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Sherpur, Bihar, situated at approximately 25.65°N, 84.98°E, occupies a geographically significant position within the Gangetic plains of India. The town’s terrain is predominantly flat, characteristic of the Indo-Gangetic alluvial plain, resulting from centuries of sediment deposition by the Ganges River and its tributaries. This flat landscape, while fertile for agriculture, contributes to poor air dispersion, particularly during periods of low wind speed. Sherpur lies within a region dominated by agricultural activity, with extensive rice paddies and other crops surrounding the town. This agricultural zone, while vital for the regional economy, introduces pollutants like ammonia from fertilizers and particulate matter from crop burning, especially during the post-harvest season. The urban–rural gradient around Sherpur is gradual, with small villages and agricultural fields seamlessly blending into the town’s periphery. The elevation is relatively low, around 128 meters above sea level, further hindering vertical mixing of pollutants. While not directly adjacent to a major river, the proximity to the Ganges influences regional weather patterns and humidity levels, which can impact the behaviour of airborne pollutants. The absence of significant topographical features means that Sherpur is susceptible to the accumulation of pollutants, particularly in stagnant air conditions. Industrial activity in the immediate vicinity is limited, but the town’s connection to larger industrial belts further west contributes to regional pollution transport.

Sherpur’s air quality exhibits a distinct seasonal pattern dictated by the region’s monsoon climate. The pre-monsoon season (March-May) typically witnesses the poorest air quality. High temperatures and minimal rainfall create stable atmospheric conditions, often leading to temperature inversions where cooler air is trapped near the ground, preventing pollutants from dispersing upwards. Agricultural burning, a common practice after the winter harvest, significantly contributes to particulate matter pollution during this period. The monsoon season (June-September) brings relief as increased rainfall and strong winds effectively flush out pollutants, leading to a noticeable improvement in air quality. However, heavy rainfall can also lead to increased humidity and the release of biogenic volatile organic compounds (BVOCs) from vegetation. The post-monsoon season (October-November) mirrors the pre-monsoon period, with cooler temperatures and reduced rainfall again fostering stagnant air and agricultural burning, resulting in elevated pollution levels. Winter months (December-February) are generally cooler, with frequent fog formation. While temperatures are lower, the fog traps pollutants near the ground, reducing visibility and exacerbating respiratory issues. Sensitive groups, including children, the elderly, and individuals with pre-existing respiratory conditions, should limit outdoor activity during the pre-monsoon and post-monsoon seasons, particularly on days with low wind speeds and prevalent agricultural smoke. Maintaining indoor air quality through ventilation and air purifiers is also advisable during these periods.