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 (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 O-3, known to be important for climate, are also relevant for air quality; for example, NOx reductions increase CH4, 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 Delta RFnet to changes in metrics of O(3)srf. Decreases in CH4 emissions cause the greatest RFnet decrease per unit reduction in O(3)srf, while NOx reductions quality, therefore, CH4 abatement best reduces climate forcing.