EPA/600/A-97/001
Program Objectives and Status
For the U.S.EPA Program on FTIR-Based Open-Path Monitoring
William A. McCIenny
National Exposure Research Laboratory, U.S.EPA
Research Triangle Park, NC 27711
ABSTRACT
The Office of Research and Development of the U.S. EPA supports a methods development program
for FTIR-based, open path monitoring of trace gases in the air. This type of system provides an
estimate of the average concentration of individual trace gases over distances up to approximately one
kilometer by interpreting changes in the infrared absorption spectrum. The EPA program has four
objectives. The first is to develop a guidance document to explain the nature of these systems, their
uses, and their performance-limiting features. The second is to provide a method describing
recommended procedures for operating the systems to take data; the third is to support an international
effort by L'Organisation Internationale de Metrologie Legale (OIML) to specify acceptable
performance levels for commercial FTIR-based systems, and the last is to support the development of a
library of reference spectra in the infrared at the National Institute of Standards and Technology
(HIST). These objectives are completed or in progress. Current year emphasis is on the review and
release of the TO-16 methods document that is intended for publication as part of the EPA's
Compendium of Methods for the Determination of Toxic Organic Compounds in Ambient Air.
INTRODUCTION
The use of open path optical techniques for monitoring of trace species has some unique and
compelling advantages. One of the most important is that no sampling is required, and questions of
sample integrity that almost always plague point monitors are avoided. Another is that multiple trace
species can usually be analyzed concurrently by interpretation of the spectral measurement data. The
National Exposure Research Laboratory, U.S.EPA has the objectives, among others, of characterizing
exposure to trace species and of developing databases to support modeling of atmospheric processes.
Because of its potential advantages, open path monitoring is being evaluated, and cooperative
arrangements with industry have been established to encourage commercial developments and interest
in this area. One of the areas of interest is the use of Fourier Transform Infrared (FTIR)-based open
path monitoring. This technique is of particular interest because of the occurrence of the spectra of
many trace gases in the middle infrared. However, water vapor and carbon dioxide absorption in this
spectral region interfere with straightforward quantitation. The process leading to a determination of

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trace gas concentration therefore represents a challenge in detecting compounds at trace levels as they
disperse from sources or are formed in the environment. At the current stage of development, the main
application for these systems is fence line monitoring around industrial emission sources or near other
concentrated sources of pollutants. The EPA is supporting the development of commercial systems
through evaluation studies and the interpretation of data taken with these systems. These efforts have
resulted in the publication of information products and in the support of complementary efforts in the
international area by the L'Organisation Internationale de Metrologie Legale (OIML) and by the
National Institute of Standards and Technology (NIS I ).
The current year interest is on the completion of the initial version of TO-16, which will be
published as a methods guidance document in an updated version of the EPA Compendium of Methods
for the Determination of Toxic Organic Compounds in Ambient Air. During the last year, the initial
draft of this document has been reviewed by the AOl committee of the Air & Waste Management
Association (A&WMA) and a revised draft has been prepared for EPA clearance.
COMPONENTS OF THE U.S.EPA's PROGRAM
FT-IR Open Path Monitoring Guidance Document
This document was first printed by ManTech Environmental Technology Inc. as a report
submitted to the EPA sponsor in March, 1993 and then in a revised form in February, 1995. A further
revised form was published in April, 1996 as an EPA/Office of Research and Development document
with the document number EPA/600/R-96/040 (1). Pending the availability of funding, this document
will be further revised by ManTech and will include guidance on the use of gas cells to establish
system response to known trace gas concentrations. Other topics to be covered include a more detailed
treatment of water vapor interference in FTIR-based measurements. New insights with respect to
existing topics will also form the basis for revisions.
TO-16 - Long-Path, Open-Path Fourier Transform Infrared Monitoring of Atmospheric Gases -
Discussion of Comments on Draft TO-16
The Chairman of the AOl Committee of the A&WMA, Dr. Bob Spellicy, agreed to coordinate
the review of the draft TO-16 document and to provide Dr. George Russwurm of ManTech
Environmental Technology (the EPA in-house contractor) with the results of the review. Dr.
Russwurm provided the draft TO-16 document in September, 1995, and completed a revision in
October, 1996. This draft revision is being distributed at this meeting and is being submitted for EPA
clearance prior to official distribution. TO-16 will also be included for the first time in an updated
version of the EPA Compendium of Methods for the Determination of Toxic Organic Compounds in
Ambient.Air, due for publication in the first quarter of 1997. The revision includes reviewer comments
and some additional information developed after the 1995 draft was completed. Some of the method
guidelines that were considered during the revision are:
Performance-Based Guidance. The method must provide performance-based guidance which
could be incorporated into standard operating procedures (SOPs) created by the user for specific
applications. As a result, no specific software packages, instrumentation packages, or operating
systems are mentioned in TO-16. The general analytical approach using classical least squares (CLS)
fitting is retained, while other competitive techniques are discussed as potentially equivalent and
possibly better. The CLS approach is explained in its most generic form, referring to any software
package that incorporates the principles embodied in the mathematical formalism for CLS as presented

