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Praia Grande occupies a distinctive coastal position within Brazil's São Paulo metropolitan region, situated on the Atlantic shoreline approximately 70 kilometers southeast of São Paulo city. This municipality's geography is defined by its location on the narrow coastal plain between the Serra do Mar mountain range to the northwest and the Atlantic Ocean to the southeast, creating a compressed urban-rural gradient where dense residential development transitions abruptly to protected Atlantic Forest remnants. The city's terrain is predominantly flat with minimal elevation variation, rarely exceeding 10 meters above sea level, which significantly influences air quality through limited natural ventilation. Proximity to the Port of Santos—Latin America's busiest port complex just 15 kilometers to the northeast—introduces maritime and industrial emissions that frequently drift southwestward with prevailing winds. The urban fabric itself generates substantial pollution through vehicle traffic concentrated along the narrow coastal corridor connecting Santos to other Baixada Santista municipalities. During atmospheric stagnation events, pollutants accumulate against the Serra do Mar escarpment, creating persistent haze that contrasts sharply with the ocean breezes that otherwise provide natural cleansing. This geographic squeeze between mountain barrier and ocean creates microclimatic conditions where pollution disperses efficiently seaward but concentrates inland, particularly affecting neighborhoods farther from the coastline.

Praia Grande experiences distinct seasonal air quality patterns influenced by South Atlantic weather systems and local topography. During summer (December-February), increased maritime breezes and convective afternoon rains typically maintain good air quality, though occasional temperature inversions can trap vehicle emissions during morning rush hours. Autumn (March-May) brings transitional conditions with decreasing rainfall and more frequent atmospheric stagnation, particularly in May when the first significant pollution episodes often occur as cooler air settles against the Serra do Mar. Winter (June-August) represents the most challenging season, with frequent temperature inversions, reduced wind speeds, and minimal precipitation creating persistent pollution accumulation that peaks in July and August; these months see the highest concentrations of particulate matter from vehicles, port activities, and occasional biomass burning from inland agricultural regions. Sensitive groups should limit outdoor exertion during winter mornings when inversion layers are strongest. Spring (September-November) offers gradual improvement as increasing frontal systems and sea breezes return, though October can experience variable conditions during the transition. The city's coastal location provides natural ventilation that typically prevents extreme pollution episodes, but the combination of urban emissions and topographic confinement creates seasonal patterns where winter requires heightened awareness, especially for those with respiratory conditions who should monitor local air quality reports during calm, cool mornings.