Analysis of pollution process of an atmospheric haze incident over Shenyang in summer of 2009 and its meteorological origin

Based on the visibility,relative humidity and particulate matter and other information,the distribution characteristic of grey haze over Shenyang during 10~(th)-20~(th) August 2009 was analyzed.The results showed that out of 11 days,there were 10 days about 142 hazy hours and the visibility during the haze was ranging from 1 312 m to 9 869 m.The severity of haze has distributed from mild to severe grade.The mild and slight grade occurred most frequently which was 92.8% of total number of haze occurrences.The visibility was 1 312 m in 12' August and the grade of haze was defined as severe grade. The daily concentration of fine particles PM_(2.5) exceeded the standard limit during the haze,and the maximum reading of the daily concentration of fine particles PM_(2.5) was recorded to be 2.88 times more than the standard limit.Anyway,the daily concentrations of reactive gases SO_2 and NO_2 did not exceed the standard.The grade of air quality has changed from excellent grade to slight pollution grade.This indicated that fine particles PM_(2.5) was the dominating air pollutant during the haze.When the haze occurred in all day,the daily concentration of particulate matter PM_(10) exceeded the standard where the maximum reading was 0.22 times more than standard limit.The grade of air quality was slight pollution grade.Under the control of uniform pressure field,the wind speed of Shenyang area was rather low.The wind field converged sometimes while the downdrafl was stronger than the updraft.There was a temperature inversion at 02: 00 everyday and the temperature inversion sustained until 08: 00 when the haze condition was deteriorated.