Size distributions and dry deposition fluxes of water-soluble inorganic nitrogen in atmospheric aerosols in Xiamen Bay, China

Size-segregated aerosol particles were collected using a high volume MOUDI sampler at a coastal urban site in Xiamen Bay, China, from March 2018 to June 2020 to examine the seasonal characteristics of aerosol and water-soluble inorganic ions (WSIIs) and the dry deposition of nitrogen species. During the study period, the annual average concentrations of PM 1 , PM 2.5 , PM 10 , and TSP were 14.8 ± 5.6, 21.1 ± 9.0, 35.4 ± 14.2 μg m −3 , and 45.2 ± 21.3 μg m −3 , respectively. The seasonal variations of aerosol concentrations were impacted by the monsoon with the lowest value in summer and the higher values in other seasons. For WSIIs, the annual average concentrations were 6.3 ± 3.3, 2.1 ± 1.2, 3.3 ± 1.5, and 1.6 ± 0.8 μg m −3 in PM 1 , PM 1-2.5 , PM 2.5–10 , and PM >10 , respectively. In addition, pronounced seasonal variations of WSIIs in PM 1 and PM 1-2.5 were observed, with the highest concentration in spring-winter and the lowest in summer. The size distribution showed that SO 4 2− , NH 4 + and K + were consistently present in the submicron particles while Ca 2+ , Mg 2+ , Na + and Cl − mainly accumulated in the size range of 2.5–10 μm, reflecting their different dominant sources. In spring, fall and winter, a bimodal distribution of NO 3 − was observed with one peak at 2.5–10 μm and another peak at 0.44–1 μm. In summer, however, the fine mode peak disappeared, likely due to the unfavorable conditions for the formation of NH 4 NO 3 . For NH 4 + and SO 4 2− , their dominant peak at 0.25–0.44 μm in summer and fall shifted to 0.44–1 μm in spring and winter. Although the concentration of NO 3 –N was lower than NH 4 –N, the dry deposition flux of NO 3 –N (35.77 ± 24.49 μmol N m −2 d −1 ) was much higher than that of NH 4 –N (10.95 ± 11.89 μmol N m −2 d −1 ), mainly due to the larger deposition velocities of NO 3 –N. The contribution of sea-salt particles to the total particulate inorganic N deposition was estimated to be 23.9—52.8%. Dry deposition of particulate inorganic N accounted for 0.95% of other terrestrial N influxes. The annual total N deposition can create a new productivity of 3.55 mgC m −2 d −1 , accounting for 1.3–4.7% of the primary productivity in Xiamen Bay. In light of these results, atmospheric N deposition could have a significant influence on biogeochemistry cycle of nutrients with respect to projected increase of anthropogenic emissions from mobile sources in coastal region.