典型区域传输过程关键源区减排对天津无机气溶胶及PM2.5的影响研究

Influence of Emission Reduction in Key Source Areas on Inorganic Aerosols and PM2.5 in Tianjin during a Typical Regional Transport Process

利用嵌套网格空气质量数值预报模式NAQPMS探究一次典型区域传输过程关键源区气态前体物减排对天津无机气溶胶(IA)及PM2.5的影响。大尺度区域高精度的IA模拟数据显示,华北平原地区生成了高浓度的IA,向华东地区传输后,按顺时针方向又返回华北平原地区。这一往返式区域传输过程导致天津出现两次污染时段。利用耦合在NAQPMS中的在线污染物来源追踪方法量化了不同源区对天津IA的贡献,识别出华北平原地区是关键源区,日均贡献为57.6%~100%。在天津污染前1天和污染天对华北平原地区SO_(2)、NH3和NO_(x)减排30%分别开展敏感性试验,研究表明NH3减排导致天津IA和PM2.5最大下降率分别为30.8%和13.3%,是SO_(2)减排对IA和PM2.5最大下降率的16倍和26.6倍,是NO_(x)减排情景对IA和PM2.5最大下降率的7倍和6.4倍,成为降低天津污染水平最显著的前体物。SO_(2)减排造成天津硝酸盐浓度上升,最大增长率为3.5%,根据热动力学平衡原理,SO_(2)减排导致生成的硫酸铵减少,气态NH3增加又引起更多的HNO_(3)被中和,生成硝酸盐。NO_(x)减排对华北平原不同地区硝酸盐产生增加/降低两种效应,双效应沿着传输路径依次向下游传播,造成天津硝酸盐、IA及PM2.5浓度先降低后增加。研究结果高度强调了在污染传输过程,关键源区正效应的传播会加快降低气溶胶浓度,但负效应的传播会增加大气污染联防联控的难度。

This study investigated the impact of gaseous precursor emission reduction over key source regions on inorganic aerosols(IAs)and PM2.5 in Tianjin during a typical regional haze process with the NAQPMS(Nested Air Quality Prediction Modeling System).Based on high-precision simulations,the high IA concentration originating from the North China Plain(NCP)was transported to East China and subsequently returned to the NCP region in a clockwise pattern,resulting in two pollution periods in Tianjin.The online pollutant source-tagging method coupled with the NAQPMS was used to quantify the contribution of different source regions to IAs in Tianjin,and the NCP region was identified as the key source area,with a daily contribution of 57.6%-100%.Sensitivity experiments were performed to analyze the impact of reducing precursor emissions by 30%in the NCP region a day before a pollution event and during the pollution days in Tianjin.NH3 control notably reduced IA and PM2.5 concentrations in Tianjin by 30.8%and 13.3%,respectively,which were 16 and 26.6 times that of SO_(2) reduction and 7 and 6.4 times that of NO_(x) reduction,respectively.SO_(2) reduction increased nitrate concentration by 3.5%in Tianjin because SO_(2) control increased gaseous NH3,and excessive NH3 in the atmosphere can neutralize HNO_(3) to nitrate production based on the thermodynamic effect.NO_(x) reduction exhibited positive and negative effects on nitrate in different areas of the NCP,and transport of the two effects occurring in upstream areas caused the concentrations of nitrate,IAs,and PM2.5 in Tianjin to decrease first and then increase.This study highlights that transporting positive effects in key source areas can contribute to PM2.5 reduction while transporting negative effects harms the joint prevention and control of air pollution.