In this study, we evaluated the influence of COVID-19 social restrictions on tropospheric ozone (O₃) concentrations in Pelotas, a mid-sized city in southern Brazil, aiming to understand how anthropogenic emission reductions and seasonal climate patterns modulate urban air quality in the South American context. Using a combination of high-precision instruments and calibrated low-cost sensors, we monitored air quality from October 2019 to June 2020, capturing spatial and temporal variations under contrasting atmospheric conditions. Contrary to the general decrease in pollutants observed during the pandemic, ozone behavior showed non-linear responses, with concentration peaks linked to solar radiation and weekly emission cycles. These results suggest complex interactions between meteorological factors, regional atmospheric circulation, and localized emissions, which are essential to characterize in subtropical regions of South America under changing climate conditions. The study highlights the relevance of accessible monitoring technologies in understudied areas and contributes to regional-scale assessments of environmental vulnerability and urban exposure to atmospheric pollutants. Findings may support public health protection and environmental management strategies in southern Brazilian urban centers, within the broader framework of climate variability and environmental geosciences in South America.