北京春季沙尘和霾期间气溶胶的对比模拟研究

A Comparative Numerical Study of Aerosols during Dust and Haze Events in Beijing Springtime

利用气象模式WRF驱动区域空气质量模式RAQMS,模拟研究了2014年北京地区春季颗粒物及气溶胶化学组分的时空变化,对比分析了沙尘期(3月17日、29日)和霾期(3月25~27日)的天气形势、气象要素和气溶胶化学组分特征,比较了沙尘和人为气溶胶表面非均相化学反应对大气化学成分的影响及相对贡献。结果显示,模式对于气象要素、PM2.5、PM10及其化学组分具有较好的模拟能力,考虑了气溶胶表面非均相化学反应后明显提高了模式对PM2.5及气溶胶化学组分模拟的准确性。沙尘期间,沙尘对PM10质量浓度贡献占主导地位(50.7%),对PM2.5的贡献与有机气溶胶(OM)和人为排放的一次颗粒物(PPM)相当;霾期间,硝酸盐NO3-(25.6%)和OM(23.6%)对PM2.5的贡献最大,在PM10中NO3-、PPM和OM的贡献相当。沙尘期,粗粒子明显增加,在PM10中所占比例与细粒子相当,为45.5%;霾期,细粒子占主导地位,占PM10质量浓度的85.6%。非均相化学反应使沙尘期间硫酸盐(SO42–)和NO3-浓度分别增加16.9%和83.8%,使霾期间的SO42-和NO3–浓度分别增加14.5%和45.0%。2014年3月,非均相化学反应使北京月均SO2、NO2、O3、SO42-、NH4+和NO3-的浓度分别变化了-2.5%、-5.7%、-3.4%、11.7%、18.6%和58.5%,本文结果表明非均相化学反应对二次无机气溶胶的生成有重要贡献。

A regional air quality model system driven by the weather research and forecasting model is applied to investigate the distribution and evolution of aerosol components in Beijing during the springs of 2014. The synoptic conditions, meteorological variables, and characteristics of aerosol chemical components are comparatively analyzed.Moreover, the effects of heterogeneous reactions on dust and anthropogenic aerosol surface on chemical compositions during the dust(17 Mar and 29 Mar 2014) and haze(25 –27 Mar 2014) periods are quantified and compared. The comparison with the observations indicates that the model is capable of reproducing the meteorological variables, PM2.5,and PM10, and their chemical component concentrations during the study period. Moreover, the inclusion of heterogeneous reactions apparently improves the prediction accuracy of PM2.5 and chemical component concentration. In dust days, dust is the dominant component of PM10 mass(50.7%), and its percentage contribution to PM2.5 is comparable to that of organic material(OM) and primary particulate matter(PPM). In hazy days, nitrate(25.6%) and OM(23.6%) contribute the most to PM2.5 mass. Meanwhile, the fractions of nitrate, PPM, and OM in PM10 are comparable.The fraction of coarse particle considerably increases during dusty days, with the mean fraction of 45.5% in PM10. In hazy days, fine particle dominates the PM10 mass, with a fraction of 85.6%. The heterogeneous reactions increase sulfate and nitrate concentrations by 16.9% and 83.8% in dusty days and by 14.5% and 45.0% in hazy days, respectively. On an average, the heterogeneous reactions lead to changes in near-surface SO2, NO2, O3, sulfate, ammonium, and nitrate concentrations by-2.5%,-5.7%,-3.4%, 11.7%, 18.6%, and 58.5%, respectively, in Beijing during March 2014 thereby highlighting the important role of heterogeneous reactions in secondary aerosol formation.