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

Changes in emissions of ozone (O 3 ) precursors affect both air quality and climate. We first examine the sensitivity of surface O 3 concentrations (O 3 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 (CH 4 ). We show that long‐term CH 4 ‐induced changes in O 3 , known to be important for climate, are also relevant for air quality; for example, NO x reductions increase CH 4 , causing a long‐term O 3 increase that partially counteracts the direct O 3 decrease. Second, we assess the radiative forcing resulting from actions to improve O 3 air quality by calculating the ratio of ΔRF net to changes in metrics of O 3 srf . Decreases in CH 4 emissions cause the greatest RF net decrease per unit reduction in O 3 srf , while NO x reductions increase RF net . Of the available means to improve O 3 air quality, therefore, CH 4 abatement best reduces climate forcing.