Nonmethane hydrocarbons in surface waters, their sea-air fluxes and impact on OH in the marine boundary layer during the First Aerosol Characterization Experiment (ACE 1)

摘要

Concentrations of six abundant alkanes (propane, 2-methylpropane, butane, 2-methyl-butane, pentane, cyclopentane) and three abundant alkenes (2-methylpropene, cis-2-butene, 1,3-butadiene) were determined in air equilibrated with surface seawater in real time during the International Global Atmospheric Chemistry First Aerosol Characterization Experiment (ACE 1) campaign to the Southern Ocean in November-December 1995. Concentrations in ocean surface water inferred from these measurements generally lay within the ranges observed by other investigators at other times in other regions of the global ocean. Concentrations tended to decrease with increasing latitude. Comparison with a limited number of dissolved organic carbon (DOC) data obtained during transit from Hawaii to Hobart, Tasmania, suggested that higher hydrocarbon concentrations were associated with higher DOC levels. During the ACE 1 intensive study period west and south of Tasmania the differences in NMHC concentrations among the three major water masses sampled, while frequently significant, were not related in a simple direct or inverse way to surface water temperature, concentrations of nitrate, chlorophyll a, or dimethylsulfide, or to calculated sea-to-air transfer velocity or solar radiation intensity. The only correlations that showed some consistency within water masses were with temperature (negative) and nitrate (positive), an essential nutrient for phytoplankton growth. Deduced sea-to-air fluxes indicated modes open-ocean emissions of C_3-C_5 NMHC in this part of the global ocean. Assuming that the deduced fluxes were balanced by reaction with hydroxyl radical, OH, we estimated that the nine measured NMHC together accounted for negligible removal of OH compared to that due to the dominant OH + CO reaction and about 5 times less than that due to the DMS + OH reaction in the region of the marine boundary layer studied during ACE 1.