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Habiganj, situated in the Sylhet Division of Bangladesh (coordinates 24.3804° N, 91.4130° E), occupies a geographically significant position within the northeast of the country. The city’s terrain is predominantly undulating, characterized by the rolling hills of the Surma Valley, a landscape sculpted by the Surma River and its tributaries. This valley setting, while visually appealing, contributes to localized air quality challenges. Habiganj lies at an elevation of approximately 30 meters (98 feet), relatively low compared to the surrounding highlands, which can trap pollutants under certain meteorological conditions. The surrounding landscape is a mosaic of agricultural land – primarily rice paddies and tea plantations – interspersed with pockets of Sal forest. This agricultural activity, particularly during harvesting and burning seasons, introduces significant particulate matter into the atmosphere. To the west, the city gradually transitions into more rural areas, while eastward, it extends towards the plains of the Barak River. The proximity to the Surma River, though providing a vital water source, can also contribute to humidity and fog formation, which exacerbates air pollution by reducing atmospheric dispersion. Industrial activity, though not as extensive as in larger Bangladeshi cities like Dhaka or Chattogram, is present, primarily centered around brick kilns and small-scale manufacturing, further impacting local air quality. The urban-rural gradient around Habiganj is relatively gradual, meaning agricultural emissions readily influence the city’s air.

Habiganj’s air quality experiences a distinct seasonal cycle heavily influenced by the monsoon climate. The monsoon season, typically spanning June to September, brings heavy rainfall and strong winds, generally leading to improved air quality as pollutants are washed away and dispersed. However, the preceding pre-monsoon period (March-May) often witnesses a concerning rise in pollution levels. This is due to a combination of factors: increased agricultural burning to clear fields for planting, rising temperatures leading to stagnant air, and the prevalence of temperature inversions, where a layer of warm air traps cooler air (and pollutants) near the ground. The dry season (November-February) presents a mixed picture. While temperatures are generally cooler, fog is common, particularly in December and January, significantly reducing visibility and trapping pollutants close to the ground. This period can be particularly challenging for vulnerable populations. The post-monsoon period (October) sees a gradual improvement as rainfall decreases and winds pick up. Outdoor activity is generally most favorable during the monsoon months and the post-monsoon period. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during the pre-monsoon and dry season months, limiting prolonged outdoor exposure and considering the use of air-purifying masks when pollution levels are elevated. Agricultural workers are particularly at risk during burning seasons and should take appropriate protective measures.