Atmospheric Circulation Affecting Summer Ozone Pollution In Eastern China And Its Projections

In summer,ground-level ozone in eastern China is a man-made air pollutant that seriously endangers human health,plants and animals.Ozone pollution exceeded 280?g m^-3in most cities in eastern China.Based on the hourly ozone observation data provided by the China Atmospheric Environment Monitoring Network,the maximum 8 hour average daily ozone concentration over eastern China was extracted.Combined with the multiple meteorological data,the impacts of meteorological conditions on the ozone over eastern China in summer were studied,and the model forecast meteorological data set was used to projecy the ozone weather conditions.The following conclusions were obtained:(1)In recent years,ground-level ozone pollution has increased year by year.Ozone pollution is most serious in summer in China.The pollution intensifies from south to north,with the highest ozone concentration in North China and the Huang-Huai region.Two dominant patterns of summer ozone pollution in eastern China were illustrated with EOF:the north-south consistent mode and the north-south inverse mode.When ozone rises in eastern China,the anomalous circulation in the north-south region of eastern China is shown as the zonally enhanced East Asia trough and the western Pacific subtropical high,and the west ridge point of which moves northward.Locally hot and dry air and strong solar radiation enhanced the photochemical reaction,leading to the increase of ozone pollution in the center of North China and the Huang-Huai region.When the anomaly of geopotential height in high latitudes significantly weakened the cold air activity and resulted in local high temperature near the surface,ozone increased in North China.However,the western Pacific subtropical high transported sufficient water vapor to the Yangtze River Delta in different ways,which provided a partial adverse environment for the formation of ground-level ozone.Thus,the ozone pollution in eastern China is reversed from north to south.(2)The historical analysis of ozone weather conditions in Beijing-Tianjin-Hebei region was carried out and the projection was made.The Ozone Weather Index(OWI)is calculated by capturing the characteristics of three important weather systems that significantly affect ground-level ozone concentrations.The Community Earth System Model was used to simulate the ozone weather conditions in the Beijing-Tianjin-Hebei region.In the future,meteorological conditions will be conducive to ozone pollution control in the Beijing-Tianjin-Hebei region.In the 21^st century,OWI has generally declined.The decrease in the OWI was mainly due to the increase in regional precipitation,partly due to changes in wind in the lower troposphere and the temperature difference between 850 h Pa and 200 h Pa.The increase of total precipitation in the 21^st century weakens the production of surface ozone,mainly due to the increase of convective precipitation.During 2061-2100,the South Asia High will move southward and the Western Pacific Subtropical High will move eastward.The convergence of water vapor will mainly occur in South China.Therefore,there will be less large-scale precipitation in North China.However,under the influence of climate warming,the increase of specific humidity in the Beijing-Tianjin-Hebei region will increase the convective precipitation,which is more than 4 times of the decrease of large-scale precipitation.