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Sonbarsa, a small town in the state of Bihar, India, sits at coordinates 25.7069°N, 86.7379°E, nestled within the Indo-Gangetic Plain. This expansive, fertile plain is characterized by relatively flat terrain, a legacy of alluvial deposits from the Ganges and its tributaries. Sonbarsa’s elevation is low, contributing to limited atmospheric dispersion of pollutants. The town is situated near the Kosi River, a historically flood-prone waterway, and benefits from the agricultural productivity of the surrounding land, primarily rice and sugarcane cultivation. However, this agricultural activity also introduces potential sources of air pollution through crop residue burning and fertilizer use. The urban-rural gradient is pronounced; Sonbarsa is surrounded by villages and agricultural fields, with limited heavy industry directly within the town itself, though regional industrial activity in nearby areas contributes to background pollution levels. The lack of significant topographical features – hills or mountains – hinders natural ventilation, trapping pollutants during periods of calm weather. The town’s location within the densely populated Bihar plain means it’s susceptible to regional air pollution transport from larger urban centres and brick kilns. This geographical setting fundamentally shapes Sonbarsa’s air quality challenges, making it vulnerable to both local and transported pollutants.

Sonbarsa experiences a distinct seasonal air quality pattern dictated by the monsoon and post-monsoon periods. The pre-monsoon months (March to May) are typically the worst for air quality. Rising temperatures create strong convective currents, but also exacerbate dust suspension from agricultural activities and unpaved roads. The lack of rainfall means pollutants accumulate. The monsoon season (June to September) brings a temporary respite, as rainfall washes away particulate matter and increased humidity suppresses dust. However, stagnant conditions during breaks in the monsoon can lead to localised pollution build-up. Post-monsoon (October to November) sees a resurgence of pollution, coinciding with the burning of crop residue after the harvest, particularly rice straw, creating significant smoke and particulate matter. Winter (December to February) brings cooler temperatures and frequent temperature inversions, trapping pollutants near the ground. Fog further reduces visibility and exacerbates respiratory issues. Sensitive groups – children, the elderly, and those with pre-existing respiratory conditions – should limit outdoor activity during the pre-monsoon and post-monsoon seasons. Monitoring wind patterns and avoiding peak pollution times are crucial for protecting health.