边界层方案对华北一次污染过程模拟的影响

采用WRF模式中YSU、MYJ和ACM2 3种边界层参数化方案，利用WRF模式和空气质量模式CAMx对2015年11月11~15日发生在京津冀地区的一次污染过程进行了模拟，同时利用地面气象要素、风廓线、秒探空和空气质量观测数据对3种参数化方案下的模拟结果进行了验证对比.一种基于临界垂直湍流交换系数确定边界高度的方法被用于对比3种参数化方案之间垂直扩散能力的差异.结果表明，MYJ方案对10m风速高估最大（平均高估0.66m/s），对2m温度和2m湿度低估最小，YSU和ACM2方案对地面气象要素的模拟效果相近；ACM2方案对于边界层内垂直廓线模拟效果优于YSU和MYJ方案，但是3种参数化方案对边界层内风速均存在高估（高估可达2.6m/s）；基于临界垂直湍流交换系数方法定义的边界层高度更能反映大气的垂直扩散能力，MYJ方案边界层高度最小，其模拟的PM_2.5浓度最高；MYJ方案对于地面风速的高估，会降低模拟的区域整体PM_2.5浓度，但是会增加风速较大区域下风向的PM_2.5浓度；ACM2方案对边界层垂直廓线模拟最好，夜间底层垂直湍流交换系数计算值较大，使得ACM2方案对于本次过程中PM_2.5等污染物的模拟优于MYJ和YSU方案.

The impacts of planetary boundary layer schemes on pollutants simulations during an air pollution episode over BTH region

The WRF model and the CAMx model were applied to simulate the meteorology variables and air pollutants over Beijing-Tianjin-Hebei (BTH) region during an air pollution episode in November 2015. The impacts of three planetary boundary layer (PBL) schemes (YSU, MYJ, ACM2) on meteorological factors and air pollutants simulations were compared. The observed surface meteorological factors and PM_2.5 over BTH region and the wind profile data at Beijing were used to evaluate the model performances. The MYJ scheme predicted the largest biases on the 10m wind speed and lowest biases on the 2m temperature and humidity. The ACM2scheme had the best performance on the simulation of vertical profile in the PBL. All the three PBL schemes overpredicted the wind speed in the PBL and the bias could reach to 2.6m/s. The model PBL heights were recalculated using a uniform method, which based on the vertical diffusivities. The MYJ scheme produced the lowest PBL heights and the highest PM_2.5 concentrations, among the three schemes. The overestimated 10m wind speed of the MYJ scheme leaded to a lower simulated PM_2.5 concentration over BTH region, but it would increase the PM_2.5 concentration in the downwind area. The ACM2scheme produced the better vertical profile and higher Kv than others in the lower layers in the night, then the ACM2scheme produced a better performance on the simulated PM_2.5 concentrations and other air pollutants in the night than the other two schemes.