SPATIO-TEMPORAL VARIATION OF OZONE OVER THE EASTERN AND WESTERN INDO-GANGETIC PLAIN

Abstract

One of the most populated and polluted parts of India is the Indo Gangetic plain (IGP), where the systematic analysis of TCO trends on a sub-regional basis over a considerable period of time is still lacking. This study examines the spatio-temporal variation and long-term trends of the TCO over two contrasting ends of the IGP — the state of Punjab in the West and the state of West Bengal in the East — covering the period of 2004–2025 using satellite data from NASA's O3 Monitoring Instrument (OMI) and ESA's Sentinel-5P TROPOMI, extracted using the Google Earth Engine (GEE). Within each state, a high-O3 and a low-O3 region were identified and studied separately to capture the intra-state variability. Trend analysis was performed out using the Mann-Kendall (MK) test and Sen's slope estimator using R, across monthly, seasonal, and annual time periods. Results show that Punjab consistently recorded higher TCO values (annual mean O3 of around 286 DU) than West Bengal (annual O3 of around 270 DU), consistent with the north-to-south O3 gradient observed over India. Both states show statistically significant increasing annual trends (p < 0.05 for all four regions). The pre-monsoon season (March–May) comes out as the period of peak O3 loading in both regions, driven by improved photochemical activity and biomass burning. The lowest O3 values appear during the post-monsoon period (October December). Sen's slope values show an increase of about 0.42–0.50 DU/year across all regions. These findings highlight the need for region-specific air quality supervision, specifically ozone.