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Mongo, situated in the Guéra region of Chad, occupies a geographically challenging position within the Sahelian zone. Located at coordinates 12.1837°N, 18.7000°E, the city rests on a relatively high plateau, approximately 580 meters above sea level. This elevation moderates temperatures somewhat, but doesn’t negate the harshness of the surrounding arid and semi-arid landscape. The terrain is characterized by undulating plains interspersed with rocky outcrops and seasonal watercourses – *wadis* – that quickly dry after the brief rainy season. Mongo isn’t proximate to any major bodies of permanent water; the nearest significant water source is Lake Chad, a considerable distance to the west. The urban character of Mongo is typical of a regional trading center in Chad, with a relatively low-density settlement pattern transitioning rapidly into rural agricultural lands dominated by subsistence farming and pastoralism. Dust from these agricultural activities, combined with the naturally erodible soils, contributes significantly to particulate matter in the air. The city’s position within a broad north-south transition zone means it’s susceptible to dust plumes originating from both the Sahara Desert to the north and degraded lands further south. The limited industrial activity is largely concentrated around small-scale processing of agricultural products, adding to localised pollution sources. The urban-rural gradient is steep, with air quality deteriorating noticeably closer to the city center due to vehicle emissions and domestic fuel burning.

Mongo experiences a distinct bi-seasonal climate, characterized by a wet season (roughly June to September) and a prolonged dry season. Air quality in Mongo is markedly worse during the dry season, peaking between November and May. This is due to several factors. The lack of rainfall means dust isn’t washed from the atmosphere, leading to high concentrations of particulate matter, particularly PM10 and PM2.5. Harmattan winds, blowing from the Sahara, exacerbate this issue, carrying vast quantities of dust southward. Temperature inversions, common during the cooler nights of the dry season, trap pollutants near the ground. The wet season offers temporary relief, as rainfall suppresses dust and washes away some pollutants. However, even during the wet season, localised pollution from vehicle exhaust and biomass burning for cooking remains a concern. October and November, the transition months, are particularly problematic as residual dust from the dry season combines with early dry-season burning. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit outdoor activity during the dry season, especially on windy days. Wearing masks can offer some protection. Avoiding cooking with solid fuels indoors is also crucial to minimise exposure to indoor air pollution.