[Role of Ammonia in Aerosol Liquid Water, pH, and Secondary Inorganic Aerosols Formation at an Ammonia-rich City in Changzhou].

Ammonia （NH） is an important alkaline reactive nitrogen, which, as a precursor of fine particulate matter, raises public health issues. In this study, online NH, SO, NO, PM, and its water-soluble inorganic ions were detected to deduce the influence of NH on aerosol liquid water content （AWC） and aerosol pH, including the formation of water-soluble secondary ions in PM in winter in Changzhou, an ammonia-rich city in the Yangtze River Delta area in winter. The results showed that NH mainly existed in the form of NHNO and （NH）SO, and the remaining NH existed as NHCl. Owing to the NH-NH buffer system, the aerosol pH values were found at 4.2 ± 0.4, which was positively correlated with the NH content. The aerosol pH value variation narrowed with the increase in PM concentration and tended to be between 4 to 5. AWC increased exponentially with the increase in humidity and SNA content, among which NHNO, （NH）SO, and NHCl contributed 58.5%, 18.4%, and 8.3%, respectively, due to their hygroscopicity. Aerosol pH, AWC, and NH-NH conversion promoted the gas-to-particle conversion of SO and NO. In Changzhou, rich NH-NH were found to maintain relatively high pH values, push up AWC, and promote the heterogeneous reaction of SO, whereas NO generation was dominated by a homogeneous reaction, which was accelerated by NH. According to the simulation results, relatively noticeable changes in aerosol pH and AWC could be found by the reduction of up to 30% of NH.