Oceanic and atmospheric hydrocarbon measurements and sea-air fluxes during ACE-1

Gary Kleiman, Ronald G. Prinn, Alexander A. Pszenny, Ashwini G. Deshpande, Xianqian Shi

Center for Global Change Science,
MIT Rm. 54-1312
77 Massachusetts Ave
Cambridge, MA 02139

Gas chromatographic in situ measurements of several C3-C5 hydrocarbons were made for both air, and air equilibrated with surface seawater, during the recent IGAC Aerosol Characterization Experiment (ACE-1). The (approximately hourly) measurements were made from the NOAA ship Discoverer, whose Leg 1 cruise track included a north-south Pacific transit and whose Leg 2 cruise track covered the Southern Ocean from 40S to 55S between 138E and 159E longitude. Measurements were obtained by cryogenically pre-concentrating between 300 and 500 ml of gas drawn from either the bow of the ship or the equilibrator headspace. These measurements show high temporal and spatial variability for concentrations of the non-methane hydrocarbon (NMHC) species observed in both the boundary layer air and surface seawater consistent with previous investigations. Oceanic variability was significantly less than atmospheric variability and the ocean was generally supersaturated with the measured NMHC. Sea-air fluxes have been calculated using a bulk flux formulation, observed winds,and NMHC concentrations in air and seawater. Generally good agreement is found between these fluxes and those observed previously by Donahue and Prinn (JGR, 98, No. D9, pg. 16,915, 1993) during the 1990 SAGA III cruise and Shi and Prinn (JGR, submitted) during the 1992 IGAC MAGE cruise. These NMHC fluxes are large enough to play a significant role in the photochemistry of the marine boundary layer. Tentative correlations between overall levels of oceanic NMHC species and tracers of biological productivity (nitrate, chlorophyll) are evident.