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São Bernardo, Maranhão, nestled within the vast Brazilian Cerrado biome, presents a unique geographic profile influencing its air quality. Located at approximately -3.3608° latitude and -42.4178° longitude, the city sits on a gently undulating plateau, part of the larger Tocantins-Araguaia River basin. The surrounding landscape is dominated by the characteristic Cerrado vegetation – a mosaic of grasslands, savannas, and gallery forests – interspersed with agricultural lands. Elevation is relatively low, averaging around 150-200 meters above sea level, contributing to a tendency for stagnant air conditions, particularly during drier periods. The city’s position within Maranhão state places it within a region experiencing a pronounced wet and dry season cycle, impacting regional wind patterns and atmospheric stability. While São Bernardo itself is a relatively small urban center with a population of just under 27,000, it’s situated within a broader agricultural zone, with significant soybean and maize cultivation occurring in the surrounding areas. This proximity to agricultural activity introduces potential sources of particulate matter, particularly from soil erosion and fertilizer application. The urban–rural gradient is gradual, with small settlements and agricultural fields transitioning seamlessly into the city limits. The lack of significant industrial belts directly adjacent to São Bernardo mitigates some industrial pollution risks, but regional transportation corridors carrying goods to and from larger urban centers like Balsas can contribute to localized traffic-related air pollution. The flat terrain and limited natural barriers exacerbate the potential for pollutants to accumulate, especially when coupled with temperature inversions.

São Bernardo’s tropical climate dictates a distinct wet and dry season cycle, profoundly impacting its air quality. The dry season, typically spanning from May to September, is characterized by reduced rainfall, increased temperatures, and a significant decrease in wind speeds. This meteorological combination frequently leads to atmospheric stability and the formation of temperature inversions, trapping pollutants near the ground. Agricultural burning, a common practice for land clearing and crop residue removal, intensifies during this period, releasing substantial amounts of particulate matter and gases into the atmosphere. Consequently, air quality tends to be poorest during August and September. The onset of the wet season, from October to April, brings increased rainfall and higher humidity, which naturally scavenges pollutants from the air, leading to a noticeable improvement in air quality. Stronger winds associated with the monsoon-like rains also help disperse pollutants. However, heavy rainfall can occasionally lead to increased levels of mold spores and allergens, impacting respiratory health. During the transitional months of October and November, the combination of lingering dry season conditions and the initial rainfall can create periods of elevated particulate matter. Sensitive groups, including children, the elderly, and individuals with pre-existing respiratory conditions, should exercise caution during the dry season, limiting outdoor activities during peak pollution periods and ensuring adequate ventilation indoors. The wet season generally offers more favorable conditions for outdoor recreation, though vigilance regarding allergens remains important.