Deteriorating haze situation and the severe haze episode during December 18–25 of 2013 in Xi’an, China, the worst event on record
Deteriorating haze situation and the severe haze episode during December 18–25 of 2013 in Xi’an, China, the worst event on record
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DOI：
10.1007/s00704-015-1509-8
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发表时间：
2016-07
影响因子：
3.4
通讯作者：
Xiao-dong Liu;Ying Hui;Z. Yin;Zhaosheng Wang;Xiaoning Xie;J. Fang
中科院分区：
文献类型：
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作者：
Xiao-dong Liu;Ying Hui;Z. Yin;Zhaosheng Wang;Xiaoning Xie;J. Fang
灰霾天气的频繁发生已被认为是中国面临的一个紧迫的环境问题，近年来也引起了世界各国的广泛关注。在这项研究中，我们研究了在西安，在中国中部的一个主要城市，从2000年以来的水平能见度的灰霾天的发生趋势。2000-2013年西安市平均每年有49天灰霾，2008年以来灰霾天数明显增加，2013年达到102天。12月是发生频率最高的月份。2013年12月18日至25日，发生了近几十年来持续时间最长、最严重的雾霾天气。西安市8天平均能见度只有2.5 km，其中5天能见度低于2 km。在此期间，西安的平均空气质量指数为486.5，其中有四天达到或超过了指数上限500。PM2.5浓度异常高的水平被推断为这次严重雾霾事件的主要原因。当地天气状况的特点是风力微弱，大气稳定性增强，相对湿度高。强对流层中层纬向气流和东亚冬季风减弱限制了高纬冷空气的入侵，为中国中东部大范围地区对流层低层和近地面低压梯度的形成创造了条件。由于本底排放水平高，空气污染物扩散受到抑制，最终导致这次严重的灰霾天气影响中国大部分地区。
Frequent occurrence of haze weather has been considered an urgent environmental problem in China and has attracted much attention worldwide in recent years. In this study, we examined the trend in the occurrence of haze days based on horizontal visibility in Xi’an, a major city in central China, since 2000. There were 49 haze days per year on average in Xi’an during 2000–2013, and the number of haze days has increased significantly since 2008, reaching 102 days in 2013. December is the month of the highest frequency of occurrence. During December 18–25 of 2013, the longest-lasting and most severe haze event in the recent decades occurred. The 8-day mean visibility in Xi’an was only 2.5 km with 5 days below 2 km. The mean air quality index in Xi’an during this period was 486.5, and in four of those days, it reached or exceeded the index’s upper limit of 500. The exceptionally high level of PM2.5concentration was inferred as the main reason of this severe haze episode. The local weather conditions were characterized by weak winds, enhanced atmospheric stability, and high relative humidity. Strong mid-tropospheric zonal flows in combination with weakened East Asian winter monsoon limited the cold air invasion from the higher latitudes, creating a condition of low pressure gradients in the lower troposphere and near the surface for a large region in central and eastern China. With high background emission levels, the suppressed dispersion of air pollutants eventually caused this severe haze episode affecting a large region in China.