ASTM E1982-98(2021)
(Practice)Standard Practice for Open-Path Fourier Transform Infrared (OP/FT-IR) Monitoring of Gases and Vapors in Air
Standard Practice for Open-Path Fourier Transform Infrared (OP/FT-IR) Monitoring of Gases and Vapors in Air
SIGNIFICANCE AND USE
4.1 An OP/FT-IR monitor can, in principle, measure the concentrations of all IR-active gases and vapors in the atmosphere. Detailed descriptions of OP/FT-IR systems and the fundamental aspects of their operation are given in Practice E1685 and the FT-IR Open-Path Monitoring Guidance Document. A method for processing OP/FT-IR data to obtain the concentrations of gases over a long, open path is given in Compendium Method TO-16. Applications of OP/FT-IR systems include monitoring for gases and vapors in ambient air, along the perimeter of an industrial facility, at hazardous waste sites and landfills, in response to accidental chemical spills or releases, and in workplace environments.
SCOPE
1.1 This practice covers procedures for using active open-path Fourier transform infrared (OP/FT-IR) monitors to measure the concentrations of gases and vapors in air. Procedures for choosing the instrumental parameters, initially operating the instrument, addressing logistical concerns, making ancillary measurements, selecting the monitoring path, acquiring data, analyzing the data, and performing quality control on the data are given. Because the logistics and data quality objectives of each OP/FT-IR monitoring program will be unique, standardized procedures for measuring the concentrations of specific gases are not explicitly set forth in this practice. Instead, general procedures that are applicable to all IR-active gases and vapors are described. These procedures can be used to develop standard operating procedures for specific OP/FT-IR monitoring applications.
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.3 This practice does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this practice to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
General Information
Relations
Standards Content (Sample)
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E1982 − 98 (Reapproved 2021)
Standard Practice for
Open-Path Fourier Transform Infrared (OP/FT-IR) Monitoring
of Gases and Vapors in Air
This standard is issued under the fixed designation E1982; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2. Referenced Documents
1.1 This practice covers procedures for using active open- 2.1 ASTM Standards:
path Fourier transform infrared (OP/FT-IR) monitors to mea- E131Terminology Relating to Molecular Spectroscopy
sure the concentrations of gases and vapors in air. Procedures E168Practices for General Techniques of Infrared Quanti-
for choosing the instrumental parameters, initially operating
tative Analysis
the instrument, addressing logistical concerns, making ancil-
E1421Practice for Describing and Measuring Performance
lary measurements, selecting the monitoring path, acquiring
of Fourier Transform Mid-Infrared (FT-MIR) Spectrom-
data, analyzing the data, and performing quality control on the
eters: Level Zero and Level One Tests
dataaregiven.Becausethelogisticsanddataqualityobjectives
E1655 Practices for Infrared Multivariate Quantitative
of each OP/FT-IR monitoring program will be unique, stan-
Analysis
dardized procedures for measuring the concentrations of spe-
E1685PracticeforMeasuringtheChangeinLengthofBolts
cific gases are not explicitly set forth in this practice. Instead,
Using the Ultrasonic Pulse-Echo Technique
general procedures that are applicable to all IR-active gases
2.2 Other Documents:
and vapors are described. These procedures can be used to
FT-IR Open-Path Monitoring Guidance Document
develop standard operating procedures for specific OP/FT-IR
Compendium Method TO-16Long-Path Open-Path Fourier
monitoring applications.
Transform Infrared Monitoring of Atmospheric Gases
1.2 The values stated in SI units are to be regarded as
standard. No other units of measurement are included in this
3. Terminology
standard.
3.1 For definitions of terms used in this practice relating to
1.3 This practice does not purport to address all of the
general molecular spectroscopy, refer to Terminology E131.
safety concerns, if any, associated with its use. It is the
3.2 For definitions of terms used in this practice relating to
responsibility of the user of this practice to establish appro-
OP/FT-IR monitoring, refer to Practice E1685.
priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use.
3.3 For definitions of general terms relating to optical
1.4 This international standard was developed in accor-
remote sensing, refer to the FT-IR Open Path Monitoring
dance with internationally recognized principles on standard-
Guidance Document.
