Opposite interdecadal variations of wintertime haze occurrence over North China Plain and Yangtze River Delta regions in 1980–2013

In this study the interdecadal variations of haze pollution during recent 34 years from 1980 to 2013 over eastern China are investigated. It is found that opposite interdecadal variations of wintertime haze days (WHDs) between the North China Plain region (NCP) and the Yangtze River Delta region (YRD) occurred in this period, i.e., a decreased interdecadal trend of anomalous WHDs appeared in NCP and an increased trend in YRD. Meteorological factors driven the opposite interdecadal variations of anomalous WHDs are revealed. In the phase of interdecadal variations with more WHDs in NCP and less in YRD before 1996, there were weaker northerly winds in the lower troposphere over eastern China accompanied with a weakened Siberia High and mid-latitude westerly jet. The decreased northerly winds are conductive to the local accumulation of air pollutants in NCP and inhibition of air pollutants to be transported from North China to YRD. Consequently, more WHDs appeared in YRD and less in NCP. On the contrary, in the phase of interdecadal variations with less WHDs in NCP and more in YRD after 1996, stronger northerly winds associated with strengthened Siberia High and westerly jet, appeared over eastern China. The increased northerly winds are favorable for the dispersion of air pollutants in NCP and transport more pollutants from North China to the downstream area in YRD, resulting in less WHDs in NCP and more in YRD. Annual variations of the anomalous WHDs in the regions of NCP (34°–42°N,114°–120°E) (orange bars) and YRD (27°–34°N,114°–122°E) (green bars) from 1980 to 2013. The red and blue lines denote the linear trends of the anomalous WHDs in NCP and YRD, respectively. [Display omitted] •Opposite variations of wintertime haze occurrence over North China Plain and Yangtze River Delta regions in 1980–2013.•Siberian High and mid-latitude westerly jet are key systems dominating the decadal various of WHDs in NCP and YRD.•The increased northerly winds are favorable for less WHDs in NCP and more in YRD.