| Due to a wide range of sources of pollution emissions,combined with the special role of the East Asian monsoon system,eastern China is one of the most polluted regions in the world.Frontal activity is one of the main manifestations of the monsoon.Lots of studies related to frontal systems were based on subjective judgments of human beings.There is still no widely accepted objective method to identify atmospheric fronts.Therefore,the study on the interrelationship between frontier activities and air pollution at long-term scales is lacking.This study establishes statistical methods for frontal objective identification in China,summarizes the spatial and temporal distribution characteristics of frontal fronts over the past 30 years,and thoroughly investigates the influence of cold front on the temporal and spatial distribution of air pollution in urban agglomerations in eastern China.Based on the global meteorological reanalysis data,the key parameters of the frontal objective identification method were tested.The detected frontal features and regions were determined using the control thresholds greater than 4.5℃/100km,and the location of the frontal plane was diagnosed using the localization function within the region.The identified fronts were compared with the actual observations and the fronts identified by the forecasters.The objectively identified front surface can reflect the relationship between the frontal process and the air pollution effect from the short-term changes in daytime and the mid-to-long-term spatial-temporal scale.The characteristics of the frontal displacement path,velocity,and intensity from 1980-2016 were further studiedBased on the regional surface observational data,the complex regional pollution of the three major urban agglomerations in eastern China was explored to investigate the characteristics of simultaneous changes in regional pollution.The cumulative rate of pollution in JJJ was 6.4pg/m3/hour,and the clearance rate was-5.7μg/m3/hour at the front.The clearance rate of the YRD and the PRD is higher than the cumulative rate;the cold front activity resulted in the lowest value in the JJJ area,but the average concentration increased 16.8μg/m3,while the average concentration of YRD and PRD region decreased-67.2μg/m3 and-9.6μg/m3.Using the regional observation data,the regional air quality model WRF-CMAQ and the Lagrangian transport model LPDM,the trends of pollution and transport changes before and after the cold front crossing were explored.Under the action of the cold front,dust,biomass burning,and mixed emissions from anthropogenic sources will appear throughout the troposphere.Long-distance transportation under cold front could lead to the mixing and stratification of inland dust,Indochina biomass combustion and anthropogenic source pollution of eastern China in the whole area.The radiation effect of mixed dust causes the temperature of 5-10 kilometers in the YRD to increase more than 1℃,while the biomass burning black carbon aerosol affects the warming effect of more than 1.5℃ in the troposphere 2-5 kilometers in the coastal area of South China.This paper uses the objectively identified location and frequency of cold fronts in eastern China to analyze the interannual variation of cold front activity in JJJ and YRD and its correlation with the monsoon index.In 2003-2016,the peak value of cold front in JJJ region was corresponding to air pollution,and the frequency of cold front increased by 1.3%each year,2003-2016 meteorological conditions are unfavorable to the improvement of air pollution in JJJ region,and the contribution of anthropogenic emission reduction is greater than the actual value.On the contrary in YRD region,the correlation coefficient reached 0.75,and the frequency of cold front increased by 6.9%each year.In the peak year of cold front in JJJ region,the cold front moving path is northerly,resulting in low pollution clearance efficiency in the south of North China Plain,there was a peak of pollution.In the peak year of cold fronts in YRD region,cold air path in the middle,the northeast wind is stronger,there has been a change in the annual valley value of pollution.The correlation was better than some monsoon indices. |
