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Ndali serves as a critical crossroads in the Borgou Department of northern Benin, acting as a vital link between the southern coastal regions and the northern hinterlands. The urban character is defined by its role as a bustling transit hub, where commercial activity clusters along the primary transport arteries and regional trade. Situated within the Guinea-Savanna zone, the terrain is predominantly flat, characterized by a mix of open grasslands and scattered woody vegetation. This low-relief topography allows for the unimpeded movement of air masses but also means that local pollutants can linger during periods of atmospheric stability. The city is surrounded by an extensive agricultural belt, where the cultivation of cotton, maize, and yams dominates the landscape. This rural-urban gradient is porous, with agricultural activities directly influencing the local air quality through seasonal biomass burning. While Ndali lacks major heavy industrial complexes, its position on a primary transit route introduces a steady stream of diesel particulate matter from heavy-duty trucks. The absence of large bodies of water in the immediate vicinity means there is limited moderating maritime influence, leaving the city exposed to the harsh continental effects of the interior. Consequently, the air quality is a complex interplay between the emissions from road transport, the smoke from traditional cooking fires, and the natural influx of mineral dust from the Sahara, all shaped by the flat, open geography of the Borgou plateau.

The air quality in Ndali is governed by the tropical wet and dry climate, creating a distinct seasonal narrative. During the dry season, particularly from December to February, the city experiences the Harmattan, a northeasterly trade wind that carries vast quantities of mineral dust from the Sahara Desert. This period marks the annual peak in particulate matter, often resulting in a thick, hazy atmosphere that reduces visibility and irritates the chronic respiratory system. Temperature inversions during these cool mornings can trap pollutants close to the ground, exacerbating the impact of wood-smoke from domestic hearths. As the transition to the first rainy season occurs around April, the onset of convective storms provides a natural scrubbing mechanism, washing particulates from the sky and significantly improving air clarity. The peak rainy season from June to September brings the lowest pollution levels, as moisture suppresses dust and rainfall clears the atmosphere. However, the late dry season in November often sees a spike in pollution due to widespread agricultural slash-and-burn practices to prepare fields for planting. For sensitive groups, including children and the elderly, the Harmattan months are the most hazardous, requiring the use of masks and limited outdoor exertion during peak haze. Conversely, the rainy season offers the healthiest window for outdoor activity. Throughout the year, managing indoor air quality remains crucial, as the reliance on biomass fuels creates localized pollution peaks within homes, regardless of the broader meteorological conditions.