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Cotia, nestled within the sprawling São Paulo metropolitan region of Brazil, occupies a strategically important position just northwest of the state capital. Located at approximately -23.6039° latitude and -46.9189° longitude, the city’s geography is characterized by undulating terrain, part of the Serra de Cotia, a low mountain range that contributes to localized microclimates. The elevation varies, generally ranging from 700 to 950 meters above sea level, influencing air drainage patterns and temperature profiles. Surrounding Cotia is a mosaic of landscapes: to the east lies the dense urban fabric of the greater São Paulo, while westward, the terrain transitions into more rural areas, including agricultural lands and patches of Atlantic Forest remnants. This urban–rural gradient is crucial; agricultural activities, particularly those involving burning for land clearing (though increasingly regulated), can contribute to regional particulate matter. The city’s proximity to the Rodovia Régis Bittencourt, a major highway connecting São Paulo to the interior of Brazil, introduces significant vehicular emissions, a primary source of air pollution. While Cotia lacks direct access to large bodies of water, the Tietê River basin lies within the broader region, impacting regional weather systems and potentially influencing humidity levels. The Serra de Cotia itself acts as a barrier, sometimes trapping pollutants and exacerbating local air quality issues, especially during periods of stagnant air. The city’s growth, driven by its relative affordability and proximity to São Paulo, has led to increased traffic and construction, further impacting the local air quality profile.

Cotia’s subtropical climate dictates a distinct seasonal pattern in air quality. The wet season, typically from October to March, generally brings improved air quality due to increased rainfall, which naturally washes away particulate matter and reduces the concentration of pollutants. Higher humidity also helps to suppress dust. However, even during this period, periods of prolonged rain can lead to fog, which, while visually appealing, can trap pollutants close to the ground, creating localized air quality concerns. The dry season, from April to September, presents a more challenging scenario. Reduced rainfall and increased sunshine lead to drier conditions, promoting dust generation and increasing the potential for wildfires in surrounding agricultural areas. Temperature inversions, common during the cooler months (June-August), are particularly problematic. These inversions trap cooler air near the ground, preventing the vertical dispersion of pollutants emitted from vehicles and industrial sources. The Rodovia Régis Bittencourt’s heavy traffic contributes significantly during this time. October and November often see a rise in particulate matter due to agricultural burning practices, although enforcement efforts are aimed at mitigating this. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during the dry season, particularly on days with stagnant air or visible haze. Limiting outdoor exertion and avoiding areas with high traffic volume are advisable. During the wet season, while generally better, monitoring local weather conditions for fog is recommended.