Size-Resolved Atmospheric Phosphorus in Shanghai: Seasonal Variations, Sources and Dry Deposition

Atmospheric deposition is an important source for the P biological cycle, especially for P-limited ecosystems. In the present study, 48 hr size-segregated aerosol samples were collected at an urban site in Shanghai for one year from May 2019 to June 2020. Total phosphorus (TP) presented a bimodal distribution in four seasons, which was mainly contributed by mineral dust in the coarse mode, and was related to anthropogenic and combustion emissions in the fine mode. Dissolved inorganic phosphorus (DIP) and dissolved organic phosphorus (DOP) presented a bimodal distribution in spring and summer, and a unimodal distribution dominated by a fine mode in autumn and winter. Size distributions and correlation analysis showed that DIP in the fine and coarse modes originated from the acid processing of SO4 (2-) and NO3-, respectively, while DOP was mainly from biomass burning emissions. Positive Matrix Factor analysis showed that phosphorus (P) in atmospheric aerosols in Shanghai was mainly contributed by four sources, including crustal sources, sea-salt, industry emissions and fossil fuel combustion, and biomass burning. Industry emissions and fossil fuel combustion, as well as biomass burning were important sources of TP in all particle sizes (50%-65%). Biomass burning was the most important source of DOP (>50%). The total deposition flux of total dissolved phosphorus (TDP) calculated based on the size-weighted deposition velocity model averaged 75.2 +/- 17.4 mu g/m (2)/d. Assuming that all of TDP is bioavailable, TDP deposition can create a primary production of 8.0 mg C/m(2)/d, which can support 1.3%-4.4% of the new production in the East China Sea. Plain Language Summary Phosphorus (P) has become one of the main factors limiting the primary productivity in many ecosystems. Currently, limited measurements of P especially soluble P leads to a large discrepancy between observations and model results and substantial uncertainties in quantifying the effect of atmospheric P deposition. Therefore, comprehensive knowledge regarding its sources, chemical compositions, atmospheric formation and evolution, and size distribution is required. Based on the collected samples, we first characterized the concentrations, size distributions, seasonal variations, sources, and dry deposition fluxes of different P forms in Shanghai. We also investigated the effects of sources and atmospheric acidic processing on the size distribution of. Based on these results. Our results showed total phosphorus presented a bimodal distribution, which was mainly contributed by mineral dust in the coarse mode and was related to anthropogenic and combustion emissions in the fine mode. Dissolved inorganic phosphorus and dissolved organic phosphorus presented a bimodal distribution in spring and summer, and a unimodal distribution dominated by a fine mode in autumn and winter. We estimated that total dissolved phosphorus flux can support 1.3%-4.4% of the new production in the East China Sea, emphasizing the important role of atmospheric P deposition to the marine ecosystem.