The role of sources and meteorology in driving PM_2.5-bound chlorine

The role of chloride in atmospheric chemistry received increased attention over recent years. Given the primary and chemical-active nature of PM_2.5-bound chlorine (p-Cl^-), it makes sense to get to know the sources and processes of p-Cl^-. The temporal behavior of observed p-Cl^- concentration based on 1-h high resolution exhibited seasonal variation of high in winter, low in summer and diurnal variation of high in the morning, low in afternoon. Meteorological normalization technique based on random forest was used to disentangle the effects of emission changes which affected the seasonal variation and meteorology which was related to diurnal variation on p-Cl^-. Generalized additive model (GAM) identified RH and temperature as the key meteorological factors of p-Cl^- generation, and p-Cl^- pollution was serious under the condition of low temperature and high RH. Dispersion-normalized positive matrix factorization (DN-PMF) was used to apportion the p-Cl^- to its sources, finding that coal combustion was the main source of p-Cl^-, followed by biomass burning and industrial process emissions. Our results will provide the basis for further analysis the causes of p-Cl^- pollution and composite air pollution control strategies.