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Dérassi, a municipality within Benin’s Borgou Department, occupies a position in the country’s central-northern region, at coordinates 10.1667° N, 3.2667° E. The terrain is generally undulating savanna, characteristic of the Benin Plateau, with an elevation ranging between 200-400 meters. This relatively high elevation, compared to coastal Benin, influences local weather patterns and air circulation. Dérassi is not directly adjacent to a major body of water, though smaller streams and seasonal waterways dissect the landscape, crucial for local agriculture. The surrounding area is predominantly agricultural, with significant cultivation of cotton, maize, and yams. While Dérassi itself isn’t heavily industrialised, the broader Borgou region experiences some activity related to agricultural processing and small-scale manufacturing. The urban-rural gradient is pronounced; Dérassi represents a relatively small urban centre embedded within a largely rural landscape. This proximity to agricultural lands introduces potential sources of particulate matter from land preparation, harvesting, and the burning of agricultural residue. Dust from unpaved roads is also a significant contributor, particularly during the dry season. The prevailing winds, influenced by the Harmattan from the Sahara, can transport dust and pollutants from distant sources, impacting local air quality. The city’s relatively small size and limited infrastructure contribute to localised pollution concentrations.

Dérassi experiences a distinct tropical climate with a pronounced wet and dry season, dictating the patterns of air quality. The dry season, typically from November to March, sees the poorest air quality. Reduced rainfall means less atmospheric cleansing, and increased dust from agricultural activities and unpaved roads dominates. The Harmattan winds, blowing from the Sahara, exacerbate particulate matter concentrations during this period. January and February are generally the months with the most challenging conditions for those with respiratory sensitivities. The transition period, April-May, brings increasing rainfall and a gradual improvement in air quality, though dust remains a concern. The wet season, from June to October, offers the best air quality. Frequent rainfall effectively washes pollutants from the atmosphere, and vegetation cover reduces dust resuspension. However, increased humidity can promote mould growth, potentially impacting indoor air quality. September and October, towards the end of the wet season, can see a slight increase in localised pollutants due to increased agricultural activity as farmers prepare for the next planting season. Sensitive groups – children, the elderly, and those with pre-existing respiratory conditions – should take extra precautions during the dry season, limiting outdoor exertion and considering the use of masks when dust levels are high.