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Arari, a municipality nestled in the eastern portion of Maranhão state, Brazil, occupies a relatively flat terrain within the Gurupi-Parnaíba plain. Its coordinates (-3.4539, -44.7800) place it inland, approximately 150km from the Atlantic coastline. The surrounding landscape is dominated by transitional ecosystems – a mosaic of Cerrado savanna woodlands gradually giving way to areas of denser, humid tropical forest as one moves eastward. The Parnaíba River, a major waterway, lies to the west, influencing regional humidity but not directly impacting Arari’s immediate urban environment. Arari’s urban character is typical of a smaller Brazilian interior city, with a central core surrounded by expanding residential areas and agricultural land. The primary economic driver is agriculture, particularly soybean and corn cultivation, alongside cattle ranching. This agricultural activity, while vital to the local economy, contributes significantly to potential air quality concerns through dust from land preparation, pesticide application, and biomass burning for land clearing. The urban-rural gradient is relatively sharp, with limited heavy industry within the city itself, but increasing agricultural intensification in the surrounding areas. The flat topography limits natural dispersion of pollutants, potentially exacerbating localized air quality issues, especially during drier periods. Understanding this interplay between land use, climate, and terrain is crucial for assessing and mitigating air pollution in Arari.

Arari experiences a distinct wet and dry season, rather than traditional four seasons. Air quality in Arari is most compromised during the prolonged dry season, typically from June to November. This period sees reduced rainfall, leading to increased dust resuspension from agricultural activities and unpaved roads. Biomass burning, often employed for land preparation for the next planting season, is also prevalent during these months, releasing significant particulate matter and other pollutants. Temperature inversions, common during the cooler nights of the dry season, trap pollutants near the ground, worsening air quality. December to May marks the wet season, bringing relief from dust and smoke. Rainfall effectively washes pollutants from the atmosphere, and increased humidity reduces dust resuspension. However, even during the wet season, localized pollution can occur from vehicle emissions and smaller-scale burning. Sensitive groups – children, the elderly, and individuals with respiratory conditions – should be particularly cautious during the dry season, limiting outdoor exertion and considering the use of respiratory protection. The months of December and January generally offer the most favourable air quality for outdoor activities. Monitoring wind patterns is also important; winds from agricultural areas can carry pollutants into the city.