关中盆地NO_(2)和SO_(2)对颗粒物污染的协同效应

Synergetic effects of NO_(2) and SO_(2) on air particulate matter pollution in the Guanzhong Basin (GZB),China

基于WRF-Chem模式模拟了关中盆地2019年1月2—14日一次颗粒物污染事件,评估了NO_(x)和SO_(2)减排及其在颗粒物污染中的协同作用对PM_(2.5)污染的影响。敏感性实验结果表明:NO_(x)减排可使PM_(2.5)中硝酸盐含量下降,但大气中O_(3)浓度上升,大气氧化能力增强,其他二次组分上升,导致PM_(2.5)下降不明显;SO_(2)人为源减排可使硫酸盐质量浓度下降,但由于硫酸盐在PM_(2.5)中占比较低,当SO_(2)减排75%时,PM_(2.5)仅下降1.74%;当减排比例较高时,NO_(x)和SO_(2)同时减排更有利于颗粒物污染防治。PM_(2.5)质量浓度在NO_(x)和SO_(2)同时减排75%时比分开减排75%时多下降0.75%,主要是硫酸盐下降所致;对气溶胶含水量进行分析,发现NO_(x)对气溶胶含水量影响较大,当NO_(x)减排75%时,气溶胶含水量可下降15.51%;此外,NO_(x)和SO_(2)同时减排比分开减排时气溶胶含水量更低,更不利于二次颗粒物生成。

Background,aim,and scope Since the implementation of the Air Pollution Prevention and Control Action Plan in 2013,particulate matter pollution has been significantly alleviated in the Guanzhong Basin(GZB).Still,heavy haze occurs frequently in winter.According to observational data of air pollutants in the winters between 2013 and 2018,the mass concentrations of CO,NO_(2),PM_(2.5),and especially SO_(2),have decreased significantly in the GZB.However,the concentration of O_(3) showed an overall upward trend.Increased atmospheric oxidation capacity due to elevated O_(3) concentration can promote the generation of secondary aerosols.According to statistical analyses of organic carbon(OC)and elemental carbon(EC),which are important components of PM_(2.5),secondary aerosols played an important role in the winter.The main purpose of the study is to quantitatively evaluate reductions in NO_(x) and SO_(2) emission and synergistic effects of these reductions on PM_(2.5).Materials and methods A large-scale heavy haze event in the GZB from 2 to 14 January 2019 was simulated with the WRF-Chem model.Multiple sensitivity experiments were conducted to reproduce actual emission reduction scenarios of NO_(x) and SO_(2),i.e.,25%,50%,and 75%reductions,simulated separately and simultaneously in the model.Results With NO_(x) and SO_(2) reduction rates of 25%,50%,and 75%in the study period,the PM_(2.5) mass concentrations at simultaneous emission reductions increased 0.10%at 25%reduction,however,at 50%and 75%reduction it went down 0.20%and 0.75%more than the sum of single emission reduction effects,respectively.Discussion Declining NO_(x) from anthropogenic emissions can decrease nitrate concentration but also increase atmospheric O_(3) concentration.Enhancing the atmospheric oxidation capacity promotes the generation of other secondary components.Therefore,the decreases in PM_(2.5) were low.When NO_(x) was reduced by 75%,PM_(2.5) was only reduced by 4.60%.Reductions of anthropogenic SO_(2) emissions can reduce the mass concentration of sulfate.However,the proportion of sulfate in PM_(2.5) was relatively low(8.62%).Therefore,its effect on overall PM_(2.5) reduction was not apparent.When SO_(2) was reduced by 75%,PM_(2.5) only decreased by 1.74%.For simultaneous reductions of NO_(x) and SO_(2) emissions,the decline in PM_(2.5) mass concentrations was higher than the sum of separate 50%and 75%emission reductions of NO_(x) and SO_(2),which was mainly caused by the reduction of sulfate,indicating that simultaneous emission reduction is conducive to preventing and controlling particulate pollution.The reduction of NO_(x) greatly influenced the aerosol water content(AWC).When NO_(x) was reduced by 75%,the AWC could be reduced by 15.51%.The AWC of simultaneous emission reductions was lower than those of separate emission reductions,which is more unfavorable to generating secondary particles.Conclusions Simultaneous reductions of NO_(x) and SO_(2) emissions were more beneficial to preventing and controlling particulate pollution than separate emission reductions at a higher reduction rate,which was mainly caused by the reduction of AWC.Recommendations and perspectives In future research,it is necessary to update emission inventories and optimize the WRF-Chem model to reduce simulation bias.In addition,future studies should investigate whether this phenomenon applies to different air pollution characteristics in different regions and seasons.