Climatic change features of fog and haze in winter over North China and Huang-Huai Area

This paper revealed the climatic change characteristics of fog and haze of different levels over North China and Huang-Huai area (NCHH). It was found that the haze-prone period has changed from winter into a whole year, and the haze days (HD) in winter have increased significantly. The foggy days (FD) are half of HD. There are little difference on the number of days and trends of fog at various levels. The HD and FD show no obvious positive correlation until the 1980s. Fog has larger spatial scale, showing more in the south than in the north. Haze occurs mainly around large cities with a discrete distribution. In the background of weakened East Asian Winter Monsoon (EAWM) and sufficient particulate matter, the negative correlation between haze and wind speed is weakened, but the positive correlation between haze and moisture conditions (precipitation and humidity) is significantly strengthened. In recent years, small wind and variability appear frequently. Meanwhile, as the stable source and strong moisture absorption of the aerosol particles, the moisture condition becomes one key control factor in the haze, especially wet haze with less visibility. In contrast, the FD presents a stable positive correlation with precipitation and relative humidity, but has no obvious negative correlation with wind speed.