兰州市大气重污染气象成因分析

The analysis of meteorological factors causing heavy air pollution in Lanzhou

兰州市曾经是全国乃至全世界空气污染最严重的城市之一,重度空气污染特征明显.根据兰州市环境保护局公布的大气污染数据及气象局的气象观测数据,采用时间序列法和相关统计方法对兰州市2002—2011年空气污染指数(Air Pollution Index,API)大于200的大气重污染特征进行研究,并探析了其气象学成因.结果表明,静稳型重污染发生天数约占重污染发生总天数的77%,而沙尘型重污染只占23%.静稳型重污染是兰州市最主要的大气重污染类型,它往往存在PM10、SO2和NO2三种污染物同步累积的过程,持续时间长,主要发生在冬季;而沙尘型重污染持续时间短,由于外来高浓度沙尘输送的影响,PM10浓度会急剧升高,而SO2和NO2浓度则会明显下降(SO2、NO2浓度明显低于静稳型重污染),几乎都发生在春季.对它们的成因分析表明:静稳型重污染的气象学成因主要是风速小,稳定能量大,大气环境稳定度大,不利于湍流扩散,本地源污染物持续积累造成;沙尘型重污染气象学成因主要是春季气候干燥,相对湿度低,造成大风沙尘天气,给兰州市输送大量沙尘颗粒形成大气重污染.此研究结果可为兰州市大气重污染的防治提供科学依据.

Lanzhou used to be one of the most air-polluted cities in China and even in the world with highly heavy air pollution characteristics. Air quality data from Lanzhou Environmental Protection Bureau and meteorology data from Lanzhou Meteorological Bureau were used to analyze the characteristics of heavy air pollution( API > 200) in Lanzhou from 2002 to 2011 with the aid of of using the time series analysis and correlation analysis approaches. The results showed that the days of static-stability heavy air pollution accounted about 77% of the total days of heavy air pollution episodes,while air pollution caused by sandstorm just accounted about 23%. The static-stability weather was the primary meteorological type leading to heavy air pollution episodes in Lanzhou,and it typically occurred in wintertime with long lasting time,during which SO2,NO2 and PM10pollutants accumulated synchronously. The heavy air pollution caused by sandstorm from external sources usually occurred in spring and lasted for a short time; during which PM10 concentration increased,while the concentrations of SO2 and NO2decreased. The concentrations of SO2 and NO2during the sandstorm air pollution episodes were obviously lower than that during the static-stability air pollution one. The wintertime static-stability air pollution episodes were caused by small wind,huge stable energy and strong stability,leading to the accumulation of local pollutants. The air pollution episodes usually happened in spring were mainly caused by strong wind and dry climate leading to transport of sand particles to Lanzhou. The conclusions drawn from this study can provide scientific basis for controlling heavy air pollution in Lanzhou.