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Tremembé, nestled in the state of São Paulo, Brazil, occupies a unique geographic position within a rolling landscape of the Paraíba Valley. Located at coordinates -22.9583, -45.5494, the city’s terrain is characterised by gentle hills and valleys, an extension of the Serra da Mantiqueira foothills. This topography significantly influences local air quality, creating pockets where pollutants can accumulate, particularly during temperature inversions. The city benefits from proximity to the Paraíba do Sul River, a major waterway, but this also introduces humidity which can exacerbate the effects of certain pollutants. Tremembé is situated within a region transitioning from rural agricultural lands – primarily sugarcane and pasture – to increasingly industrialised areas closer to larger cities like São José dos Campos and Taubaté. This urban-rural gradient is crucial; agricultural practices contribute particulate matter from burning and soil disturbance, while industrial activity introduces nitrogen oxides and volatile organic compounds. The city’s elevation, around 530 meters, moderates temperatures but doesn’t fully negate the impact of regional pollution transport. The surrounding landscape, while visually appealing, limits natural ventilation, trapping pollutants and impacting the air quality experienced by Tremembé’s 47,714 residents.

Tremembé experiences a humid subtropical climate, with a pronounced wet and dry season rather than traditional four seasons. Air quality generally improves during the wet season (October to April) due to rainfall effectively scavenging pollutants from the atmosphere. However, increased humidity can also foster mold growth, impacting respiratory health. The dry season (May to September) consistently presents the poorest air quality. Lower rainfall means pollutants accumulate, and agricultural burning for sugarcane harvest is prevalent during this period, significantly increasing particulate matter levels. August and September are typically the worst months for outdoor activity, particularly for those with pre-existing respiratory conditions. Temperature inversions, common during the cooler dry season nights, trap pollutants near ground level, worsening conditions. Winds are generally light, offering limited dispersion. Sensitive groups – children, the elderly, and individuals with asthma – should limit strenuous outdoor activity during dry season afternoons. Fog, frequent during cooler months, can also trap pollutants, reducing visibility and exacerbating respiratory issues. Monitoring wind patterns and avoiding peak agricultural burning times are crucial for mitigating exposure.