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Kétou, situated in the Plateau Department of southeastern Benin, serves as a vital cultural and historical nexus near the Nigerian border. Geographically, the city sits within a transitional zone characterized by rolling plateaus and fertile savannah-forest mosaics, positioning it at an elevation that facilitates moderate drainage despite the humid tropical climate. The urban character of Kétou is defined by its dense, traditional core radiating into an expanding rural-urban gradient, where agricultural practices—primarily cassava, maize, and oil palm cultivation—dominate the surrounding landscape. This proximity to extensive agricultural zones significantly influences local air quality, as seasonal land clearing and traditional biomass burning practices introduce substantial particulate matter into the lower atmosphere. Kétou lacks large-scale heavy industrial belts, yet the urban air profile is shaped by the trans-border trade corridor connecting Benin to Nigeria, leading to sustained vehicular emissions along key arterial routes. The terrain, mostly undulating, lacks significant natural barriers, allowing prevailing winds—specifically the moisture-laden southwesterly monsoon and the dry, dust-heavy Harmattan—to move freely across the region. Consequently, the atmospheric composition in Kétou is a complex interplay between localized vegetative organic aerosol emissions from surrounding farmland and the episodic influx of regional dust transported from the north. As the city continues to modernize, the spatial distribution of its population remains concentrated, creating micro-climates where traffic congestion and biomass dependency for domestic energy converge. Understanding Kétou’s geography requires acknowledging this delicate balance between its traditional agrarian heritage and the inevitable environmental pressures exerted by its role as a regional transit hub.

Kétou experiences a distinct tropical climate governed by the oscillation of the Intertropical Convergence Zone, which dictates a biannual cycle of wet and dry seasons that fundamentally alter local air quality. The dry season, peaking between November and March, is dominated by the Harmattan, a northeasterly trade wind that carries fine Saharan dust particles across the plateau. During these months, the air often becomes hazy, and the concentration of suspended particulate matter increases, posing challenges for sensitive groups. This period, characterized by lower humidity and atmospheric stability, can lead to temperature inversions that trap ground-level pollutants from biomass burning and vehicular exhaust. Conversely, the transition into the long wet season, spanning from April to October, brings relief through convective rainfall. These frequent, heavy downpours act as a natural atmospheric scrubber, effectively washing out particulate matter and significantly improving air clarity. For residents and visitors, the months of June through September are generally the most favorable for prolonged outdoor activities due to the lower dust load and cleaner air post-precipitation. However, sensitive individuals, particularly those with pre-existing respiratory conditions like asthma, should exercise caution during the peak of the Harmattan, when the combination of dry air and wind-blown dust can exacerbate irritation. During the onset of the dry season, it is advisable to limit vigorous outdoor exercise during early mornings when stagnant air conditions are most prevalent. By aligning activities with the moisture cycles of the wet season, one can maximize the health benefits of Kétou’s refreshing, albeit seasonally variable, tropical atmosphere.