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Samāstipur sits in the fertile Gangetic plains of northern Bihar, approximately 60 kilometers north of the Ganges River, at a low elevation of around 50 meters above sea level. This positioning places it within one of India's most intensive agricultural zones, where rice and wheat cultivation dominate the landscape, interspersed with mango orchards and sugarcane fields. The city itself represents a classic Indian district headquarters—a bustling urban center surrounded by rural hinterlands, creating a distinct urban–rural gradient where traditional brick kilns, small-scale industries, and vehicular emissions mix with agricultural residue burning from surrounding farmlands. Samāstipur's flat terrain and proximity to the Himalayan foothills to the north influence local meteorology, often trapping pollutants due to limited wind dispersal. While not part of a major industrial belt like western Bihar's coal regions, it experiences pollution from local sources such as diesel generators, construction dust, and biomass cooking fuels. The Burhi Gandak River flows nearby, but its seasonal nature means it offers little moderating effect on air quality. This geographic context—flat, agricultural, and semi-urban—makes Samāstipur vulnerable to particulate matter accumulation, especially during post-harvest periods when crop burning peaks and temperature inversions are common in the cooler months.

In Samāstipur, air quality follows a distinct seasonal rhythm shaped by the monsoon cycle and agricultural calendar. Winter (December–February) brings the worst pollution, with cold temperatures, frequent fog, and temperature inversions trapping particulate matter from sources like biomass burning and vehicular emissions; sensitive groups should limit outdoor activities during morning hours when fog is thickest. Spring (March–May) sees moderate improvement as temperatures rise and winds increase, though occasional dust storms from the Thar Desert can spike particulate levels. The monsoon (June–September) offers the cleanest air, as heavy rains wash away pollutants and strong southwesterly winds disperse emissions—this is the ideal time for outdoor exercise. Post-monsoon (October–November) marks a sharp decline in air quality due to crop residue burning after the kharif harvest, compounded by calm winds and rising humidity that aid pollutant accumulation. Throughout the year, vulnerable populations—children, the elderly, and those with respiratory conditions—should monitor local air quality reports, use masks during high-pollution periods, and consider indoor air purifiers during winter months when household heating adds to the pollution burden.