Sources of HULIS-C and its relationships with trace metals, ionic species in PM2.5 in suburban Shanghai during haze and non-haze days

Humic-like substances (HULIS), the most ubiquitous class of water-soluble organic compounds in the atmosphere could enhance the generation of reactive oxygen species (ROS), and play a significant role in impacting aerosol chemistry and health effects. In this study, twenty-three PM_2.5 samples were collected in the atmosphere of suburban Shanghai from November 29 to December 17, 2015, and March 17 to April 30, 2016, during haze and non-haze days. The mean concentrations of HULIS in spring both in haze and non-haze days (2.34?±?0.70 μg/m³ and 1.94?±?0.88 μg/m³) were relatively higher than in that of winter (1.93?±?0.95 μg/m³ and 1.31?±?0.28 μg/m³). The ammonium, sulfate, and nitrate are the dominant ionic species in both winter and spring during haze days in suburban Shanghai. Correlation results revealed that HULIS formation was highly associated with the biomass burning (K) and secondary aerosols formation (SIA: NH₄⁺, SO₄^2?, NO₃^?) and also well-correlated with F^? and ca.²⁺ ions, crustal elements (Al and Fe) and anthropogenic pollution metals (As, Se, Rb, Sr, and Pb), suggesting that HULIS-C formation might be from biomass burning and secondary aerosol processes and also mixed formation (marine, crustal and industrial emissions) sources. From the coinciding results of the clustering analysis and weighted-CWT model, the principal potential source regions were the short transports from the Yangtze River Delta (YRD) regions, local regions, marine areas (the Bohai Sea, the Yellow Sea, the East China Sea) and also the long-range transports from northwestern in those seasons.