边界层方案对山西冬季一次静稳天气PM_(2.5)浓度模拟的影响

准确的空气质量数值预报模式依赖于精确的气象条件模拟,尤其依赖于大气边界层的准确模拟.为理解边界层过程如何影响空气污染物的传输与混合,利用WRF-Chem模式不同边界层方案(YSU和MYJ)进行敏感性试验,针对山西冬季典型静稳天气,对地面温度场、地面风场、PM_(2.5)浓度及边界层内部的动力和热力层结进行模拟分析,并与观测资料进行对比,分析不同PBL方案对于气象要素和PM_(2.5)浓度分布的模拟能力,探讨边界层内部热力层结和湍流输送差异对PM_(2.5)浓度模拟的影响.结果表明:2种边界层方案均能较好模拟出冬季静稳天气背景下地面温度、风速及PM_(2.5)浓度的空间分布和日变化特征,气温模拟的较大误差主要出现在夜间,而地面风速和PM_(2.5)浓度的模拟结果在午后误差较大;相对于YSU方案,局地MYJ方案模拟的温度、风场和PM_(2.5)浓度的误差更小,模拟结果更接近于实况观测.地面PM_(2.5)浓度的模拟误差可能与近地面逆温层、混合层及地面风速等的模拟误差有关;不同边界层参数化方案导致的边界层内热力层结和湍流输送的模拟差异,可能是影响近地面PM_(2.5)浓度模拟差异的主要原因;夜间MYJ方案逆温层厚度较厚,地面PM_(2.5)模拟浓度较低;午后MYJ方案混合层高度较低,加之地面风速较弱,导致地面PM_(2.5)模拟浓度较高.

The effects of different planetary boundary layer schemes on PM2.5 concentration simulations in winter stable weather of Shanxi

Adequate air quality modeling is reliant on accurate meteorological simulation especially in the planetary boundary layer (PBL). To further understand how the boundary layer processes affect the mixing and transmission of air pollutants, the sensitivity tests of WRF-Chem model with different PBL schemes were utilized. Surface temperature, wind field, PM_2.5 concentration, dynamic and thermal PBL stratification were simulated in the typical winter stable weather condition of Shanxi province, and the results were compared with the observational data. The simulation ability of different schemes were analyzed, and the effects of PBL thermal stratification and turbulent transportation differences on PM_2.5 concentration simulation were discussed. The results indicated that both of the two schemes could simulate the spatial distribution and diurnal variation characteristics of surface temperature, wind speed, and PM_2.5 concentration in the winter stable weather. The relatively larger error of temperature simulated normally occurred at night, while the simulation error of surface wind speed and PM_2.5 concentration mainly appeared in the afternoon. Surface temperature, wind field and PM_2.5 concentration simulated by MYJ scheme showed less error, and more close to the observations. The differences of PBL thermal stratification and turbulent transportation simulated by different PBL schemes led to the differences of surface PM_2.5 concentration simulation. The thicker inversion layer of MYJ scheme caused the lower surface PM_2.5 concentration at night, while the lower mixing layer and weaker surface wind speed simulated by MYJ scheme resulted in a higher surface PM_2.5 concentration in the afternoon.