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Mahtha, a small town in the Bihar plains of India (26.5988°N, 86.3158°E), occupies a low-lying position within the Indo-Gangetic Plain. The terrain is remarkably flat, characteristic of alluvial deposits from the Ganges River system, though subtle undulations exist due to ancient river courses. Situated at an elevation of approximately 53 meters, Mahtha’s geography significantly influences its air quality. The surrounding landscape is dominated by intensely cultivated agricultural land, primarily rice and wheat fields, with pockets of deciduous forests further afield. This agricultural intensity contributes to seasonal biomass burning, a major source of particulate matter. The town’s proximity to larger urban centres like Patna, roughly 100km to the east, means it’s susceptible to regional pollution transport. The urban-rural gradient is relatively sharp; Mahtha itself is a small settlement, but surrounding villages contribute to localised emissions from household cooking and small-scale industries. The lack of significant topographical features hinders natural dispersion of pollutants, leading to their accumulation, particularly during stable atmospheric conditions. The climate is subtropical monsoon, with hot, humid summers and cool, dry winters, further impacting pollution dynamics. The flat terrain and agricultural practices combine to create a challenging environment for maintaining good air quality.

Mahtha experiences a distinct seasonal air quality pattern dictated by the monsoon and post-monsoon cycles. The pre-monsoon months of April and May are typically the worst, with high temperatures and stagnant air promoting the build-up of dust and pollutants from agricultural fires preparing fields for sowing. Temperature inversions are common during this period, trapping pollutants near the ground. The arrival of the monsoon in June brings temporary relief, as rainfall washes away particulate matter and increased humidity suppresses dust. However, increased cloud cover can also exacerbate ozone formation. Post-monsoon (October-November) sees a resurgence of pollution, driven by the burning of crop residue after the harvest, particularly rice straw, creating a dense haze. Winter (December-February) brings cool, dry conditions and stable atmospheric layering, leading to prolonged periods of poor air quality, especially in the mornings. Fog further reduces visibility and traps pollutants. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit outdoor activity during April-May and October-November. Avoiding peak hours and using masks can offer some protection. The monsoon months offer the most favourable conditions for outdoor activity, though localised flooding can present other hazards.