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Samastipur occupies a strategic position in northern Bihar's fertile Gangetic Plain, situated approximately 60 kilometers north of the Ganges River and 120 kilometers northeast of Patna. This district headquarters city lies at a modest elevation of around 53 meters above sea level, characterized by flat alluvial terrain typical of the Indo-Gangetic Basin. The urban center functions as a crucial agricultural market hub surrounded by intensive rice and wheat cultivation zones, with the Burhi Gandak River flowing nearby. Samastipur's geography profoundly influences air quality through multiple mechanisms: its location in the densely populated and heavily farmed Mithila region means agricultural burning emissions readily accumulate, while the city's position within the Indo-Gangetic Plain's 'pollution valley' creates a natural basin where pollutants become trapped. The flat topography offers little natural ventilation, allowing particulate matter from brick kilns, road dust, and vehicle exhaust to linger. Proximity to rural areas where biomass burning for domestic cooking is prevalent introduces additional pollution sources, creating a pronounced urban-rural gradient where urban emissions blend with agricultural and residential pollution. The city's development along major transportation corridors ensures continuous vehicle emissions, while its humid subtropical climate interacts with these geographic factors to create persistent air quality challenges.

Samastipur's air quality follows a dramatic seasonal rhythm dictated by the region's monsoon climate and agricultural calendar. During winter (November-February), pollution reaches hazardous peaks as cold temperatures create frequent temperature inversions that trap pollutants near the surface, while dense fog combines with emissions from brick kilns operating at full capacity, agricultural residue burning after harvests, and increased domestic biomass burning for heating. Sensitive groups should avoid outdoor activities entirely during these months, particularly during morning hours when fog and inversion layers are most intense. Spring (March-May) brings gradual improvement as temperatures rise and winds increase, though extreme heat waves can elevate ozone levels and dust storms worsen particulate pollution intermittently. The monsoon season (June-September) offers the cleanest air as heavy rains effectively wash pollutants from the atmosphere and strong southwesterly winds provide natural ventilation, making this the optimal period for outdoor activities. Autumn (October) marks a rapid deterioration as monsoon winds cease, temperatures drop, and post-monsoon agricultural burning commences, creating a sharp transition toward winter pollution conditions. Throughout the year, weather hazards like flooding can temporarily disrupt pollution patterns by washing away accumulated particulates but may also increase mold spores and biological pollutants in damp conditions.