Investigation of the atmospheric importance of organic nitrates through laboratory and field experiments.

摘要

The atmospheric concentrations of several organic nitrates were measured in both rural and urban environments. Air samples were collected on charcoal traps, extracted with benzene and analyzed using a gas chromatograph equipped with both electron capture and specific nitrate detectors. In addition, several hydroxy nitrate product yields were determined under simulated atmospheric conditions involving the photo-oxidation of selected alkenes.; Measurements of alkyl and multifunctional organic nitrates were conducted at a rural site in Ontario during periods with varying levels of photochemical activity. During periods in the summer of 1992 and 1993, a total of 19 organic nitrates (12 C3-C6 alkyl nitrates, 6 C2-C 4 hydroxy nitrates and a dinitrate) were quantitatively determined in atmospheric samples. The sum of the organic nitrate concentrations was found to be correlated with ozone and ranged from 12 to 284 ppt. The total concentration of organic nitrates measured contributed from 0.5 to 5% to the total odd nitrogen species. On average, the alkyl nitrates represented 79%, the hydroxy nitrates 20% and the dinitrate 1% of the total measured organic nitrates. Unidentified organic nitrate peaks determined using an organic nitrate specific detector were found to represent ∼10-15 % of the total organic nitrates measured in this environment. Some inconsistencies were found when comparing the distribution of alkyl and hydroxy nitrates measured with the computed relative production rates for photochemically active air masses. Although the inclusion of the multifunctional organic nitrates does not significantly change the measured contribution of these species to NOy, it is shown that the isoprene nitrates may contribute as much as the combined contribution of all the measured organic nitrates.; As part of the PACIFIC '93 field study, measurements of organic nitrates were conducted in a suburban environment downwind from the city of Vancouver, B.C. In this environment in which production dominates over destruction, the hydroxy nitrates represented a substantial fraction of the total measured organic nitrates. In addition, several unidentified organic nitrates were found to contribute up to 38% (215 ppt) to the total quantity of organic nitrates during the daytime maximum. The relationship between the alkyl nitrates and the corresponding carbonyl compounds indicates that up to 90% of the carbonyl compounds measured are produced from sources other than the precursor alkoxy radical of the same carbon number. (Abstract shortened by UMI.)