Characteristics Of Haze And API Distribution And The Influence Of Weather Conditions On Them In Four Large Cities

Using the MICAPS ground conventional observations data in 1994-2013 from 756 national base stations and the air pollution index (API) data in 2002-2012 from 47 cities published by the state environmental protection administration, the weather conditions within haze days and relationship with API of Beijing, Nanjing, Shapingba district of Chongqing and Guangzhou are analyzed. The results show that:(1) The haze and high API mainly concentrate in central and eastern China, the annual frequency of haze days has begun to rise since 1998 and reached the maximum in 2013; and the haze occurred most in January, and least in August. During the period of 2002-2012, different with the annual frequency of haze days, the annual frequency of API is on the decline, and the API occurred most in December, and least in August. Among the four cities, the interannual variations and monthly variations of haze and API are different.(2)In general case, when haze occurs, the relative humidity is high in Beijing, Nanjing, Shapingba district of Chongqing and Guangzhou. When haze occurs, Beijing is dominated by southwestly, Nanjing and Guangzhou dominated by southeastly and Shapingba district of Chongqing dominated by northeastly. Among the four cities, the speed are mainly in the range of 1-4m/s. The more stable of lower atmosphere and katallobaric, the more haze days occurred. At the same time, four big city with haze level increases, the relative humidity of haze appeared high probabilities corresponding to the higher wind speed is small, the dominant wind direction is different.(3) The lower atmosphere stability has slightly different effects on API among four major cities. Beijing and Shapingba district of Chongqing is negatively correlated with γ850. The more stable, the higher the value of API. On the other hand, they are positively correlated in Nanjing and Guangzhou. The more unstable, the higher the value of API.(4) When the air quality is excellent and good grades, non-haze days are more than the number of days of haze days, when the air quality is mild, mild, moderate and severe pollution levels, haze days more than in non-haze days.Based on multiple linear regression equation, the results show that both thermal factor and dynamic factor have contribution to the visibility of haze days and API in the winter in the four cities.