摘要
Long-term trends in fog episodes, vertical variations of atmospheric boundary structure, and air pollutant concentrations during two different heavy fog events in the Tianjin area were analyzed. The total amount of fog has increased since 1980 due to the stability of the boundary layer and an increase of pollutant emissions. The variation in the characteristics of the boundary layer and air pollutant concentrations were significantly different between the two fog processes （fog I and fog ll）. The onset of fog I was accompanied by a temperature inversion in the low atmosphere, and the average kinetic energy showed a clear diurnal trend and vertical variation, which increased with height. The dissipation of fog I was mainly due to turbulence. However, the atmospheric stratification was not stable in the lower layer before the onset of fog If. The diurnal and vertical changes in kinetic energy were very small, in which turbulent momentum at each measurement height tended to be zero. In the dissipation process of fogⅡ, wind speed increased significantly. Surface PM2.s concentrations decreased, but the ratio of PMzs to PM10 increased from 0.66 to 0.82 until fog I dissipated. However, the concentration of PMzs did not decrease at the early stage of fog Ⅱ, but the ratio of PM2.5 to PM10 PM2.5JPM10 decreased to 0.21 when fog Ⅱ dissipated. This study showed that there was a clear difference in the evolution of pollutant concentration for different pollutants and in different developing stages during the fog events. PM2.5 concentration accumulated faster than those of SO2 and NOx, and the PM2.5 cumulative rate was greater in the mid-term of the fog process.
Long-term trends in fog episodes, vertical variations of atmospheric boundary structure, and air pollutant concentrations during two different heavy fog events in the Tianjin area were analyzed. The total amount of fog has increased since 1980 due to the stability of the boundary layer and an increase of pollutant emissions. The variation in the characteristics of the boundary layer and air pollutant concentrations were significantly different between the two fog processes （fog I and fog ll）. The onset of fog I was accompanied by a temperature inversion in the low atmosphere, and the average kinetic energy showed a clear diurnal trend and vertical variation, which increased with height. The dissipation of fog I was mainly due to turbulence. However, the atmospheric stratification was not stable in the lower layer before the onset of fog If. The diurnal and vertical changes in kinetic energy were very small, in which turbulent momentum at each measurement height tended to be zero. In the dissipation process of fogⅡ, wind speed increased significantly. Surface PM2.s concentrations decreased, but the ratio of PMzs to PM10 increased from 0.66 to 0.82 until fog I dissipated. However, the concentration of PMzs did not decrease at the early stage of fog Ⅱ, but the ratio of PM2.5 to PM10 PM2.5JPM10 decreased to 0.21 when fog Ⅱ dissipated. This study showed that there was a clear difference in the evolution of pollutant concentration for different pollutants and in different developing stages during the fog events. PM2.5 concentration accumulated faster than those of SO2 and NOx, and the PM2.5 cumulative rate was greater in the mid-term of the fog process.
基金
funded by the Tianjin Science and Technology Projects(13ZCZDSF02100)
the Special Grant in Meteorological Sciences Field supported by CMA(GYHY201006011)
the SpecialGrant in Environmental Sciences Field supported by the Ministry of Environmental Protection(201009001)
the National Natural Science Foundation of China(NSFC) under Grant No.41205089
