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Formoso do Araguaia, nestled in the heart of Tocantins, Brazil, occupies a unique geographical position within the Cerrado biome. The city’s coordinates (-11.7969, -49.5289) place it on the eastern bank of the Araguaia River, a major tributary of the Tocantins River. The terrain is generally flat, characteristic of the Amazon-Cerrado transition zone, with a subtle undulation towards the interior. Elevation is relatively low, averaging around 150-200 meters above sea level. This flatness contributes to limited natural air dispersion. Formoso do Araguaia’s urban character is that of a developing regional hub, serving surrounding agricultural areas. The dominant land use is extensive cattle ranching and soybean cultivation, creating a significant agricultural zone immediately surrounding the city. The urban-rural gradient is sharp, transitioning quickly from the small city center to vast open grasslands and forested areas. Dust from agricultural activities, particularly during dry periods, is a key factor influencing local air quality. The Araguaia River, while providing a water source, can also contribute to humidity and potentially trap pollutants during temperature inversions. The lack of significant industrial belts within the immediate vicinity means that agricultural emissions are the primary concern, though long-range transport from deforestation further north can also play a role.

Formoso do Araguaia experiences a distinct wet and dry season, rather than traditional four seasons. Air quality is generally better during the wet season (October to April) due to rainfall effectively washing particulate matter from the atmosphere. However, high humidity can also promote the formation of mold and allergens. The dry season (May to September) presents the most significant air quality challenges. This period coincides with increased agricultural activity – land preparation, planting, and harvesting – leading to higher levels of dust and particulate matter (PM10 and PM2.5) in the air. Temperatures are also highest during the dry season, exacerbating the problem through increased evaporation and potential for temperature inversions, trapping pollutants near the ground. August and September are typically the months with the poorest air quality. Winds are generally light and variable, offering limited dispersion. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should limit strenuous outdoor activity during these months. Monitoring for smoke from agricultural burns is crucial. The transition periods – October and April – offer the most favourable conditions for outdoor activities, with moderate temperatures and improving air quality.