Net radiative forcing and air quality responses to regional CO emission reductions

摘要

Carbon monoxide (CO) emissions influence global and regional air quality andglobal climate change by affecting atmospheric oxidants and secondaryspecies. We simulate the influence of halving anthropogenic CO emissionsglobally and individually from 10 regions on surface and tropospheric ozone,methane, and aerosol concentrations using a global chemical transport model(MOZART-4 for the year 2005). Net radiative forcing (RF) is then estimatedusing the GFDL (Geophysical Fluid Dynamics Laboratory) standalone radiative transfer model. We estimate that halvingglobal CO emissions decreases global annual average concentrations ofsurface ozone by 0.45 ppbv, tropospheric methane by 73 ppbv, and globalannual net RF by 36.1 mW m, nearly equal to the sum of changes fromthe 10 regional reductions. Global annual net RF per unit change inemissions and the 100 yr global warming potential (GWP) areestimated as −0.124 mW m (Tg CO) and 1.34, respectively, forthe global CO reduction, and ranging from −0.115 to −0.131 mW m(Tg CO) and 1.26 to 1.44 across 10 regions, with the greatestsensitivities for regions in the tropics. The net RF distributions showwidespread cooling corresponding to the O and CH decreases, andlocalized positive and negative net RFs due to changes in aerosols. Thestrongest annual net RF impacts occur within the tropics(28° S–28° N) followed by the northern midlatitudes (28° N–60° N),independent of reduction region, while the greatest changes in surface COand ozone concentrations occur within the reduction region. Some regionalreductions strongly influence the air quality in other regions, such as EastAsia, which has an impact on US surface ozone that is 93% of that fromNorth America. Changes in the transport of CO and downwind ozone productionclearly exceed the direct export of ozone from each reduction region. Thesmall variation in CO GWPs among world regions suggests that futureinternational climate agreements could adopt a globally uniform metric forCO with little error, or could use different GWPs for each continent. Doingso may increase the incentive to reduce CO through coordinated policiesaddressing climate and air quality.