关中盆地NO2和SO2对颗粒物污染的协同效应

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SO₂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O₃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；SO₂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SO₂减排75%时，PM_2.5仅下降1.74%；当减排比例较高时，NO_x和SO₂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SO₂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SO₂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。

Synergetic effects of NO2 and SO2 on air particulate matter pollution in the Guanzhong Basin (GZB), China

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, NO₂, PM_2.5, and especially SO₂, have decreased significantly in the GZB. However, the concentration of O₃ showed an overall upward trend. Increased atmospheric oxidation capacity due to elevated O₃ 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 SO₂ 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 SO₂, i.e., 25%, 50%, and 75% reductions, simulated separately and simultaneously in the model. Results With NO_x and SO₂ 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 O₃ 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 SO₂ 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 SO₂ was reduced by 75%, PM_2.5 only decreased by 1.74%. For simultaneous reductions of NO_x and SO₂ 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 SO₂, 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 SO₂ 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.