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Olímpia, nestled in the interior of São Paulo state, Brazil, occupies a gently undulating terrain within the Bauru Plateau. Its coordinates (-20.7369, -48.9150) place it approximately 430 meters above sea level, a moderate elevation that influences local atmospheric circulation. The city is not directly adjacent to large bodies of water, though the Rio Tietê flows nearby, impacting regional humidity. Olímpia’s urban character is defined by a blend of agricultural influence and growing tourism, particularly related to its thermal parks. Surrounding the city is a landscape dominated by sugarcane plantations and cattle ranching, typical of the São Paulo interior. This agricultural activity contributes to seasonal particulate matter from field preparation and burning, while the sugarcane processing generates localised emissions. The urban-rural gradient is relatively sharp, transitioning quickly from denser residential areas to expansive agricultural lands. The regional climate is tropical savanna, characterised by distinct wet and dry seasons. The lack of significant topographical barriers means that wind patterns play a crucial role in dispersing or concentrating pollutants, with prevailing winds often originating from the south-southeast. The city’s position within a broader agricultural belt means it’s susceptible to long-range transport of pollutants from other areas.

Olímpia experiences a pronounced wet and dry season cycle that heavily influences air quality. The wet season, typically from November to March, brings increased rainfall which effectively scrubs the atmosphere, leading to generally improved air quality. Higher humidity also suppresses dust and particulate matter. However, intense rainfall can also lead to localised flooding and the spread of pollutants from agricultural runoff. The dry season, from May to September, presents the most challenging air quality conditions. Reduced rainfall allows pollutants to accumulate, and the drier vegetation is more susceptible to wildfires, contributing significantly to particulate matter (PM2.5 and PM10). August and September are often the worst months, coinciding with peak sugarcane burning practices. Temperature inversions, common during the cooler dry season nights, trap pollutants near the ground, exacerbating the problem. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit strenuous outdoor activity during these periods. Fog, prevalent in the cooler months, can also trap pollutants. April and October offer a transitional period with moderate conditions, generally favouring outdoor activities. Monitoring wind direction is crucial, as pollutants can be transported from surrounding agricultural areas.