We assert the role of methane and other drivers of change in explaining the growing tropospheric ozone (O₃) trend at Tololo (30.17° S, 70.80° W, 2154 m a.s.l.), and we quantify the contributions of biomass burning and stratospheric and upper tropospheric O₃, particularly during the late winter and spring. These findings enhance understanding of O₃ variability in the Southern Hemisphere free troposphere and underscore the importance of sustained observations at Tololo amid climate change.