We investigated the acidity and concentrations of water-soluble ions in PM2.5 aerosol samples collected from an urban site in Beijing and a rural site in Gucheng, Hebei Province from November 2016 to January 2017 to g...We investigated the acidity and concentrations of water-soluble ions in PM2.5 aerosol samples collected from an urban site in Beijing and a rural site in Gucheng, Hebei Province from November 2016 to January 2017 to gain an insight into the formation of secondary inorganic species. The average SO4^2–, NO3^–, and NH4^＋ concentrations were 8.3,12.5, and 14.1 μg m^–3, respectively, at the urban site and 14.0, 14.2, and 24.2 μg m^（–3）, respectively, at the rural site.The nitrogen and sulfur oxidation ratios in urban Beijing were correlated with relative humidity（with correlation coefficient r = 0.79 and 0.67, respectively） and the aerosol loadings. Based on a parameterization model, we found that the rate constant of the heterogeneous reactions for SO2 on polluted days was about 10 times higher than that on clear days, suggesting that the heterogeneous reactions in the aerosol water played an essential role in haze events.The ISORROPIA II model was used to predict the aerosol pH, which had a mean（range） of 5.0（4.9–5.2） and 5.3（4.6–6.3） at the urban and rural site, respectively. Under the conditions with this predicted pH value, oxidation by dissolved NO2 and the hydrolysis of N2O5 may be the major heterogeneous reactions forming SO4^2– and NO3^– in haze.We also analyzed the sensitivity of the aerosol p H to changes in the concentrations of SO4^2–, NO3^–, and NH4^＋ under haze conditions. The aerosol p H was more sensitive to the SO4^2– and NH4^＋ concentrations with opposing trends, than to the NO3^– concentrations. The sensitivity of the p H was relatively weak overall, which was attributed to the buffering effect of NH3 partitioning.展开更多
基金Supported by the National Key Project of Ministry of Science and Technology of China(2016YFC0203302)National Natural Science Foundation of China(91544103)
文摘We investigated the acidity and concentrations of water-soluble ions in PM2.5 aerosol samples collected from an urban site in Beijing and a rural site in Gucheng, Hebei Province from November 2016 to January 2017 to gain an insight into the formation of secondary inorganic species. The average SO4^2–, NO3^–, and NH4^＋ concentrations were 8.3,12.5, and 14.1 μg m^–3, respectively, at the urban site and 14.0, 14.2, and 24.2 μg m^（–3）, respectively, at the rural site.The nitrogen and sulfur oxidation ratios in urban Beijing were correlated with relative humidity（with correlation coefficient r = 0.79 and 0.67, respectively） and the aerosol loadings. Based on a parameterization model, we found that the rate constant of the heterogeneous reactions for SO2 on polluted days was about 10 times higher than that on clear days, suggesting that the heterogeneous reactions in the aerosol water played an essential role in haze events.The ISORROPIA II model was used to predict the aerosol pH, which had a mean（range） of 5.0（4.9–5.2） and 5.3（4.6–6.3） at the urban and rural site, respectively. Under the conditions with this predicted pH value, oxidation by dissolved NO2 and the hydrolysis of N2O5 may be the major heterogeneous reactions forming SO4^2– and NO3^– in haze.We also analyzed the sensitivity of the aerosol p H to changes in the concentrations of SO4^2–, NO3^–, and NH4^＋ under haze conditions. The aerosol p H was more sensitive to the SO4^2– and NH4^＋ concentrations with opposing trends, than to the NO3^– concentrations. The sensitivity of the p H was relatively weak overall, which was attributed to the buffering effect of NH3 partitioning.
