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Três Marias, nestled in the heart of Minas Gerais, Brazil, occupies a geographically significant position within the Brazilian Cerrado biome. Located at approximately -18.2058° latitude and -45.2419° longitude, the city sits at an elevation of around 750 meters (2,460 feet) above sea level, contributing to a relatively mild climate. The surrounding landscape is characterized by undulating plains and gently sloping hills, typical of the transition zone between the Brazilian Highlands and the Cerrado's vast savannas. The Rio São Francisco, a vital waterway for Brazil, flows nearby, influencing local humidity and microclimates. Três Marias’s urban fabric is a blend of historical architecture, reflecting its origins as a mining town, and more modern residential areas. The city’s economy is rooted in agriculture, particularly soybean and maize cultivation, alongside some cattle ranching, creating a rural-urban gradient extending outwards into the Cerrado. While not directly adjacent to major industrial belts, the region experiences agricultural activity that can contribute to particulate matter, especially during harvest seasons. The Cerrado’s vegetation, while generally sparse, can release biogenic volatile organic compounds (BVOCs), which, under certain atmospheric conditions, can react to form ozone. The terrain, with its gentle slopes, can sometimes trap pollutants, particularly during periods of low wind speed. The city’s location within a relatively open landscape generally allows for good air circulation, but localized sources of pollution can still impact air quality.

Três Marias experiences a tropical savanna climate, with distinct wet and dry seasons significantly influencing air quality. The dry season, typically from April to September, often sees a build-up of particulate matter. Reduced rainfall and lower humidity during these months contribute to drier vegetation and increased dust emissions from agricultural fields, particularly during plowing and harvesting. The lack of rainfall also limits the natural cleansing effect of precipitation, allowing pollutants to persist longer. Temperature inversions, common during the cooler dry season nights, can trap pollutants near the ground, exacerbating localized air quality issues. Conversely, the wet season (October to March) brings increased rainfall, which effectively washes pollutants from the atmosphere, leading to improved air quality. Higher humidity also reduces dust generation. However, intense rainfall events can occasionally lead to flooding and the release of contaminants from soil and runoff. The months of August and September, coinciding with peak harvest activity, are generally periods to be mindful of outdoor air quality, especially for individuals with respiratory sensitivities. During the wet season, while overall air quality is better, heavy downpours can temporarily impact visibility and potentially release mold spores. Sensitive groups, including children, the elderly, and those with pre-existing respiratory conditions, should monitor local conditions and limit prolonged outdoor exposure during periods of elevated particulate matter, particularly during the dry season’s harvest months.