Atmospheric inorganic nitrogen in marine aerosol and precipitation and its deposition to the North and South Pacific Oceans

Aerosol and rain samples were collected between 48A degrees N and 55A degrees S during the KH-08-2 and MR08-06 cruises conducted over the North and South Pacific Ocean in 2008 and 2009, to estimate dry and wet deposition fluxes of atmospheric inorganic nitrogen (N). Inorganic N in aerosols was composed of similar to 68% NH (4) (+) and similar to 32% NO (3) (-) (median values for all data), with similar to 81% and similar to 45% of each species being present on fine mode aerosol, respectively. Concentrations of NH (4) (+) and NO (3) (-) in rainwater ranged from 1.7-55 mu mol L-1 and 0.16-18 mu mol L-1, respectively, accounting for similar to 87% by NH (4) (+) and similar to 13% by NO (3) (-) of total inorganic N (median values for all data). A significant correlation (r = 0.74, p < 0.05, n = 10) between NH (4) (+) and methanesulfonic acid (MSA) was found in rainwater samples collected over the South Pacific, whereas no significant correlations were found between NH (4) (+) and MSA in rainwater collected over the subarctic (r = 0.42, p > 0.1, n = 6) and subtropical (r = 0.33, p > 0.5, n = 6) western North Pacific, suggesting that emissions of ammonia (NH3) by marine biological activity from the ocean could become a significant source of NH (4) (+) over the South Pacific. While NO (3) (-) was the dominant inorganic N species in dry deposition, inorganic N supplied to surface waters by wet deposition was predominantly by NH (4) (+) (42-99% of the wet deposition fluxes for total inorganic N). We estimated mean total (dry + wet) deposition fluxes of atmospheric total inorganic N in the Pacific Ocean to be 32-64 mu mol m(-2) d(-1), with 66-99% of this by wet deposition, indicating that wet deposition plays a more important role in the supply of atmospheric inorganic N than dry deposition.