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Supaul, situated in the northern plains of Bihar at coordinates 26.1200°N, 86.6000°E, occupies a strategic position in South Asia's Ganges River basin. This small urban centre of 48,000 people lies approximately 50 kilometres north of the Kosi River, a major tributary of the Ganges known for its frequent flooding, which shapes both the region's agricultural patterns and pollution dynamics. The terrain is predominantly flat alluvial plains with an elevation of just 50 metres above sea level, creating conditions that trap pollutants near ground level. Supaul's location places it within Bihar's intensive agricultural belt, where rice and wheat cultivation dominate the landscape, interspersed with numerous brick kilns that operate seasonally. The urban-rural gradient is subtle, with the town serving as a commercial hub for surrounding villages, leading to significant biomass burning for domestic cooking and heating. Proximity to the Himalayan foothills to the north influences local wind patterns, but the absence of significant water bodies nearby means there's limited natural cleansing of airborne pollutants. This geographic setting, combined with its position in the densely populated Indo-Gangetic Plain, creates a perfect storm for air quality challenges, as emissions from multiple sources accumulate in the stagnant air typical of this basin topography.

Supaul's air quality follows a distinct seasonal pattern shaped by its humid subtropical climate and agricultural calendar. During winter (October-January), pollution peaks dramatically due to multiple converging factors: agricultural burning of crop residues after the monsoon harvest, increased domestic biomass burning for heating, and persistent temperature inversions that trap pollutants near the ground. Dense fog frequently blankets the region during these months, combining with smoke to create hazardous smog that reduces visibility and exacerbates respiratory issues. The post-monsoon period sees little wind dispersal, making outdoor activities particularly risky for sensitive groups like children, elderly, and those with pre-existing conditions. Spring (February-March) brings gradual improvement as temperatures rise and winds increase, though brick kiln operations and road dust remain concerns. The summer monsoon (June-September) provides the cleanest air, as heavy rains wash pollutants from the atmosphere and winds disperse emissions effectively—this is the optimal time for outdoor activities. However, extreme heat in pre-monsoon months (April-May) can increase ground-level ozone formation. Sensitive residents should monitor local air quality reports, use air purifiers indoors during peak pollution months, and schedule outdoor activities for early mornings when pollution levels are typically lower.