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 μg/m²/d. Assuming that all of TDP is bioavailable, TDP deposition can create a primary production of 8.0 mg C/m²/d, which can support 1.3%–4.4% of the new production in the East China Sea.