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Nazaré Paulista, nestled within the sprawling São Paulo state of Brazil, occupies a strategically significant position within the Paraíba do Sul River Valley. Located approximately 80 kilometers northeast of São Paulo city, its coordinates (-23.1808, -46.3950) place it within a transitional zone between the densely populated urban core and the more rural landscapes of the interior. The municipality’s terrain is characterized by rolling hills and valleys, a consequence of the river’s erosional activity, with elevations ranging from roughly 500 to 800 meters above sea level. This moderate elevation contributes to localized temperature inversions, particularly during cooler months, which can trap pollutants near the ground. The Paraíba do Sul River itself acts as a natural boundary and a vital water source, though its proximity can also lead to localized humidity and fog, impacting pollutant dispersion. Surrounding Nazaré Paulista is a mosaic of agricultural land, primarily dedicated to sugarcane cultivation and fruit orchards, alongside smaller-scale farming operations. Further afield, the industrial belt of São Paulo exerts an influence, with occasional transport of pollutants carried by prevailing winds. The urban–rural gradient is relatively sharp, with Nazaré Paulista exhibiting a distinct small-town character, though increasingly influenced by the expansion of the greater São Paulo metropolitan area. The valley’s topography, combined with agricultural practices and distant industrial emissions, creates a complex interplay of factors influencing local air quality.

Nazaré Paulista’s tropical climate dictates a wet and dry seasonal pattern, significantly impacting air quality dynamics. The dry season, typically spanning from April to September, often witnesses a build-up of pollutants. Reduced rainfall and lower humidity contribute to a decrease in atmospheric cleansing, while increased solar radiation can exacerbate photochemical smog formation, particularly during periods of stagnant air. Temperature inversions are more frequent during these months, trapping pollutants closer to the ground, especially in the mornings. Conversely, the wet season (October to March) brings increased rainfall and higher humidity, naturally washing away particulate matter and diluting gaseous pollutants. Stronger winds associated with convective storms also aid in dispersion. However, agricultural burning, a common practice in the surrounding sugarcane fields during the transition from dry to wet season (October/November), can introduce significant spikes in particulate matter. Fog, common during the cooler, drier months, further restricts pollutant dispersal, creating localized pockets of poor air quality. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during the dry season, particularly during periods of stagnant air or agricultural burning. Outdoor activities are generally more favorable during the wet season, although vigilance regarding smoke from agricultural practices remains crucial. The interplay of rainfall, temperature, and wind patterns creates a dynamic air quality profile throughout the year, demanding adaptive strategies for public health.