太原市PM_(2.5)周期性特征及其成因分析

The Periodicity and Cause Analysis of PM_(2.5) in Taiyuan

为研究太原市城区PM_(2.5)浓度不同时间尺度的演变特征及其与气象要素之间的关系,基于PM_(2.5)监测浓度、气象观测数据和再分析资料,利用小波功率谱和交叉小波方法分析了2014年1月1日—2016年5月31日太原市PM_(2.5)的周期变化,及其同气象要素的协同关系,同时研究了对应时段的太原市PM_(2.5)与天气形势的相关关系。结果表明,太原市PM_(2.5)浓度变化存在2~8 d和10~16 d的显著周期,与2 m相对湿度、混合层高度、近地面逆温强度和10 m风速具有相似的共振变化,显著时段主要在每年9月份左右至次年3月份。特定的天气形势是太原市冬季PM_(2.5)持续偏高的背景因素之一,特定的天气形势下PM_(2.5)与同期的气象要素存在密切的协同关系。在研究时段内,太原市PM_(2.5)浓度与华北地区海平面气压呈负相关关系,与朝鲜半岛、日本海的海平面气压呈正相关关系,与500 hPa高度场相关性最显著的区域主要分布在中国华北、东北以及朝鲜半岛,主要表现为正相关关系。研究时段内,中国东部上空500 hPa高度场异常偏高,海平面气压偏低,近地面风速减弱等不利于污染物扩散的形势是造成太原市冬季PM_(2.5)浓度持续偏高的背景因素之一。研究结果有利于从不同时间尺度了解太原市PM_(2.5)的变化规律及气象影响因素,对太原市大气污染防治,重污染预报预警工作具有较大的意义。

In order to study the periodic characteristics of PM2.5 and its synergetic relationship with meteorological elements,the variation period of PM2.5 concentration and cooperative relation with meteorological elements in Taiyuan urban area were investigated by using the Morlet wavelet analysis and Cross wavelet transform method,and the relationship between PM2.5 in Taiyuan and the weather situation,the abnormal characteristics of climate background were also revealed.The reanalysis data and observation data of PM2.5 concentration and meteorological elements from January 1,2014 to May 31,2016 were applied in this study.The results indicated that there were two significant change cycles of 2~8 d and 10~16 d in the concentration sequence of PM2.5 in Taiyuan.The similar resonance had been revealed for PM2.5 with 2 m relative humidity,mixed layer height,near ground inversion intensity and 10 m wind speed,and its significant period was from September to March the following year.The specific weather situation was one of the background factors for the continuous high PM2.5 during the winter in Taiyuan.In the research period of this article,the PM2.5 concentration was negatively related with the sea level pressure in north China,and was positive correlation with the sea level pressure in Korean Peninsula,Japan Sea,and positively correlated with 500 hPa potential height in the North China,Northeast China and the Korean Peninsula.In the study period,the 500 hPa potential height was abnormal high,the sea level pressure was abnormally low,and the wind velocity near the ground was weak,which was one of the background factors,resulting in the continuous high PM2.5 concentration in winter in Taiyuan.The research demonstrated the variations of PM2.5 on different time-scale in a heavy energy-consumption city,and also provided a new perspective for effective prevention and control of atmospheric pollution,as well as the scientific basis of forecast and early warning work for relevant departments.