Katihar occupies a strategic position in northeastern Bihar, India, situated at the confluence of the Ganges and Kosi rivers at approximately 40 meters above sea level. This low-lying terrain in the fertile Gangetic Plain creates a unique urban-rural gradient where the city's 240,000 residents interface directly with intensive agricultural zones, particularly rice paddies and jute cultivation. The city's geography as a railway junction—connecting eastern and northeastern India—amplifies its industrial character, with the railway yard serving as a persistent pollution source. Proximity to the Himalayan foothills to the north influences local meteorology, often trapping pollutants under temperature inversions, while the surrounding flat floodplains and river systems contribute to high humidity that exacerbates particulate matter formation. Katihar's location in the Mithila region places it within an industrial-agricultural belt where traditional brick kilns, jute processing, and biomass burning for domestic fuel are prevalent. The urban core, though modest in size, experiences concentrated emissions from vehicle exhaust and railway operations, while the rural periphery contributes agricultural residue burning and dust. This geographic setting—low elevation, riverine environment, and transitional zone between urban infrastructure and agrarian economy—creates a perfect storm for air quality degradation, as pollutants accumulate rather than disperse across the flat landscape.

Katihar's air quality follows a dramatic seasonal cycle shaped by its humid subtropical climate. During winter (November-February), pollution peaks as cold waves and dense fog trap emissions from diesel trains, brick kilns, and biomass burning under persistent temperature inversions, with calm winds failing to disperse particulate matter—these months are particularly hazardous for outdoor activity, especially for children, elderly, and those with respiratory conditions. Spring (March-May) brings extreme heat that increases ozone formation from vehicle exhaust, though occasional pre-monsoon winds provide some relief by dispersing pollutants. The monsoon (June-September) dramatically cleanses the air as heavy rainfall washes away particulate matter and strong southwesterly winds from the Bay of Bengal sweep through the Gangetic Plain, making this the best period for outdoor activities despite flooding risks. Autumn (October) sees a rapid deterioration as agricultural burning resumes post-harvest and meteorological conditions transition toward winter stagnation. Sensitive groups should avoid prolonged exposure during peak pollution months, use air purifiers indoors, and schedule essential outdoor activities for morning hours when pollution levels are relatively lower. The dense winter fog combined with high particulate concentrations creates particularly dangerous conditions for asthmatics and cardiac patients.