Winter haze over North China Plain from 2009 to 2016: Influence of emission and meteorology

Proportion of the four pollution levels for (a) original observation, (b) met-influenced observation and (c) new met-influenced observation when doubled emission influence is removed. Changes begin to distinct since 2014. Percentage of clean days decreases and that of polluted and heavily polluted days increases from (a) to (b) and (c), indicating that the meteorology conditions from 2013 to 2016 winter would make the air quality worse than it was if the emission control strategies had not been implemented. Notably, the percentage of extremely polluted days stays stable, demonstrating that the emission control since 2013 is of no help to reduce the extremely polluted days in NCP.329