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Cotonou, Benin's economic capital and largest city, occupies a strategic position on the narrow strip of land between the Atlantic Ocean's Gulf of Guinea and Lake Nokoué, creating a unique coastal geography that profoundly influences its air quality. Situated in the Littoral Department at just 6.3654°N, 2.4183°E, the city rests on flat, low-lying terrain with an average elevation of only 3 meters above sea level, limiting natural ventilation and allowing pollutants to accumulate near ground level. Cotonou's urban character is defined by its dual role as Benin's primary port and commercial hub, with dense urban development concentrated along the coast and extending inland toward agricultural zones. The city's location between the ocean and lake creates a distinctive microclimate where sea breezes can disperse pollutants during certain periods, but also traps emissions when winds are calm. Surrounding landscapes include coastal lagoons, marshy areas, and expanding peri-urban agricultural belts that contribute biomass burning emissions. The urban-rural gradient shows intense pollution sources concentrated in the port area and along major transportation corridors, particularly the Cotonou-Porto-Novo highway, where vehicle exhaust and road dust dominate. Industrial emissions emanate primarily from the port's activities and scattered manufacturing facilities, while domestic biomass cooking remains widespread in informal settlements. This geographic configuration—coastal yet poorly ventilated, urban yet interspersed with agricultural practices—creates complex pollution dynamics where marine influences compete with terrestrial emissions to shape Cotonou's air quality challenges.

Cotonou's air quality follows a distinct seasonal pattern driven by the interplay between Harmattan winds, monsoon systems, and local emission sources. During the dry season from November through February, pollution peaks dramatically as northeast Harmattan winds transport Saharan dust particles into the region while simultaneously suppressing rainfall that would otherwise cleanse the atmosphere. These months experience the highest concentrations of particulate matter from combined sources: road dust becomes airborne in dry conditions, vehicle exhaust accumulates under temperature inversions, and increased waste burning and domestic cooking emissions persist. Sensitive groups including children, elderly residents, and those with respiratory conditions should minimize outdoor activities during morning and evening hours when pollution concentrations are highest. From March through May, the transition to the rainy season brings some relief as increasing precipitation washes pollutants from the air, though occasional dust storms can still cause temporary spikes. The main rainy season from June to September offers the cleanest air conditions, with southwest monsoon winds bringing cleaner oceanic air and frequent rainfall effectively scrubbing the atmosphere—this period is optimal for outdoor activities. October marks another transition period as rains diminish and pollution begins to rebuild ahead of the Harmattan season. Throughout the year, coastal fog can occasionally trap pollutants near the surface, particularly during overnight and early morning hours. Health guidance emphasizes monitoring local air quality reports during peak pollution months and using protective masks when pollution levels are elevated, especially for vulnerable populations.