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Barriers to Trade (TBT) Committee.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
EPA/600/R-96/040, National Technical Information Service Technology
This practice is under the jurisdiction ofASTM Committee E13 on Molecular Administration,U.S.DepartmentofCommerce,Springfield,VA22161,NTISOrder
Spectroscopy and Separation Science and is the direct responsibility of Subcom- No. PB96–1704771NZ.
mittee E13.03 on Infrared and Near Infrared Spectroscopy. Compendium of Methods for the Determination of Toxic Organic Compounds
Current edition approved April 1, 2021. Published April 2021. Originally in Ambient Air, 2nd Ed., EPA/625/R-96/010b, Center for Environmental Research
approved in 1998. Last previous edition approved in 2013 as E1982–98(2013). Info., Office of Research & Development, U.S. Environmental Protection Agency,
DOI: 10.1520/E1982-98R21. Cincinnati, OH 45268, Jan. 1997.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1982 − 98 (2021)
4. Significance and Use collecting or analyzing the data. For example, the spectral
resolution affects the type of background spectrum that can be
4.1 An OP/FT-IR monitor can, in principle, measure the
used, the method for generating a water vapor reference
concentrations of all IR-active gases and vapors in the atmo-
spectrum, and the choice of analysis method. The following
sphere. Detailed descriptions of OP/FT-IR systems and the
stepscanbetakentochoosethebestresolutionforaparticular
fundamental aspects of their operation are given in Practice
application.
E1685 and the FT-IR Open-Path Monitoring Guidance Docu-
5.3.1 Examine reference spectra of the target gases and
ment. A method for processing OP/FT-IR data to obtain the
potential interfering species. If possible, acquire or obtain
concentrations of gases over a long, open path is given in
reference spectra of these gases at various resolutions. Deter-
Compendium Method TO-16. Applications of OP/FT-IR sys-
minethelowestresolutionthatresolvesthespectralfeaturesof
tems include monitoring for gases and vapors in ambient air,
interest. Use this resolution as a starting point for future
alongtheperimeterofanindustrialfacility,athazardouswaste
measurements.
sites and landfills, in response to accidental chemical spills or
5.3.2 If the appropriate facilities are available, develop
releases, and in workplace environments.
calibration curves of the target gases at different resolutions. If
an inadequate resolution is used, the relationship between the
5. Instrumental Parameters
peak absorbance and concentration will not be linear. This
5.1 Several instrumental parameters must be chosen before
relationship is also affected by the apodization function (see
data are collected with an OP/FT-IR system.These parameters 5.4).Ifthecompoundofinterestdoesnotrespondlinearlywith
include the measurement time, spectral resolution, apodization
respect to concentration, a correction curve must be applied to
function, and zero filling factor. In some cases, the choice of the data during quantitative analysis.
these parameters might be limited by the parameters used to
5.3.3 Determine the effect of resolution on the other proce-
acquire and process the available reference spectra. Use the dures involved with generating OP/FT-IR data, such as the
following procedures to select the instrumental parameters for
creation of a synthetic background spectrum (see 10.3) and a
each OP/FT-IR monitoring study. water vapor reference spectrum (see 10.6.1) from the field
spectra. These procedures rely on a series of subjective
5.2 Measurement Time—Determine the measurement time
judgements, which require a visual inspection of the field
requiredtoachievethedesiredsignal-to-noiseratio(S/N)atthe
spectra. The use of a higher resolution generally facilitates the
selected resolution (see 5.3 and 6.7). Verify that this measure-
ability of the operator to visualize the pertinent features of the
ment time is appropriate for capturing the event being studied.
field spectra.
Ifthemeasurementtimeislongerthantheresidencetimeofthe
5.3.4 Assess the resolution requirements of the analysis
plume in the path, the interferograms collected after the plume
method. If the comparison (see 10.8.1) or scaled subtraction
has exited the path will not contain spectral information from
(see 10.8.2) method is used, the resolution should be sufficient
the target gas. Adding these signals in the interferogram
to separate the spectral features of the target gases from those
domain to signals that contain information from the target gas
of the interfering species. If classical least squares (CLS) is
will result in a dilution effect and can cause band distortions
−1
used (see 10.8.3), a resolution higher than 4 cm is generally
and nonlinearities. The variability in the water vapor concen-
required (1). Ifpartialleastsquares(PLS)isused(see10.8.3),
tration along the path can also limit the use of extensive signal
−1
a resolution as low as 16 cm may be sufficient (2).
averaging to improve the S/N. Measurement times from 1min
to 5 min are typical for ambient monitoring, whereas shorter
NOTE 1—Most volatile organic compounds of interest in OP/FT-IR
monitoringapplicationshaveabsorptionenvelopeswithfullwidthsathalf
measurement times may be required for plume modeling
−1
heights (FWHHs) of approximately 20 cm . This observation would
studies.
indicate that low-resolution spectra would be adequate for OP/FT-IR
measurements. However, each OP/FT-IR spectrum will also contain
5.3 Resolution—The choice of what spectral resolution to
featuresduetoambientgases,suchaswatervapor,carbondioxide,carbon
use while collecting OP/FT-IR data depends on the spectral
−1
monoxide, and methane, which have FWHHs on the order of 0.2 cm at
characteristics of the target gases, the measurement time
atmospheric pressure. If low resolution measurements are made, the
required to observe the pollutant plume, the concentrations of
analysis method must be able to handle the spectral overlap and
the target gases, the presence of interfering species, the choice nonlinearities caused by an inadequate resolution of these atmospheric
gases.
