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Yei, situated in Central Equatoria State, South Sudan, occupies a crucial position within the country’s agricultural heartland. Located at approximately 4.0904°N, 30.6800°E, the city rests on gently undulating terrain, part of the broader East African Plateau. The elevation, around 600 meters above sea level, contributes to relatively moderate temperatures, though humidity remains consistently high. Yei is surrounded by lush, fertile land primarily dedicated to agriculture – coffee, cassava, and various fruits are key crops. This extensive agricultural activity, while vital to the local economy, introduces significant particulate matter into the air through land preparation (often involving burning), harvesting, and the drying of crops. The city’s proximity to the Nile River system, though not immediately adjacent, influences local humidity and can contribute to the formation of fog, trapping pollutants near the ground. The urban-rural gradient is relatively sharp; Yei itself is a growing urban centre, but quickly transitions to rural farmland. Limited industrial development within Yei itself means the primary pollution sources are largely non-industrial, stemming from domestic fuel use (wood and charcoal) and agricultural practices. Dust from unpaved roads is also a significant contributor, particularly during the dry season. The surrounding landscape offers limited natural ventilation, exacerbating localised pollution events.

Yei experiences a distinct wet and dry season, dictating the city’s air quality patterns. The dry season, roughly November to April, sees a significant increase in particulate matter. Agricultural burning for land preparation is most prevalent during this period, releasing substantial smoke and ash. Dust from unpaved roads, stirred up by vehicle traffic and wind, also contributes heavily. Temperature inversions, common during the cooler nights of the dry season, trap pollutants close to the ground, worsening air quality. February and March are typically the months with the poorest air quality. The onset of the wet season (May-October) brings a dramatic improvement. Rainfall effectively washes away dust and suppresses agricultural burning. However, increased humidity can promote mould growth indoors, impacting respiratory health. While overall particulate matter decreases, the wet season can also see localised flooding, potentially spreading contaminants. September and October, as the rains begin to subside, can experience a temporary increase in pollutants as drying activities resume. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit outdoor exposure during the peak of the dry season and take precautions during periods of high humidity. Monitoring local conditions and staying indoors when visibility is reduced is advisable.