Monthly and annual oscillation of methane and ozone in eastern India using Sentinel-5P TROPOMI: assessment and validation

The eastern India has greater Global Warming Potential with increased greenhouse gases emissions due to extensive rice production, coal burning, and rapid urbanization. The present study aimed to assess the monthly and annual dynamics of methane and ozone over the eastern Indian sates from February, 2019 to February, 2024 using Sentinel-5P Tropospheric Monitoring Instrument (TROPOMI). Chhattisgarh recorded the lowest concentration in most of the years. Chhattisgarh experienced the maximum growth in methane content by 3.41% followed by Bihar with 2.44% growth from 2019 to 2023. Although West Bengal recorded the highest average annual methane concentration, the methane growth is the minimum over the state with 1.87%. Periodical oscillation of methane concentration was characterized by the pre-monsoon (March-May) low and post-monsoon (September-November) high. Cloud interference during monsoon months caused data gap. In all the districts except Bihar, ozone concentration increased from 2019 and continued to rise up to 2022 followed by a subsequent decline in 2023. Linear trend of annual mean ozone concentration revealed a non-significant rising trend. Ozone concentration was found to be the minimum during post-monsoon months and the maximum during pre-monsoon months indicating a seasonal oscillation. Atmospheric Infrared Sounder (AIRS) and Ozone Monitoring Instrument (OMI) generated datasets were used to validate the methane and ozone concentration respectively obtained from TROPOMI observations. AIRS and TROPOMI datasets exhibited a good agreement with a correlation coefficient (r) of 0.45 and coefficient of determination (R²) of 0.204. On the other hand, OMI and TROPOMI showed an excellent agreement with an r value of 0.99 and an R² value of 0.978. The study assessed the spatial and temporal pattern of methane and ozone content in the recent times which helps the planners and policy makers to understand the trends and to develop effective mitigation strategies.