Improvement on numerical simulation by variational assimilation of surface PM2.5 and aerosol lidar during a heavy pollution episode in winter in Tianjin
YANG Xu1,2, FAN Wen-yan1,2, CAI Zi-ying1,2, ZHU Yu-qiang1,2, TANG Ying-xiao1,2, DONG Qi-ru3
1. Tianjin Environmental Meteorological Center, Tianjin 300074, China; 2. CMA-NKU Cooperative Laboratory for Atmospheric Environment-Health Research, Tianjin 300074, China; 3. Tianjin Institute of Meteorological Science, Tianjin 300074, China
Abstract：For the transport-type heavy pollution episodes, the vertical simulation deviation of atmospheric chemical model was large, the ground observation assimilation could not significantly improve the vertical initial field of pollution, and the upper air transport was underestimated. A heavy pollution episode was taken as an example in Tianjin, which occurred from January 5 to 6, 2023, the aerosol variational assimilation technology was developed for the joint application of surface PM2.5 and aerosol lidar vertical observations, to improve the vertical pollution simulation of atmospheric chemical model and serve forecast, early warning and mechanism analysis of heavy pollution episodes. The results showed that during the heavy pollution episode, growth rate and peak concentration of ground PM2.5 was significantly underestimated, simulated pollution layer height was about 200~300m lower than observed value and characteristics such as higher PM2.5 concentration in upper air than that on the ground in transportation phase of daytime and high pollution values above the stable boundary layer at night were not effectively reflected; Assimilation of surface PM2.5 observations effectively optimized PM2.5 spatial distribution, average simulation error decreased by 35.3μg/m3 and 77.3μg/m3 respectively in Shijiazhuang and Hengshui, the upstream cities and decreased by 39.7μg/m3 in Tianjin. However, its improvement on vertical distribution simulation was limited, especially for the complex change of PM2.5 vertical distribution in transport-type pollution episode, which was not accurately reflected. By adding assimilation of vertical PM2.5 observations obtained from aerosol lidar, vertical PM2.5 simulation was further improved, the maximum reduction of PM2.5 mass concentration RMSE was 19.8μg/m3 at about 500m. There was obvious positive effect at the assimilated time and within 2~3h, as for subsequent time, simulated pollution layer height was basically same with observation in S2 phase, the difference between them reduced to 50~100m, compared with 200~300m in CTRL experiment without assimilation and 100~200m in DA_SFC experiment with surface PM2.5 assimilation. High value of pollution above stable boundary layer was effectively simulated and the simulation error of PM2.5 mass concentration in the heavy polluted layer was significantly reduced; Assimilation effect in the daytime on January 5 was not good as that of S2 phase, accurate simulation of vertical PM2.5 could be achieved in a short time, but the deviation of vertical simulation had been significantly enlarged again with simulation time increasing. In spite of this, positive effect still existed compared with DA_SFC and the simulation error of pollution layer height was reduced by at least 50m.
杨旭, 樊文雁, 蔡子颖, 朱玉强, 唐颖潇, 董琪如. 地面PM2.5和气溶胶激光雷达联合变分同化对天津冬季一次重污染过程数值模拟改进研究[J]. 中国环境科学, 2023, 43(10): 5088-5097.
YANG Xu, FAN Wen-yan, CAI Zi-ying, ZHU Yu-qiang, TANG Ying-xiao, DONG Qi-ru. Improvement on numerical simulation by variational assimilation of surface PM2.5 and aerosol lidar during a heavy pollution episode in winter in Tianjin. CHINA ENVIRONMENTAL SCIENCECE, 2023, 43(10): 5088-5097.
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