Ozone air quality and radiative forcing consequences of changes in ozone precursor emissions

Changes in emissions of ozone (O₃) precursors affect both air quality and climate. We first examine the sensitivity of surface O₃ concentrations (O₃^srf) and net radiative forcing of climate (RF_net) to reductions in emissions of four precursors - nitrogen oxides (NO_x), 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, NO_x 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 ΔRF_net to changes in metrics of O₃ ^srf. Decreases in CH₄ emissions cause the greatest RF_net decrease per unit reduction in O₃ ^srf, while NO_x reductions increase RF_net. Of the available means to improve O₃ air quality, therefore, CH₄ abatement best reduces climate forcing.