气象条件对上海世博会期间空气质量影响

观测资料显示，2010年世博会期间上海的空气质量为2001年以来同期最优。利用近10年上海近地面气象观测数据、美国环境预报中心NCEP/NCAR再分析资料和中国气象局国家气候中心的环流指数监测数据，分析了有利于空气污染扩散的近地面气象条件及大气环流特征，及其对上海世博会期间空气质量的影响。结果表明:2010年世博会期间，上海近地面东风明显偏多且偏大, 近地层接地逆温明显少于往年, 降水量和降水日数也较常年明显偏多，综合气象条件有利于空气质量的提高。西太平洋副热带高压较常年异常偏大、偏强、偏西，影响上海地区的夏季风更多源自西太平洋副热带高压南侧的偏东气流输送，这为上述区域的东风活跃创造了条件。尽管上海世博会期间的空气质量联防联控措施使得污染排放低于常年，但气象条件不利时，大气环流的输送扩散仍导致了上海世博会期间上海的3次污染事件，这说明气象条件是上海世博会期间空气质量优良的主要影响原因之一。

Weather Impacts on Air Quality of the World Expo in Shanghai

From the statistics of environmental observations, it shows that the air quality in Shanghai during the 2010 World Expo (1 May to 31 Oct) is the best for the same period since 2001. The number with good air quality days adds up to 181, accounting for 98.4% of the total 184 days. From the integrated data of the near-surface meteorological observation in Shanghai in recent 10 years, NCEP/NCAR reanalysis data from 1981, and the circulation indices of National Climate Center of CMA since 1951, the phenomenon is preliminary investigated, revealing the near-surface meteorological situation and the atmospheric circulation characteristics which affect the dispersion and deposition of air pollution during the 2010 World Expo and the same period in history. The detailed mechanisms for the impact of atmospheric condition on air quality are further investigated, and the major results are as follows.The greatly enhanced easterly winds, less calm wind days, significantly less near-surface temperature inversion and more precipitation favor the dispersion and deposition of air particles and the improvement of air quality in Shanghai during the 2010 World Expo.Subtropical high over the western Pacific during the 2010 World Expo is more intensive and extensive, and extending further west compared to that of recent years. As a result, the easterly airflow to the south of subtropical high is strengthened which leads to the prevailing easterly winds in Shanghai.During the 2010 World Expo in Shanghai under the same situation of various dominant wind, e.g., calm wind, NNE-SSE wind, or NNW-SSW wind, corresponding API indices are lower than the value of the same period in 2001—2009, which reflects the effect of pollution reduction due to "Joint Implementation of Air Quality Regulating and Controlling over the Yangtze River Delta Region during the World Expo" carried out by Jiangsu, Zhejiang and Shanghai.Although, with the joint action and its advantage, it is noticed that there are three heavy pollution episodes occurred in Shanghai during the World Expo due to the depressed weather conditions of transportation and dispersion. This result depicts that weather situation plays one of the major roles which decide the good air quality during the World Expo in Shanghai.