冬季PM2.5中无机水溶性离子与大气相对湿度的相关性

依托河北省灰霾污染防治重点实验室，对2019年11月26日—12月31日石家庄市大气PM_2.5中的NO₃^-和SO₄^2-进行连续在线观测，研究NO₃^-和SO₄^2-与环境空气相对湿度的相关性，解析冬季发生PM_2.5重污染天气的RH阈值.观测期间，RH为10%~60%时，NO₃^-的浓度与RH呈显著正相关，为PM_2.5中浓度最高的无机水溶性离子.RH超过70%后，NO₃^-与RH呈负相关，NO₃^-浓度和NOR开始下降.SO₄^2-浓度与RH在整个湿度区间均呈正相关.RH低于50%时，SO₂向SO₄^2-的转化以气相反应为主.RH高于50%以后，颗粒物达到潮解点，SO₂的主要反应转入液相，转化速率加快，SO₂液相反应贡献逐渐增加至64.6%.RH超过70%后，SO₄^2-成为PM_2.5中浓度最高的无机水溶性离子.RH超过PM_2.5潮解点以后，NO₃^-和SO₄^2-大量合成，推高PM_2.5环境浓度，易于形成重污染天气.

Correlation analysis on inorganic water soluble ions in PM2.5 and relative humidity of atmosphere in winter

The mass concentration of NO₃^- and SO₄^2- in PM_2.5 was continuously observed on-line from November 26 to December 31, 2019 at Hebei Key Laboratory of Haze Pollution Prevention and Control in Shijiazhuang. The quantitative relationship between the relative humidity (RH) of ambient air and the concentration of NO₃^- and SO₄^2- was analyzed, and the RH threshold of heavy pollution of PM_2.5 in winter was determined. When RH was in the range of 10%~60%, NO₃^- was the most abundant inorganic water-soluble ion in PM_2.5, and the concentration of NO₃^- was significantly positively related to RH. When RH was over 70%, NO₃^- was negatively correlated with RH. The concentration of SO₄^2- was positively correlated with RH in the whole humidity range. When RH was below 50%, the transformation from SO₂ to SO₄^2- was dominated by gas phase reaction route. When RH exceeded 50%, the particles reached the deliquescence point, which made the main reaction route of SO₂ transferring to liquid phase, and the reaction rate was accelerated. The contribution of liquid phase reaction to SO₄^2- formation was gradually increased to 64.6%. When RH was over 70%, SO₄^2- became the most abundant inorganic water-soluble ion in PM_2.5. When RH exceeded the deliquescence point of PM_2.5, NO₃^- and SO₄^2- formation were enhanced, increasing the concentration of PM_2.5 to the heavy pollution level.