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Ouésso, nestled in the Sangha region of the Republic of the Congo, occupies a geographically significant position within the Congo Basin rainforest. Located at approximately 1.6106° N, 16.0514° E, the city’s terrain is predominantly low-lying, characterized by gently undulating plains dissected by numerous small rivers and streams, a consequence of the region’s extensive fluvial network. The elevation rarely exceeds 300 meters above sea level, contributing to a relatively stable atmospheric layer. Ouésso sits on the edge of the Lefini Department, bordering Cameroon and the Central African Republic, placing it within a crucial transboundary ecosystem. The surrounding landscape is overwhelmingly dominated by dense tropical rainforest, a vast expanse of biodiversity that influences local climate and air circulation patterns. Agriculture, primarily small-scale subsistence farming (manioc, plantains, maize), is the dominant land use in the immediate vicinity, creating a gradual urban–rural gradient. While there are no major industrial belts directly adjacent to Ouésso, logging activities are prevalent in the surrounding forests, and occasional transport of timber through the city can contribute to localized particulate matter. The Sangha River, though not directly bordering the city center, plays a vital role in regional hydrology and influences humidity levels. The city’s location deep within the rainforest means that air quality is inherently linked to the health and stability of this ecosystem, with deforestation and unsustainable practices posing potential long-term threats.

Ouésso experiences a tropical climate with distinct wet and dry seasons, significantly impacting air quality dynamics. The wet season, typically spanning from March to November, brings consistent rainfall and high humidity. While the rain naturally helps to cleanse the atmosphere by removing particulate matter, the increased humidity can trap pollutants closer to the ground, particularly during periods of reduced wind. The dry season, from December to February, is characterized by lower rainfall and increased sunshine. This often leads to a build-up of dust and smoke from agricultural burning practices, a common method for land clearing and crop residue disposal. Stagnant air conditions, occasionally occurring during the transition periods between seasons, can exacerbate this issue, trapping pollutants and creating localized pockets of poorer air quality. Fog, though infrequent, can also form during cooler nights, further reducing air dispersion. During the wet season, sensitive individuals, such as those with respiratory conditions, may experience relief from drier air, but the high humidity can still trigger discomfort. The dry season presents a greater risk, and outdoor activities should be limited during periods of visible smoke or haze. Children, the elderly, and individuals with pre-existing respiratory or cardiovascular illnesses are particularly vulnerable and should take extra precautions, such as wearing masks and avoiding strenuous activity during peak pollution episodes. Maintaining good ventilation indoors and monitoring local conditions are crucial for minimizing exposure.