基于多源资料和数值模拟的雾对PM_(2.5)影响研究

The role of fog on the PM2.5 based on multi-source data and numerical model

为探究雾-霾过程中雾对PM_(2.5)质量浓度的影响机制,选取2021年1月24~27日一次典型雾-霾过程,采用常规自动气象站、环境小时浓度、微波辐射计、风廓线雷达、气溶胶激光雷达、255m气象塔上梯度观测的气象、环境和湍流等多源数据资料及WRF-Chem过程分析数值模拟方法对此次污染过程进行综合分析.结果表明,此次雾相对湿度增加是由于辐射冷却和平流引起的,雾类型是辐射平流雾,其特征是水汽自上而下输送,雾过程雾顶高度250m,逆温层底高度为80~120m,雾顶高度>逆温层底高度;雾发生前由于相对湿度、垂直平流和湍流混合影响,地面及垂直方向PM_(2.5)质量浓度先增长再下降,总体有利于PM_(2.5)质量浓度扩散;雾成熟期根据逆温层底的高度,辐射-平流雾对PM_(2.5)影响分为两种,其中雾对高于逆温层底的PM_(2.5)为湿清除作用,而对低于逆温层底的PM_(2.5)为积聚作用;雾消散后霾阶段40m湍流动能增高至0.78m^(2)/s^(2),并逐渐和200m处湍流动能大小趋于一致,湍流混合贡献量为-40~-23μg/(m^(3)·h),总体有利于地面PM_(2.5)质量浓度扩散.

In order to explore the impact mechanism of fog on the PM_(2.5)concentration during the process of the fog-haze,the multi-source observation data such as automatic meteorological station data,environmental hourly concentration data,microwave radiation data,wind profile radar,aerosol lidar,255m meteorological tower data and WRF-Chem process analysis method were used to analyze the role of advection-radiation fog on the PM_(2.5)in Tianjin from January 24 to 27,2021.The results show that:The increasing in relative humidity during fog formation phase is attributed to the radiative cooling and advection,indicating that the fog type is advection-radiation fog.The water vapor was transported from top to down during the formation of fog.The fog-top height was 250m,and the bottom of the inversion layer height was 80~120m,so the fog-top height was higher than inversion layer bottom height during the process of the fog.Because the role of the relative humidity、vertical advection and turbulent mixing before fog formation,the PM_(2.5)mass concentration of the ground and vertical direction was growth first then slowed again,and the overall benefit of PM_(2.5)mass concentration was diffusion.According to the inversion layer bottom height,there were two situations of the role of fog on the PM_(2.5)during the fog mature period.One was removing PM_(2.5)when the fog height was higher than the bottom height of inversion.The other was scavenging PM_(2.5)When the fog height was lower than the bottom height of inversion.The turbulent kinetic energy was active after fog dissipation,turbulent mixing amount of contribution-40~-23μg/(m^(3)·h),fog was conducive to the ground PM_(2.5)mass concentration diffusion.