Hydrocarbons in the Non-Urban Atmosphere: Analysis, Ambient Concentrations and Impact on the Chemistry of the Atmosphere

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Abstract
The role of hydrocarbons for the chemistry of the atmosphere outside of heavily polluted urban or industrial areas is not yet fully understood. One of the reasons is the rather limited data base for hydrocarbon mixing ratios in rural and semi-rural areas. This is-at least partly-due to analytical problems. The mixing ratios of hydrocarbons-except methane-in remote and semi-remote areas are very low, a few ppb or even less. In addition, the hydrocarbon pattern is-especially in semi-rural areas-extremely complex, a potpourri of engine exhaust, refinary emissions, natural gas leakage, biogenic emissions from plants, decaying leaves etc. In the past few years we have developed gas chromatographic technics for the identification and quantification of low and medium molecular weight hydrocarbons outside polluted areas. The results of these measurements show that these non-methane hydrocarbons (NMHC) are present in the non-urban atmosphere at very low mixing ratios-generally fractions of a ppb, rarely more than 1 ppb. Nevertheless, many of these hydrocarbons are very reactive (rather high rate constants for reaction with OH, some of these hydrocarbons-the alkenes-also react with ozone) and thus are of considerable importance for the chemistry of the atmosphere. In this paper we present atmospheric measurements of some non-methane hydrocarbons in different remote, rural and semi-rural areas. These measurements allow some inferences on the impact of man made hydrocarbons on the chemistry of the atmosphere outside urban and industrialized areas.

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