This paper investigates how large-scale weather systems control fine particulate matter (PM_2.5) air quality in China. We show that winter monsoons, onshore winds and frontal rains can drive daily PM_2.5 variability in different regions of China. We further project future PM_2.5 concentration change by 2050s due to climate change, and verify that climate change has little benefit on future PM_2.5 in Beijing, implying cutting down emissions is necessary to mitigate pollutions in megacities of China.