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Kayes, situated in the Bouenza province of the Republic of the Congo, occupies a geographically significant position within the broader Congo Basin. Located at approximately -4.1683° latitude and 13.2933° longitude, the city’s terrain is characterized by gently undulating plains, transitioning into low hills to the east. This relatively flat landscape, typical of the coastal plains of the Congo, influences air circulation patterns, potentially trapping pollutants under certain meteorological conditions. Kayes lies near the Nianga River, a vital waterway for regional transport and agriculture, and its proximity to this river impacts local humidity and temperature, which in turn can affect the dispersion of airborne particles. The surrounding landscape is predominantly a mosaic of dense tropical rainforest and small-scale agricultural plots, primarily focused on cassava, maize, and plantains. This agricultural activity, while crucial for local livelihoods, can contribute to localized air pollution through the burning of vegetation for land clearing, particularly during the dry season. The urban–rural gradient around Kayes is gradual, with small villages and agricultural fields blending seamlessly into the city’s periphery. There are no major industrial belts immediately adjacent to Kayes, but regional logging operations and limited artisanal mining activities further inland can contribute to broader air quality concerns. The city’s elevation, relatively low, means it is susceptible to ground-level ozone formation during periods of high solar radiation and stagnant air.

Kayes experiences a tropical climate with distinct wet and dry seasons, significantly influencing its air quality profile. The dry season, typically spanning from June to September, is often characterized by lower rainfall and higher temperatures, leading to increased evapotranspiration and a reduction in atmospheric moisture. This drier air, coupled with periods of stagnant wind conditions, can exacerbate the accumulation of particulate matter, particularly from agricultural burning and dust resuspension. Temperature inversions, where cooler air is trapped beneath a layer of warmer air, are more frequent during this period, further hindering vertical mixing and trapping pollutants close to the ground. The wet season, from October to May, brings increased rainfall and higher humidity, which naturally helps to cleanse the atmosphere by washing away particulate matter and diluting gaseous pollutants. However, heavy rainfall can also lead to increased fungal spore counts, impacting respiratory health. Months like August and September, coinciding with peak agricultural burning, are generally periods to avoid strenuous outdoor activity, especially for individuals with respiratory sensitivities. Conversely, the months of March and April, following the heaviest rains, often offer the best air quality. Sensitive groups, including children, the elderly, and those with pre-existing respiratory conditions, should be particularly mindful of air quality during the dry season, limiting prolonged exposure to outdoor environments and taking precautions such as wearing masks when necessary. The interplay of these seasonal factors dictates a dynamic air quality landscape in Kayes.