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Salempur, a small town nestled in the northern plains of Bihar, India, occupies a geographically significant position within the fertile Gangetic plains. Located at approximately 26.4588° N latitude and 84.6517° E longitude, the town’s terrain is predominantly flat, characteristic of the Indo-Gangetic alluvial plain. The elevation is relatively low, contributing to a tendency for pollutants to accumulate, particularly during periods of atmospheric stability. Salempur sits within a predominantly rural landscape, surrounded by agricultural fields – primarily rice and wheat cultivation – which, while vital for the regional economy, can contribute to seasonal particulate matter through crop residue burning. The town’s proximity to the Ghaghara River, though providing a water source, also influences local weather patterns, occasionally leading to humidity and fog, which can trap pollutants. While not directly adjacent to major industrial belts, Salempur’s location within Bihar places it within reach of industrial activity concentrated in areas like Barauni and Hajipur, with associated transport corridors carrying emissions. The urban–rural gradient around Salempur is gradual, with smaller villages and agricultural land transitioning seamlessly into the town’s limited urban footprint. This blending of rural and urban characteristics means that agricultural practices and local transportation significantly impact the town’s air quality, alongside any industrial influences carried by prevailing winds. The flat topography and limited natural ventilation exacerbate the potential for pollutant build-up, making the town particularly vulnerable to poor air quality episodes.

Salempur’s air quality follows a distinct seasonal pattern dictated by the region’s monsoon climate. The monsoon season, typically spanning June to September, brings relief from accumulated pollutants due to frequent rainfall and strong winds that disperse contaminants. However, the preceding pre-monsoon months (March-May) often witness a significant deterioration in air quality. This period is characterized by rising temperatures, stagnant air, and the prevalence of temperature inversions, where a layer of warm air traps cooler air near the ground, preventing vertical mixing and concentrating pollutants. The post-monsoon season (October-November) presents a mixed picture. While winds generally increase, crop residue burning by farmers preparing fields for the winter harvest becomes a major source of particulate matter, leading to hazy conditions and reduced visibility. Winter months (December-February) are typically the most challenging, with cold temperatures, frequent fog, and low wind speeds creating ideal conditions for pollutant accumulation. Fog, common during these months, significantly reduces visibility and traps pollutants close to the ground. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should limit outdoor activity during the pre-monsoon and winter months, particularly on days with dense fog or visible haze. During the monsoon, while generally cleaner, heavy rainfall can still lead to localized flooding and associated waterborne illnesses. Maintaining indoor air quality through ventilation and air purification can be beneficial throughout the year, especially during periods of elevated pollution.