Interactions between the sulfur and reduced nitrogen cycles over the central Pacific Ocean

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In April and May of 1988 along 170°W from 53°N to 14°S, simultaneous concentration measurements were made of the major components of the sulfur and reduced nitrogen cycles. The species measured included sea water dimethylsulfide, DMS (s), and total ammonia, NH3 (s,tot) = NH3 (s) + NH4+ (s); atmospheric gas phase DMS (g), NH3 (g), and SO2 (g); and atmospheric particulate phase NH4+ (p), non‐seasalt sulfate, nss SO4= (p), and methanesulfonate, MSA (p). Based on isentropic calculated back trajectories at 1000, 950, 850, and 700 mbar arrival heights, three apparent air mass regimes were encountered; one from 50°N to 30°N which recently had been in contact with Asia, one from 29°N to 15°N which had passed over Hawaii during a volcanic eruption several days earlier, and one from 14°N to 11°S which was the most representative of remote marine air. Changes in the relative concentrations of the atmospheric S and NH3 species reflected the origin of the air masses sampled. The NH3 (g) concentrations were low over the entire region studied, indicating that the lifetime of NH3 in the marine boundary layer is on the order of hours. These low NH3 concentrations led to only partially neutralized sulfate aerosol particles. The mean NH4+ (p) to nss SO4= (p) molar ratio was 1.3±0.71. The highest ratios were found in continentally influenced air masses where the NH4+ (p) was most likely of continental origin and in remote marine air masses with an absence of continentally derived nss SO4= (p). The lowest ratios found were a result of high nss SO4= (p) concentrations in air masses influenced by the Hawaiian volcanic plume. Seawater concentrations of DMS (s) and NH3 (s,tot) were lowest in the North Pacific central gyre and highest in the northern latitudes and near and south of the equator.