Satellite-Derived Seasonal CO₂ Dynamics Over a Northern Indian Megacity: OCO-2 Observations for Delhi (2019–2024)

Delhi, located within the Indo-Gangetic Plain (IGP), has undergone rapid urbanisation over the past few decades and today represents one of the most densely populated megacities, with nearly 40 million people in the wider National Capital Region regularly exposed to severe air-quality stress. Despite this significance, long-term ground-based CO₂ measurements remain sparse, making Delhi a data-scarce environment for greenhouse-gas assessment. In such context, satellite observations offer an essential alternative for evaluating broad-scale CO₂ behaviour, particularly for cities lacking extensive monitoring networks.

This study examines the seasonal variability of column-averaged CO₂ (XCO₂) over Delhi using six years (2019–2024) of quality-filtered observations from NASA’s Orbiting Carbon Observatory-2 (OCO-2). To understand how XCO₂ evolves through the year, monthly values were compared against their multi-year averages, allowing us to identify recurring seasonal tendencies rather than year-specific fluctuations. Using this approach, the satellite data consistently show elevated CO₂ levels during the pre-monsoon months (April–June), followed by a noticeable reduction during the monsoon season, attributed to the precipitation-induced scavenging of CO₂, and increased vegetation growth. As winter approaches, XCO₂ begins to rise again, reflecting the influence of shallow boundary-layer height and larger wind-speed stagnation over northern India.

Delhi’s strong seasonal contrasts provide a clear setting for investigating how satellite-retrieved CO₂ responds to regional meteorology within a dense megacity. The patterns identified in this study highlight the capability of spaceborne observations to capture physically meaningful CO₂ dynamics even in complex, polluted urban environments. These findings also emphasise the value of publicly accessible satellite datasets for cities where continuous ground-based measurements are limited.