Musāpur, Bihar, situated at approximately 25.6417° N, 87.4154° E, occupies a geographically significant position within the Gangetic plains of eastern India. The city’s terrain is predominantly flat, characteristic of the Indo-Gangetic alluvial plain, resulting in minimal elevation changes. This flatness, while facilitating urban expansion, also contributes to air quality challenges as it limits natural dispersion of pollutants. Musāpur lies close to the Ghaghara River, a major tributary of the Ganges, which influences local humidity and temperature patterns. The surrounding landscape is a mosaic of agricultural fields – primarily rice and maize cultivation – interspersed with small villages and scattered industrial units. This agricultural activity, particularly during harvest seasons, contributes to seasonal particulate matter pollution through crop residue burning. The urban–rural gradient around Musāpur is relatively gradual, with agricultural land quickly transitioning to residential and commercial areas within the city limits. Further afield, the landscape gradually rises towards the Chota Nagpur Plateau, though this is a considerable distance. The proximity to the Farakka Barrage, impacting the flow of the Ganges, also subtly influences regional weather patterns. The lack of significant topographical features means that Musāpur is susceptible to stagnant air conditions, especially during periods of low wind speed, exacerbating the impact of local pollution sources. The city’s location within a densely populated region of Bihar means it is also influenced by transboundary pollution from neighboring urban centers and industrial belts.

Musāpur’s air quality follows a distinct seasonal pattern dictated by the region’s monsoon climate. The dry season, typically spanning October to May, presents the most significant air quality concerns. November and December often experience dense fog, trapping pollutants near the ground and significantly reducing visibility. This period is characterized by temperature inversions, where cooler air settles below warmer air, preventing vertical mixing and concentrating pollutants. Agricultural practices, specifically the widespread burning of crop residue after the harvest of rice and wheat, are a major contributor to particulate matter pollution during these months. The monsoon season, from June to September, brings relief as rainfall washes away pollutants and strong winds disperse them. However, even during the monsoon, localized pollution from construction activities and vehicular emissions persists. The pre-monsoon period (March-May) is often hot and dry, with increasing levels of dust and pollutants due to increased construction and road traffic. The summer months (April-June) can also see elevated ozone levels due to photochemical reactions. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should minimize outdoor activity during the dry, foggy months (November-December) and the hot, dusty pre-monsoon period. Maintaining indoor air quality through ventilation and air purifiers is advisable during these times. The monsoon months offer a window for improved air quality and increased outdoor activity, though vigilance regarding localized pollution sources remains important.