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Ilesa is a historic city in southwestern Nigeria's Osun State, situated at coordinates 7.6167°N, 4.7167°E within the Yoruba cultural heartland. Nestled at approximately 400 meters above sea level on the undulating terrain of the Yoruba Plateau, the city occupies a transitional zone between the coastal rainforests to the south and the drier savanna to the north. This elevation provides some natural ventilation but also creates microclimatic conditions that can trap pollutants. Ilesa lies about 30 kilometers northeast of Osogbo, the state capital, and 100 kilometers from the Atlantic coast, placing it inland enough to avoid direct maritime influences but within reach of seasonal moisture-laden winds. The city is surrounded by mixed agricultural lands producing cocoa, yams, and cassava, with pockets of light manufacturing and artisanal mining contributing to local emissions. Urban expansion has created a distinct urban-rural gradient, with the densely populated core experiencing higher pollution concentrations from vehicular traffic, generator use, and domestic biomass burning, while outlying areas face dust from unpaved roads and agricultural burning. The absence of major water bodies nearby means limited natural cleansing through precipitation or humidity moderation, though seasonal rains provide temporary relief. Ilesa's position along transportation corridors connecting larger cities like Ibadan and Akure exacerbates transit-related pollution, while its location in a region with significant artisanal gold mining activities introduces particulate matter from dust and processing emissions.

Ilesa experiences a tropical savanna climate with distinct wet and dry seasons, shaping its air quality patterns throughout the year. The dry season, from November to March, brings the highest pollution levels, particularly in December and January when Harmattan winds from the Sahara Desert carry fine dust particles southward, significantly reducing visibility and increasing respiratory irritants. During these months, temperature inversions are common in the early mornings, trapping pollutants near the ground and creating hazardous conditions for outdoor activities, especially for sensitive groups like children, the elderly, and those with asthma or heart conditions. The wet season, from April to October, offers relief as monsoon rains wash pollutants from the air, with June through August being the cleanest months for outdoor exercise and recreation. However, high humidity during the rainy season can combine with emissions to form ground-level ozone on sunny days, though this is less pronounced than in coastal cities. September and October mark a transitional period with reduced rainfall but increasing agricultural burning, leading to moderate pollution spikes. For health protection, residents should avoid strenuous outdoor activities during peak Harmattan months and on days with visible haze, using masks when necessary. Sensitive groups should monitor local weather reports for dust advisories and plan indoor activities during pollution episodes, while the rainy season provides a safer window for outdoor engagement.