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by Haaland(2). This approach is in keeping with EPA's general policy of documenting an approach
that is known to work but allowing that equivalent methods can be used if they can meet performance
objectives.
Automation of Systems. The method should explain the steps in obtaining quantitative data
with the FTIR-based systems while leaving the automation of these steps to the operator/manufacturer.
The commercial incentive to provide automation is definitely present in this case and will depend on
the cooperation of operators and manufacturers. Automation of this type is already available for some
systems and the offering companies enjoy a commercial advantage by virtue of it.
Adding a List of Examples to the Text. A listing of specific examples of applications for FTIR-
based systems was considered to be beyond the scope of this document and, if attempted, might
compromise the completion and eventual improvement of TO-16. Such a document has been
discussed previously with members of the AOl committee, but as a review appropriate for a journal
article.
Sequence of Procedures. In some cases the order of performance of a procedure, e.g.,
generating a background spectrum, requires the results of another procedure which may not have been
explained yet, e.g., accounting for spectral shifts. A subsection entitled "Additional Procedures
Referenced" has been added to direct the reader to the information needed from another place in the
document.
Revision of Section 8 - Specific Standard Procedures. The original Sections 8.2 and 8.3 have
been revised. Section 8.2 of the revised draft is a statement of a general procedure for the generation of
concentration data, and Section 8.3 combines the original sections 8.2 and 8.3 to give the
recommended approach to developing both a means of identifying a spectral analysis region
appropriate for a given target gas and a means for accounting for interferences.
Background Generation. Alternate means of background acquisition and use are now included
as part of Section 8 since in some cases (such as isolation of a nearby emission source contribution
from other sources) the synthetic background approach is not the method of choice. The generation
procedure for synthetic backgrounds is however still considered challenging and ways to simplify the
procedure are continuing.
Water Vapor Reference Spectra. Field-generated water vapor reference spectra are
indispensable for attempting quantitation so their generation has been emphasized in TO-16. Although
the possibility of providing some minimum number of clean water vapor reference spectra with TO-16
has been considered, at this point TO-16 is envisioned as part of a large volume containing the
seventeen TO documents and no supplemental materials.
Dealing with Spectral Shifts. Depending on the width of spectral absorption features of the
target gas, correction of spectral shifts may not be necessary. A discussion of the importance of
spectral shifts is provided, showing that the wavenumber shift of the target gas absorbance spectra
must be considered relative to the full width half height (FWHH) of the absorbance feature used for
analysis and to the error in measurement acceptable under the data quality objectives (DQOs) for the
specific project. Deutrated water vapor (HDO) lines have been suggested as a reference point for
determining spectral shifts in one spectral region with the possibility of shifting field spectra as they
are acquired. However, no general consensus has been achieved in the user community as to the actual
reference lines to be used.
Dealing with Stray Light and Background Radiation. Stray light is not a problem when its
contribution is low, which is the most frequent situation. The analyst has to determine if stray light is a
problem in a particular system; coadding spectra over a half hour period to define the stray light (in the

