São João dos Poleiros Air Quality Index (AQI)

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São João dos Poleiros, nestled in the interior of Maranhão state, Brazil, occupies a relatively flat terrain at approximately 100 meters above sea level. Its coordinates (-5.1000, -43.8500) place it within the transition zone between the Amazon rainforest and the Cerrado savanna, a landscape characterized by scattered forests and grassy plains. The city’s location is deeply intertwined with the Parnaíba River basin, though it isn’t directly on the river itself, being situated inland. This proximity influences local humidity and temperature patterns. The surrounding landscape is predominantly agricultural, with significant areas dedicated to soybean and corn cultivation, alongside cattle ranching. While not a major industrial hub, regional agricultural processing contributes to localized emissions. The urban-rural gradient is quite sharp; the city centre is compact, quickly giving way to extensive farmland. This proximity to agricultural activities is a key factor influencing air quality, as seasonal burning for land preparation releases particulate matter. The prevailing winds, generally from the east during the wet season and shifting to the southwest during the dry season, play a crucial role in dispersing or concentrating pollutants. The lack of significant topographical features means pollutants aren’t readily flushed out by valley breezes or channeled by mountains, increasing the potential for stagnation.

São João dos Poleiros experiences a distinct wet and dry season, rather than traditional four seasons. Air quality is generally better during the wet season (roughly November to April) due to increased rainfall which effectively washes particulate matter from the atmosphere. Higher humidity also suppresses dust. However, this period can see localized flooding impacting sanitation and potentially increasing biological pollutants. The dry season (May to October) presents the greatest air quality challenges. This is when agricultural burning for land clearing is most prevalent, releasing significant amounts of smoke and particulate matter, particularly PM2.5 and PM10. Temperature inversions, common during the cooler nights of the dry season, trap pollutants near the ground, exacerbating the problem. August and September are typically the worst months for air quality. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit strenuous outdoor activity during these periods. The shifting winds can bring smoke from distant fires, impacting air quality even when local burning is minimal. Monitoring wind direction is crucial. Even during the wet season, occasional dry spells can lead to dust resuspension, requiring vigilance.