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Niterói occupies a strategic position across Guanabara Bay from Rio de Janeiro, forming part of the Greater Rio metropolitan region in southeastern Brazil. The city's geography is defined by dramatic coastal topography, with steep hills and mountains like the Serra da Tiririca rising directly from the shoreline, creating a compressed urban–rural gradient. Situated at approximately 22.88°S latitude, Niterói experiences a tropical savanna climate influenced by its coastal location on the Atlantic Ocean. The city's elevation varies significantly from sea level along its extensive beaches to over 400 meters in its northern districts, creating microclimates that affect pollution dispersion. Niterói's air quality is shaped by its position within the densely populated Rio de Janeiro metropolitan area, with pollution transport across Guanabara Bay from industrial zones in Rio's North Zone and the Duque de Caxias petrochemical complex. The city's own pollution sources include vehicular emissions concentrated along narrow coastal corridors, limited industrial activity in the Centro and São Lourenço districts, and occasional biomass burning from informal settlements on hillsides. The surrounding landscape—comprising ocean to the south, bay to the west, and protected forests to the north—creates a complex airshed where sea breezes can dilute pollutants but topographic barriers sometimes trap emissions in valleys. Urban expansion along constrained coastal plains has created pollution hotspots where traffic congestion meets limited atmospheric ventilation.

Niterói's air quality follows distinct seasonal patterns shaped by South Atlantic weather systems and urban activity cycles. During the austral summer (December-February), increased tourism and vehicular traffic combine with frequent temperature inversions in the early morning, particularly in valleys like Ingá and São Francisco, creating brief pollution episodes that typically dissipate with afternoon sea breezes. The autumn months (March-May) bring the most favorable air quality conditions as steady southeast trade winds provide excellent ventilation, making this the ideal time for outdoor activities for all residents, especially those with respiratory conditions. Winter (June-August) presents the greatest air quality challenges, with cooler temperatures reducing atmospheric mixing heights and occasional calm periods that allow pollutants to accumulate, particularly from increased residential heating in informal settlements and persistent traffic emissions. Sensitive groups should monitor air quality reports during July and August morning hours when cold fronts sometimes stall, creating multi-day pollution events. Spring (September-November) sees improving conditions as increasing solar radiation enhances vertical mixing, though occasional biomass burning from land clearance in surrounding areas can cause short-term particulate matter spikes. Throughout the year, the city's coastal location provides natural ventilation that prevents extreme pollution episodes, but sensitive individuals should avoid strenuous outdoor activity during winter mornings and near major traffic corridors during rush hours regardless of season.