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Chandanais, nestled within the Chattogram District of Bangladesh (coordinates 22.2113° N, 92.0111° E), occupies a geographically significant position within the broader deltaic landscape. The city’s terrain is gently undulating, transitioning from the coastal plains towards the foothills of the Chittagong Hill Tracts to the east. This proximity to the hills creates a localized rain shadow effect, influencing precipitation patterns and, consequently, atmospheric dispersion. Chandanais sits near the Karnaphuli River, a major waterway vital for regional trade and industry, and benefits from the moderating influence of the Bay of Bengal, though this influence is often overridden by prevailing winds. The surrounding landscape is a mix of agricultural land – primarily rice paddies and vegetable farms – and small-scale industrial zones, particularly related to textiles and light manufacturing. This urban-rural gradient is relatively sharp, with agricultural activities contributing to seasonal particulate matter. The city’s location within a densely populated region of Bangladesh means it’s susceptible to transboundary pollution, with industrial emissions and agricultural burning from neighboring areas impacting air quality. The elevation is relatively low, averaging around 15 meters above sea level, which limits vertical mixing and can exacerbate ground-level pollution events. The prevailing southwest monsoon winds during the summer months bring moisture but can also carry pollutants from upstream sources, while the drier winter months often experience temperature inversions that trap pollutants closer to the ground. The city’s growth, while relatively modest compared to Chattogram itself, is steadily increasing, placing further strain on local environmental resources.

Chandanais experiences a distinct wet and dry season, profoundly impacting its air quality profile. The monsoon season, typically spanning June to October, brings frequent rainfall and high humidity. While the rain helps to cleanse the atmosphere by removing particulate matter, the increased humidity can trap gaseous pollutants, particularly during periods of reduced wind. The preceding pre-monsoon months (April-May) often see a build-up of pollutants due to stagnant air and increased agricultural burning as farmers clear fields. This period is generally characterized by hazy conditions and elevated levels of particulate matter. The dry season (November to March) presents a different set of challenges. Cooler temperatures during these months can lead to temperature inversions, where a layer of warm air traps cooler air and pollutants near the ground, resulting in poor air quality. Fog, common in December and January, further restricts atmospheric dispersion. The combination of reduced wind speeds and temperature inversions during the dry season often leads to the most concerning air quality episodes. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should limit outdoor activity during these periods, particularly in the early morning when fog is prevalent. During the monsoon, while overall particulate matter may be lower, those with asthma or allergies should be mindful of increased mold and pollen levels. Agricultural practices, including the burning of crop residue, are a significant contributor to pollution during the transition periods between seasons, necessitating awareness and mitigation strategies.