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Deoria, a small city nestled in the fertile plains of Bihar, India, occupies a geographically significant position within the broader Indo-Gangetic Plain. Located at approximately 26.1791° N, 85.0234° E, its terrain is predominantly flat, characteristic of the alluvial soil deposits left by the Ghaghara River, a major tributary of the Ganges. The surrounding landscape is overwhelmingly rural, dominated by agricultural fields – primarily rice and wheat cultivation – which contribute to seasonal biomass burning. Deoria’s elevation is relatively low, around 118 meters (387 feet) above sea level, further exacerbating air quality challenges due to reduced atmospheric mixing. The city’s proximity to the Terai region, a low-lying, swampy area bordering the foothills of the Himalayas, introduces unique microclimatic conditions. This region often experiences dense fog during the colder months, trapping pollutants close to the ground. While Deoria lacks significant large-scale industrial zones within its immediate vicinity, it serves as a regional trading hub for agricultural produce, leading to vehicular traffic and associated emissions. The urban–rural gradient is gradual, with smaller towns and villages blending seamlessly into the agricultural landscape. The Ghaghara River, though providing a vital water source, can also contribute to localized humidity and stagnant air conditions, particularly during the monsoon season, influencing pollutant dispersion. The flat topography and surrounding agricultural activity create a setting where air pollutants can accumulate, especially under stable atmospheric conditions.

Deoria’s air quality follows a distinct seasonal pattern dictated by its subtropical climate and agricultural practices. The dry season, spanning roughly October to May, presents the most significant air quality concerns. November and December are often characterized by dense fog, a consequence of cooler temperatures and high humidity, which severely restricts visibility and traps pollutants near the surface. Agricultural residue burning, a common practice after the harvest of rice and wheat, intensifies during this period, releasing substantial amounts of particulate matter and other harmful gases. January and February typically experience the poorest air quality due to the combined effects of fog and persistent burning. The onset of the monsoon season (June to September) brings a temporary reprieve, as rainfall washes away pollutants and strong winds disperse them. However, the monsoon can also introduce moisture and humidity, potentially leading to the formation of secondary pollutants. The pre-monsoon period (April-May) can be problematic, with rising temperatures and decreasing rainfall leading to stagnant air and a build-up of pollutants. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during the dry season, particularly during periods of dense fog and agricultural burning. Limiting outdoor exertion and wearing appropriate masks are advisable. During the monsoon, while air quality generally improves, those with allergies should be mindful of increased pollen and mold counts. The transition periods between seasons often present unpredictable air quality conditions, requiring vigilance and awareness of local conditions.