冬奥管控时期淄博市PM_(2.5)中水溶性无机离子变化特征及影响因素

Change characteristics and influencing factors of water-soluble inorganic ions in PM_(2.5)before,during and after the Beijing Winter Olympics in Zibo City

为探究淄博市在北京冬奥会(以下简称“冬奥”)不同管控阶段的控制措施对PM_(2.5)中水溶性无机离子的影响,本研究收集了2022年1月8日—3月14日淄博市在线水溶性无机离子监测数据,分析了冬奥会不同管控阶段主要污染物和PM_(2.5)载带的水溶性离子的变化.同时,运用ISORROPIA II热力学平衡模型分析了气溶胶液态水含量(Aerosol liquid water content,ALWC)和pH值对硝酸盐和硫酸盐形成的影响,并探讨了该地区富铵条件对硝酸盐生成的影响.结果表明,淄博市在冬奥管控的不同阶段PM_(2.5)载带的水溶性离子中以硝酸盐为主,占总离子浓度的26%,且这一比例在超标天会进一步增加至33%.ALWC在管控前期的平均浓度为31.4μg·m^(-3),管控中、后期则分别下降了56%和36%.其中,管控中期较低的ALWC不利于硝酸盐和硫酸盐的生成.管控前、中期的气溶胶pH值相对接近,而管控后期明显增加,3个阶段气溶胶pH值>2.5有利于颗粒态硝酸盐转化生成.淄博市在冬奥3个管控阶段皆处于富铵环境,均有利于硝酸盐的生成.冬奥时期施行的管控措施有效降低了局地排放对该地区细颗粒污染的影响.综合来看,此次管控措施有效降低了淄博市空气污染水平,可为其他类似工业城市在重大事件期间制定管控措施提供案例和支持.

To investigate the effects of different control measures during the Beijing Winter Olympics 2022 on the inorganic water-soluble ions(IWSIs)of PM_(2.5)in Zibo City,we collected real-time monitoring data of IWSIs from January 8 to March 14,2022.We analyzed the variations of criteria air pollutants and IWSIs associated with PM_(2.5)during different periods of the Winter Olympics control(WOC),and used the ISORROPIA II thermodynamic equilibrium model to analyze the effects of aerosol liquid water content(ALWC)and pH on the formation of nitrate and sulfate.In addition,we investigated the influence of ammonium-rich conditions on the formation of particulate nitrate.The results showed that across all three periods of the Winter Olympics control in the study City,the nitrate was the dominant IWSI in PM_(2.5)mass,accounting for 26%of the total ion concentrations.The proportion increased up to 33%on days exceeding the secondary limit of Chinese National Ambient Air Quality Standard.ALWC had an average concentration of 31.4μg·m^(-3)before the WOC,but decreased by 56%and 36%during the middle and post periods of the WOC,respectively.The lower ALWC during the middle period of WOC was not conducive to the formation of nitrate and sulfate.The aerosol pH values were comparative during the periods of before and middle WOC,but increased during the period of post WOC,with the pH value of all three periods higher than 2.5,which favored the formation of particulate nitrate.Zibo City was in an ammonium-rich environment during all three control periods,which was conducive to nitrate formation.In summary,the control measures implemented during the Winter Olympics in Zibo city effectively reduced the impact of local emissions on PM_(2.5)pollution,and provided a case and support for other similar industrial cities to develop control measures during major events.