Abstract:

We aims to report the crosscorrelation characteristics and the temporal evolution properties of air pollution between Chengdu City and 14 surrounding towns. In this study, we collected the daily air pollution index (API) data of Chengdu City and 14 surrounding towns provided by Sichuan Provincial Environmental Monitoring Center. The 5 years regular monitoring data, from Jan.1 2008 to Dec.31 2012, were analyzed by using the detrended crosscorrelation analysis (DCCA) method. The DCCA exponent quantitatively measures the crosscorrelation of two series in terms of longterm crosscorrelation exists. The results show that the relationships of air pollution between Chengdu City and its surrounding towns display a long range crosscorrelation at the time scale ranging from one day to 5 years. The long range crosscorrelation suggests that the correlations of air pollution between Chengdu City and its surrounding towns do not obey the classical Markovtype stochastic behavior (exponential decrease with time), but display more slowly decaying correlations in a powerlaw fashion with time. For example, there is a varied tendency in air pollution of Chengdu City (its surrounding towns) to be followed by another varied tendency in air pollution of its surrounding towns (Chengdu City) at a different time in a powerlaw fashion. It has been found that the long range crosscorrelation properties will follow changes in different months. In order to further clarify this result, the crosscorrelations properties were analyzed based on monthly mean wind field. It is found that the results of DCCA analysis and the monthly mean wind field between Chengdu City and its surrounding towns have a good synchronization. These results correspond to atmospheric circulation and regional transport hypothesis. It suggests that in specific geographical and meteorological conditions, it exists intercity transport of air pollutants between Chengdu City and its surrounding towns. The atmospheric pollution type of Chengdu Plain may have been changed from local pollution into regional air pollution. The intercity transport has been the important factor of air pollution in the Chengdu Plain, which provides conditions for the formation and aggravation of heavy air pollution in Chengdu City. Therefore, in the air pollution forecasting model of Chengdu City, the long range crosscorrelation properties of air pollution between Chengdu City and its surrounding towns should be considered. This paper helps to understand the nature of regional air pollution in the Chengdu Plain. The prevention and control of air pollution in the Chengdu Plain should be developed towards regional jointly prevention and control in the planning and construction of Chengdu City and its surrounding towns