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Iriba, nestled within the Wadi-Fira region of Chad (15.1167° N, 22.2500° E), occupies a geographically significant position on the edge of the Chadian Sahara. The city’s terrain is predominantly characterized by undulating sandy plains and sparse rocky outcrops, typical of the Sahelian transition zone. Elevation is relatively low, averaging around 450 meters above sea level, contributing to a stable atmospheric layer that can, under certain conditions, trap pollutants. Iriba’s location is crucial; it sits near the periphery of a significant agricultural zone, where traditional farming practices, often involving burning vegetation for land clearing and crop residue management, contribute to localized particulate matter. The surrounding landscape is dominated by arid grasslands and scattered acacia woodlands, offering limited natural air filtration. The urban–rural gradient around Iriba is gradual, with small villages and nomadic settlements blending into the wider desert environment. While Iriba lacks direct proximity to major rivers or lakes, seasonal watercourses occasionally flow through the area after rainfall, influencing humidity levels and potentially impacting aerosol composition. There are no major industrial belts immediately adjacent to Iriba, but regional trade routes pass through, bringing occasional vehicle emissions. The prevailing winds, generally from the north during the dry season, can transport dust and pollutants from distant sources, impacting air quality and visibility. The city’s compact urban form, with closely packed dwellings, can exacerbate localized pollution concentrations, particularly from cooking fires and limited vehicular traffic.

Iriba’s air quality follows a distinct seasonal pattern dictated by the region’s arid climate. The dry season, spanning roughly November to May, is characterized by consistently low rainfall and high temperatures. This period often witnesses a significant increase in particulate matter, primarily due to windblown dust from the surrounding Sahara and Sahel. Strong, persistent northerly winds lift fine sand and dust particles, reducing visibility and impacting respiratory health. Temperature inversions, common during the cooler nights of the dry season, can trap pollutants close to the ground, further worsening air quality. The months of January and February are typically the most challenging, with frequent dust storms and reduced air quality. Conversely, the brief wet season (June to October) brings a temporary respite. Rainfall helps to settle dust and wash pollutants from the atmosphere. However, the burning of agricultural residues after the harvest, typically in September and October, can lead to localized spikes in smoke and particulate matter. Humidity increases during this period, which can affect the dispersion of pollutants. Sensitive groups, including children, the elderly, and individuals with pre-existing respiratory conditions, should exercise caution during the dry season, limiting outdoor activity during peak dust storm periods. During the wet season, while overall air quality improves, caution is advised during and immediately after agricultural burning events. Maintaining indoor air quality through proper ventilation and avoiding exposure to smoke is crucial throughout the year.