珠三角一次严重雾霾混合污染数值模拟分析

Numerical Simulation Analysis of a Severe Mixed Pollution of Smog and Haze in the Pearl River Delta

为了解2017年1月1日到12日珠江三角洲地区一次严重的雾霾混合污染演变过程的气象条件及微物理特征,运用区域空气质量模式(WRF-CMAQ)对这次过程进行数值模拟。结果表明,模式系统对此次过程中温度、湿度模拟效果较好,风速模拟值总体偏高,模拟的PM_(2.5)浓度总体偏低。该模式较好地模拟了该次雾霾污染的时空分布。通过分析污染严重的肇庆市的边界层高度、温度、风的垂直分布和气溶胶粒子的精细模拟值,探讨了霾转化为浓雾污染的发生发展过程。结果发现:持续稳定的高空环流形势是雾霾混合污染的前提条件,925 hPa西南风转为偏东南风是霾转化为雾的湿度因素,925 hPa弱小风辐合是浓雾产生的有利的大气环流形势。肇庆市近地面平均风速低于3 m·s^(-1)和接地逆温的存在,使污染物浓度增加,易形成较轻的雾霾污染;当925850 hPa转吹偏东南风,地面平均风速出现低于2 m·s^(-1)甚至是持续5~16 h的静风,空间上周边出现小风辐合,边界层高度低至100 m,小风层增厚至925 hPa以上,同时接地逆温与近地面湿度的增长叠加,相对湿度增长到接近100%时,是霾转化为浓雾污染的气象因素。此外,还发现这次污染气溶胶粒子爱根核(d≤0.05μm)质量浓度很低,在10μg·m^(-3)以下;较轻的霾污染时细颗粒污染物积聚核模态(0.05μm<d<2.00μm)浓度明显高于粗粒核模态(d≥2.00μm)浓度;出现浓雾严重污染时粗粒核模态与积聚核模态浓度相当。而广州的表现则与肇庆不同,霾污染过程粗粒核模态比积聚核模态质量浓度略高,浓雾时则约高出1倍。

A regional air quality model,WRF-CMAQ,is used to simulate meteorological conditions and microphysical characteristics of a severe smog-haze mixed pollution process seen in the Pearl River Delta Economic Zone from 1 to 12 January 2017.The results show that the model system has a good performance in simulating temperature and humidity as well as the spatial and temporal distribution of the mixed pollution.But the simulated wind speed is higher than observation and the simulated concentration of PM_(2.5) is lower.By analyzing the height of the boundary layer,temperature,vertical distribution of wind and refined simulation values of aerosol particles in Zhaoqing,where severe pollution occurred,we investigate the occurrence and transforming process of the haze to dense fog pollution.The results show that the sustained-stable upper-air circulation is the precondition of the smog-haze mixed pollution,the change of 925 hPa wind field from southwest to southeast provides humidity condition of haze to fog,and the convergence of 925 hPa weak wind is the favorable atmospheric circulation for dense fog.The average wind speed in Zhaoqing is lower than 3 m·s^(-1) and the surface temperature inversion increases the concentration of pollutants,forming moderate fog-haze pollution.When the 925—850 hPa wind turns to southeast and the average wind speed is less than 2 m·s^(-1) or even calm condition for 5—16 hours,there is a strong convergence of small wind around the area,and the effect of the unique topography of Zhaoqing intensifies the accumulation and convergence of pollutants on the surface.The height of the boundary layer descends to as low as 100 m,the small wind layer thickens to above 925 hPa,and the near-surface inversion is superposed with the increasing humidity(making the relative humidity increases to nearly 100%),all these are the meteorological elements for haze to transform into continuous dense fog pollution.In addition,it is found that the concentration of Aerosol Particle aegen nucleus(d≤0.05μm)is very low,below 10μg·m^(-3).The concentration of the accumulated nuclear mode of Aerosol particles(0.05μm<d<2.00μm)in haze pollution is higher than that of the coarse nuclear mode(d≥2.00μm),and the coarse nuclear mode of Aerosol particles in dense fog pollution is similar to that of the accumulated nuclear mode.Compared with Zhaoqing,Guangzhou has a different situation.The mass concentration of coarse-grained nuclear mode is about 1 times higher than that of accumulated nuclear mode during dense pollution.