苏州市初夏臭氧污染成因及年际变化

Ozone Pollution in Suzhou During Early Summertime:Formation Mechanism and Interannual Variation

以2017~2021年的5~6月苏州市城区站点的大气污染物浓度为研究对象,分析了臭氧(O_(3))、氮氧化物(NO_(x))、总氧化剂(O_(x))、一氧化碳(CO)和挥发性有机物(VOCs)等污染物的变化特征,利用基于观测的模型(OBM)研究了O_(3)污染成因及其年际变化,解析了环境空气VOCs的主要来源及其变化趋势.结果表明:(1)近年来苏州O_(x)平均体积分数以及NO_(x)和CO平均浓度整体呈下降趋势,但VOCs的体积分数整体呈上升趋势;O_(3)污染天光化学反应前体物浓度水平仍较高,且显著高于优良天.(2)近年来苏州O_(3)生成处于VOCs控制区;苏州市VOCs和NO_(x)长期减排比例应不低于5∶1,在VOCs控制方面应注重对芳香烃和烯烃的减排.(3)源解析结果显示,工业排放、汽油车尾气和柴油机尾气是苏州市VOCs的主要排放源;近年来工业排放源和溶剂使用源有所下降,但汽油车尾气源和油气挥发源贡献率上升明显,且上述两类污染源排放VOCs的O_(3)生成潜势较高.(4)综合分析各排放源对O_(3)生成潜势的贡献发现,溶剂使用源和汽油车尾气源的VOCs排放是影响苏州市O_(3)生成的关键因素.

This study investigated the concentrations of atmospheric pollutants in the urban area of Suzhou from May to June,2017-2021.The variation characteristics and annual changes of ozone(O_(3)),nitrogen oxide(NO_(x)),total oxidant(O_(x)),carbon monoxide(CO),and volatile organic compounds(VOCs)were analyzed.The O_(3) formation mechanism and its annual changes were studied using an Observation-Based Model(OBM),and VOCs source apportionments and their trends were discussed.The results indicated that①The volume fractions of O_(x) and the concentrations of NO_(x) and CO have decreased in the urban area of Suzhou in recent years,while the volume fractions of VOCs have increased,and sufficient photochemical conditions for O_(3) formation still existed during polluted days.②The O_(3)-NO_(x)-VOCs sensitivity in Suzhou was in the VOCs-limited regime.The long-term reduction ratio between VOCs and NO_(x) should not be less than 5∶1,and aromatics and alkenes were the critical VOCs for mitigating O_(3) pollution.③The results of VOCs source apportionment revealed that industrial emissions,gasoline vehicle exhaust,and diesel engine exhaust were the major sources of VOC emissions in Suzhou.Industrial emissions and solvent usage declined from 2017 to 2021;however,gasoline vehicle exhaust and gasoline evaporation,which possess higher O_(3) formation potential(OFP),increased significantly.④The OFP source apportionments results indicated that controlling VOC emissions from solvent usage and gasoline vehicle exhaust is crucial for O_(3) pollution control in Suzhou.