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Cachoeirinha, nestled in the state of Rio Grande do Sul, Brazil, occupies a gently undulating terrain within the broader metropolitan area of Porto Alegre. Located at coordinates -29.9508, -51.0939, the city’s geography is significantly shaped by its proximity to the Jacuí River and its tributaries, influencing local humidity and wind patterns. The surrounding landscape is a mosaic of agricultural lands – primarily soybean, rice, and corn cultivation – interspersed with patches of Atlantic Forest remnants. This agricultural activity, while economically important, contributes to potential particulate matter pollution from field preparation and harvesting. Cachoeirinha’s urban character is transitioning, exhibiting a gradient from denser, more industrialised zones closer to Porto Alegre to more residential and rural areas further afield. The city’s elevation, relatively low-lying, doesn’t provide significant natural dispersion for pollutants. The expanding urban sprawl from Porto Alegre, a major industrial hub, exerts a considerable influence on Cachoeirinha’s air quality, with pollutants transported by prevailing winds. The urban-rural fringe presents a complex interplay of emissions from both sources, creating localised hotspots. Understanding this interplay is crucial for effective air quality management in Cachoeirinha.

Cachoeirinha experiences a humid subtropical climate, with distinct seasonal variations impacting air quality. Winter (June-August) often sees increased particulate matter concentrations due to temperature inversions trapping pollutants near the ground, coupled with increased residential heating using wood and coal. Calm wind conditions exacerbate this. Spring (September-November) brings a gradual improvement as temperatures rise and rainfall increases, washing away accumulated pollutants. However, agricultural burning during this period can cause temporary spikes in PM2.5. Summer (December-February) is generally the period of best air quality, with frequent rainfall and stronger winds dispersing pollutants. Humidity remains high, potentially fostering the formation of secondary pollutants. Autumn (March-May) is a transitional season, with fluctuating conditions. Fog, common in the cooler months, can trap pollutants and reduce visibility. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit strenuous outdoor activity during winter mornings and periods of agricultural burning. Monitoring wind direction is key; winds from the north and west often carry pollutants from agricultural areas, while those from the east bring influences from Porto Alegre.