| With the development of economy and urban scale,the air pollution increases serious.The growing environmental pressure poses a serious threat to the health of residents.In recent years,remote sensing technology has been widely used in the field of atmospheric pollution monitoring.Lidar,with high temporal resolution and vertical resolution,can monitor the changes of aerosol concentrations at different heights over the urban areas in real time,which is a powerful supplement to traditional air pollution monitoring methods.The main purpose of this paper is to investigate the potentiality and feasibility of fine particle(PM2.5)monitoring using Mie scattering lidar data.The specific objectives of this study were:1)to collect the radar echo data from 2013 to 2016 by the 532nm Mie scattering lidar in Xianlin area of Nanjing;2)to analyze the aerosol extinction characteristics using the extinction coefficient at different heights retrieved by Fernald method based on radar echo data;3)to investigate the influence of each factor,which are generated based on the extinction coefficient and meteorological data obtained from the WRF model,on PM2 5;4)to establish the estimation models of PM2 5 concentrations based on multiple regression analysis and random forest.The main research results and finding are as follows:(1)The daily variation characteristic of extinction coefficient across different height was analyzed in the study area.The results show that the extinction coefficient in near-surface under 0.2 km is relatively large,and is concentrated to above 0.8 km-1.A stable aerosol layer is in the height range of 0.2-2 km,and the extinction coefficient is about 0.4 km-1.However,the extinction coefficient above 3 km is very small which means low concentration of aerosol.The atmospheric boundary layer also shows an obvious diurnal variation.In the afternoon,the height of boundary layer is rising associate with the intensity of solar radiation,and it reaches its peak in early evening.In terms of seasons,the variation of extinction coefficient at different height in spring and autumn is similar to that of the annual average variation.In summer,due to the strong convection,the extinction coefficient within 1 km varies greatly at different times.In winter,the extinction coefficient changes smoothly.(2)Taking the haze weather(2013.11.30-2013.12.1)as an example,the variations of extinction coefficient were analyzed combined with PM 10/PM2 5 concentrations.The results imply that the stable atmosphere stratification appears in the study area under the influence of temperature inversion,which result in the weakening of near-surface aerosol diffusion and the rapid increase of PM10/PM2.5 concentrations.In addition,it can be seen that the change trend of extinction coefficient in 0.03 km is consistent with that of PM10/PM2.5 concentrations,indicating that the increase of near-surface extinction coefficient is mainly caused by the gradual accumulation of particles and the extinction coefficient can also reflect the change of particle concentration.(3)The correlation between the PM2.5 measured concentrations and the extinction coefficient,the meteorological factors derived from WRF model was analyzed,respectively.The results demonstrate that the extinction coefficient has a positive correlation with PM2.5 concentrations,so it can be used to estimate the PM2.5 concentrations.Additionally,the effect of single meteorological factor on the PM2.5 concentrations is limited.It is the interactions between different meteorological factors that impact the PM2.5 concentrations in the study area.(4)The different estimation models of PM2.5 concentrations were established using the meteorological data and the extinction coefficient,based on multiple regression analysis and random forest,.By comparison,the estimation model based on random forest with the meteorological factors at different height is the optimal model. |
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