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Iwo, located in Osun State, Nigeria, sits at coordinates 7.6333° N, 4.1833° E, serving as a critical urban node within the Yoruba heartland. The city is situated in a transition zone between the tropical rainforest belt to the south and the more open Guinea savanna to the north. This unique positioning influences its terrain, which is characterized by gently undulating hills and tropical plains. Iwo’s urban character is deeply rooted in its traditional history, yet it faces modern pressures from rapid population expansion and agricultural intensification. The city’s elevation, while modest, provides a subtle relief that influences local wind patterns, though it remains largely dictated by the broader regional atmospheric circulation of the Gulf of Guinea. The surrounding landscape consists of mosaics of secondary forests, smallholder cocoa plantations, and subsistence farmlands, which create a distinctive urban–rural gradient. In terms of air quality, Iwo’s location is a double-edged sword. While it lacks the heavy industrial mega-factories found in Lagos, the city experiences localized air quality challenges driven by biomass burning, vehicular emissions from outdated transport fleets, and regional dust transport. The lack of significant large-scale industrial belts means that pollution is predominantly localized and ground-level. However, during the harmattan season, the city’s geographic exposure to north-easterly trade winds brings significant particulate matter from the Sahara. The urban morphology, characterized by dense, unplanned residential clusters and narrow street networks, complicates the dispersion of these pollutants, often trapping smoke and dust in the city’s core, thereby impacting the overall respiratory health of its residents.

Iwo experiences a distinct tropical wet and dry climate that dictates the rhythm of air quality throughout the year. The dry season, typically spanning from November to March, is dominated by the harmattan—a dry, dusty trade wind originating from the Sahara Desert. During these months, air quality frequently deteriorates as fine particulate matter (PM2.5) blankets the region, reducing visibility and increasing the concentration of atmospheric aerosols. This period is exacerbated by local agricultural practices, specifically the burning of crop residues and brush clearing, which introduce significant amounts of smoke and carbonaceous particles into the local atmosphere. Sensitive groups, including those with asthma or chronic obstructive pulmonary disease, should exercise extreme caution during the peak harmattan months of December and January, often favoring indoor activities during the early morning hours when cool temperatures can lead to localized thermal inversions that trap pollutants near the surface. Conversely, the wet season, which lasts from April to October, brings relief through the influence of the moisture-laden south-westerly monsoon winds from the Atlantic Ocean. Frequent, intense precipitation events act as a natural atmospheric scrubber, effectively washing out suspended particulates and significantly improving air quality. The lush vegetation growth during this period also aids in carbon sequestration and dust suppression. For residents, the late wet season—specifically July and August—offers the cleanest air of the year, making it the most favorable time for outdoor exercise. Nevertheless, residents should remain vigilant during transitional months, as rapid shifts in humidity and wind patterns can lead to unpredictable spikes in pollution levels.