Coupled biogenic and soil emissions amplify heatwave-driven secondary pollution

Global air pollution policies have drastically lowered anthropogenic emissions, yet climate change threatens regional air quality through poorly understood natural feedbacks. Extreme heat accelerates biogenic volatile organic compound and soil nitrogen emissions, fueling ozone and secondary organic aerosol formation. Although standalone impacts of these biogenic sources are documented, chemical interactions between co-elevated vegetation and soil fluxes remain unconstrained. Here we show that a temperature-driven synergistic mechanism between biogenic terpenoids and soil nitrogen emissions severely exacerbated secondary air pollution during China's unprecedented 2022 heatwave. Integrating ground observations, satellite data, and chemical transport modeling, we demonstrate that a massive surge in biogenic terpenoids enhances atmospheric oxidation capacity by generating reactive peroxy radicals. These radicals accelerate the conversion of soil nitric oxide to nitrogen dioxide without consuming ozone, driving a 21% regional ozone increase across the Yangtze River Basin and boosting secondary organic aerosol loads by up to 4 μg m^-3. These findings reveal a potent natural feedback loop that counteracts anthropogenic mitigation gains, underscoring the necessity of integrating coupled ecological dynamics into future climate adaptation and pollution control strategies.