| The horizontal visibility has decreased significantly and the occurrence of haze-fog weather is quite frequent in Beijing-Tianjin-Hebei district in recent years. By employing integrated surface and satellite observations from 2002 to 2012, such as ground meteorological observation data, aerosol optical properties provided by AERONET and vertical structures and optical characteristics of aerosol layers detected by CALIPSO, this paper presents a multi-scale study on the role of atmospheric aerosols and meteorological conditions on regional haze-fog weather. Spatial and temporal distribution of haze-fog days in this region, aerosol and meteorological elements in the vertical direction during regional haze-fog weather as well as aerosol optical properties are analyzed in detail.To match with satellite data, this paper chooses the date of regional haze-fog weather from 2006 to 2012, resulting in the days decline from 12d in 2006 to 3d in 2012. As for seasonal variation, the numbers reach a maximum of 22d in summer, followed by autumn of 20d, and drop to the minimum of only 3d in spring. The decrement of the regional haze-fog days is mainly induced by the strong surface wind. Besides, high relative humidity can accelerate the process of gas-to-particle, and heighten the scattering power of secondary aerosols. Moreover, the diffusion of pollutants is restrained by weak wind and low mixing layer, which affects the visibility and benefits the occurrence and maintenance of haze-fog.More than 95 percent of aerosol particles appear in the middle and low troposphere where the atmospheric height is no more than 5km during the regional haze-fog weather in Beijing-Tianjin-Hebei district, especially in the height of 1～3km, which is related to the strong inversion layers and human activities.Smoke and dust aerosols exist all the time during the regional haze-fog weather with a considerable proportion. Polluted dust aerosols get together under 2km, while dust ones tend to appear in the high layer. Compared with tiny amount of marine aerosols,95 and 82 percent of regional haze-fog days contain polluted and clean continental aerosols, respectively. Below 5km in the sky, the ratio of continental, marine and smoke aerosols is about 25%, and they prefer the atmosphere under 2km. In summary, when the atmospheric height is lower than 5km, there are more anthropogenic regular fine particles like smoke and continent aerosols-especially when the height range is 0"2km, the fine aerosols absolutely transcend the coarse ones. The regularity and scattering is stronger as well.Taking Beijing as an example, the ambient aerosols in this area are fine particles. When the regional haze-fog weather occurs, a marked growth happens in fine aerosols, meanwhile, the scattering and absorbing power precedes the non-haze-fog days. The main reason of haze-fog in Beijing is regarded as the submicron aerosol growth and the increasement of the volume concentration. |
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