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Serrana, a municipality nestled in the state of São Paulo, Brazil, occupies a unique geographic position within the southeastern region of the country. Located at coordinates -21.2108, -47.5958, the city’s terrain is characterized by gently rolling hills, typical of the state’s interior plateau. With an elevation around 600 meters, Serrana benefits from a moderate climate, but this also influences air quality. The surrounding landscape is a mosaic of sugarcane plantations – São Paulo state is a major producer – and patches of Atlantic Forest remnants. This agricultural dominance is a key factor in local pollution patterns, particularly during sugarcane harvest and burning. Serrana isn’t directly adjacent to large bodies of water, though the Rio das Almas flows nearby, influencing local humidity. The urban-rural gradient is relatively sharp; the city centre is densely populated, while the periphery quickly transitions into agricultural land. While not a major industrial hub itself, Serrana’s proximity to larger industrial centres in the São Paulo metropolitan area means it can experience the effects of long-range pollutant transport. The prevailing winds, generally from the south and southeast, can carry pollutants from these areas, impacting Serrana’s air quality, especially during periods of atmospheric stability. The city’s relatively small size and limited public transport infrastructure contribute to vehicle emissions as a significant local source.

Serrana experiences a distinct wet and dry season, rather than traditional four seasons. Air quality in Serrana is most compromised during the dry season, typically from May to September. This period coincides with the sugarcane harvest, and unfortunately, the practice of pre-harvest burning is still prevalent, releasing substantial particulate matter (PM2.5 and PM10) and other pollutants into the atmosphere. Low humidity and stable atmospheric conditions during these months exacerbate the problem, trapping pollutants near the ground. Temperature inversions are common, further hindering dispersion. October and November mark the transition to the wet season, bringing increased rainfall and improved air quality as pollutants are washed away. The wet season, from December to April, generally offers the best air quality, with frequent rainfall and higher humidity levels. However, even during the wet season, vehicle emissions remain a consistent source of pollution. Sensitive groups – children, the elderly, and individuals with respiratory conditions – should be particularly cautious during the dry season, limiting outdoor activity on days with visible haze or smoke. Monitoring weather patterns and avoiding strenuous activity during peak burning periods is crucial for protecting respiratory health. Fog can also occur, trapping pollutants at ground level.