Air Pollution Characteristics And Their Relationship With Meteorological Variables During The Autumn And Winter Of 2014-2017 In The Yangtze River Delta Region

Monitoring and estimating the air pollutant concentrations are essential for evaluating air quality and its effects on the climate,environment and human health.The aim of this study is to examine the potential characteristics and relationship between surface measured particulate matter（PM）concentration and column aerosol optical properties,and meteorological variables in the Yangtze River Delta（YRD）region.For this purpose,a four-year（from 2014 to 2017）observations of PM(both PM_2.5 and PM₁₀)are obtained to study for Nanjing in the YRD area.The satellite-derived aerosol optical depth（AOD）data was used as auxiliary data to supplement the analysis.The emission source and meteorology datasets are also used and analyzed to reveal the causes of changes in PM pollution.The annual mean PM_2.5 and PM₁₀were observed to be 59.878 and 102.124,respectively for the entire study period.Furthermore,in the overall study period,the mean ratio of PM_2.5/PM₁₀ was 57%,with the lowest（53%）during autumn and highest（60%）in winter.This revealed the dominance of fine-mode particles at Nanjing which is mainly attributed from anthropogenic activities（biomass burning,urban-industrial,vehicular emissions,and other pollutants generated by construction activities）and conducive meteorological phenomena.Different statistical techniques include the rate of change,influence of winds through bivariate function were used to examine the changes in PM and its role with meteorology.The bivariate plot results showed that increase in PM_2.5 concentrations were due to decrease（increase）in wind speeds represent the presence of local anthropogenic emissions（long range transported dust particles）.Apart from this,the source identification was carried out from the Potential Source Contribution Function（PSCF）and Concentration-Weighted Trajectory（CWT）methods utilizing the air mass trajectories obtained from the Hybrid Single Particle Lagrangian Integrated Trajectory（HYSPLIT）model.The results revealed that regional transport of smoke particles from biomass-burning during autumn and winter seasons resulting in high PM.The results derived in this study contribute to an in-depth understanding of PM concentrations over the YRD,and forms a basis for the extension of future research over this major aerosol hotspot region in China.The present study also aims to investigate spatiotemporal evolution and trend in the aerosol optical properties（Aerosol Optical Depth,AOD;Angstrom exponent,AE）,qualitatively identify different aerosol types and sources over an urban city,Nanjing in the YRD area,East China.For this purpose,the Collection 6 Level-2 data obtained from the MODIS sensor onboard Terra and Aqua satellites for the period between 2014 and 2017 have been analyzed.A notable spatiotemporal heterogeneity was observed in the optical properties of aerosols on the seasonal scale over Nanjing（East China）.The seasonal mean AOD₄₄₀(AE_470-870)was found to be maximum with 0.97±0.31 during autumn（1.14±0.23）and a minimum of 0.62±0.34（1.29±0.19）in winter.However,during winter the spatial correlation between AOD and AE was found to be negative with correlation coefficients ranging from-0.5 to 0.1.The mean value of precipitable water vapor（PWC）was found to be higher（1.58±0.80 cm）during autumn and lower value of 0.60±0.27 cm observed during the winter season.Further,the HYSPLIT model was used for presenting cluster trajectory analysis,which demonstrated that the air masses are originated from different source regions contributed significantly to column aerosol loading.Using the air pollutant concentrations of PM_2.5 and PM₁₀ obtained at different locations in the YRD area,we identified and studied the causes for the occurrence of six major air pollution episodes during the autumn and winter seasons of 2014-2017.The results observed showed the predominance of fine-mode particles with high values of PM_2.5 and PM₁₀exceeding the national air quality standards greatly and significantly affecting the visibility,air quality,and climate system.These resulting serious pollution episodes at different locations in the YRD are likely related to several anthropogenic activities.