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 NOx-saturated conditions. Furthermore, it emphasizes the importance of dynamic boundary-layer processes and increased VOC concentrations resulting from fugitive emissions during the heatwave.