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Ouïnhri, nestled in the Zou Prefecture of Benin (coordinates 7.0000° N, 2.4500° E), presents a unique geographic profile influencing its air quality. Situated in a transitional zone between the wooded savannas of northern Benin and the more humid coastal regions, the city’s terrain is gently undulating, characterized by low hills and valleys. Its elevation, though modest, contributes to localized microclimates. The surrounding landscape is predominantly agricultural, with small-scale farming dominating the rural areas immediately adjacent to Ouïnhri. This includes cultivation of crops like maize, cassava, and vegetables, often involving traditional burning practices for land clearing and residue management, a significant potential source of particulate matter. The urban–rural gradient is relatively sharp; the city transitions quickly from built-up areas to agricultural fields. While Ouïnhri lacks direct proximity to major rivers or lakes, it benefits from seasonal rainfall patterns characteristic of the tropical climate. The regional position within Benin places it away from major industrial hubs, minimizing large-scale industrial pollution. However, the city’s location within a fertile agricultural belt means that agricultural emissions, particularly during dry seasons when winds can carry smoke over considerable distances, are a key factor in local air quality. The prevailing winds, generally from the south-west, can transport pollutants from surrounding agricultural areas into the city, impacting air quality, especially during periods of stagnant air.

Ouïnhri’s tropical climate dictates a distinct wet and dry season cycle, profoundly impacting its air quality. The dry season, typically spanning November to March, presents the greatest air quality challenges. Reduced rainfall leads to lower atmospheric moisture, promoting the persistence of particulate matter, especially from agricultural burning. Wind patterns during this period can be variable, sometimes leading to stagnant air conditions where pollutants accumulate. Temperature inversions, common during the cooler nights of the dry season, trap pollutants near the ground, exacerbating the problem. The months of January and February often experience the poorest air quality due to a combination of widespread agricultural burning and stable atmospheric conditions. Conversely, the wet season (April to October) brings relief. Frequent rainfall effectively ‘washes’ pollutants from the atmosphere, significantly improving air quality. Higher humidity also reduces the suspension of particulate matter. However, periods of intense rainfall can lead to flooding, which can temporarily release pollutants from soil and water sources. During the wet season, outdoor activities are generally safer, particularly for vulnerable populations like children and the elderly. The transition months (March and October) can be unpredictable, with fluctuating air quality depending on the interplay of diminishing dry season conditions and the onset of rainfall. Individuals with respiratory conditions should monitor local conditions and limit outdoor exposure during periods of haze or smoke, especially during the dry season.