In situ measurements of butane and pentane isomers over the subtropical North Pacific

Abstract

Butane and pentane isomers were measured in situ in the remote marine atmosphere at the Bellows Beach, on the east side of the Island of Oahu, Hawaii during July and August 1998. Air masses arriving at Bellows Beach site originated mainly from the eastern North Pacific, and sometime polluted air masses of island origin arrived at the sampling site. The median mixing ratios were 11 pptv (i-butane), 18 pptv (n-butane), 1 pptv (i-pentane), and 3 pptv (n-pentane) in clean marine air, which were 3-12 times lower than those encountered in the polluted island air. The observed mixing ratios of the alkanes in marine air are within the range of those previously reported in the Atlantic and Pacific Ocean. The concentration ratios of pentane isomers suggest that the sources of the observed pentanes in marine air were not only derived from the ocean but also from the unidentified anthropogenic sources. Based on the comparison with values in the literature on sea-to-air fluxes, oceanic emissions of these alkanes were estimated to account for less than 30% of the observed mixing ratios. Continental emissions are not the important anthropogenic source due to the air mass trajectory analysis, suggesting that there are unidentified anthropogenic sources associated with ship activity and oceanic oil pollution.