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absence of variations other than random fluctuations) is recommended.
Production of a Recommendation on FTIR Spectrometer Systems by the Working Group for the
OIML Technical Committee 16 on "Instruments for Measurement of Pollutants"
EPA has supported the effort by the OIML Technical Committee 16, under the leadership of
Sam Chappell of the NIST, to complete the first committee draft OIML recommendation "FTIR
Spectrometer Systems for Measurement of Air". This document has been formulated and has been
distributed to the OIML member nations.
Support of the NIST Spectral Reference Standards Program Directly and Through the
A&WMA Spectral Reference Standards Subcommittee
EPA has encouraged the NIST to generate a set of reference spectra for general use, much the
same as NIST Standard Reference Materials are used. Interest in this project was formalized at the
1994 Optical Sensing Symposium with the formation of the A&WMA Spectral Reference Standards
Subcommittee. Based on initial discussions with Walt Lafferty and his co-workers at NIST and their
successful efforts at finding internal NIST support, Pamela Chu of the NIST is now leading a program
to develop this data base. She has recently provided an update of progress at the 1996 Annual Meeting
of A&WMA in Nashville, TN (3). Table I shows a list of the first twenty target compounds chosen for
analysis by NIST and is current as of this date. As originally projected, the spectra for ten of these
compounds were completed in the FY96. The availability of these spectra, their format, and who the
distributer will be are topics being decided at the NIST. The initial indications are that the spectra will
be provided in an ASCII format suitable for all users along with a software package to degrade the
spectra to match spectra at different resolutions.
CONCLUSIONS
The EPA-sponsored program on the use of open-path FTIR-based systems for monitoring of
trace species is in place, with the distribution of the draft version of the methods guidance document
TO-16 as of November, 1996. The guidance deals with most aspects of field monitoring, leaving
however, some few issues such as the use of short in-line cells (for checking performance) to the
discretion of the system operator as an open issue. The development of additional guidance
information is planned in the near future. A strong emphasis is placed on quality assurance, with many
individual checks on system performance as specified in Section 9 of the document.
ACKNOWLEDGMENTS
Dr. George Russwurm and Dr. Hunter Daughtrey, Jr. of ManTech Environmental Technology,
Inc., Dr. Pamela Chu of NIST, Dr. Sam Chappell of the NIST, Dr, Bob Spell icy of Radian
International, and Dr. Bill Herget are acknowledged as having provided the major part of the
information making this presentation possible.

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DISCLAIMER
This article has been subjected to review by the U.S. Environmental Protection Agency and
cleared for publication. Mention of trade names of commercial products does not constitute
endorsement or recommendation for use.
REFERENCES
1.	G.M. Russwurm and J. W. Childers; FT-IR Open-Path Monitoring Guidance Document,
EPA/600/R-96/040, U.S. Environmental Protection Agency, Research Triangle Park, NC 1996.
2.	Haaland, D.M., and Easterling, R.G. Appl, Spectrosc. 1982 36,665-673.
3.	Chu, P., Rhoderick, G.,Wetzel, S., Lafferty, W. and Fuenther, F., "A Quantitative Infrared Database
of the Hazardous Air Pollutants," 1996 Annual Meeting of the Air & Waste Management Association,
Paper 96-TA26A.05, Nashville, TN.
TABLE I. NIST INITIAL TARGET COMPOUND LIST*
This column completed FY96
Methanol
Ethanol
Acetonitrile
Acetone
Propylene oxide
Methyl ethyl ketone
Benzene
Toluene
Ethylene
Sulfur dioxide
This column under study
trans 1,3-Butadiene
Ethylene oxide
2-Propanol
Acrylonitrile
Methyl t-butvl ether
Vinyl acetate
Ethyl acetate
Ethyl t-butyl ether
N-Butanol
Ethyl aerylate
* Provided by Dr. Pamela Chu of the National Institute of Standards and Technology.

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Key Words: FOURIER TRANSFORM, INFRARED, OPEN-PATH, ABSORPTION

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TECHNICAL REPORT DATA
1. REPORT NO.
EPA/600/A-37/QL'1
4. TITLE AUD SUBTITLE
Program Objectives and Status for the U.S.EPA
Program on FTIR-Based Open-Path Monitoring
5.REPORT DATE
6.PERFORMING ORGANIZATION CODE
7. AUTHORSS?
William A. McCIenny
8.PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
National Exposure Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
10.PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
National Exposure Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
13.TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
The Office of Research and Development of the U.S.EPA supports a methods development
program for FTIR-based, open path monitoring of trace gases in the air. This type
of system provides an estimate of the average concentration of individual trace
gases over distances up to approximately one kilometer by interpreting changes in
the infrared absorption spectrum. The EPA program has four objectives. The first
is to develop a guidance document to explain the nature of these systems, their
uses, and their performance-limiting features. The second is to provide a method
describing recommended procedures for operating the systems to take data; the third
is to support an international effort by L'Organisation Internationale de Metrologie
Legale (OIML) to specify acceptable performance levels for commercial FTIR-based
systems, and the last is to support the development of a library of reference
spectra in the infiared at the National Institute of Standards and Technology
(NIST). These objectives are completed or in progress. Current year emphasis is on
the review and release of the TO-16 methods document that is intended for
publication as part of the EPA's Compendium of Methods for the Determination of
Toxic Organic Compounds in Ambient Air.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/ OPEN ENDED
TERMS
C.COSATI
IS. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (This
Report)
UNCLASSIFIED
21.NO. OF PAGES
20. SECURITY CLASS (Thia
Page)
UNCLASSIFIED
22. PRICE

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