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Mogi Mirim, nestled in the state of São Paulo, Brazil, occupies a gently undulating terrain within the broader Piracicaba River Valley. Located at approximately 610 meters above sea level, the city benefits from a moderate elevation that influences local climate patterns. The surrounding landscape is a mosaic of sugarcane plantations – a defining characteristic of the region – interspersed with patches of Atlantic Forest remnants. The Piracicaba River itself flows nearby, providing a crucial water source but also potentially contributing to humidity and localized temperature inversions. Mogi Mirim’s urban character is that of a developing inland city, experiencing growth linked to its agricultural base and increasing industrial activity, particularly related to the sugar and ethanol industries. This industrial presence, concentrated around the city’s periphery, is a key factor influencing air quality. The urban-rural gradient is relatively sharp, with agricultural lands dominating the immediate surroundings. The city’s position within a valley can trap pollutants during periods of calm weather, exacerbating air quality concerns. Prevailing winds generally move from the southeast, potentially carrying pollutants from larger industrial centres further east towards Mogi Mirim, and dispersing local emissions to the northwest. Understanding this geographical context is crucial for interpreting air quality trends.

Mogi Mirim experiences a tropical climate with distinct wet and dry seasons, rather than traditional four seasons. Air quality generally improves during the wet season (October to April) due to increased rainfall which effectively washes particulate matter from the atmosphere. However, high humidity can also contribute to the formation of secondary pollutants. The dry season (May to September) consistently presents the poorest air quality. This is largely due to increased dust from agricultural activities – particularly sugarcane harvesting and preparation – and a greater concentration of emissions from industrial sources as atmospheric dispersion is reduced. August and September are typically the months with the highest pollution levels. Temperature inversions, common during the cooler, drier mornings of the dry season, trap pollutants near ground level. Sensitive groups, including children, the elderly, and those with respiratory conditions, should limit strenuous outdoor activity during these periods. Fog, frequently occurring during the cooler months, can exacerbate respiratory issues by trapping pollutants. Monitoring wind patterns is crucial; periods of calm wind are associated with pollution build-up. The transition months of October and April offer the most favourable conditions for outdoor activities.