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Shamshernagar, a small town in Bihar, India, sits at coordinates 25.0796°N, 84.4540°E, within the Indo-Gangetic Plain. This region is characterised by flat, fertile alluvial terrain formed by the deposition of sediments from the Ganges and its tributaries. The town’s elevation is relatively low, contributing to limited atmospheric dispersion of pollutants. Shamshernagar is situated within a predominantly agricultural landscape, with rice paddies and wheat fields dominating the surrounding areas. The Kosi River flows nearby, influencing local humidity and potentially contributing to localised fog formation during cooler months. While not a major industrial hub itself, Shamshernagar’s air quality is impacted by regional industrial activity concentrated further west towards Patna and the broader Bihar industrial corridor. The urban-rural gradient is pronounced; the town represents a concentrated point of activity within a largely agrarian setting. This creates a microclimate where emissions from domestic sources – cooking fires, small-scale industries, and vehicle traffic – become relatively concentrated. The lack of significant natural barriers like hills or forests exacerbates the potential for pollutant build-up, making Shamshernagar particularly vulnerable to air quality fluctuations linked to seasonal changes and regional emissions transport.

Shamshernagar experiences a distinct seasonal air quality pattern dictated by the monsoon and post-monsoon climate. The monsoon season (June-September) generally brings temporary relief from pollution due to rainfall washing away particulate matter and increased wind speeds dispersing pollutants. However, high humidity can also foster mould growth, impacting respiratory health. October-November sees a deterioration in air quality as the monsoon retreats, and temperatures drop, leading to temperature inversions that trap pollutants near the ground. This period coincides with post-harvest crop residue burning, a significant source of PM2.5. December-February are typically the worst months, with consistently poor air quality due to stagnant air, low temperatures, and continued burning of biomass for heating and cooking. March-May witness a gradual improvement as temperatures rise and winds pick up, but dust storms originating from the arid regions to the west can temporarily elevate particulate matter levels. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit outdoor activity during the post-monsoon and winter months. Avoiding peak traffic hours and using well-fitted masks when outdoors are recommended precautions.