Surrounding Areas The Focus Of The Photochemical Pollution Source Tracing Simulation Study

Tropospheric photochemical pollution is one of principal environmental issues which make great troubles to the developments of many cities and regions in the world. In China many economic developed regions such as Beijing also suffer from the photochemical pollution,and problems continue to deteriorate. Researches showed that meteorological conditions played a crucial role in regional air quality,and quantitative analysis showed that physical factors(advection and vertical diffusion) were important as well as chemical factors. And under special synoptic situations the impacts from the pollution sources in the regions around Beijing on the air pollution in Beijing were not neglected. So it is very important to investigate the variation trend of NO₂ pollution over Beijing in recent years and under special synoptic situations the impacts of key pollution sources on regional photochemical pollution in the regions around Beijing to make effective policy of controlling photochemical pollution in Beijing.The seasonal variation and trend of NO₂ concentrations over Beijing were analyzed using monthly averaged tropospheric NO₂ column data from GOME (Global Ozone Monitoring Experiment) measurements from January 1996 to December 2002. The data of GOME monthly averaged NO₂ column reveal that NO₂ pollution in Beijing had be aggravated from 1996 to 2002 in general, with serious pollution happening in the years of 2002. Furthermore, the seasonal variation of GOME Iropospheric NO₂ column over Beijing was compared with that of monthly averaged surface mass concentrations of NO₂, which were calculated according to the daily pollution index of NO₂ for Beijing for a period from 1 January 2001 to 31 December 2002. GOME tropospheric NO₂ and surface NO₂ mass concentration present the same distinct seasonal variation characteristics, with high values in winter and low values in summer. It is showed that for the comparison period the variations of monthly averaged tropospheric NO₂ columns over Beijing are well consistent with the variations of the monthly averaged surface NO₂ mass concentrations in Beijing. It can be concluded that GOME tropospheric NO₂ column data can be used to analyze the seasonal variation and trend of NO₂ pollution over a specific region.NO_x and O3 key source tracing method was implemented in a regional chemical transport model associated with meteorological fields from Mesoscale Model MM5. This source tracing method was apllied to study the impacts of key pollution sources on regional photochemical pollution in the regions around Beijing. As a case study, the temporal and spatial distributions and variations of NO_x and O₃ produced by surface emission in Taiyuan and Shijiazhuang were simulated for a summmertime period. It is found that: Under conditions of clear days with few clouds, high temperature, low humidity and under the control of local downdraft, NO_x with a source from Taiyuan and Shijiazhuang can not be transported into Beijing. However, ozoneand HNO₃ produced via NO_x emitted from Taiyuan and Shijiazhuang can be transported into Beijing, and have an impact on the pollution near surface in Bejing. But the amount of ozone arriving in Beijing near surface is small, contributing to the local ozone levels by about 2%. With the atmospheric lifetime analysis of the traced species, it is indicated that NO_x emissions from a specific source at the surface have a strong influence on ozone pollution in the regions that are 100²00 kilometers away.