Dry deposition fluxes of inorganic nitrogen and phosphorus in atmospheric aerosols over the Marginal Seas and Northwest Pacific

Abstract

To improve estimation of the dry deposition flux (Fd) of nitrogen and phosphorus over the ocean, the concentrations of NO2−, NO3−, NH4+, and PO43− in aerosol particles were measured from 2005 to 2017, and their deposition rates (Vd) were modeled over the marginal seas of China and the northwest Pacific (NWP). Combined with the modeled rates and the measured size distribution, the Vd values of NO2−, NO3−, NH4+, and PO43− over the studied ocean region were calculated to at 0.92 ± 0.06, 0.95 ± 0.08, 0.68 ± 0.03 and 0.65 ± 0.06 cm·s−1 on average, respectively. The spatial variation in Vd for these species was dependent on the wind speed and mass concentration size distribution. Based on the multiyear observations over the region, the average concentrations of atmospheric NO2−, NO3−, NH4+, and PO43− were 2.07 ± 1.58 nmol·m−3, 58.5 ± 44.3 nmol·m−3, 107.9 ± 56.7 nmol·m−3 and 1.13 ± 1.10 nmol·m−3, respectively. The estimated Fd of NO2− was lower than 1 μmol·m2·d−1 in most ocean regions, although the Fd of NO3−, NH4+ and PO43− were 42.74 ± 25.02, 57.40 ± 29.50 and 0.66 ± 0.72 μmol·m2·d−1, respectively. Except for the South China Sea, the Fd values of NO3− and NH4+ were 3–6 times higher over the marginal seas than the NWP while the PO43− flux was only high over the Yellow and Bohai Seas. The dissolved N/P ratio influx varied from 84 to 338, indicating that N was equivalent to the relative abundance of P during the atmospheric input to the China marginal seas and the NWP. Our results showed that the long-term input of atmospheric anthropogenic nutrients would cause different influences on the stoichiometric ratios of nutrients and primary productivity between marginal seas and open ocean.