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Dassari, nestled within the Atacora Region of Benin, occupies a geographically significant position at approximately 10.8158° N, 1.1406° E. The city’s terrain is characterized by undulating hills and valleys, typical of the northern Beninese landscape, reflecting the transition zone between the forested south and the Sahelian north. Dassari sits at a modest elevation, contributing to localized temperature variations and influencing air circulation patterns. The surrounding landscape is predominantly rural, a mosaic of small-scale agriculture – primarily maize, millet, and sorghum – interspersed with savanna grasslands and scattered shea trees. This agricultural activity, while vital to the local economy, can contribute to seasonal particulate matter emissions, particularly during harvesting and burning practices. The urban–rural gradient around Dassari is relatively sharp; the city itself is a small market town, and the transition to agricultural land is immediate. There are no major rivers or lakes immediately adjacent to Dassari, which limits natural air purification processes through precipitation and deposition. Dassari’s location, far removed from major industrial belts, means that industrial pollution is not a primary concern. However, the reliance on wood for cooking and heating, a common practice in the region, represents a significant localized source of air pollutants, especially during the cooler months. The prevailing winds, generally from the north during the dry season, can transport dust and smoke from agricultural fires across the region, impacting air quality in Dassari. The topography creates pockets where pollutants can accumulate, particularly in the lower-lying areas of the town.

Dassari experiences a tropical savanna climate with distinct wet and dry seasons, profoundly impacting its air quality. The dry season, roughly from November to March, is characterized by lower humidity, higher temperatures, and a greater frequency of dust storms originating from the Sahel. This period often sees a noticeable increase in particulate matter, as winds lift dust and smoke from agricultural burns used to clear fields. Temperature inversions, common during the cooler nights of December and January, can trap pollutants close to the ground, exacerbating the situation. The wet season, from April to October, brings increased rainfall and higher humidity, which naturally helps to cleanse the air by washing away particulate matter and diluting gaseous pollutants. However, the onset of the wet season can be preceded by a period of intense burning as farmers prepare their fields, leading to a temporary spike in air pollution. Fog, particularly in the early mornings during the transition periods between seasons, can also trap pollutants, reducing visibility and increasing respiratory irritation. Sensitive groups, including children, the elderly, and individuals with pre-existing respiratory conditions, should exercise caution during the dry season, particularly during periods of dust storms or agricultural burning. Limiting outdoor exertion and wearing masks can offer some protection. The months of January and February often present the most challenging air quality conditions, while April and June, coinciding with the start of the rains, typically offer the cleanest air. Maintaining indoor air quality through proper ventilation is crucial throughout the year.