Cross influences of ozone and sulfate precursor emissions changes on air quality and climate

Tropospheric O-3 and sulfate both contribute to air pollution and climate forcing. There is a growing realization that air quality and climate change issues are strongly connected. To date, the importance of the coupling between O-3 and sulfate has not been fully appreciated, and thus regulations treat each pollutant separately. We show that emissions of O-3 precursors can dramatically affect regional sulfate air quality and climate forcing. At 2030 in an A1B future, increased O-3 precursor emissions enhance surface sulfate over India and China by up to 20% because of increased levels of OH and gas-phase SO2 oxidation rates and add up to 20% to the direct sulfate forcing for that region relative to the present day. Hence, O-3 precursors impose an indirect forcing via sulfate, which is more than twice the direct O-3 forcing itself (compare -0.61 vs. + 0.35 W/m(2)). Regulatory policy should consider both air quality and climate and should address O-3 and sulfate simultaneously because of the strong interaction between these species.