| Regional air pollution in China is very serious, not only have an impact on climate and environmental changes, but also greatly damage the ecosystem and human health. The adverse effects of human activities on their own living environment has become an insurmountable bottleneck, also caused great challenges to national environmental diplomacy. As the haze event occurred under stable weather conditions, when the region without strong weather systems. Local circulation caused by undersurface difference plays a decisive role on regional pollution transport. Therefore, carry out the effect of local circulation on regional air pollution transport mechanism study has important scientific significance and practical needs urgent.Detailed analysis on the variation characters of air pollutants, such as O3、 NOX、CO、SO2、PM10and PM2.5, are taken during June2007by use of the monitoring data from atmospheric environment monitoring net in Beijing、Tianjin and Hebei Provence. A coupled WRF-Chem air quality modeling system is applied to simulate temporal and spatial variation of atmospheric pollutants under the Local Circulation.The main research objective of this paper are perceive diurnal variation of local circulation, and its impact on spatial and temporal variation of atmospheric pollutants, and analysis of the role of local circulation during serious regional pollution process, and study the impact of transport dominated by local circulation on air quality in Beijing, Tianjin and Hebei Provence. The main research results including:(1) Local circulation dominant the area of Beijing, Tianjin and Hebei Provence during Jnue2010, medium and large-scale weather systems is weak at this time, the stable stratification, easily lead to serious regional environmental pollution. Local circulation occur at higher frequencies, the presence of a few days in June more than half of local circulation, valley wind circulation have15days, 50%of the total number of days; sea-breeze circulation have18days the,60%of the total number of days; among nine days there are obvious the convergence zone,30%of the total number of days.(2) When in Beijing, Tianjin and Hebei Provence were controlled by local circulation, valley wind circulation mainly occur in mountainous region in northwest Beijing area, and west of Xianghe, Langfang and Gucheng, the combination of plains and mountainous zone. Valley wind driven air pollutants accumulate in northwest mountain area, high concentrations of pollutants at night can not be completely removed and returned to the plains with the mountain, causing secondary pollution area. About100km inland sea breeze can make air quality in the coastal region as better than inland during the day, the night breeze carry atmospheric pollutants to the coastal city at night result the increase of pollutants.(3) Mountain-Plain wind replacement process occur in evening and early morning hours, at Xianghe, Langfang and Gucheng city appears a convergence zone. Convergence zone in summer almost all year round presence due to coupling of local circulation, pollutant concentration was significantly higher than both sides of convergence. The change of convergence position directly affect the regional transportation.(4)Model for the simulation results with the observations of pollutants are in good agreement. Simulate pollutant concentration distribution in June2010under the typical local circulation show that the presence of local circulation result similar air quality trend in Beijing, Tianjin and Hebei provence. Polluted air masses with diurnal variation in local circulation through enhanced transport and accumulation of a wide range of sources, result in serious regional pollution. |
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