Accelerated O₃ formation triggered by summer heatwaves in megacity Seoul

As compelling evidence of global warming, heatwaves are expected to elevate O₃ mixing ratios in highly polluted urban areas. In summer 2018, Seoul, an Asian megacity, experienced elevated O₃ levels in conjunction with a temperature surge (maximum of 38.9 °C). This study quantitatively estimates the O₃-climate penalty through measurements of nitrogen oxide species, volatile organic compounds (VOCs), and the boundary-layer height, as well as model simulations. The results highlight an acceleration of O₃ concentration increment with increased temperature and elevated ozone production efficiency in NO_x-saturated conditions. Furthermore, it emphasizes the importance of dynamic boundary-layer processes and increased VOC concentrations resulting from fugitive emissions during the heatwave.