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Olho d’Água das Cunhãs, nestled in the state of Maranhão, Brazil, occupies a position within the transition zone between the Amazon rainforest and the Cerrado savanna. Located at approximately -4.1389 latitude and -45.1200 longitude, the city’s geography is characterised by a relatively flat terrain typical of the Maranhão interior. The surrounding landscape is predominantly agricultural, dominated by extensive cattle ranching and increasingly, soybean cultivation, a pattern common across this part of Brazil. The city itself is small, with a population of around 17,919, exhibiting a typical rural-urban gradient; denser settlement cores give way to scattered homesteads and pastureland. Its proximity to the Parnaíba River basin, though not immediately adjacent, influences local humidity and drainage patterns. The lack of significant industrial development within the city limits is notable, however, regional agricultural practices contribute to particulate matter through land clearing and burning. Air quality is therefore heavily influenced by seasonal agricultural activities and the prevailing wind patterns which can transport dust and smoke from surrounding areas. Elevation is low, increasing the potential for temperature inversions that trap pollutants near the ground. The urban form is relatively dispersed, limiting natural ventilation in some areas.

Olho d’Água das Cunhãs experiences a distinct wet and dry season, rather than traditional four seasons. Air quality is generally poorer during the dry season (roughly June to November). This is due to increased land preparation for planting, often involving controlled burns to clear vegetation for agriculture. These fires release significant amounts of particulate matter (PM2.5 and PM10) and other pollutants, exacerbated by lower wind speeds and reduced rainfall which limits atmospheric cleansing. The dry season also sees increased dust resuspension from unpaved roads and agricultural fields. The wet season (December to May) typically brings improved air quality. Increased rainfall effectively washes pollutants from the atmosphere, and higher humidity reduces dust levels. However, even during the wet season, localised pollution can occur from vehicle emissions and domestic wood burning. February and March, during peak rainfall, are generally the most favourable months for outdoor activity. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit outdoor exposure during the peak of the dry season (August-October) and be mindful of smoke haze. Monitoring wind direction is crucial; pollutants often drift from upwind agricultural areas.