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Gaya, situated in the Dosso Region of Niger (coordinates 11.8853° N, 3.4549° E), occupies a geographically significant position within the Sahelian zone. The city’s terrain is predominantly flat, characteristic of the expansive plains that define this part of West Africa. Elevation is minimal, averaging around 220 meters above sea level, contributing to a lack of natural vertical mixing of air pollutants. Gaya lies within a transitional zone between the semi-arid Sahel and the slightly more humid Sudan savanna, influencing its climate and agricultural practices. The surrounding landscape is dominated by grasslands and sparse acacia woodlands, interspersed with agricultural fields – primarily millet, sorghum, and cowpea – which are crucial to the local economy. This proximity to intensive agricultural zones introduces potential sources of particulate matter, particularly during harvesting and land preparation. While not directly adjacent to major rivers, the Niger River is located approximately 150 kilometers to the south, influencing regional weather patterns and potentially impacting humidity levels. The urban–rural gradient around Gaya is gradual, with small villages and agricultural settlements blending seamlessly into the urban fabric. There are no major industrial belts immediately surrounding Gaya; however, the city serves as a regional market town, with increased vehicular traffic and associated emissions. The flat topography and limited natural ventilation exacerbate the potential for pollutant accumulation, especially during periods of stagnant air, making Gaya’s air quality particularly sensitive to local emission sources.

Gaya’s air quality follows a distinct seasonal pattern dictated by its Sahelian climate, characterized by a prolonged dry season and a shorter, less intense wet season. The dry season, spanning roughly from November to May, typically sees the poorest air quality. During these months, temperatures are high, and wind speeds are generally low, leading to atmospheric stability and frequent temperature inversions, trapping pollutants near the ground. Dust storms, a common feature of the Sahel, are also more frequent during this period, significantly increasing particulate matter concentrations. The Harmattan wind, a dry, dusty trade wind blowing from the Sahara, can further degrade air quality by transporting fine particles over long distances. Conversely, the wet season (June to October) brings a relative improvement in air quality. Rainfall helps to wash pollutants from the atmosphere, and increased humidity can help to suppress dust. However, agricultural activities, such as burning crop residue after harvest (typically in September and October), can temporarily elevate pollution levels. Fog, though infrequent, can also occur during the transition periods, trapping pollutants and reducing visibility. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during the dry season, particularly during periods of dust storms or stagnant air. Outdoor activities are generally more favourable during the wet season, although vigilance regarding agricultural burning is advised. The intensity of the monsoon influences the degree of relief from dust and pollutants, with stronger monsoon periods offering better air quality.