资源环境科技发展态势分析平台

Aerosol pH is a useful diagnostic of aerosol chemistry for formation of secondary aerosol and has been hypothesized to be a key factor in specific chemical reaction routes producing sulfate and nitrate. In this study, we measured hourly concentrations of water-soluble ions in particulate matter with an aerodynamic diameter less than 2.5 mu m, along with gaseous pollutants in Tianjin, China, from 4 to 31 January 2015. The following source contributions to water-soluble ions were estimated by positive matrix factorization: secondary sulfate (13%), secondary nitrate (44%), coal (14%), vehicle (16%), and dust (13%). ISORROPIA-II was used to investigate the complex relationships among aerosol pH, ammonia, and secondary aerosol formation. The estimated hourly aerosol pH varied from -0.3 to 7.7, with an average of 4.9 (+/- 0.78); the median value was 4.89, and the interquartile range was 0.72. During less polluted conditions, aerosol pH ranged from less than 0 to about 7; during heavily polluted conditions, pH was close to 5 (3.9-7.9) despite large amounts of sulfate. Sufficient ammonia/ammonium was present to balance high sulfate and nitrate formation. NH4+/NH3 (g) helped stabilize pH while nonvolatile cations contributed less to decreasing aerosol acidity. High acidy (pH < 3), light pollution (total water soluble ions < 30 mu g/m(3)), and low water content (less than 5 mu g/m(3)) were more correlated with higher rates of sulfate formation than nitrate formation in the winter.