Study On Land Aerosol Fine-mode Fraction Retrievals

In recent years,aerosols have played an important role in influencing the environment,however,with rapid industrialization and urbanization,the main source of environmental impact is aerosols generated by human activities.The aerosol finemode fraction(FMF)is the ratio of the optical thickness of aerosols with fine particles in the 550 nm band to the total optical thickness in the atmosphere,and the aerosols generated by human activities are mainly small particles,so the retrieval of the aerosol fine-mode fraction will be useful to identify and quantify the extent and role of anthropogenic aerosols in the climate,and thus help to study the impact of human activities on climate and atmospheric environment.In this paper,we propose an independent retrieval algorithm to retrieve the FMF of terrestrial aerosols using satellite aerosol optical depth(AOD)and the (?)ngstr(?)m exponent(AE),which has the following two innovative points:(1)a more accurate aerosol model is adopted;(2)a more concise two-mode model consisting of AOD and FMF to form a more concise two-dimensional look-up table.The main tasks are as follows.(1)Selection of study area and data.In this paper,Beijing and Jaipur stations are selected as the study area,and AERONET(Aerosol Robotic Network)L2.0 data from2001 to 2018 are selected for the construction of the aerosol model,which is also filtered and processed to obtain data with guaranteed accuracy.(2)Construction of aerosol models.For the three main terrestrial aerosol types,AERONET data were used to study the problems in existing models and propose new description methods to establish stable and reliable dynamic aerosol models.30 aerosol models were finally constructed for Beijing station and 19 aerosol models for Jaipur station,and they were classified and organized according to seasons.(3)Establishment of two-dimensional look-up tables.A two-dimensional look-up table with AOD and FMF as variables were established for each model,and then the total optical thickness and (?)ngstr(?)m index from the satellite aerosol data were used as data sources to invert the FMFs corresponding to different models,and the inverse FMFs were used to obtain the final FMFs by interpolation.(4)Algorithm validation.The FMFs of the new algorithm were compared with those of AERONET and MODIS(Medium Resolution Imaging Spectroradiometer),and the results showed that the correlation coefficient of the FMFs inverted by the new algorithm and those of AERONET was 65.6%,which was higher than that of MODIS C6(43.6%);The RMSE(the root mean square error)is 0.156,while the RMSE of MODIS C6 is 0.318;90% of the inversion results of the new algorithm fall within the error range of ±0.4,which is higher than that of MODIS C6 at 57.4%.