Environ. Sci. Techno/. 1991,25,61-67
Analysis of Alkyl Nitrates and Selected Halocarbons in the Ambient Atmosphere Using a Charcoal Preconcentration Technique Elliot Atlas**+and Sue Schaufflert Department of Oceanography, Texas A&M University, College Station, Texas 77843
A method has been developed to measure I C 3 alkyl nitrates and C1-C2 halocarbons, such as perchloroethylene and bromoform, in ambient air. The method preconcentrates analytes on a 5-mg charcoal trap from multiliter volumes of air. Analytes are desorbed from the charcoal with a small volume of solvent and are analyzed by highresolution gas chromatography with electron capture detection. Laboratory and field tests have been performed to evaluate method precision, analyte breakthrough, and compound recovery from the charcoal. Tests verified that the sampling/analytical system is free from artifact formation under clean to moderately polluted conditions, but further tests are required for areas of high concentrations of hydrocarbons, NO,, and oxidants. The method allows measurement of halocarbons and >_C3alkyl nitrates at concentrations in the pptv range.
Introduction Hydrocarbon and nitrogen oxide (NO,) emissions are known to have a significant impact on the chemistry of urban atmospheres (1, 2). Photochemical reactions of hydrocarbons and NO, contribute to the formation of ozone, peroxyacetyl nitrate (PAN), and other reactive chemical species in the urban atmosphere. Transport of reactive hydrocarbons and NO, combined with emission of natural hydrocarbons in rural and remote areas also can produce a significant impact on the chemistry of the clean troposphere (3-7). To fully understand the chemical interactions and transformations of carbon species and NO,, it is necessary to measure the full range of reactants and products. One of the potentially important products that form from the interaction of hydrocarbons and NO, are alkyl nitrates (RON02) (8, 9). Alkyl nitrates are formed in the atmosphere during the OH-radical-initiated oxidation of alkanes in the presence of NO, (NO + NO2). The mechanism proposed for the formation of alkyl nitrates involves the reaction of an alkylperoxy radical with NO to form an alkyl nitrate (10, 11). The reaction mechanism favors the formation of secondary alkyl nitrate species over primary and tertiary alkyl nitrates of a given carbon chain length. Also, the yield of akyl nitrates from the oxidation of alkanes increases with carbon chain length. For typical atmospheric conditions, the yield of alkyl nitrates increases from