of analysis method, and the data quality objectives of the
monitoring study. This choice might be limited by the capa-
5.4 Apodization—Use the same apodization function that
bilities of the specific OP/FT-IR monitor used to collect data.
was used to process the reference spectra. If a choice of
Most commercially available, portableOP⁄FT-IR monitors are
apodization function can be made, the Norton-Beer-medium
capable of producing spectra at a maximum resolution of 0.5
function typically yields the best representation of the true
−1 −1
cm or1cm , although instruments are available that will
absorbanceascomparedtoHapp-Genzelortriangularapodiza-
−1
producespectraat0.125cm resolution.Thereiscurrentlyno
tion.
consensus as to the optimum resolution to use while collecting
5.5 Zero Filling—Assuming that the field spectra were
field data. Most current practitioners use a resolution of either
acquiredatthesameresolutionasthereferencespectra,choose
−1 −1
0.5cm or 1.0 cm , although recent advances in instrumen-
tation and data analysis techniques provide for the potential of
using much lower resolutions. The choice of resolution can
The boldface numbers in parentheses refer to a list of references at the end of
also affect other decisions that the operator must make before this standard.
E1982 − 98 (2021)
zero-filling parameters that allow the data point density of the 6.3.5 If nonphysical energy is observed in the single-beam
field spectra to match that of the reference spectra. In general, spectrum obtained at the initial pathlength, increase the path-
the original interferogram should be zero filled to the degree length until the instrument response below the detector cutoff
that the number of data points used in the Fourier transform is frequency is flat and at the baseline. This distance represents
twicethatintheoriginalinterferogram.Noadvantageisgained
the minimum operating pathlength.
by zero filling by more than a factor of two for most
6.3.6 If the instrument response below the detector cutoff
applications.
frequency is flat and at the baseline in the single-beam
spectrum obtained at the initial pathlength, decrease the path-
6. Initial Instrument Operation
length until nonphysical energy is observed in the single-beam
spectrum. This distance represents the minimum operating
6.1 Several tests should be conducted before the OP/FT-IR
pathlength.
monitor is deployed for a field study. These tests include
measuring the electronic noise, the distance at which the 6.3.7 If nonphysical energy is observed at the desired
monitoring pathlength and the pathlength cannot be increased,
detector saturates, the linearity of the system, the signal due to
internal stray light or ambient radiation, the signal strength as attenuatetheIRsignalbyplacingafinewiremeshscreeninthe
modulated,collimatedbeam.Changingthegainofthedetector
a function of distance, and the random baseline noise. Use the
instrumental parameters chosen in 5.2 through 5.5 for these preamplifier to lower the magnitude of the signal is not useful
because the detector nonlinearity does not depend on gain.
tests.
6.2 Measure the Electronic Noise—Place a piece of opaque
NOTE 2—Determining the distance at which the detector becomes
material in front of the detector element while the detector is saturated is particularly important for MCT detectors. Detector saturation
is not as severe a problem for thermal detectors, such as deuterated
operational, for example after the mercury-cadmium-telluride
triglycine sulfate detectors.
(MCT) detector has been cooled and has equilibrated. Record
the signal either as the interferogram or as a single-beam
6.4 Linear Response—There are two types of nonlinearity
spectrum with the detector blocked. This signal represents the
that can affect OP/FT-IR data: detector nonlinearity and non-
electronic noise of the system. The magnitude of this signal
linearity in absorbance. Evidence of detector nonlinearity can
should be less than 0.25% of the signal without the detector
be observed by conducting the tests described in 6.3, although
blocked, remain relatively constant over time, and decrease
theabsenceofnonphysicalenergyinthesingle-beamspectrum
with the square root of the measurement time. If this signal is
doesnotguaranteethatthedetectorisoperatinglinearly.Some
uncharacteristically large, an electrical component is most
MCT detectors exhibit nonlinear response even when there is
likely producing spurious noise. When this is the case, service
no evidence of detector saturation. The OP/FT-IR system can
of the system is indicated.
also exhibit nonlinearity in the change in absorbance with
respect to changes in concentration due to the convolution of
6.3 Measure the Distance to Detector Saturation—The
theinstrumentallineshapefunctionwiththespectraldata.The
distance at which the detector becomes saturated determines
choice of apodization function affects the severity of this
the minimum pathlength over which quantitative data can be
nonlinearity. If a multipoint calibration
...
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