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Dehri is a mid-sized industrial city situated in the Rohtas district of Bihar, India, positioned at coordinates 24.9100°N, 84.1800°E along the southern bank of the Sone River. This strategic location places Dehri within the fertile Gangetic Plain, approximately 85 meters above sea level, where flat alluvial terrain dominates the landscape. The city serves as a crucial urban node in eastern India's industrial belt, bridging agricultural hinterlands with manufacturing zones, particularly cement production and brick kilns that cluster along its periphery. Dehri's proximity to the Sone River historically supported trade and agriculture but now contributes to seasonal flooding risks that can stir up sediment and industrial waste, exacerbating particulate matter pollution. The urban-rural gradient here is sharply defined, with dense urban cores transitioning abruptly to agricultural fields and small-scale industries, creating a mosaic of pollution sources. This geography traps emissions due to the valley-like effect of the surrounding low hills to the south, which inhibit wind dispersion, especially during winter months. The city's position in a humid subtropical climate zone means high humidity often combines with industrial and vehicular emissions, while its location in the Indo-Gangetic Plain—a notorious pollution hotspot—subjects it to regional air quality degradation from crop residue burning in neighboring states. The lack of significant water bodies beyond the Sone River limits natural cleansing of airborne pollutants, making Dehri's air quality particularly vulnerable to local industrial activities and seasonal weather patterns.

Dehri's air quality follows a distinct seasonal rhythm shaped by its humid subtropical climate and local emission sources. During winter (October to January), pollution peaks dramatically due to a combination of meteorological factors: temperature inversions trap pollutants close to the ground, while dense fog—common in the Gangetic Plain—combines with emissions from brick kilns, domestic biomass burning for heating, and industrial operations, creating hazardous smog. This period should be avoided for strenuous outdoor activities, especially by sensitive groups like children, the elderly, and those with respiratory conditions, who should limit exposure and use masks. Spring (February to March) sees gradual improvement as temperatures rise and winds increase, dispersing some pollutants, though industrial dust remains a concern. The summer months (April to June) bring extreme heat that can elevate ground-level ozone from vehicle exhaust, but stronger winds and occasional pre-monsoon showers provide temporary relief, making early mornings the best time for outdoor exertion. The monsoon (July to September) offers the cleanest air, as heavy rains wash away particulate matter and high winds sweep emissions eastward; however, flooding can resuspend contaminants. Post-monsoon (October onward), pollution escalates again as agricultural burning in the region coincides with cooling temperatures and reduced ventilation, marking the start of another hazardous cycle. Residents should monitor local air quality advisories and plan activities accordingly, with winter requiring the most stringent precautions.