Carbon dioxide (CO2) variations across India: Synthesis of observations and model simulations

<p>India is the 3rd largest emitter of fossil fuel carbon dioxide (CO₂), making it essential to understand CO₂ dynamics to manage carbon emissions. This study examines CO₂ variability and its dynamics based on observations at eleven observational sites in India, satellite observations and model simulations. Results reveal distinct diurnal and seasonal patterns, along with an overall increasing trend in CO₂. Deeper (shallower) seasonal cycle amplitudes (SCA) observed over northern (southern) part of India are due to the influence of the monsoon system, seasonal climate and terrestrial biosphere. The lowest SCA is observed over the high-altitude site, Hanle in north India (7.4 ppm), followed by the coastal sites, Pondicherry (8.0 ppm) and Thumba (8.4 ppm) in south India. Deepest SCA, 26.7 ppm, is observed at Mohali with one of the peaks observed in November attributed to crop residue burning activities in the Indo-Gangetic Plain. We have used an Atmospheric Chemistry Transport Model (ACTM) to simulate spatial and temporal variations in CO₂. While the ACTM generally reproduces diurnal variability in January, it fails to capture the CO₂minima in July. The model simulates seasonal patterns at Thumba reasonably well, whereas underestimates the SCA at Gadanki. Satellite observations of column CO₂ (XCO₂) show higher values (410&ndash;414 ppm) during the pre-monsoon season, while they remain lower (407&ndash;410 ppm) during winter and post-monsoon seasons during 2014&ndash;2024. Mean XCO₂ trend (2.41&ndash;2.46 ppm yr^-1) and growth rate variations are similar to Mauna Loa observations.</p>