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Tonj, situated in the heart of Warrap State, South Sudan, occupies a geographically challenging yet strategically important position within the Bahr el Ghazal region. Located at approximately 7.2739°N, 28.6775°E, the town rests on relatively flat, low-lying terrain characteristic of the vast floodplains formed by the Bahr el Ghazal River system. The surrounding landscape is dominated by *toich* grasslands and seasonally flooded areas, transitioning into wooded savanna further afield. Tonj’s elevation is modest, contributing to limited natural dispersion of pollutants. The urban character is largely defined by its role as a market and administrative centre for the surrounding rural communities, resulting in a dispersed settlement pattern rather than a densely concentrated urban core. The immediate vicinity is overwhelmingly agricultural, with subsistence farming being the dominant economic activity. This agricultural practice, while vital for livelihoods, contributes to particulate matter pollution through land clearing and seasonal burning of vegetation. The urban-rural gradient is sharp; Tonj represents a concentrated point of activity within a largely rural expanse. The lack of significant industrial development means the primary air quality concerns stem from localized sources and regional dust transport, exacerbated by the flat topography and limited wind flow.

Tonj experiences a distinct wet and dry season, profoundly influencing its air quality. The dry season, roughly November to April, is characterized by consistently high temperatures and minimal rainfall. This period sees a significant increase in airborne dust and particulate matter, stirred up by winds and agricultural activities like bush burning to prepare fields for planting. January and February are typically the dustiest months, posing risks to respiratory health. The wet season, from May to October, brings relief from dust but introduces new challenges. While rainfall washes away some particulate matter, increased humidity can trap pollutants closer to the ground, and stagnant air conditions are common. The peak of the wet season, August and September, can see localized flooding which disrupts sanitation and potentially increases biological contaminants in the air. Temperature inversions, though not as pronounced as in temperate climates, can occur during cooler nights within both seasons, trapping pollutants. Sensitive groups – children, the elderly, and those with pre-existing respiratory conditions – should limit strenuous outdoor activity during the dry season and take precautions during periods of heavy rainfall and flooding. Monitoring wind direction is crucial, as dust plumes from surrounding areas can rapidly impact Tonj.