Production and distribution of organic nitrates, and their relationship to carbonyl compounds in an urban environment

As part of the PACIFIC ʹ93 field study, measurements of a series of hydrocarbon oxidation products, specifically 12 alkyl nitrates, six hydroxy nitrates and the carbonyl compounds propanal, acetone, butanal and methyl ethyl ketone, were quantitatively determined in atmospheric samples in a suburban environment downwind of the city of Vancouver, BC. In this study we found that the hydroxy nitrates represent a substantial fraction of the total measured organic nitrates. In addition, several unidentified organic nitrates were found to contribute up to 38% (215 pptv) 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. These sources are believed to be the decomposition of larger alkoxy radicals, or direct anthroprogenic/biogenic emissions.