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Improvement of the Real-time PM2.5 Forecast over the Beijing-Tianjin-Hebei Region using an Optimal Interpolation Data Assimilation Method

Category: Air Pollution Modeling

Accepted Manuscripts
DOI: 10.4209/aaqr.2017.11.0522
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Haitao Zheng1,2,3, Jianguo Liu 1, Xiao Tang3, Zifa Wang 3, Huangjian Wu3, Pingzhong Yan3, Wei Wang4

  • 1 Key Laboratory of Environmental Optics and Technology, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, China
  • 2 University of Science and Technology of China, Hefei 230026, China
  • 3 The State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China
  • 4 China National Environmental Monitoring Centre, Beijing 100012, China

Highlights

Established a routine air quality data assimilation system in CNEMC for China.
Evaluated the impact of the data assimilation on the real-time PM2.5 forecast.
The DA effects on the PM2.5 forecast had a rapid decay.
Increasing the assimilation frequency can improve the DA system performance.


Abstract

A routine air quality data assimilation (DA) system was established in the China National Environmental Monitoring Center (CNEMC) based on the optimal interpolation (OI) method. The surface observations from more than 1,400 stations over China were assimilated into a real-time air quality forecast system with three nested domains. The initial conditions of NO2, SO2 and PM2.5 in the three domains were optimized by the data assimilation system. The impact of the data assimilation on the real-time PM2.5 forecast over the Beijing-Tianjin-Hebei (BTH) region during the heavy haze season of 2015 was evaluated. The results show that the DA can significantly improve real-time PM2.5 forecasts with the root mean square error (RMSE) reduced by 23%, 8.2%, 4.8% for the forecasts of the first day, second day and the third day respectively. The mean fractional bias and the mean fractional error of the forecast were reduced from 50.9% and 70.67% to 40% and 62.3% respectively, and the performance was changed from "criteria" to approach "goal" (defined by Boylan and Russell, 2006). It is also found that increasing the assimilation frequency can improve the DA system performance for real-time forecasts. As can be seen from the various case studied here, the improvement of data assimilation is more significant when the bias of the model is higher, and there is still a lot of room for correction. The results also show a rapid decay of the DA effects on the PM2.5 forecast, which highlights the limitations of the current routine data assimilation system in which only initial conditions are optimized. Further improvements of the data assimilation system with meteorological data assimilation and chemical parameter optimization are needed.

Keywords

Real-time PM2.5 forecast Data assimilation Optimal interpolation Beijing-Tianjin-Hebei region


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