This study investigates the influence of the winter large-scale circulation on daily concentrations of PM_2.5 and their sensitivity to emissions. The new proposed circulation index can effectively distinguish different levels of air pollution and explain changes in PM_2.5 sensitivity to emissions from local and surrounding regions. We then project future changes in PM_2.5 concentrations using this index and find an increase in PM_2.5 concentrations over the region due to climate change.