclusions

Tests of the NO-CL method using the Teledyne API Model 

T265 analyzer show it to meet all existing performance 

requirements for candidate ozone FRM and FEM analyzers. 

It has previously been shown to meet all FEM performance 

requirements and is listed by EPA as a designated equivalent 

method (EQOA-0611-199). The tests also show it would meet 

proposed revised requirements for ozone FRM and FEM 

analyzers as well. The analyzer is commercially available and 

is shown to be operationally fully acceptable as an alternative 

FRM analyzer if the proposed new ozone FRM is adopted as 

a modification to 40 CFR Part 50, Appendix D. Therefore, 

the NO-CL method, as represented by the Teledyne API T265 

analyzer, is shown to be well suited as an FRM for ozone 

to serve in the FRM role as a practical reference standard 

for candidate FEMs and for quality assurance of ozone 

monitoring data.

 19

6.0

References

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