Precipitation effects on autumn PM2.5 composition in a Yangtze River Delta coastal city: Temporal variation, source apportionment and health risk

Based on chemical composition data from the Yangtze River Delta in November 2022, this study conducted a comparative analysis of precipitation impacts on PM_2.5 chemical composition variation, sources, and light extinction using methods such as PMF (Positive Matrix Factorization), while also assessing local health risks. During the observation period, the mean PM_2.5 concentration was relatively low (25.1 μg/m³), primarily composed of SNA (SO₄^2-, NO₃^-, and NH₄⁺) (67 %) and OC (18.9 %). Precipitation reduced secondary transformations of NO₂ and SO₂ (with SOR and NOR decreasing by 23 % and 33 %, respectively), leading to lower NO₃^- and SO₄^2- concentrations and consequently reduced PM_2.5. During precipitation, OC and EC concentrations decreased proportionally, whereas SOC increased by 0.34 μg/m³. Metal concentrations exhibited minimal reduction (6-121 ng/m³) during precipitation. Precipitation differentially influenced various sources: dust sources showed the largest concentration reduction (-56.2 %), while traffic and sea salt sources had the smallest decrease (-0.4 %). The diurnal variation of precipitation effects on five sources correlated with their baseline concentrations: lower initial concentrations resulted in negligible or even increased post-precipitation, whereas higher initial concentrations experienced significant removal. In Jiaxing, the risk index (RI) reached 26273, indicating an extremely strong risk (with Cd being the primary contributor). Both children and adults in Jiaxing faced carcinogenic (HQ > 1) and non-carcinogenic (CR > 10^-4) risks, with hand-to-mouth ingestion identified as a critical exposure pathway. Cr was the dominant metal affecting carcinogenic and non-carcinogenic risks for both children and adults. Additionally, the extinction coefficient increased during precipitation due to enhanced contributions from NH₄NO₃ and (NH₄)₂SO₄.