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Auchi, nestled in the heart of Edo State, Nigeria, occupies a strategically important position within the southwestern region. Located at approximately 7.0667° N, 6.2667° E, the city sits on a gently undulating plateau, part of the larger Niger-Benue Trough, characterized by a mix of derived savanna woodland and agricultural land. Its elevation, averaging around 300 meters above sea level, contributes to localized temperature variations and influences atmospheric stability. Auchi’s surrounding landscape is predominantly rural, a mosaic of small-scale farming plots cultivating crops like cassava, maize, and yam, interspersed with oil palm plantations – a significant economic driver for the region. The Etsako River flows nearby, though its influence on Auchi’s immediate microclimate is limited. The urban–rural gradient transitions relatively quickly, with the city acting as a commercial hub for the surrounding agricultural communities. While not directly adjacent to major industrial zones, Auchi’s role as a trading center means it experiences vehicular traffic from connecting routes, a key factor in its air quality profile. The plateau terrain can trap pollutants, particularly during periods of low wind speed. The city’s growth, while moderate, is driven by its market significance and proximity to Benin City, leading to increased construction activity and associated dust emissions. The local geology, composed primarily of sedimentary rocks, also influences the dispersion of airborne particulate matter. The prevailing winds generally flow from the southwest, impacting the distribution of pollutants across the city.

Auchi’s tropical savanna climate dictates a distinct wet and dry season cycle, profoundly impacting its air quality. The dry season, typically spanning from November to March, presents the most significant air quality challenges. Reduced rainfall leads to lower atmospheric moisture, promoting the accumulation of particulate matter, particularly dust originating from agricultural fields and construction sites. Temperature inversions, common during the cooler nights of this period, trap pollutants close to the ground, exacerbating the problem. Wind speeds are often lower during the dry season, further hindering pollutant dispersal. The Harmattan wind, a dry, dusty trade wind blowing from the Sahara Desert, frequently impacts Auchi during January and February, significantly degrading air quality with Saharan dust. The wet season, from April to October, brings relief through frequent rainfall, which naturally washes pollutants from the atmosphere. However, periods of intense rainfall can also lead to flooding, which can stir up sediment and temporarily worsen air quality. Humidity increases during the wet season, which can affect the respiratory system. Outdoor activities are generally more favorable during the wet season months of June to September. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during the dry season, particularly during Harmattan periods, and consider limiting prolonged outdoor exposure. Agricultural burning, a common practice at the start of the wet season to clear fields, can also contribute to localized air pollution spikes.