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São Francisco, Minas Gerais, nestled within the Serra da Mantiqueira mountain range, occupies a geographically significant position in southeastern Brazil. Its coordinates (-15.9489, -44.8639) place it at an elevation of approximately 880 meters (2887 feet) above sea level, contributing to a cooler, more temperate climate compared to lower-lying regions of Minas Gerais. The surrounding landscape is dominated by rolling hills, dense Atlantic Forest remnants, and small agricultural plots, creating a distinct urban–rural gradient. The city’s terrain is characterized by steep slopes and valleys, influencing urban development patterns and potentially impacting air circulation. While not directly adjacent to a major river, São Francisco benefits from several smaller streams and springs originating in the Mantiqueira range, providing a crucial water source. The region’s economy is a blend of agriculture (coffee, sugarcane, and livestock farming are prevalent in the broader area) and small-scale industry, primarily focused on processing agricultural products. Larger industrial belts are located further east, towards the metropolitan areas of Belo Horizonte and São Paulo, but their influence, particularly in terms of transported pollutants, can still be felt. The mountainous terrain often traps air masses, particularly during periods of stable atmospheric conditions, which can exacerbate localized air quality issues. The Atlantic Forest, though fragmented, plays a vital role in filtering pollutants and regulating humidity, but its diminished extent limits its overall impact. The city’s relatively small population (52,762) means that local emissions are less of a concern than regional transport of pollutants.

São Francisco’s climate, typical of the Brazilian Highlands, exhibits a distinct wet and dry season rather than the four traditional seasons. The dry season, generally from April to September, often brings clearer skies and reduced rainfall, but also heightened air quality concerns. During this period, temperature inversions are more frequent, trapping pollutants closer to the ground, particularly in the valleys. The lack of rainfall means fewer natural cleansing events, allowing particulate matter to accumulate. Agricultural burning, a common practice in the surrounding rural areas to clear land for planting, significantly contributes to elevated particulate levels during the dry season, especially in August and September. The wet season, from October to March, brings increased rainfall and higher humidity, which naturally washes away pollutants and improves air quality. Stronger winds associated with convective storms also help disperse stagnant air. However, heavy rainfall can occasionally lead to increased levels of mold and fungal spores, impacting respiratory health. Fog, common during the cooler months of June and July, can also trap pollutants, creating localized pockets of poor air quality. Sensitive groups, such as children, the elderly, and individuals with respiratory conditions, should exercise caution during the dry season, limiting outdoor activities during periods of visible haze or smoke. Maintaining indoor air quality through proper ventilation and air filtration is also recommended. The transition months of March and October often experience variable conditions, with periods of both improved and degraded air quality, requiring vigilance and awareness of local weather patterns.