| Tropospheric ozone(O3)is an important secondary pollutant which plays an oxidation role in atmospheric chemistry and climate change.In recent years,the ozone pollution in China has become extremely severe.The synoptic circulation controls the local meteorological factors,which affect the photochemical reaction and regional ozone concentration,and the synoptic circulation is obviously different in various regions in China.Therefore,it is of great significance to study the evolution characteristics and meteorological formation mechanisms of ozone on a regional scale.This study uses the multi-city in situ air pollutant and meteorological data as well as meteorological reanalysis data in 2013-2018,combined with K-means clustering method,Lamb-Jenkinson weather classification method,and stepwise regression model(MLR)method.The results analyzed the evolution characteristics of ozone regionalization in China,clarified the quantitative relationship between weather types and regional ozone,explored the meteorological formation mechanism of regional ozone pollution,and quantified the impact of changes of meteorological conditions on ozone concentration.First,according to the temporal distribution characteristics of ozone,we clustered cities into nine regions,namely:North China(NCP),Yangtze River Delta(YRD),Jilin,Liaoning,Hebei(JLJ),Sichuan and Shanxi(CS),Guangdong and Fujian(PRD),Central China(CC),Hainan,Guangxi,Guizhou(HGG),Northwestern(NW),Heilongjiang,Inner Mongolia,Yunnan(HNY).NCP,YRD,and JLJ are the most ozone polluted areas,followed by CS,PRD and CC.A comprehensive analysis of the ozone concentration and meteorological factors corresponding to different weather patterns in each region shows that,except for PRD,the high ozone concentration in all regions is related to the front or bottom of the low pressure system,the back of the high pressure and the equalizing field,which corresponds to before the cold front passes the border or the pressure gradient is weak(weak wind).The responses to temperature and humidity vary in different regions;the main control meteorological element for ozone concentration in the northern region is temperature,and the southern region is temperature or both temperature and humidity.The meteorological mechanism of regional pollution(the domain-averaged maximum daily 8-h running average O3(MDA8 O3)>160?g m-3)varies from region to region.The main cause of NCP regional pollution is the meteorological conditions corresponding to high temperature,medium relative humidity,and strong radiation when the area is on the edge of the subtropical high or when the area is under zonal airflow control,the diffusion conditions are unfavorable,leading the continuously accumulate of ozone.Pollution in the YRD area mainly occurs when the region situated at the edge of the subtropical high or the control of the high-pressure center with high temperature,strong radiation,and moderate relative humidity.The regional pollution of JLJ is mainly related to the upwind polluted air flow by the strong southerly wind and southwesterly wind.Unfavorable diffusion conditions and the continuous accumulation of local pollutants is the main cause of ozone pollution in the CS.High temperature,low relative humidity,and strong radiation under the control of the strong high-pressure center or the high-pressure front cause the ozone pollution in the CC.The contribution of weather-types changes to the annual fluctuations of O3 in the six regions and 14 cities of six provinces in North China is 62.2-89.3%and 44-70%,respectively.High temperature,moderate relative humidity and southerly winds are the main causes of ozone pollution in northern cities of six provinces in North China,while southern cities are mainly affected by high temperature and relative humidity.Local meteorological parameters explained55%–64%and 43%–49%of the day-to-day MDA8 O3 variability for the northern cities and southern cities,respectively. |
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