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Guarujá occupies a strategic position on the southeastern coast of Brazil, situated on the western shore of Santos Bay within the metropolitan region of São Paulo. This coastal city is part of the Baixada Santista, a densely populated urban corridor that stretches along the Atlantic coastline. The terrain is characterized by low-lying coastal plains interspersed with small hills and the Serra do Mar mountain range to the northwest, which creates a dramatic topographic contrast. Guarujá's elevation ranges from sea level to approximately 100 meters in its interior areas, with the city center built primarily on flat, reclaimed land. Its geography profoundly influences air quality through multiple mechanisms. The proximity to the Atlantic Ocean provides natural ventilation, with sea breezes typically dispersing pollutants eastward. However, the city's location adjacent to the Port of Santos—Latin America's busiest port—introduces significant pollution sources from shipping emissions, port operations, and associated truck traffic. The urban-rural gradient is sharply defined, with Guarujá transitioning abruptly from dense urban development to preserved Atlantic Forest remnants in nearby conservation areas. The surrounding landscape includes mangrove ecosystems along the estuary, which can trap pollutants during stagnant conditions. The city's position within the São Paulo metropolitan region means it's influenced by regional pollution transport, particularly when westerly winds carry industrial emissions from Cubatão's industrial complex, located approximately 15 kilometers inland. This combination of local port activity, regional industrial influence, and coastal meteorology creates a complex air quality dynamic unique to Guarujá's geographic setting.

Guarujá experiences distinct seasonal air quality patterns shaped by its subtropical coastal climate. During summer (December-February), increased solar radiation and higher temperatures accelerate photochemical reactions, potentially elevating ozone levels, particularly during afternoon hours when sea breezes weaken. However, frequent rainfall and stronger onshore winds generally keep particulate matter concentrations moderate. Autumn (March-May) brings transitional conditions with decreasing rainfall and more variable winds, occasionally allowing pollutants to accumulate during periods of atmospheric stability. Winter (June-August) presents the most challenging air quality scenario, as cooler temperatures and frequent temperature inversions trap pollutants near the surface, especially during calm mornings. This season often sees elevated levels of fine particulate matter from port operations and regional transport, with July typically being the month of poorest air quality. Sensitive groups should limit strenuous outdoor activities during winter mornings and monitor local air quality reports. Spring (September-November) marks improvement as increasing temperatures and more vigorous sea breezes enhance dispersion, though occasional Saharan dust intrusions can temporarily degrade air quality. The city's coastal location generally prevents extreme pollution episodes, but the combination of port emissions, urban traffic, and occasional biomass burning from agricultural areas upwind can create moderate pollution events. Visitors seeking optimal air quality should favor spring and early summer months, while residents with respiratory conditions should be particularly cautious during winter inversion periods.