Significance and Use
Many industrial processes require determination of NMOC in the atmosphere.
Accurate measurements of ambient concentrations of NMOC are important for the control of photochemical smog because these organic compounds are primary precursors of atmospheric ozone and other oxidants (7, 8).
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, measurement of NMOC upwind of the area 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.
Conventional test methods that depend on gas chromatography and qualitative and quantitative species evaluation are excessively difficult and expensive to operate and maintain when speciated measurements are not needed. The test method described here involves a simple, cryogenic preconcentration procedure with subsequent direct detection with the FID. The test method is sensitive and provides accurate measurements of ambient total NMOC concentrations where speciated data are not required.
An application of the test method is the monitoring of the cleanliness of canisters.
Another use of the test method is the screening of canister samples prior to analysis.
Collection of ambient air samples in pressurized canisters provides the following advantages:
Convenient integration of ambient samples over a specific time period,
Capability of remote sampling with subsequent central laboratory analysis,
Ability to ship and store samples, if necessary,
Unattended sample collection,
Analysis of samples from multiple sites with one analytical system,
Collection of replicate samples for assessment of measurement precision, and
Specific hydrocarbon analysis can be performed with the same sample system.
Scope
1.1 This test method covers a procedure for sampling and determining concentrations of non-methane organic compounds (NMOC) in ambient, indoor, or workplace atmospheres.
1.2 The test method describes the collection of cumulative samples in passivated stainless steel canisters and subsequent laboratory analysis.
1.2.1 This test method describes a procedure for sampling in canisters at final pressures above atmospheric pressure (referred to as 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 simple flame ionization detector (FID), without the gas chromatographic columns and complex procedures necessary for species separation.
1.5 The range of this test method is from 20 to 10 000 ppbC (1, 2). See for procedures for lowering the range.
1.6 The test method may yield less accurate results for some halogenated or oxygenated hydrocarbons emitted from nearby sources of industrial air pollutants. This is especially true if there are high concentrations of chlorocarbons or chlorofluorocarbons present.
1.7 The values stated in SI units are regarded as 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.
