Particulate nitrate atmospheric sampling

Spicer, C. W. and Schumacher, P. M., 1977 Interferences in sampling atmospheric particulate nitrate. Atmospheric Environment IL 873-876. 

Common Pathways for Loss of Nitric Acid (Without Artifact Particulate Nitrate Formation). Introduction. Loss of HN03 can result from sorption on the surfaces of sampler inlets and inlet lines this situation is common to all collection procedures for atmospheric HN03. Such inlet losses are rarely determined, so it is difficult to assess the accuracy of atmospheric HN03 measurements or to pinpoint the source of bias between methods in intermethod comparisons (e.g., see reference 26). In addition to sampler-associated losses, N03 can be lost from samples during storage. 

The problems associated with sampling particulate organic C in the atmosphere crudely parallel those with sampling nitrates. However, the very large number of carbonaceous species, the range of vapor pressures involved, and the ubiquitous nature of carbon severely complicate development of improved sampling techniques based on total (or organic) carbon measurements. 

High efficiency denuders that concentrate atmospheric S02 were coupled to an ion chromatograph to yield detection limits on the order of 0.5 ppt (106). A newer approach has been introduced for the quantitative collection of aerosol particles to the submicrometer size (107). When interfaced to an inexpensive ion chromatograph for downstream analysis, the detection limit of the overall system for particulate sulfate, nitrite, and nitrate are 2.2,0.6, and 5.1 ng/m3, respectively, for an 8-min sample. A two-stage membrane sampling system coupled with an ion trap spectrometer has been utilized for the direct analysis of volatile compounds in air, with quantitation limits to low ppt levels (108). Toluene, carbon tetrachloride, tricholoroethane, and benzene were used in these studies. The measurement of nitrogen dioxide at ppb level in a liquid film droplet has been described (109) (see Air pollution). A number of elements in environmental samples have been determined by thermal ionization ms (Table 6). The detection limit for Pu was as low as 4 fg. 

In addition to the need to monitor known problematic compounds, newer compounds are being identified as potential threats to humans and as such need to be monitored in the atmosphere. For example, researchers reported (10) that several chemical and instrumental analyses of HPLC fractions provided evidence for the presence of /V-nitroso compounds in extracts of airborne particles in New York City. The levels of these compounds were found to be approximately equivalent to the total concentrations of polycyclic aromatic hydrocarbons in the air. Since 90% of the N-nitroso compounds that have been tested are carcinogens (10), the newly discovered but untested materials may represent a significant environmental hazard. The procedure involved collecting samples of breathable, particulate matter from the air in New York City. -These samples were extracted with dichloro-methane. Potential interferences were-removed by sequential extractions with 0.2 N NaOH (removal of acids, phenols, nitrates, and nitrites) and 0.2 N H2S04 (removal of amines and bases). The samples were then subjected to a fractional distillation and other treatments. Readers interested in the total details should consult the original article (10). Both thin-layer chromatography (TLC) and HPLC were used to separate the compounds present in the methanolic extract. 

Recently, the application of short term bio-assays to a variety of emission and ambient particulate samples has demonstrated that other compounds than PAH, most likely PAH-derivatives, can be responsable for a major part of the observed biological activity of the extracts. These results have forced us to widen our interest to the field of particulate polycyclic organic matter (POM), which besides hetero-atomic PAH (polycyclic aromatic compounds, PAC, containing nitrogen or sulfur) may also contain oxidized, nitrated, or sulfonated derivatives of PAH, formed in exhausts, emission stacks, plumes or during transport through the atmosphere. 

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