C-3-C-14 alkyl nitrates in remote South Atlantic air

Alkyl nitrates with chain lengths up to fourteen carbons have been detected in the remote troposphere of the South Atlantic Ocean. The concentrations of numerous iso- and n-alkyl nitrates in the range of C-3-C-12 have been me asured. Tenax-GC analysis was applied to determine short chain alkyl nitrat es (< C-6), while the novel detection of long chain iso- and n-alkyl nitrat es was achieved with a high volume sampling technique using silica gel. C-3 -C-12-alkyl nitrates show the lowest concentrations in the trade wind regio n (3.5 pptv). Higher concentrations in the west wind belt (11.1 pptv) revea l the influence of the South American continent as the source for the alkyl nitrates after long range transport. The concentrations of alkyl nitrates increase in proximity to South America. Measurements of long chain alkyl ni trates in rural air near the city of Ulm (Germany) are given for comparison . In addition, pattern analysis of long chain alkyl nitrates reveal this co mplex mixture of new compounds to be useful as trace indicators to distingu ish continental and marine air masses. Despite the lower photochemical form ation yields of primary n-alkyl nitrates compared to secondary n-alkyl nitr ates, the primary n-alkyl nitrates are relatively increased in marine air. The reason for this finding cannot be explained so far, but the correlation of secondary/primary n-alkyl nitrates shows a significant differentiation of air samples with continental or marine character. (C)1998 Elsevier Scien ce Ltd. All rights reserved.