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Nioro, situated in the Kayes Region of Mali, occupies a strategic position within the Sahelian belt, a transitional zone between the Sahara Desert and West Africa’s savanna. Located at approximately 15.18°N, 9.55°W, the city’s geography is dominated by gently undulating plains, characteristic of the wider inland Niger Delta region. The terrain is largely flat, averaging around 220 meters above sea level, which unfortunately limits natural air dispersion, particularly during periods of atmospheric stability. Nioro sits near the banks of the Niger River, though the river’s influence on local air quality is somewhat moderated by the distance and the prevailing wind patterns. The surrounding landscape is a mosaic of agricultural land – primarily cotton and millet cultivation – interspersed with sparse acacia woodlands and grasslands. This agricultural activity, coupled with traditional burning practices for land clearing, contributes to localized particulate matter pollution. To the north and east, the landscape gradually transitions into drier Sahelian scrubland, while to the south and west, the fertile delta extends. The urban–rural gradient around Nioro is relatively sharp; the city acts as a regional market town and transport hub, drawing in rural populations and goods, which intensifies local activity and potential pollution sources. The lack of significant topographic barriers exacerbates the impact of emissions, trapping pollutants within the city’s footprint and limiting their dispersal. The region's semi-arid climate further influences air quality, with dry conditions promoting dust generation and hindering pollutant washout.

Nioro’s air quality follows a distinct seasonal pattern dictated by its tropical savanna climate. The dry season, spanning roughly from November to May, presents the most significant air quality challenges. During these months, reduced rainfall and consistently high temperatures create stable atmospheric conditions, often leading to temperature inversions, which trap pollutants near the ground. Wind speeds are generally lower during this period, further hindering dispersion. Agricultural burning, a common practice for preparing fields for planting, intensifies significantly in February and March, releasing substantial amounts of smoke and particulate matter. Dust storms, driven by strong, dry winds, are also more frequent, particularly in the early dry season (November-December), contributing to elevated levels of coarse particulate matter. The wet season, from June to October, brings a welcome respite. Increased rainfall effectively ‘washes out’ pollutants from the atmosphere, and higher humidity can help to settle dust particles. However, periods of intense rainfall can also lead to flooding, which can release pollutants from stagnant water sources. The monsoon winds, though generally beneficial for dispersion, can occasionally carry dust from the Sahara Desert, impacting air quality. The transitional months of May and October experience variable conditions, with a gradual shift in wind patterns and rainfall, leading to fluctuating air quality. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during the dry season, particularly during periods of agricultural burning and dust storms. Limiting outdoor exertion and wearing appropriate masks can help mitigate exposure.