Synergy of natural sources exacerbates ozone pollution in China during drought-heatwave extremes

Abstract

In August 2022, a record-breaking compound drought–heatwave (CDHW) event coincided with severe ozone pollution in central eastern China (CEC), causing severe threats to human health. Using observations and model simulations, we demonstrate that increases in natural sources of air pollutants, including a 74.7% increase in soil reactive oxidized nitrogen (Nr) and a 27.8% increase in biogenic volatile organic compounds (VOCs), enhanced daily maximum 8 h average (MDA8) ozone levels by 4.4 ppb (7.8%) over the CEC region, which dominated ozone exacerbation during the regional CDHW days. Under China’s carbon neutrality policy with natural sources fixed at 2022 levels, stringent anthropogenic emission controls could lower the total CDHW-induced ozone enhancements. However, the impacts of soil Nr emissions, including their direct effects and synergistic interactions with biogenic VOCs, are projected to intensify due to the transition of ozone sensitivity. Consequently, the efficacy of anthropogenic emission control is diminished, leading to a limited mitigation of 0.4 ppb in the ozone surge during the 2022-like CDHW events by 2060. Our study highlights the need to consider soil Nr emissions in future air quality management.