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Ilobu, situated in Osun State, Nigeria, occupies a pivotal position within the Yoruba heartland of southwestern Nigeria. Located at approximately 7.8400°N latitude and 4.4860°E longitude, the city rests on gently undulating terrain, characteristic of the region’s pre-Cambrian basement complex. The elevation is modest, generally between 300-400 meters above sea level, influencing local wind patterns and contributing to temperature variations. Ilobu is not directly adjacent to major bodies of water, though it benefits from seasonal rainfall and groundwater resources. The surrounding landscape is predominantly agricultural, with extensive cultivation of crops like cocoa, yam, cassava, and plantain. This agricultural activity, while vital to the local economy, contributes to particulate matter pollution through land preparation, harvesting, and the burning of agricultural residue. The urban-rural gradient is relatively sharp, with Ilobu serving as a regional trading centre for surrounding rural communities. While not a major industrial hub, small-scale processing of agricultural products and local artisanal activities contribute to localised emissions. The city’s growth, like many in Nigeria, is rapid and often unplanned, leading to increased vehicle traffic and dust from unpaved roads, further impacting air quality. The prevailing winds, influenced by the Harmattan from the northeast and the moist air masses from the Atlantic, play a crucial role in dispersing or concentrating pollutants.

Ilobu experiences a distinct tropical wet and dry climate, profoundly influencing its air quality. The dry season, spanning November to March, is typically associated with poorer air quality. The Harmattan wind, blowing from the Sahara, carries significant amounts of dust and particulate matter, reducing visibility and exacerbating respiratory issues. Temperature inversions during cooler mornings in this period can trap pollutants near the ground. April to October marks the wet season, bringing relief from dust but also presenting unique challenges. Heavy rainfall can wash pollutants into waterways, impacting water quality, and increased humidity can foster mould growth indoors. However, rainfall generally clears the air of particulate matter. August and September, the peak of the rainy season, often see the cleanest air. The transition months – March/April and October/November – are periods of fluctuating conditions, with unpredictable wind patterns and potential for localised pollution build-up. Sensitive groups, including children, the elderly, and those with pre-existing respiratory conditions, should limit strenuous outdoor activity during the Harmattan and periods of high humidity. Monitoring local weather patterns and avoiding peak traffic hours are also advisable. The burning of agricultural waste after harvest in November/December significantly degrades air quality.