An Analysis of the Multi-scale Variations of Persistent Haze Events in Central and Eastern China from 1980 to 2014

The spatial and temporal variations of persistent haze events and their related impact factors were analyzed by using 324 stations in the central and eastern China during 1980-2014. The results show that the annual average frequency of persistent haze events and their contributions to total haze events increase year by year, with growth rates of 0.79 (10 a)^-1 and 2.7% (10 a)^-1, respectively. It is represented by three large-value areas: The North China Plain (including Shanxi Province, Beijing-Tianjin-Hebei region), the Yangtze River Delta, and the eastern Sichuan Basin. The most significant increase appears mainly in Huang-Huai area, with a growth rate of 6.3 (10 a)^-1 and 13.95 d (10 a)^-1. At the same time, persistent haze events show obvious seasonal and monthly changes. January is the highest incidence month with 2.56 d, meanwhile high frequency appears in summer and autumn, with a growth rate of 0.38 (10 a)^-1 and 0.46 (10 a)^-1. Unfavorable meteorological conditions, such as increasing windless days, decreasing wind speed and gale days, and adverse circulation situations, such as the weakening of the East Asian winter monsoon, have resulted in an increase in persistent hazy days and its abnormal maintenance.