One-year online observation of PM_2.5 composition in jiaxing city: Temporal evolution, source apportionment, and...

High-resolution pollution data for coastal industrial cities remain scarce compared to megacities, limiting effective regional management. This study investigates PM_2.5 chemical compositions and identifies sources and transport impacts in Jiaxing, a representative manufacturing hub in the Yangtze River Delta, using one-year online observations (August 2024-July 2025) from the Wuzhen Superstation via the PMF and HYSPLIT models. The dominant components were: NO₃^- (32.94%), NH₄⁺ (15.63%), POC (11.92%), SO₄^2- (11.62%), and SOC (7.65%). Winter concentrations of NO₃^-, NH₄⁺, and SO₄^2- were 1.75-5.90 times higher than summer levels. NO₃^- dominated in winter (39.15%), but halved in summer, while POC became more significant (15.33%). Photochemical activity (related to O₃ formation) was the primary annual source (42.56%), peaking in spring (58.71%). Diurnal variation: SO₄^2- exhibited an afternoon peak in summer, autumn, and winter, with mild fluctuations in spring, while other ions showed minor seasonal differences; Carbonaceous components displayed bimodal distributions in most seasons (peaking at 07:00 and 17:00) but a unimodal peak in summer. (peaking at 10:00); Diurnal variations of elements were significant in spring and summer, with clear distinctions among the respective components. Continental air masses generally carried higher pollution. Summer-autumn marine air masses favored NO₃^- formation, while winter southern marine air masses carried elevated elements. High PM_2.5 pollution (150-200 μg/m³) was primarily dominated by NO₃^-, NH₄⁺, and SO₄^2- (collectively 78.85%), with pollution sources co-dominated by secondary and vehicle-coal combustion (collectively 75.65%). Under high O₃ pollution (250-300 μg/m³), photochemical activity predominated (80%), SNA concentrations halved and SOC increased 7.64-fold (collectively 62.98%) compared to low O₃ levels (0-50 μg/m³). These findings highlight the necessity of NO_x and VOCs control in coastal industrial cities.