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Chèddra, situated in Barh-El-Gazel, Chad, occupies a challenging geographical position within the Sahelian zone. Located at approximately 13.4428°N, 16.0508°E, the city is characterized by a relatively flat terrain, typical of this part of central Africa, with an elevation generally below 300 meters. This low-lying landscape contributes to limited natural dispersion of pollutants. The surrounding landscape is predominantly semi-arid savanna, transitioning to desert further north and east. Chèddra isn’t directly adjacent to a major body of water, though seasonal watercourses and ephemeral lakes appear during the rainy season. The urban-rural gradient is sharp; the city itself is a concentrated settlement amidst a sparsely populated agricultural zone, primarily focused on subsistence farming and livestock rearing. Dust from agricultural activities and the natural erosion of the dry soil are significant contributors to particulate matter. While Chèddra isn’t a major industrial hub, localized brick-making and small-scale processing of agricultural products contribute to localized emissions. The city’s position within a broad depression can also exacerbate temperature inversions, trapping pollutants near the ground. The prevailing wind patterns, influenced by the Harmattan winds from the Sahara, further impact air quality by transporting dust and sand southward.

Chèddra experiences a distinct wet and dry season, heavily influencing its air quality. The dry season, roughly from November to May, is characterized by consistently poor air quality. The Harmattan winds, laden with Saharan dust, dominate this period, dramatically increasing particulate matter concentrations. January and February are typically the worst months, with reduced visibility and heightened respiratory issues. Temperature inversions are also common during the cooler nights of the dry season, trapping pollutants close to the ground. The onset of the wet season in June brings a temporary improvement. Rainfall washes away dust and suppresses particulate matter, offering a respite. However, increased humidity can also promote the growth of mold and allergens. July and August, the peak of the rainy season, generally have the best air quality, though localized flooding can stir up sediment. As the wet season wanes in September and October, dust levels begin to rise again. Sensitive groups – children, the elderly, and those with pre-existing respiratory conditions – should limit outdoor activity during the dry season and take precautions, such as wearing masks, when dust storms occur. Monitoring local weather patterns is crucial for anticipating pollution spikes.