| Particulate matters have become the primary air pollutant in most major cities in China.As it pose a threat to environment and human health,PMs concentration has become an important index of air pollution.Because of the rapid development of urbanization and industrialization process,the pollution of the atmospheric particulates in Chinese cities is worsening,and the increasing hazy weather has seriously affected the people's ordinary life.According to the existing data,the Beijing-Tianjin-Hebei region is one of the regions which have been severely polluted in China.Therefore,the study on aerosol particles has great significance.Some studies have indicated that the aerosol optical thickness(AOT)and surface-level PM2.5 concentration has a positive correlation.With this correlation,the remote sensing monitoring of AOT can make up for the deficiency of the ground measurement of PM2.5 concentration.In order to estimate the PM concentration in large aera,a model between the concertration of PM2.5 and AOT needs to be established.Considering the scale height of aerosol and relative humidity as well as the effect of surface temperature and wind velocity,a seasonal multivariate linear equation of PM2.5 concentrations and AOT was established,using the 2013 full year MODIS AOT data and ground measurement of PM2.5 concentration,and the model accuracy has been validated.Based on this model,PM2.5 concentration from 2004 to 2013 was estimated,and an analysis of the spatial and temporal distribution of PM2.5 concentration has indicated that,the concentration of PM2.5 appears different between the southeast and the northwest of the study area,the area with high values is concentrated in the southeast of the Beijing-Tianj in-Hebei region where many big cities with developed industry and large populations are located.The burning of large amounts of straw resulted in a significant increase in PM2.5 concentration in June.Combustion of fossil fuel during the heating period,combined with unfavorable atmosphere environment,made the winter become another fastigium of PM2.5 concentrition.Four typical haze episodes in four different seasons were sampled,during which the spatial distribution of PM2.5 concentration and the backward air trajectories of three major cities computed by HYSPLIT were displayed together.Directions of trajectories and dot density illustrated that,the obstacle of the mountains located in the north and west of the Beijing-Tianjin-Hebei region has a significant adverse effect on the transportation and dispersal of air parcels carrying particulate matters.The specific terrain of the Beijing-Tianjin-Hebei region is one of the reasons contributing to the deterioration of air quality.However,The end of haze episodes mainly rely on natural factors such as the change of wind direction and washing out by precipitation.Comparison of the distribute of PM2.5 concentration grades in different land cover types suggested that,the PM2.5 concentration estimated in the region covered with forest,shrubland or grassland,generally has lower grades than that estimated in the region covered with urban land or cropland which has more human activities.Thus,more intense human activities may have a certain impact on the environment,and induce an obvious increase in PM concentration in specific regions. |
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