Tropospheric ozone formation depends on the emissions of volatile organic compounds (VOC) and nitrogen oxides (NO_x). In megacities, abundant VOC and NO_x sources cause relentlessly high ozone episodes, affecting a large share of the global population. This study uses data from the Ozone Monitoring Instrument for formaldehyde (HCHO) and nitrogen dioxide (NO₂) as proxy data for VOC and NO_x emissions, respectively, with their ratio serving as an indicator of ozone sensitivity. Ground-level ozone (O₃) reanalysis from the Copernicus Atmosphere Monitoring is used to assess the O₃ trends. We evaluate changes from 2005 to 2019 and their relationship with the warming environment in 41 megacities worldwide, applying seasonal Mann-Kendall, trend decomposition methods, and Pearson correlation analysis. We reveal significant increases in global HCHO (0.1 to 0.31 × 10¹⁵ mol cm⁻² year⁻¹) and regionally varying NO₂ (−0.22 to 0.07 × 10¹⁵ mol cm⁻² year⁻¹). O₃ trends range from −0.31 to 0.70 ppb year⁻¹, highlighting the relevance of precursor abundance on O₃ levels. The strong correlation between precursor emissions and increasing temperature suggests that O₃ will continue to rise as climate change persists.

The plans to introduce next-generation hybrid and zero-emission vehicles in the market are now enacted by governments in many countries to manage both global warming and air pollution problems. There are only a few studies evaluating the effects of the next-generation vehicles on the changes in concentrations of ozone generated by the photochemical reactions between volatile organic compounds and nitrogen oxides (NO_x). To evaluate these changes, we performed chemical transport modeling in the Kanto region, Japan in the summer of 2013. The results show that if the vehicles are substituted by hybrid vehicles, average ozone concentrations increase in urban areas and decrease in suburban areas due to NO_x titration. Substitution with zero-emission passenger vehicles decreases the concentrations in both urban and suburban areas. Substitution with both hybrid and zero-emission passenger and heavy-duty vehicles highly increases the concentrations in urban areas. Using the model results, we also discuss the effect of ozone concentration changes on premature mortality of humans in summer. The results suggest that, in some cases the introduction of next-generation vehicles might exasperate ozone concentrations, even leading to 5 to 10 times higher premature mortality during the summer compared to that of influenza and heat stroke in Japan.