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Roh, Bihar, a small town nestled in the fertile plains of North India, occupies a geographically significant position within the Ganges River basin. Located at approximately 24.89°N, 85.67°E, its terrain is predominantly flat, characteristic of the Indo-Gangetic Plain, with an elevation of around 138 meters above sea level. This low-lying topography contributes to a tendency for pollutants to accumulate, particularly during periods of atmospheric stability. The surrounding landscape is dominated by agricultural fields – primarily rice and wheat cultivation – which, while vital to the regional economy, can contribute to particulate matter through seasonal burning practices. Roh’s proximity to the Ganges River, though providing a crucial water source, also influences local weather patterns and can, under certain conditions, trap pollutants. The urban–rural gradient around Roh is gradual; the town is surrounded by a patchwork of agricultural land and smaller villages, meaning that agricultural activities directly impact the local air quality. There are no major industrial belts immediately adjacent to Roh, however, the broader region of Bihar does contain industrial areas that can contribute to transboundary pollution. The flat, expansive nature of the plain limits vertical mixing of air, and the lack of significant topographical features exacerbates the potential for stagnant air masses, especially during cooler months. The climate, characterized by hot summers and a distinct monsoon season, further complicates the atmospheric dynamics affecting air quality.

Roh’s air quality experiences a distinct seasonal cycle heavily influenced by the region’s monsoonal climate. The pre-monsoon months (March-May) typically see the worst air quality, driven by agricultural residue burning – a common practice to clear fields for the next planting season. This releases significant quantities of particulate matter and other pollutants, creating hazy conditions and reduced visibility. The hot temperatures during this period also contribute to ozone formation. The monsoon season (June-September) brings relief, with increased rainfall and stronger winds that naturally disperse pollutants. However, heavy rainfall can also lead to increased humidity and, occasionally, localized flooding, which can temporarily worsen air quality due to resuspended dust and mold spores. The post-monsoon season (October-November) mirrors the pre-monsoon period, with a resurgence of agricultural burning and cooler temperatures that can lead to temperature inversions, trapping pollutants near the ground. Winter months (December-February) are often characterized by fog, which further restricts air movement and concentrates pollutants. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during the pre-monsoon and post-monsoon periods, limiting outdoor activity during peak pollution times. During the foggy winter months, it’s advisable to wear masks and avoid strenuous outdoor exertion. The monsoon season generally offers the most favourable conditions for outdoor activities, though vigilance regarding potential flooding is still necessary.