Comment on egusphere-2025-6166

<strong class="journal-contentHeaderColor">Abstract.</strong> This study presents results from an Intensive Measurement Period conducted during the European heatwave of July 2022, focusing on ozone, volatile organic compounds (VOCs), and carbonaceous aerosols at 31 sites across Europe. The episode featured persistent high-pressure systems, record-breaking temperatures, widespread ozone exceedances and concurrent atmospheric new particle formation and growth events. Although the roles of biogenic and anthropogenic precursors in ozone, secondary organic aerosol (SOA) formation and nanoparticle growth are recognized, their relative importance during extreme events remains poorly constrained. This work therefore aimed to quantify these interactions using coordinated measurements and model simulations. Measurements showed that oxygenated VOCs formed the largest fraction of total VOCs, followed by non-methane hydrocarbons (NMHCs) and aromatics, with substantial contributions from both anthropogenic and biogenic sources. Elevated ozone and SOA levels were driven by the combined influence of biogenic VOCs and NO_x emissions under predominantly NO_x-limited conditions. Isoprene, NMHCs, and O-VOCs dominated the ozone formation potential, while aromatics and monoterpenes were the most important SOA precursors. Model simulations indicated that higher NO_x concentrations can reduce SOA formation by about 10 %. The campaign also highlighted observational gaps underscoring the need for broader and higher-resolution VOC monitoring across Europe. Overall, further reductions in NO_x emissions, alongside targeted control of key anthropogenic VOCs, would benefit air quality, during extreme pollution episodes. These findings illustrate the complex interplay between meteorology, emissions, and atmospheric chemistry during heatwaves and emphasize the need for comprehensive precursor monitoring and improved modelling for effective air-quality management under future climate conditions.