Spatio-temporal variation of haze days and atmospheric circulation pattern in China (1961-2013)

The analysis also shows that the probability of rainless days and windless days to occur before or at a haze day ranges between 80% and 90%. Furthermore, the frequency of haze days shows a strong positive correlation with the frequency of windless days and rainless days. The time series of both meteorological indicators have shown steady increasing trends since 1961. Next to industrial emissions, windless days and rainless days can be attributed to be the major climate factors related to the worsening of the haze events in China. This relation is underlined by the atmospheric circulation pattern, which were dominated by a weaker than usual cold wave over China in December 2013. This pressure system led to warm-dry weather conditions and enabled inversions, and hence supported the formation of more than average haze days.