MM5/WRF气象场模拟差异对CMAQ空气质量预报效果的影响

评估了为公共多尺度空气质量模式(CMAQ)提供气象输入场的第五代NCAR/Penn State中尺度 (MM5) 模式与天气研究和预报(WRF)模式模拟的多种气象要素的准确性;比较了2个模式提供的气象场对华北地区SO_2和NO_2源同化反演效果及其质量浓度预报的差异;分析了相对湿度和边界层高的变化对ρ(SO_2),ρ(NO_2)预报的影响及其物理机制.结果表明:WRF模式模拟的各气象要素准确性优于MM5模式,其中MM5模式对相对湿度和边界层高度的模拟值与实测值的偏差较明显,而WRF模式的模拟值与实测值较接近;相对湿度和边界层高度参数是影响CMAQ空气质量预报的关键气象要素,这2个参数的变化对ρ(SO_2)和ρ(NO_2)的预报有显著影响,因此,对2个参数的改进可显著减小预报误差;ρ(SO_2)模拟误差减小的主要原因是垂直输送和质量调整过程对ρ(SO_2)的贡献减小;而ρ(NO_2)模拟误差减小的主要原因是化学反应过程对ρ(NO_2)的贡献明显减小.

Differences in MM5 and WRF Meteorological Field Simulations and Impact on Air Quality Forecasting by CMAQ Model

The impacts of meteorological fields simulated by MM5 and WRF models on air quality forecasting by the CMAQ model are explored. Emphasis is placed on comparing the inverse effect of SO_2 and NO_2 sources by adaptive Nudging scheme and the two models in North China, the difference of their forecasting concentrations, and on analysis of physical mechanism of improved simulation of planet boundary layer (PBL) height and relative humidity. The results indicate that diurnal variation and vertical profile of four meteorological elements simulated by the WRF model are in better agreement with MICAPS observations than those by the MM5 model. The relative humidity and the PBL height simulated by the MM5 model are far from the observed values, but those simulated by WRF model are closer to the observations. The relative humidity and PBL height are key factors in the forecasting of SO_2 and NO_2 mass concentrations with the CMAQ model. The variation of these factors significantly influences the forecasting of SO_2 and NO_2 mass concentrations. Therefore, improved simulation of PBL height and relative humidity has positive impacts on SO_2 and NO_2 mass concentration forecasting accuracy. The main reason for smaller simulative error of SO_2 mass concentration is less contribution of vertical transportation and mass adjusting process to SO_2 mass concentration;the main reason for smaller simulative error of NO_2 mass concentration is less contribution of chemical reactive process to NO_2 mass conentration.