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Hojāi, nestled in the heart of Assam, India (26.0000°N, 92.8700°E), is a rapidly developing urban centre with a population of approximately 36,638. The city’s geography is defined by the Brahmaputra Valley, a fertile floodplain characterized by relatively flat terrain. This low-lying landscape, averaging around 50 meters above sea level, contributes to localized humidity and potential for stagnant air masses. Hojāi is situated amidst a mosaic of agricultural lands, primarily rice paddies and tea gardens, which are integral to the regional economy. While not directly on the Brahmaputra River, the city is influenced by its proximity and the network of smaller tributaries that crisscross the region. The surrounding landscape features rolling hills transitioning towards the Karbi Anglong hills to the south. The urban-rural gradient is pronounced, with agricultural activity dominating the immediate periphery. Industrial activity, though growing, is concentrated in specific zones, contributing to localized pollution hotspots. The valley’s topography can trap pollutants, particularly during periods of calm weather, exacerbating air quality concerns. The region’s climate, a humid subtropical type, further influences pollutant dispersion patterns, with monsoon rains offering periodic cleansing but also contributing to damp conditions that can foster mould growth.

Hojāi’s air quality follows a distinct seasonal pattern. The monsoon season (June-September) generally brings temporary relief, as heavy rainfall washes away particulate matter. However, the increased humidity can also promote the growth of mould and biological pollutants. October-November sees a deterioration in air quality as the monsoon recedes and agricultural burning increases, linked to post-harvest practices. This period often experiences stagnant air, trapping smoke and dust. Winter (December-February) is typically the worst period for air quality, with cooler temperatures leading to temperature inversions – a layer of warm air trapping cooler, polluted air near the ground. Reduced wind speeds further exacerbate the problem. March-May brings a gradual improvement as temperatures rise and winds pick up, though dust from construction and road traffic remains a concern. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit outdoor activity during the winter months and periods of agricultural burning. Monitoring local weather patterns and avoiding peak traffic hours can also help mitigate exposure. The pre-monsoon season (May-June) can see dust storms impacting air quality.