Interdecadal increase of haze in winter over North China and the Huang-huai Area and the weakening of the East Asia Winter Monsoon

Abstract

The relationship between the interdecadal increase of haze in winter over North China and the Huang-huai area (HW-NCHH) and the weakening of the East Asia Winter Monsoon (EAWM) was investigated. The trend of the HW-NCHH showed significant interdecadal variation with a slow increase from 1961 to 1970, rapid increase from 1971 to 1985, and slight decrease thereafter. The HW-NCHH trend was influenced considerably but not monotonically by the emission of pollution. Based on an 11-year running mean, the correlation coefficient between the HW-NCHH and EAWM was -0.77, above the 95% confidence level. Therefore, the EAWM should be considered a factor that has important influence on the HW-NCHH over the decadal scale. Compared with the climatic state from 1961 to 1970, the EAWM was clearly weaker from 1986 to 2010 and the horizontal and vertical circulations adverse to pollution diffusion. The distribution of sea level pressure was typical of the positive phase of the Arctic Oscillation, and thus cold air was restricted to the Arctic. The surface wind and humidity both presented negative anomalies over the NCHH area, which favored the production of haze. The meridional circulation in the high latitudes was weak and zonal circulation occupied the NCHH area, which prevented the advection of cold air southward to disperse the particulate matter in the NCHH area. Meanwhile, vertical diffusion was inhibited by an anomalous high pressure and thermal inversion potential over the NCHH area, such that the particulate matter gathered within a shallow layer, which exacerbated the concentration of pollution.