Nitrogen burden from atmospheric deposition in East Asian oceans in 2010 based on high-resolution regional numerical modeling

Abstract

East Asian oceans are possibly affected by a high nitrogen (N) burden because of the intense anthropogenic emissions in this region. Based on high-resolution regional chemical transport modeling with horizontal grid scales of 36 and 12 km, we investigated the N burden into East Asian oceans via atmospheric deposition in 2010. We found a high N burden of 2–9 kg N ha−1 yr−1 over the Yellow Sea, East China Sea (ECS), and Sea of Japan. Emissions over East Asia were dominated by ammonia (NH3) over land and nitrogen oxides (NOx) over oceans, and N deposition was dominated by reduced N over most land and open ocean, whereas it was dominated by oxidized N over marginal seas and desert areas. The verified numerical modeling identified that the following processes were quantitatively important over East Asian oceans: the dry deposition of nitric acid (HNO3), NH3, and coarse-mode (aerodynamic diameter greater than 2.5 μm) NO3−, and wet deposition of fine-mode (aerodynamic diameter less than 2.5 μm) NO3− and NH4+. The relative importance of the dry deposition of coarse-mode NO3− was higher over open ocean. The estimated N deposition to the whole ECS was 390 Gg N yr−1; this is comparable to the discharge from the Yangtze River to the ECS, indicating the significant contribution of atmospheric deposition. Based on the high-resolution modeling over the ECS, a tendency of high deposition in the western ECS and low deposition in the eastern ECS was found, and a variety of deposition processes were estimated. The dry deposition of coarse-mode NO3− and wet deposition of fine-mode NH4+ were the main factors, and the wet deposition of fine-mode NO3− over the northeastern ECS and wet deposition of coarse-mode NO3− over the southeastern ECS were also found to be significant processes determining N deposition over the ECS.