Research On The Variation Characteristics Of Atmospheric Particulate Matter In Major Cities In The Yangtze River Delta Based On Multi-source Observations

Environmental issues have growingly attracted attention and become one of the most urgent issues that need to be addressed.Yangtze River Delta region,as China's most developed economic area,has been observed increasing frequent haze pollution caused by high concentrations of particulate matter in recent years.The emission and accumulation of particulate matter is as a result of a combination influence of human activities,meteorological conditions and the natural environment.Therefore,the analysis of the temporal and spatial changes of particulate matter,the characteristics of regional differences,and the in-depth exploration of the complex reasons behind the differences is pivotal revealing the mechanism of regional haze pollution,which further helps strengthening environmental governance and plays a key role in studying air quality and public policy decisions.In this study,four provincial capitals?Shanghai,Nanjing,Hangzhou,and Hefei?in the Yangtze River Delta region were selected.A comprehensive analysis of the characteristics of atmospheric particulate matter in major cities in the Yangtze River Delta region was conducted through the combination use of ground-based atmospheric pollutant monitoring data,meteorological parameters observation data and satellite atmospheric aerosol remote sensing product data.The main conclusions are listed as follows:1.Time variation characteristics of atmospheric particulates in major cities in the Yangtze River Delta in recent yearsThe annual ground-observed PM_2.5(PM₁₀)concentrations in Shanghai,Nanjing,Hangzhou,and Hefei in 2014 were 46.98±12.21?g·m^-3,54.84±46.14?g·m^-3,52.82±16.98?g·m^-3,64.03±20.57 respectively,exceeding China's national air quality standard GB3095-2012.However,atmospheric particulate matter pollution level behaves a downward trend after 2014 indicating air quality has improved.The annual PM_2.5 concentration exceeds the standard much higher than PM₁₀,in other words,fine particulate matter predominant in this region.Highest PM_2.5 monthly concentrations occur in winter?In December and January?,whereas the lowest comes in summer?August?.The relative frequency distribution of atmospheric particulate matter concentration shows that the highest frequency of PM_2.5 concentration in Hefei area is 59?g·m^-3,which is much higher than the other three places.The diurnal variation of particle concentration presents the characteristics of periodic pulse variation.The daily average concentration of PM in the atmosphere is characterized by peak in the morning?08:00–10:00 LT?and low in the night?18:00–20:00 LT?,which are mainly caused by traffic rush in the morning.A good correlation between PM_2.5 concentration and gaseous precursor?SO₂ NO₂ NO?indicating gaseous pollutants will be converted into particles under favorable meteorological conditions,thereby increasing the concentration of fine particles.2.Particle size characteristics and heterogeneity of atmospheric particles in major Yangtze River Delta citiesFine particle and coarse particle mass concentration ratio PM_r(PM_r=PM_2.5/PM₁₀)exhibits unimodel distribution pattern in all seasons with less frequency in the range of less than 0.4 and more in the range of 0.5-0.8,indicating fine-mode particles(PM_2.5)are major pollutant in major cities in YRD.Influenced by the variation of local emission sources,the particle concentration between different cities shows spatial differences.Correlation analysis between coarse(PM₁₀)and fine particles(PM_2.5)was then studied and Pearson's correlation coefficient is found higher than 0.90,indicating that the similar sources of coarse and fine mode particles.Inter-regional heterogeneity COD analysis results show that higher COD is observed in coarse particulate matter PM_10-2.5,which represents greater spatial heterogeneity between cities mainly due to the generation of coarse particles from long-distance transmission whereas large particles tend to settle resulting in greater heterogeneity in spatial distribution.3.Relationship between atmospheric aerosol optical thickness AOD of satellite remote sensing and ground observation PM_2.5concentration on the groundDue to the limited number of ground particulate monitoring stations and uneven regional distribution,remote sensing satellite data possesses the advantages of extremely wide coverage,low cost,and data continuity,which can make up for the corresponding deficiencies of ground monitoring stations,thus Based on the MODIS Aerosol Optical Depth AOD data from 2014 to 2017 and PM_2.5concentration data at the ground monitoring site,a preliminary statistic correlation analysis was performed between AOD and PM_2.5concentration.Correlation coefficients were obtained at intermediate levels?P<0.01?,which were Shanghai 0.55,Nanjing 0.51,Hangzhou 0.53,and Hefei0.60,respectively.Furthermore,Meteorological effects on atmospheric particulate in Yangtze River Delta region were analyzed,temperature,Precipitation,Relative Humidity,Visibility,and Wind Speed were found negative correlation for both PM_2.5 and PM₁₀.Humid atmospheric conditions,rainfall wet removal and strong diffusion due to higher wind speed play key role in reducing pollutant concentrations(especially fine particulate matter PM_2.5).Due to the strong correlation between particle concentration and key meteorological parameters such as Relative Humidity,the satellite MOIDS AOD₅₅₀was made further correction both altitude and relative humidity.As a result,the correlation coefficients have been found improvement at different levels among four cities,where Hangzhou and Hefei is most obvious.In terms of seasonal characteristic,the correlation between PM and AOD in spring and summer is found higher compared to winter due to the better inversion results of satellite AOD data caused by dense vegetation.