Analysing the Changing Trends of Aerosol Optical Depth (AOD) using 6S Radiative Transfer Model for Chennai City

Increase in urbanization in metropolitan cities like Chennai is leading to decrease in air quality and an increase in the particulate emissions in the air year by year. Monitoring of aerosols is difficult due to the limited number of ground stations, large data gaps, and lowerresolution aerosol products. This study is carried out to overcome the existing spatial resolution limitation of aerosol optical depth retrieval by merging High spatial resolution data Landsat 8 Operational Land Imager with Moderate Resolution Imaging Spectroradiometer surface reflectance data MOD09GA. The 6S radiative transfer model is used for radiative transfer simulation for the existing conditions of Chennai. A lookup table is prepared based on the input parameters given and the Aerosol Optical depth is estimated using an inversion model utilizing surface reflectance from MODIS data. Aerosol Optical Depth maps are retrieved from 2015- 2023 to perform trend analysis and the map is compared and validated with ground-based sensor Particulate Matter data acquired from the Central Pollution Control Board to determine the accuracy of retrieval. The validation shows that the Aerosol Optical depth retrieval approach yields a R2 value of 70.35% indicating a higher correlation between the retrieved Aerosol Optical depth value and ground-based PM2.5 data.