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Alto Parnaíba, nestled in the southeastern Maranhão state of Brazil, occupies a geographically significant position within the Cerrado biome. Located at approximately -9.1108° latitude and -45.9300° longitude, the city’s terrain is characterized by undulating plains and gently sloping hills, typical of the transition zone between the Amazon rainforest and the drier savanna landscapes. The surrounding landscape is dominated by the Cerrado’s distinctive vegetation – a mosaic of grasslands, shrubs, and scattered trees adapted to seasonal drought. While not directly adjacent to major rivers, Alto Parnaíba benefits from proximity to smaller tributaries and seasonal streams that contribute to the region’s water resources. The urban footprint is relatively small, reflecting the city’s modest population of 11,109, and exhibits a clear urban–rural gradient, with agricultural activities – primarily cattle ranching and soybean cultivation – prevalent in the immediate periphery. This agricultural activity, coupled with potential burning practices during land clearing, can contribute to localized air quality challenges. The city’s elevation, though not exceptionally high, influences local air circulation patterns. The prevailing winds, often influenced by regional weather systems, play a crucial role in dispersing or concentrating pollutants. The lack of significant industrial belts within Alto Parnaíba itself means that air quality is primarily affected by regional agricultural practices and residential emissions, rather than large-scale industrial sources. The Cerrado’s unique soil composition also impacts dust levels, which can be a factor in air quality, particularly during drier periods.

Alto Parnaíba experiences a tropical savanna climate, defined by distinct wet and dry seasons, profoundly impacting its air quality profile. The dry season, typically spanning from May to September, is characterized by reduced rainfall, increased temperatures, and a higher frequency of windless days. This meteorological configuration often leads to temperature inversions, where a layer of warm air traps cooler air near the ground, hindering the vertical dispersion of pollutants. Agricultural burning, a common practice for land preparation during this period, significantly elevates particulate matter concentrations, creating hazy conditions and impacting visibility. The months of July and August are particularly susceptible to these conditions, making outdoor activities potentially challenging for sensitive individuals. Conversely, the wet season, from October to April, brings frequent rainfall and increased humidity. The abundant precipitation effectively ‘washes’ pollutants from the atmosphere, leading to a noticeable improvement in air quality. Stronger winds associated with the wet season also facilitate the dispersal of any remaining pollutants. While rainfall helps, periods of dense fog can occasionally trap moisture and pollutants close to the ground, creating localized pockets of reduced 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 strenuous activities on days with visible haze. During the wet season, while generally cleaner, vigilance regarding potential mold and mildew growth in damp environments remains important for respiratory health.