Climatic characteristics of haze weather from 1961 to 2008 in Yinchuan

Based on the observational data from 1961 to 2008 in Yinchuan,the days of haze weather were analyzed.The results indicate that the days of haze weather are in increasing trends.They increase slowly before 1980s,significantly after 1980s and sharply after 2000.The days of haze weather appear frequently in December,then in November,and least in May,namely,winter autumn spring summer.In general,the duration of haze weather is 1-3 days.17% haze weather could last 2 days or more,while 1% haze weather could last 5 days or more.The persistent haze weather concentrates from November to February.The haze weather duration is related to its annual change.The haze weather persisting 5 days or more never occurs before 2000 in Yinchuan,while the haze duration extends with the increase of haze days after 2000.