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Tenente Portela, nestled in the northwestern reaches of Rio Grande do Sul, Brazil, occupies a unique geographic position within the rolling hills of the Alto Uruguai region. Situated at coordinates -27.3708, -53.7578, the city’s terrain is characterised by undulating landscapes, a product of ancient geological formations and fluvial erosion. The elevation, averaging around 550 meters above sea level, contributes to a temperate climate, but also influences air quality through potential temperature inversions. The city is not directly adjacent to major bodies of water, though the Uruguay River lies approximately 60km to the west, impacting regional humidity patterns. Tenente Portela’s economy is heavily reliant on agriculture, particularly soybean, corn, and wheat cultivation, alongside a growing agro-industrial sector. This agricultural dominance introduces potential sources of particulate matter from field preparation, harvesting, and the use of agricultural chemicals. The urban-rural gradient is relatively sharp, with significant agricultural land surrounding the city limits. The prevailing winds, generally from the northeast, can transport pollutants from agricultural activities into the urban centre, while the city’s limited industrial base means localised emissions are less dominant. Understanding this interplay between agricultural practices, terrain, and wind patterns is crucial for assessing and mitigating air quality concerns in Tenente Portela.

Tenente Portela experiences a humid subtropical climate with distinct seasons that significantly impact air quality. The spring (September-November) often sees increased particulate matter from agricultural burn-off as farmers prepare fields for planting, coupled with moderate rainfall that can temporarily cleanse the air. Summers (December-February) are warm and humid, with potential for stagnant air masses leading to localised pollutant build-up, particularly from vehicle emissions and minor industrial activity. However, frequent thunderstorms provide some atmospheric flushing. Autumn (March-May) is generally the most pleasant period for air quality, with cooler temperatures and more consistent winds dispersing pollutants. The winter months (June-August) present the greatest challenges. Lower temperatures create temperature inversions, trapping pollutants near the ground, and increased use of wood-burning stoves for heating contributes to higher levels of particulate matter. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit outdoor exertion during these winter months. Fog, common in winter mornings, exacerbates particulate matter concentrations. Months to avoid prolonged outdoor activity are July and August, while April and May typically offer the best air quality. Monitoring wind direction is key, as pollutants can be transported from surrounding agricultural areas.