长江三角洲夏季干/湿型热浪及其期间大气污染特征研究

Characteristics of Dry/Wet Heat Wave and Related Air Pollution over the Yangtze River Delta in Summer

本文选用中国1973~2018年地面综合观测数据、2015~2018年地面空气质量监测站数据、美国国家环境预报中心和欧洲中期天气预报中心的再分析资料,从合成统计和个例分析两个角度分析长江三角洲(长三角) (干/湿)热浪期间的大气环流形势及近地面污染物浓度的时空分布,结果表明:1) 西太平洋副热带高压(西太副高)偏西偏强有利于热浪天气的形成。长三角区域热浪日期间西太副高位置偏西、偏北,强度偏强,干热浪日表现更明显。2) 高温干燥的气象背景促使近地面臭氧浓度升高。热浪日、干热浪日、湿热浪日和夏季平均的臭氧浓度分别为89.7 μg/m3、91.8 μg/m3、86.0 μg/m3和76.3 μg/m3。干热浪期间副高中心位于长三角东部上空,太湖以东站点天气形势稳定,近地面臭氧和PM2.5浓度高于太湖以西站点。3) 2017年7月、2018年8月长三角两次热浪个例期间西太副高异常偏强且西伸明显,为长三角带来大范围的下沉运动,大气绝热与非绝热加热异常增强,干热浪中偏多的太阳短波辐射使地面获得更多能量,偏多的向上长波辐射和感热、潜热通量使近地面气温偏高而出现热浪天气。4) 长三角两次热浪个例期间近地面均发生臭氧污染事件,干热浪期间天气形势稳定,低层风速很小,高温、干燥的稳定环流形势为地面臭氧的形成和污染物累积提供了有利条件,臭氧污染较湿热浪个例更严重。

The surface meteorology observation data (during1973 to 2018), the ground air quality monitoring data (during 2015 to 2018) and the NCEP and ERA5 reanalysis data are used to analyze the atmospheric circulation and the spatial-temporal distribution of near-surface air pollution during the (dry/wet) heat wave (HW) events over the Yangtze River Delta (YRD) of China with composite and case analyses. The results show that: 1) the enlarged and intensified Western Pacific Subtropical High (WPSH) is conducive to the formation of HW. The regional heat wave days (HWD) over YRD are accompanied with an enlarged and intensified WPSH, which is more obvious during the regional dry heat wave days (DHWD). 2) The higher ozone level near surface is associated with hotter and drier weather conditions. The average ozone concentration during the HWD, DHWD, wet heat wave days (WHWD) and the whole summer are 89.7 μg/m3, 91.8 μg/m3, 86.0 μg/m3, and 76.3μg/m3, respectively. During the DHWD, the WPSH center is located over the east part of YRD, and the stations to the east of the Taihu Lake are controlled by more stable weather conditions, associated with higher ozone and PM2.5 concentrations near surface than the stations to the west of the Taihu Lake. 3) During the two typical HW cases over YRD (in Jul. 2017 and Aug. 2018), the enlarged and intensified WPSH is associated with descending over a large area of YRD, the adiabatic and non-adiabatic heating of the atmosphere enhanced. More short-wave (solar) radiation reaches the surface during the dry HW case, with subsequently more upward long-wave radiation, sensible heat and latent heat flux which can heat the atmosphere near surface and result in HW. 4) Regarding ozone pollution during the two HW cases, the weather during the dry HW case is associated with hotter and drier air as well as smaller wind speed and more stable boundary layer, which provide more favorable conditions for ozone formation and pollutants accumulation over ground, thus more severe ozone pollution compared to the wet HW case.