Estimate of dry deposition fluxes of nutrients over the East China Sea: The implication of aerosol ammonium to non-sea-salt sulfate ratio to nutrient deposition of coastal oceans

Atmospheric deposition is one of important sources for nutrients to the surface ocean. Previous estimates for dry deposition fluxes of nutrients have mainly employed a single-mode particle model, and here we attempt to use size-segregated samples collected at Huaniao Island of the East China Sea (ECS) and dry deposition velocities derived from particle size and meteorological conditions of each sampling day. The dry deposition fluxes of NO3−, NH4+, and SP are estimated to be 6080, 10,006, and 26 μmol m−2 yr−1 respectively over the ECS using size-segregated samples. It is found that assuming a constant deposition velocity could overestimate the dry flux of NO3− by a factor of 6 while underestimate the flux of NH4+, which would alter the dry flux ratio of NH 4 + / NO 3 − from 1.6 to 0.1 with potential effects on the primary production and phytoplanktonic structure in the ECS. For coastal oceans influenced significantly by NH3 sources, aerosol NH4+ to non-sea-salt (nss-) SO42− ratio could be high and excess NH4+ may drag 34–54% of NO3− to fine mode aerosols, which may cause a large overestimation of dry flux of NO3− over the ocean by assuming its deposition velocity similar to that of coarse particle.