2014—2018年重庆主城区大气污染的特征及其与大气环流之间的关系

Characteristics of Air Pollution and Its Relationship with Atmospheric Circulation in Chongqing City from 2014 to 2018

采用重庆市生态环境局2014—2018年主城区空气污染物监测数据、沙坪坝气象站观测数据、美国NCEP再分析数据和美国怀俄明大学的探空数据,分析了重庆主城区的空气质量指数(AQI)、主要污染物浓度、不同程度污染日数和首要污染物的月、季、年变化特征。探讨了不同污染程度日500 hPa高度场和850 hPa风场特征,分析了重污染时段垂直速度和探空条件。结果表明,重庆主城区AQI月变化呈“W”型,PM_(2.5)、PM_(10)和CO呈“U”型,O 3呈倒“U”型。除O 3浓度在盛夏最高外,其余各污染物浓度在12月和1月都较高,空气质量也相对最差。O 3浓度呈逐年上升趋势,其他污染物浓度都呈下降趋势,空气质量明显改善。PM_(2.5)为重庆首要污染物,冬季最为明显,PM_(10)污染在春季有所增加,NO 2污染主要出现在初春和深秋,O 3污染则主要出现在盛夏。大气污染主要出现在冬季,当欧亚中高纬地区环流形势呈北低南高,以纬向环流为主,低层大气受较强偏南风影响时,重庆的气象扩散条件较差;当欧亚中高纬地区环流形势呈北高南低,经向环流明显时,冷空气容易气南下,促进大气对流发展,有利于重庆污染物的扩散和清除。污染较重日重庆上空对流层整层存在异常的下沉运动,水汽上升辐合较弱,低层相对湿度较小。近地面逆温层和较薄的湿层长时间维持,使大气层结较长时间处在较稳定状态,是重庆主城区大气污染持续发展和维持的关键。

Based on daily air pollution data,meteorological observation data and sounding data from Weather Station of Shapingba in Chongqing,and the NCEP/NCAR reanalysis data during 2014-2018,the characteristics of monthly,seasonal and annual AQI,different air pollutant concentration and the day numbers with different air pollutant concentrations are analyzed systematically.Besides,the 500 hPa geopotential height field,850 hPa wind field,vertical velocity field and the skew T-ln p diagram of heavy pollution days are also analyzed.The results show that the monthly variation of AQI in Chongqing is W-shaped,while those of PM 2.5,PM 10 and CO are U-shaped,and that of O 3 is inverted U-shaped.Except that the concentration of O 3 is the highest in midsummer,the concentrations of other pollutants are so high in December and January that the air quality becomes the worst in the two months.The concentration of O 3 shows an increasing trend but other pollutants major decreasing year by year,and the air quality was significantly improved.PM 2.5 was the main pollutant in Chongqing,especially in winter.PM 10 pollution increases in spring,NO 2 pollution mainly occurs in early spring and late autumn,and O 3 pollution mainly appears in midsummer.Air pollution usually happens in winter.The meteorological diffusion condition is poor in Chongqing when the circulation in the middle and high latitudes of Eurasia in the middle troposphere has a distribution of low in the north and high in the south,and the cold air force is so weak that the lower troposphere is dominated by the south wind in most of the southern region.The condition is favorable for diffusion and clearance of air pollutant when the circulation in the middle and high latitudes of Eurasia in the middle troposphere has a distribution of high in the north and low in the south,and the meridional circulation is obvious.The rising convergence of water vapor is so weak that the relative humidity of the lower troposphere is low on heavy pollution days.The near-surface inversion layer and the thin wet layer maintain for a long time making atmospheric stratification relatively stable,which is the key of development and maintenance of air pollution in Chongqing.