复杂地形上气象场对空气质量数值模拟结果影响的研究

The Impacts of Various Meteorological Conditions on Air Quality Modeling Results over Complex Terrain

利用WRF模式三种边界层参数化方案(YSU、MYJ、ACM2)产生的气象场分别驱动多尺度空气质量模式CMAQ,对兰州市西固区冬季2005年1月27日至2月2日期间SO2和NO2浓度进行了数值模拟,将模拟结果与同期监测的污染物浓度进行对比分析,结果表明:WRF模式不同边界层参数化方案模拟输出的气象场驱动CMAQ模式所模拟的SO2和NO2浓度均可以反映出污染物的时空变化特征,CMAQ模式具有模拟复杂下垫面高分辨率污染物输送特征的能力;WRF模式的边界层参数化方案选为局地与非局地闭合方案(ACM2)时,模拟的气象场驱动CMAQ模式得到的空气污染物浓度分布特征最优,这主要是由于ACM2的湍流输送机制较为合理,模拟的边界层低层气象场更接近实际,从而可以较好地模拟污染物的输送特征;当CMAQ模式的垂直混合方案与WRF模式的湍流输送方案一致时(均采用ACM2方案),模式间的兼容性好。

Meteorological conditions are critical in the transport and final fate of air pollutants. In this paper, meteorological data simulated by three different planetary boundary layer （PBL） schemes in the Weather Research and Forecasting （WRF） model for the period January 27-February 2, 2005, were used to drive the Community Multi-scale Air Quality （CMAQ） model. The results show that discrepancies in the turbulent closure method employed by the various PBL schemes in the WRF cause a significant impact on the wind and the temperature fields in the PBL and lead to differences in pollutant concentrations simulated by the CMAQ model. Compared with monitored pollutant concentration, the CMAQ model has been determined as suitable for obtaining high spatial and temporal resolution pollutant characteristics in complex terrain areas. In addition, the results of WRF simulation with the Asymmetric Convective Model version 2 （ACM2） PBL scheme coupled with CMAQ yields more reasonable results than those of other two schemes. The local and non-local combined ACM2 scheme represents actual meteorological conditions more accurately due to its reasonable turbulence transport mechanism. Thus, usage of the same vertical turbulent mixing scheme in a coupled meteorological and air quality model would be advantageous. This tight coupling would improve mass conservation because air density and pollutants mix in the same manner, eliminating the risk of accruing mass error in mixing ratios of trace species in air mass.