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Buriti, a municipality nestled in the eastern reaches of Maranhão state, Brazil, presents a unique geographic context influencing its air quality. Located at -3.9419, -42.9250, the city sits within the transition zone between the Amazon rainforest and the Cerrado savanna, a landscape of rolling hills and scattered forests. The terrain is generally flat to gently undulating, typical of the eastern Maranhão plateau, with an elevation around 50-100 meters. Buriti is not directly on the coast, but is situated inland, approximately 60km from the Parnaíba River delta, a significant estuarine system. The surrounding area is predominantly agricultural, focused on subsistence farming and increasingly, large-scale soybean and corn cultivation. This agricultural activity, alongside limited industrial development concentrated around transport routes, contributes to potential particulate matter emissions. The urban-rural gradient is relatively sharp; Buriti itself is a small city of around 30,000 inhabitants, surrounded by sparsely populated rural areas. This proximity to agricultural lands means seasonal burning for land clearing is a key factor. The prevailing winds, influenced by the trade winds and regional weather systems, play a crucial role in dispersing or concentrating pollutants, often channeling them from agricultural zones towards the city center. The lack of significant topographical barriers allows for relatively easy air mass movement, but also means Buriti is vulnerable to pollutants originating from wider regional sources.

Buriti experiences a distinct wet and dry season, rather than traditional four seasons. Air quality in Buriti is most compromised during the dry season, typically from June to November. This period coincides with increased agricultural burning for land preparation, releasing substantial amounts of particulate matter (PM2.5 and PM10) and other pollutants. Lower humidity and stable atmospheric conditions during these months exacerbate the problem, trapping pollutants near the ground. Temperature inversions, common in the early mornings, further contribute to poor air quality. December to May marks the wet season, bringing relief from the dry season’s pollution. Rainfall effectively washes away particulate matter, and increased humidity reduces the likelihood of inversions. However, even during the wet season, localized pollution can occur from vehicle emissions and dust from unpaved roads. August and September are typically the worst months for respiratory health due to peak burning activity. Sensitive groups – children, the elderly, and individuals with pre-existing respiratory conditions – should limit outdoor exertion during the dry season. Monitoring wind direction is crucial; winds from agricultural areas signal potentially elevated pollution levels. The transition months (May and November) can be unpredictable, with fluctuating air quality.