Analysis of aerosol chemical components and source apportionment during a long-lasting haze event in the Yangtze River Delta, China.

Based on the chemical composition data of a regional long-lasting haze event that occurred in the Yangtze River Delta (YRD) region from 17 December 2023 to 8 January 2024, the evolutionary characteristics of the chemical components and sources of fine particulate matter (PM) under different pollution levels were comparatively analyzed using PMF (Positive Matrix Factorization) and backward trajectory analysis. SNA (NO, NH, SO) was found to be the primary chemical component of PM, making up 63.6 % (clean days) to 69.7 % (heavy pollution) of it. The NO concentration was 3.14 (clean days) to 6.01 (heavy pollution) times higher than that of SO. NO, POC, Fe, Mn, Al concentrations increased, while SOC, EC, crustal elements (Ca, Si) and other water-soluble ions (WSIs) concentrations decreased as the pollution level increased. The contribution of secondary inorganics and biomass-burning emissions and industrial and ship emissions increased significantly as the pollution level increased, which accounted for 40.3 % and 36.7 %, respectively, in the heavy pollution stage. The contribution of traffic sources decreases gradually with increasing pollution levels, accounting for only 59.1 % of the light pollution stage in the heavy pollution stage. PM and its main chemical components showed similar potential source distribution, located in the northwest (Fuyang, Huainan, Nanjing), south (Taizhou, Lishui, Jiande) and north (Taizhou, Yancheng). However, distinct transport routes were observed under the different air quality levels. During the heavy pollution period, the polluted air masses primarily came from the harbor regions, whereas during the light pollution period they were transported from the southeast (Taizhou) and the North China Plain.