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Cananéia, nestled within the sprawling coastal municipality of São Paulo state, Brazil, occupies a uniquely sensitive geographic position. Located at approximately -25.0150 latitude and -47.9269 longitude, the city sits at the mouth of the Paranaguá River, where it converges with the Atlantic Ocean, forming a complex estuarine environment. This location dictates much of Cananéia’s character; it’s a historic fishing village, the oldest in Brazil, with a low-lying terrain rarely exceeding 10 meters above sea level. The surrounding landscape is dominated by the Mata Atlântica rainforest, a biodiversity hotspot now fragmented but still exerting a significant influence. To the west, the land gradually rises, transitioning into rolling hills and agricultural zones, primarily dedicated to sugarcane and cattle ranching. The urban–rural gradient is relatively sharp, with the rainforest quickly giving way to cultivated land and then to more developed areas further inland. The proximity to the Paranaguá River and the Atlantic Ocean creates a maritime climate, characterized by high humidity and moderate temperatures. While Cananéia itself has limited heavy industry, it’s within reach of industrial belts concentrated along the São Paulo coastline, and agricultural practices in the surrounding region contribute to regional air quality challenges. The prevailing winds, often influenced by coastal breezes, play a crucial role in dispersing or concentrating pollutants, making the city’s air quality particularly susceptible to external factors and regional agricultural emissions. The intricate network of waterways also influences local microclimates and pollutant transport.

Cananéia’s tropical climate dictates a wet and dry season pattern, significantly impacting air quality throughout the year. The wet season, typically spanning from November to March, brings consistent rainfall and increased humidity. While the rain itself can help cleanse the atmosphere, the increased humidity often traps pollutants closer to the ground, particularly during periods of reduced wind. The dry season, from April to October, is characterized by lower rainfall and higher temperatures. This can lead to increased photochemical smog formation, especially during the drier months of August and September, as sunlight interacts with pollutants. Temperature inversions, where a layer of warm air sits above cooler air near the ground, are more frequent during the dry season, further trapping pollutants. The surrounding agricultural lands contribute significantly; sugarcane burning, a common practice during the dry season to prepare fields for planting, releases substantial particulate matter and other pollutants into the atmosphere, impacting Cananéia’s air quality. Coastal breezes, while generally beneficial for dispersion, can sometimes become stagnant, exacerbating the problem. During the wettest months, fog can form, further reducing visibility and trapping pollutants. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during periods of stagnant air and high humidity, particularly during the dry season when agricultural burning is prevalent. Outdoor activities are generally more favourable during the wetter months, although vigilance regarding humidity levels is still advised.