Source and Sink of Ammonia in the Marine Boundary Layer

During the June, 1992 ASTEX/MAGE experiment conducted in the area of the Azores and Madeira Islands, we made a series of chemical measurements from aircraft, ship and island. The mean NH4+/nss SO4 = molar ratios in marine airmasses and continental polluted airmasses were 0.87 ± 0.85 and 1.3 ± 0.43 respectively, which indicate that sulfur-containing aerosols were only partially neutralized by gaseous ammonia. Similar average diurnal variations of MS and ammonium were observed in marine airmasses. The size distributions show that most NH4+ and nss SO4 = were contained in a submicron mode; the Na+, Cl- and NO3-, by contrast, were in a supermicron mode; MSA showed bimodal behavior. The average dry deposition fluxes for nss SO4 =, MSA, NH4+ and NO3- in this experiment were 1.49, 0.09, 0.18 and 3.25 μmol m-2day-1 respectively. The flux of ammonia from the ocean surface was estimated during a Lagrangian experiment at 22-40 ± 40 μmol m-2day-1. This implies that the ammonia cycling may be a significant way to move marine ammonia from place to place, but is not likely to be a net new foxed N input