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São Lourenço d’Oeste, nestled in the westernmost reaches of Santa Catarina state, Brazil, occupies a unique geographic position within the broader context of the Brazilian Highlands. The city’s coordinates (-26.3589, -52.8508) place it within a gently undulating terrain, characteristic of the region’s transition zone between the plains and the more pronounced hills further east. Elevation averages around 580 meters above sea level, influencing temperature patterns and contributing to localized atmospheric conditions. The surrounding landscape is dominated by agricultural lands, primarily dedicated to soybean, corn, and wheat cultivation, alongside significant areas of native *mata* (forest) remnants. The Uruguay River forms a natural boundary to the west, impacting local humidity and wind direction. While not directly within a major industrial belt, the increasing mechanization of agriculture contributes to particulate matter emissions. The urban-rural gradient is relatively sharp; the city centre is compact, quickly giving way to expansive farmland. This proximity to agricultural activity, coupled with the region’s topography, can lead to the concentration of airborne pollutants, particularly during harvest seasons and periods of limited atmospheric mixing. The prevailing winds, generally from the northeast, can transport pollutants from agricultural sources towards the city, affecting air quality.

São Lourenço d’Oeste experiences a humid subtropical climate, with distinct wet and dry seasons rather than traditional four seasons. Air quality generally improves during the wetter months (October to March) as rainfall effectively scrubs the atmosphere of particulate matter generated by agricultural activities. However, high humidity can also foster the formation of fog, potentially trapping pollutants near the ground. The dry season (April to September) presents the greatest air quality challenges. During this period, agricultural burning for land preparation is common, leading to significant spikes in particulate matter, especially PM2.5 and PM10. Wind patterns are less consistent, and temperature inversions – where a layer of warm air traps cooler air below – are more frequent, exacerbating pollution build-up. August and September are typically the months with the poorest air quality. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should limit strenuous outdoor activity during these periods. Conversely, April and May offer a transitional period with generally favourable conditions. Monitoring wind direction is crucial; winds from agricultural areas signal potential pollution events. Local meteorological forecasts should be consulted regularly to anticipate and mitigate exposure.