Changes in emissions of ozone (O3) precursors affect both air quality and climate. We first examine the sensitivity of surface O3 concentrations (O3srf) and net radiative forcing of climate (RFnet) to reductions in emissions of four precursors – nitrogen oxides (NOx), non-methane volatile organic compounds, carbon monoxide, and methane (CH4). We show that long-term CH4-induced changes in O3, known to be important for climate, are also relevant for air quality; for example, NOx reductions increase CH4, causing a long-term O3 increase that partially counteracts the direct O3 decrease. Second, we assess the radiative forcing resulting from actions to improve O3 air quality by calculating the ratio of ΔRFnet to changes in metrics of O3srf. Decreases in CH4 emissions cause the greatest RFnet decrease per unit reduction in O3srf, while NOx reductions increase RFnet. Of the available means to improve O3 air quality, therefore, CH4 abatement best reduces climate forcing.
