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Paraibuna, nestled within the Serra do Mar mountain range in São Paulo state, Brazil, occupies a geographically significant position within the broader Southeast region. Located approximately 130 kilometers northeast of São Paulo city, its coordinates (-23.3861, -45.6622) place it at an elevation of roughly 850 meters above sea level, contributing to a cooler, more humid climate than the coastal areas. The surrounding landscape is dominated by rolling hills, dense Atlantic Forest remnants, and agricultural land, creating a distinct urban–rural gradient. The city’s terrain is characterized by steep slopes and valleys, influencing drainage patterns and potentially trapping pollutants under certain meteorological conditions. While not directly adjacent to a major river, Paraibuna benefits from several smaller streams and tributaries flowing down from the Serra do Mar, providing a source of freshwater but also potentially acting as pathways for pollutants if industrial or agricultural runoff is not properly managed. The proximity to the Tietê River basin, a major industrial and agricultural zone, means Paraibuna is indirectly influenced by activities further downstream. The city’s relatively small population (18,263) suggests a primarily rural character, with agriculture and small-scale industry playing key roles. This combination of mountainous terrain, Atlantic Forest influence, and proximity to larger industrial areas creates a complex interplay that can significantly impact local air quality, particularly concerning particulate matter and volatile organic compounds from agricultural practices and potential industrial emissions.

Paraibuna’s subtropical climate dictates a distinct seasonal pattern influencing air quality. The region experiences a wet season (roughly November to March) and a drier season (April to October). During the wet season, increased rainfall generally leads to improved air quality as precipitation washes away particulate matter and dilutes gaseous pollutants. However, intense storms can temporarily worsen conditions due to wind-driven dust and debris. The dry season, particularly during September and October, often sees a build-up of pollutants. Temperature inversions, common during this period, trap cooler air near the ground, preventing the vertical dispersion of emissions from agricultural burning (a common practice for land clearing) and any localized industrial activity. Fog, frequently occurring in the mornings during the dry season due to the region’s humidity and elevation, further exacerbates this trapping effect, concentrating pollutants near ground level. The Atlantic Forest, while generally acting as a carbon sink, can also contribute to ozone formation during periods of intense sunlight and high temperatures. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during the drier months, particularly on days with fog or stagnant air. Outdoor activities are generally more favorable during the wet season, although vigilance regarding storm conditions is advised. Agricultural practices, especially controlled burns, are a key factor to monitor, and local authorities often implement restrictions during periods of high fire risk to mitigate air quality impacts. The interplay of temperature, humidity, and wind patterns creates a dynamic air quality profile throughout the year.