pH变化对不同粒径气溶胶活度系数的差异分析

Analysis of the Differential Effects of Aerosol pH Variation on Aerosol Activity Coefficients for Different Particle Sizes

气溶胶酸度对气溶胶的形成、气-固分配、沉降通量和营养输送等大气活动密切相关,该文在2015年3月-2016年2月利用ACSA-14对邯郸市PM_(2.5)与PM_(2.5-10)及其成分进行了连续一年的监测。研究表明,邯郸市的PM_(2.5)年均浓度为142.2μg/m^(3),高于PM_(2.5-10)的77.0μg/m^(3),PM_(2.5)在PM10中的比例为64.9%。PM_(2.5)中硫酸根、硝酸根和可溶性有机物比例高于PM_(2.5-10)的,且年均值分别为15.5、17.5和9.8μg/m^(3)。邯郸市PM_(2.5)和PM_(2.5-10)呈中度酸性,pH值分别为4.5和4.3,春季和冬季的酸性较强。PM_(2.5)中硝酸根的活度系数较低,硝酸根更易分配进入颗粒相。pH值的增大有助于硝酸根进入颗粒相,pH对硫酸根、硝酸根和铵根的活度系数影响呈明显季节性差异;冬季pH轻微升高,较强的碱性使硫酸快速进入液相参与液相化学反应。研究结果对了解邯郸市大气颗粒物的污染特征和二次成分形成具有重要意义。

The acidity of aerosols is closely related to various atmospheric activities such as aerosol formation,gas-parti⁃cle partitioning,deposition flux,and nutrient transport.In this study,continuous one-year monitoring of PM_(2.5),PM_(2.5-10),and their components was conducted in Handan City,Hebei Province from March 2015 to February 2016 using ACSA-14.The study revealed that the annual mean concentration of PM_(2.5)in Handan was 142.2μg/m^(3),exceeding that of PM_(2.5-10),which measured at 77.0μg/m^(3).PM_(2.5)constituted 64.9%of PM10.Additionally,the proportions of sulfate,nitrate,and solu⁃ble organic compounds in PM_(2.5)were higher than those in PM_(2.5-10),with annual mean values of 15.5μg/m^(3),17.5μg/m^(3),and 9.8μg/m^(3),respectively.Both PM_(2.5)and PM_(2.5-10)exhibited moderate acidity,with respective pH values of 4.5 and 4.3,and they were more acidic during the spring and winter.The activity coefficients of nitrate in PM_(2.5)were lower,making nitrate more readily partition into the particulate phase.Increasing the pH facilitated the transfer of nitrate into the particu⁃late phase,and the effect of pH on the activity coefficients of sulfate,nitrate,and ammonium displayed significant sea⁃sonal variations.During winter,the activity coefficients of sulfate,nitrate,and ammonium showed a slight increase,with nitrate and ammonium displaying stronger alkaline values in the winter months.This stronger alkalinity facilitated the rapid transition of sulfate into the liquid phase,allowing it to engage in chemical reactions within the liquid phase.These findings hold significant implications for understanding the characteristics and formation mechanisms of atmospheric particulate matter in Handan.