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São João do Araguaia, nestled in the southern reaches of Pará state, Brazil, occupies a geographically significant position within the Amazon biome. Located at approximately -5.3578° latitude and -48.7908° longitude, the city’s terrain is predominantly characterized by gently undulating lowlands, typical of the Amazon basin. The Araguaia River, a major tributary of the Tocantins River, flows nearby, influencing local climate and providing a vital water source. The surrounding landscape is a mosaic of dense tropical rainforest interspersed with areas of pastureland and small-scale agricultural plots, reflecting the region’s transition from pristine wilderness to a landscape shaped by human activity. The urban–rural gradient is relatively sharp; São João do Araguaia itself is a small municipality, and the immediate periphery quickly gives way to extensive agricultural zones and the vast expanse of the Amazon rainforest. Elevation is low, rarely exceeding 150 meters above sea level, which contributes to a stable atmospheric layer, potentially exacerbating localized pollution events. While large-scale industrial belts are absent, the presence of agricultural activities, particularly cattle ranching and soybean cultivation, introduces potential sources of particulate matter and ammonia into the air. The city’s location within the Amazon also means it experiences high humidity and rainfall, which can naturally cleanse the air, but also influence the dispersion of pollutants. The prevailing winds, often influenced by the Amazonian weather systems, play a crucial role in determining the movement of airborne contaminants.

São João do Araguaia’s tropical climate dictates a wet and dry seasonal cycle, profoundly impacting air quality. The wet season, typically spanning from November to April, brings consistent rainfall and high humidity. This abundant precipitation naturally acts as a scrubber, removing particulate matter and gaseous pollutants from the atmosphere, leading to generally improved air quality during these months. However, intense rainfall can also lead to soil erosion and the suspension of fine dust particles, temporarily degrading air quality. The dry season, from May to October, is characterized by reduced rainfall and increased temperatures. This period often sees a build-up of pollutants due to reduced atmospheric cleansing. Temperature inversions, where a layer of warm air traps cooler air near the ground, are more frequent during the dry season, hindering vertical mixing and concentrating pollutants. Agricultural burning, a common practice for land clearing and crop residue management, significantly contributes to particulate matter pollution during this time, particularly in September and October. The combination of reduced rainfall, temperature inversions, and agricultural activities creates conditions conducive to poorer air quality. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during the dry season, limiting prolonged outdoor exposure and avoiding areas with visible smoke. The high humidity throughout the year can also exacerbate respiratory issues for some individuals, regardless of the season. Periods of intense heat can also increase ground-level ozone formation, further impacting air quality.