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Dahāria, a small town in the Muzaffarpur district of Bihar, India, sits at coordinates 26.1807°N, 87.0043°E. The town’s geography is characteristic of the Indo-Gangetic Plain – a flat, fertile alluvial landscape. Elevation is low, averaging around 52 meters above sea level, contributing to limited atmospheric dispersion of pollutants. Dahāria is situated within a predominantly agricultural zone, with rice paddies and wheat fields dominating the surrounding terrain. The Burhi Gandak river flows relatively close, influencing local humidity and potentially contributing to localised fog formation during cooler months. While not directly within a major industrial belt, the broader Muzaffarpur region experiences industrial activity related to sugar processing and food production, which can contribute to particulate matter and gaseous emissions. The urban-rural gradient is sharp; Dahāria itself is a relatively small settlement, quickly transitioning to rural farmland. This proximity to agricultural practices introduces seasonal biomass burning – post-harvest crop residue burning – as a significant localised pollution source. The flat terrain and lack of significant windbreaks exacerbate the concentration of pollutants, particularly during periods of calm weather. The town’s location within the densely populated Bihar plain means it’s susceptible to regional transport of pollutants from larger urban centres.

Dahāria’s air quality follows a distinct seasonal pattern. The post-monsoon period, from October to November, typically sees the worst conditions. The cessation of monsoon rains reduces atmospheric washing, while widespread agricultural burning of crop residue releases substantial particulate matter. Shallow temperature inversions are common during these cooler, calmer months, trapping pollutants near the ground. December and January bring cooler temperatures and often dense fog, further exacerbating particulate matter concentrations and reducing visibility. February and March see a gradual improvement as temperatures rise and wind speeds increase, dispersing pollutants. The pre-monsoon months of April and May are characterised by hot, dry winds, which can carry dust and pollutants from surrounding areas, though increased mixing height can offer some relief. The monsoon season, from June to September, generally provides the cleanest air due to rainfall washing away pollutants and increased wind speeds. However, increased humidity can also promote secondary pollutant formation. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit outdoor activity during October-November and December-January. Avoiding peak burning times and using N95 masks can offer some protection. Monitoring local conditions is crucial.