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Nāhan, nestled in the foothills of the Shivalik Range within Himachal Pradesh, India, occupies a unique geographic position at approximately 30.55°N, 77.30°E and an elevation of around 940 meters. This location profoundly influences its air quality. The city is situated within a valley, a characteristic that can exacerbate pollution by trapping emissions and hindering dispersion, particularly during temperature inversions. Surrounding Nāhan are dense forests of pine and deciduous trees, contributing to a generally cleaner baseline than many heavily industrialized Indian cities. However, the region is also experiencing increasing urbanization and agricultural activity. The proximity to the plains of Haryana and Punjab means that seasonal winds can carry pollutants from those more heavily industrialized areas into Nāhan. The urban-rural gradient is relatively sharp; the city centre is densely populated, while the surrounding areas remain largely agricultural, with terraced farming common on the slopes. The absence of major rivers flowing *through* Nāhan, though smaller streams exist, limits natural flushing of pollutants. The terrain, being hilly, also affects wind patterns, creating localized eddies and stagnant air pockets. This combination of factors makes Nāhan’s air quality sensitive to both local emissions and regional transport.

Nāhan’s air quality follows a distinct seasonal pattern. Winter (November to February) typically sees the poorest air quality. Lower temperatures create strong temperature inversions, trapping pollutants near the ground, and reduced wind speeds limit dispersion. Smoke from household heating using wood and biomass contributes significantly. Fog, common during these months, further reduces visibility and exacerbates particulate matter concentrations. March and April bring a slight improvement as temperatures rise, but dust from agricultural activities becomes a concern. The monsoon season (July to September) offers a period of respite. Heavy rainfall effectively washes pollutants from the atmosphere, leading to cleaner air. However, increased humidity can also promote the formation of secondary pollutants. Post-monsoon (October to November) sees a gradual deterioration as temperatures fall and agricultural burning increases. Summer (May to June) experiences moderate air quality, with higher temperatures and some wind aiding dispersion, but increasing vehicle traffic and construction activity can offset these benefits. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit outdoor activity during winter and post-monsoon periods. Monitoring local conditions and avoiding peak pollution times is crucial.