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Bertioga, nestled along the northern coast of São Paulo state, Brazil, occupies a geographically significant position where the Serra do Mar mountain range meets the Atlantic Ocean. Its coordinates, -23.8539, -46.1389, place it within a subtropical climate zone characterized by high humidity and significant rainfall. The city’s terrain is dramatically shaped by the escarpment of the Serra do Mar, resulting in steep slopes and a narrow coastal plain. This topography significantly influences local air circulation patterns; cool, dense air often descends from the mountains, trapping pollutants close to the surface, particularly during periods of calm weather. Bertioga’s proximity to the Atlantic Ocean introduces a maritime influence, moderating temperatures but also contributing to coastal fog and humidity, which can affect pollutant dispersion. The surrounding landscape is a mix of dense Atlantic Forest, remnants of which are still visible, and increasingly, areas converted to agricultural land and industrial zones. The city serves as a crucial port for the broader São Paulo metropolitan region, facilitating the transport of goods and contributing to industrial activity. A gradual urban–rural gradient exists, with denser urban development concentrated along the coastline and transitioning to more rural, agricultural areas further inland. The presence of the Santos-Guarujá industrial belt to the south introduces a regional pollution source, with prevailing winds occasionally carrying pollutants towards Bertioga. The elevation varies considerably, from sea level along the coast to higher elevations within the Serra do Mar, impacting local microclimates and pollutant behaviour.

Bertioga’s subtropical climate dictates a distinct seasonal pattern in air quality, though the transition between seasons is less pronounced than in temperate regions. The wet season, typically spanning from October to March, brings frequent rainfall and high humidity. While rain naturally helps to cleanse the atmosphere, the increased humidity can trap pollutants, especially during periods of reduced wind. Fog, common during these months, further exacerbates this effect, creating stagnant air conditions. The dry season, from April to September, generally sees improved air quality due to increased ventilation and lower humidity. However, periods of drought can lead to increased dust and particulate matter from agricultural activities and construction. Temperature inversions, where a layer of warm air sits above cooler air near the ground, are more frequent during the dry season, particularly in the mornings, trapping pollutants released from industrial sources and vehicle emissions. Outdoor activities are generally more favourable during the drier months (May-August), though vigilance is still advised, especially for individuals with respiratory sensitivities. During the wetter months (November-February), those with asthma or other respiratory conditions should limit prolonged outdoor exposure, particularly during foggy or stagnant air days. The agricultural cycle, with burning practices sometimes employed, can contribute to localised pollution spikes, regardless of the season. The maritime influence helps to disperse pollutants, but the city’s topography can create pockets of poor air quality, demanding careful monitoring and targeted public health advisories.