Recently, the contribution of inorganic salts (nitrates in particular) to the mass concentration of particulate matter with an aerodynamic diameter of less than 2.5 μm (PM2.5) has been increasing across China. However, it is urgent to understand how the increased inorganic salts affect the crucial properties of PM2.5. Here, we conducted continuous field observations at Zhenjiang Ecology and Environment Protection Bureau from January 1 to December 31, 2021. The mass concentrations of ammonium sulfate[(NH4)2SO4] and ammonium nitrate (NH4NO3) were calculated using different methods. The contributions of (NH4)2SO4 and NH4NO3 to the extinction coefficient, hygroscopic growth, and acidity of PM2.5 were discussed in detail. Our results demonstrated that the mean mass concentrations of (NH4)2SO4 and NH4NO3 during the study period were (6.5±4.5) and (15.0±13.3) μg·m-3, which contributed (20.5±18.2)% and (34.5±18.4)% to the mass concentration of PM2.5, respectively. The total extinction coefficient of PM2.5 was (224.5±194.2) Mm-1, in which NH4NO3 was the largest contributor[(40.1±20.9)%] followed by (NH4)2SO4[(19.1±10.8)%]. (NH4)2SO4 and NH4NO3 were also the dominant contributors to the hygroscopic growth of PM2.5. In particular, NH4NO3contributed from (53.8±13.4)% to (61.6±14.6)% to the aerosol water content of PM2.5 under pollution conditions. Thus, NH4NO3 was a key air pollutant to be targeted for further improving the visibility and air quality in Zhenjiang in the future. However, the reduction in the precursors of NH4NO3 would lead to an increase in aerosol acidity, particularly in the spring and winter seasons. Our results help us understand the evolution of air quality and the related impacts and also provide important information on air quality improvement in Zhenjiang in the future.
Keywords: aerosol acidity; aerosol water content; ammonium nitrate (NH4NO3); ammonium sulfate[(NH4)2SO4]; atmospheric particulate matter; extinction coefficient.