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Barharwa Kalān, nestled in the fertile plains of Bihar, India, occupies a geographically significant position within the Ganges River basin. Located at approximately 26.5434° N, 84.8286° E, the town’s terrain is predominantly flat, characteristic of the Indo-Gangetic Plain, with an elevation of roughly 118 meters above sea level. This low-lying topography, while conducive to agriculture, presents challenges regarding air quality dispersion. The surrounding landscape is dominated by agricultural fields – primarily rice and maize cultivation – interspersed with small villages and scattered groves of trees. Barharwa Kalān sits within a gradual urban–rural gradient, transitioning from the denser population centers of nearby Sahibganj district to the more sparsely populated agricultural hinterland. The proximity to the Ganges River, though providing a vital water source, can also contribute to localized humidity and fog formation, impacting pollutant dispersal. While not directly adjacent to major industrial belts, the town’s location within a region experiencing increasing agricultural intensification means that practices like stubble burning, particularly during post-harvest seasons, significantly influence local air quality. The flat terrain limits vertical mixing of pollutants, and the prevailing wind patterns, often influenced by regional weather systems, can either disperse or trap pollutants, depending on their direction and strength. The lack of significant natural barriers further exacerbates this issue, making Barharwa Kalān susceptible to transboundary pollution events originating from larger urban centers and industrial regions to the north and west.

Barharwa Kalān experiences a distinct wet and dry season, profoundly impacting its air quality profile. The dry season, typically spanning from October to May, is characterized by lower rainfall and increased temperatures, leading to a significant deterioration in air quality. During this period, agricultural practices, particularly the widespread burning of crop residue after the harvest of rice and maize, become a major source of particulate matter. The lack of rainfall and lower humidity allow these pollutants to persist and accumulate. Temperature inversions, common during the cooler months (November-February), trap pollutants near the ground, further worsening conditions. Fog, frequently occurring in December and January due to high humidity and low temperatures, restricts visibility and hinders pollutant dispersion. The monsoon season (June-September) brings relief, with frequent rainfall washing away pollutants and strong winds dispersing them. However, even during the monsoon, localized pollution can arise from construction activities and vehicular emissions. The pre-monsoon period (April-May) often sees a build-up of pollutants as temperatures rise and rainfall is scarce. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during the dry season, particularly during periods of stubble burning and fog. Limiting outdoor exertion and wearing masks are advisable. The monsoon months generally offer the most favorable conditions for outdoor activities, though vigilance regarding localized pollution sources remains important.