Standard Test Method for Determination of Non-methane Organic Compounds (NMOC) in Ambient Air Using Cryogenic Preconcentration and Direct Flame Ionization Detection
5.1 Many regulators, industrial processes, and other stakeholders require determination of NMOC in atmospheres.
5.2 Accurate measurements of ambient NMOC concentrations are critical in devising air pollution control strategies and in assessing control effectiveness because NMOCs are primary precursors of atmospheric ozone and other oxidants (7, 8).
5.2.1 The NMOC concentrations typically found at urban sites may range up to 1 to 3 ppm C or higher. In order to determine transport of precursors into an area monitoring site, measurement of NMOC upwind of the site may be necessary. Rural NMOC concentrations originating from areas free from NMOC sources are likely to be less than a few tenths of 1 ppm C.
5.3 Conventional test methods based upon gas chromatography and qualitative and quantitative species evaluation are relatively time consuming, sometimes difficult and expensive in staff time and resources, and are not needed when only a measurement of NMOC is desired. The test method described requires only a simple, cryogenic pre-concentration procedure followed by direct detection with an FID. This test method provides a sensitive and accurate measurement of ambient total NMOC concentrations where speciated data are not required. Typical uses of this standard test method are as follows.
5.4 An application of the test method is the monitoring of the cleanliness of canisters.
5.5 Another use of the test method is the screening of canister samples prior to analysis.
5.6 Collection of ambient air samples in pressurized canisters provides the following advantages:
5.6.1 Convenient collection of integrated ambient samples over a specific time period,
5.6.2 Capability of remote sampling with subsequent central laboratory analysis,
5.6.3 Ability to ship and store samples, if necessary,
5.6.4 Unattended sample collection,
5.6.5 Analysis of samples from multiple sites with one analytical system,
5.6.6 Collection of replicate samples for assessment of measurement precision, and
5.6.7 Specific hydrocarbon analysis can be performed with the same sample system.
1.1 This test method2 presents a procedure for sampling and determination of non-methane organic compounds (NMOC) in ambient, indoor, or workplace atmospheres.
1.2 This test method describes the collection of integrated whole air samples in silanized or other passivated stainless steel canisters, and their subsequent laboratory analysis.
1.2.1 This test method describes a procedure for sampling in canisters at final pressures above atmospheric pressure (pressurized sampling).
1.3 This test method employs a cryogenic trapping procedure for concentration of the NMOC prior to analysis.
1.4 This test method describes the determination of the NMOC by the flame ionization detection (FID), without the use of gas chromatographic columns and other procedures necessary for species separation.
1.5 The range of this test method is from 20 to 10 000 ppb C (1, 2).3
1.6 This test method has a larger uncertainty for some halogenated or oxygenated hydrocarbons than for simple hydrocarbons or aromatic compounds. This is especially true if there are high concentrations of chlorocarbons or chlorofluorocarbons present.
1.7 The values stated in SI units are to be regarded as standard. The values given in parentheses are mathematical conversions to inch-pound units that are provided for information only and are not considered standard.
1.8 This standard 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 standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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