I. Introduction
Air pollution in most cities in China is quite serious. The dominant pollutant, especially PM2.5, has been of a particular concern due to its negative effects on the ambient air quality and the public health. To protect public health and the environment, various organizations and agencies have established a large number of monitoring stations and different emission standards for regulating permissible concentrations of the PM into the atmosphere. However, the monitoring data are only the representations of the current air quality without reflecting the air quality changes in the future. Therefore, it is necessary to implement an accurate forecasting model for the PM2.5 concentration that can provide early warning for guiding the works of air pollution control and public health protection.