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Ourém, nestled in the state of Pará, Brazil, occupies a significant position within the Amazon rainforest basin. Located at -1.5478 latitude and -47.1189 longitude, the city’s geography is defined by the undulating terrain typical of the Amazonian periphery, transitioning from dense rainforest to more open landscapes. The elevation is relatively low, contributing to high humidity levels. Ourém is situated near the Tapajós River, a major tributary of the Amazon, which influences local climate patterns and provides a crucial transportation artery. The surrounding landscape is predominantly rainforest, interspersed with areas of agricultural activity, primarily cattle ranching and small-scale farming. This agricultural expansion, while vital to the local economy, contributes to deforestation, a key driver of regional air quality issues. The urban-rural gradient is pronounced; Ourém itself is a relatively small city, with a population of approximately 17,855, surrounded by vast, sparsely populated rural areas. The proximity to the rainforest means that biomass burning, both natural and anthropogenic, is a significant factor influencing air quality. The city’s location within the Amazonian biome makes it particularly vulnerable to the effects of climate change and deforestation, impacting both local and regional air quality.

Ourém experiences a distinct wet and dry season, rather than traditional four seasons. Air quality in Ourém is most compromised during the dry season, typically from July to December. This period coincides with increased deforestation activities and intentional burning for land clearing, releasing substantial particulate matter (PM2.5 and PM10) and other pollutants into the atmosphere. Reduced rainfall during these months also limits the natural cleansing effect of precipitation. Temperature inversions, common during the cooler nights of the dry season, trap pollutants near the ground, exacerbating air quality issues. The wet season, from January to June, generally brings improved air quality due to increased rainfall washing away pollutants and higher humidity suppressing dust. However, even during the wet season, localised burning can still occur. August and September are typically the worst months for respiratory health, while February and March offer the most favourable conditions for outdoor activities. Sensitive groups – children, the elderly, and individuals with pre-existing respiratory conditions – should limit outdoor exposure during the dry season and consider using air purifiers indoors. Monitoring fire hotspots and avoiding areas with visible smoke is crucial for protecting health.