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Sāsan, nestled in the Jamui district of Bihar, India, occupies a geographically significant position within the Chota Nagpur Plateau region. Its coordinates (25.6883° N, 86.1907° E) place it at an elevation of approximately 335 meters above sea level, contributing to a relatively undulating terrain characterized by gently sloping hills and valleys. The surrounding landscape is predominantly rural, transitioning from agricultural fields – primarily maize, rice, and pulses – to denser patches of deciduous forest typical of the eastern plateau. This proximity to agricultural zones introduces seasonal biomass burning as a potential pollution source, particularly during harvest periods. Sāsan’s location is far removed from major industrial belts, however, the region experiences some influence from industrial activity in nearby Jharkhand. The urban–rural gradient is sharp; Sāsan itself is a small town, and the immediate surroundings are overwhelmingly agrarian. The lack of significant water bodies within immediate proximity—no major rivers flow directly through the town—limits natural air purification processes. The plateau’s topography can also contribute to localized air stagnation, especially during periods of calm weather. The prevailing winds, generally from the east, can carry pollutants from further afield, though the relatively isolated location mitigates this to some extent. The soil composition, largely lateritic, can also influence dust generation, particularly during the dry season, impacting local air quality. The town's small size and limited infrastructure mean that vehicle emissions, while not currently a major factor, could become increasingly relevant with future growth.

Sāsan’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 increased wind speeds, effectively flushing the atmosphere. However, the preceding pre-monsoon period (March-May) often witnesses a significant deterioration in air quality. High temperatures exacerbate the formation of ground-level ozone, while stagnant air masses and frequent dust storms, driven by dry winds, contribute to particulate matter pollution. Agricultural burning, a common practice during this period to clear fields for the monsoon planting, is a major contributor. The post-monsoon season (October-November) sees a gradual improvement, but often experiences periods of dense fog, particularly in November, which traps pollutants near the ground, leading to localized episodes of poor air quality. Winter months (December-February) are generally characterized by cooler temperatures and calmer winds, which can lead to temperature inversions – a phenomenon where a layer of warm air sits above cooler air, preventing pollutants from dispersing vertically. This can result in a build-up of pollutants, especially during foggy conditions. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during the pre-monsoon and winter months, limiting outdoor exertion and monitoring local air quality reports. During the monsoon, while generally cleaner, heavy rainfall can still trigger localized flooding and associated waterborne illnesses, impacting overall health.