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São João Evangelista, nestled in the heart of Minas Gerais, Brazil, occupies a unique geographic position within the expansive Brazilian Highlands. Located at coordinates -18.5478, -42.7628, the city’s terrain is characterized by rolling hills and valleys, typical of the region’s eroded plateau landscape. The elevation, while not extreme, contributes to localized meteorological patterns influencing air quality. The city is situated relatively close to the São Francisco River, a vital waterway that, while providing irrigation for surrounding agriculture, can also contribute to humidity and potential fog formation, trapping pollutants. The surrounding landscape is predominantly agricultural, with significant areas dedicated to cattle ranching and crop cultivation, including coffee and corn. This agricultural activity, while economically important, introduces potential sources of particulate matter from land preparation, harvesting, and the use of fertilizers. The urban-rural gradient is relatively sharp, with the city centre transitioning quickly to rural farmland. There are no major industrial belts directly within São João Evangelista, however, regional industrial activity further south can occasionally contribute to long-range transport of pollutants. The city’s position within a valley can exacerbate pollutant concentration during periods of atmospheric stability, limiting dispersion.

São João Evangelista experiences a distinct wet and dry season, rather than traditional four seasons. Air quality is generally better during the wet season (October to April) due to increased rainfall which effectively washes particulate matter from the atmosphere. However, high humidity can also promote the formation of mold and allergens, impacting respiratory health. The dry season (May to September) presents the greatest air quality challenges. Reduced rainfall means pollutants accumulate, and agricultural burning, common during land preparation for the next planting cycle, significantly increases particulate matter levels. August and September are typically the months with the poorest air quality. Temperature inversions, where a layer of warm air traps cooler air below, are frequent during the cooler dry season mornings, exacerbating pollution. Winds are generally light during this period, further limiting dispersion. Sensitive groups – children, the elderly, and those with pre-existing respiratory conditions – should limit strenuous outdoor activity during the dry season, particularly in the mornings. Monitoring local conditions and staying indoors on days with visible haze is advisable. The transition periods, October and May, offer the most favourable conditions for outdoor activities.