Heavy air pollution occurred frequently in Nanjing in recent years. To estimate local and regional source contributions of air pollutants (PM2.5, SO2, NO2, CO) in Nanjing during different seasons, the air monitoring data between January 2015 and April 2016 was collected from China National Environmental Monitoring Center and analyzed with time series approach of Granger causality test and vector autoregressive (VAR) model. It is found that the correlations of pollutions among cities during Southeast prevailing wind (SP) period were weaker than North prevailing wind (NP) period, partly due to low pollution level in SP period. The Granger causality tests indicate that there were more causal relationships of air pollutants between Nanjing and 9 surrounding cities in NP period partly due to heavier regional pollution and the causalities were not always consistent with prevailing wind direction. Variance decomposition in VAR model suggests that local source played a more important role than regional source during SP period, as it donated 68.6%, 65.3%, 69.7% and 76.9% for PM2.5, SO2, NO2 and CO, respectively. However, Nanjing was strongly affected by regional transport during NP period, as North direction contributed 64.4%, 58.1%, 60.2% and 56.8% of PM2.5, SO2, NO2 and CO in Nanjing, respectively. Furthermore, the observed air pollutant concentrations in Nanjing were well consistent with the model-simulated results, except highly active pollutant of NO2. These results indicated that the time series approach could be a simple tool for understanding the impacts of regional transport and monsoons the air quality in a particular city.
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