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

Abstract

Carbon monoxide (CO) emissions influence global and regional air quality and global climate change by affecting atmospheric oxidants and secondary species. We simulate the influence of halving anthropogenic CO emissions globally 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 estimated using the GFDL (Geophysical Fluid Dynamics Laboratory) standalone radiative transfer model. We estimate that halving global CO emissions decreases global annual average concentrations of surface ozone by 0.45 ppbv, tropospheric methane by 73 ppbv, and global annual net RF by 36.1 mW m⁻², nearly equal to the sum of changes from the 10 regional reductions. Global annual net RF per unit change in emissions and the 100 yr global warming potential (GWP₁₀₀) are estimated as −0.124 mW m⁻² (Tg CO)⁻¹ and 1.34, respectively, for the global CO reduction, and ranging from −0.115 to −0.131 mW m⁻² (Tg CO)⁻¹ and 1.26 to 1.44 across 10 regions, with the greatest sensitivities for regions in the tropics. The net RF distributions show widespread cooling corresponding to the O₃ and CH₄ decreases, and localized positive and negative net RFs due to changes in aerosols. The strongest 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 CO and ozone concentrations occur within the reduction region. Some regional reductions strongly influence the air quality in other regions, such as East Asia, which has an impact on US surface ozone that is 93% of that from North America. Changes in the transport of CO and downwind ozone production clearly exceed the direct export of ozone from each reduction region. The small variation in CO GWPs among world regions suggests that future international climate agreements could adopt a globally uniform metric for CO with little error, or could use different GWPs for each continent. Doing so may increase the incentive to reduce CO through coordinated policies addressing climate and air quality

The Impact of Individual Anthropogenic Emissions Sectors on the Global Burden of Human Mortality due to Ambient Air Pollution

“…Simulated 2005 surface concentrations show similar agreement with observations to that of other global models (see Supplemental Material, “MOZART-4 performance evaluation” and Figures S1–S6), and to that of previous MOZART-4 simulations at a coarser resolution using the same meteorology and emissions inputs (Fry et al 2013). Additionally, we ran a simulation with no anthropogenic emissions to estimate the total mortality burden of present-day anthropogenic ozone and PM 2.5 (see Supplemental Material, “Simulation with zeroed-out anthropogenic emissions”).…”

Implications of carbon monoxide bias for methane lifetime and atmospheric composition in chemistry climate models

“…Since neither CO nor ozone is well mixed in the atmosphere, the location of the CO perturbation affects its climate impact. CO emissions in the tropics have a greater impact on ozone radiative forcing than emissions at high latitudes (Bowman and Henze, 2012) due the intense photochemistry in the tropics as well as the presence of deep convection, which can loft ozone precursors to the upper troposphere where the ozone radiative forcing is greatest (Fry et al, 2013;Naik et al, 2005).…”

“…The effect of CO on OH also leads to impacts on oxidation of SO 2 to sulfate, providing another climate forcing (Shindell et al, 2009). Previous studies calculated global warming potentials due to these effects using box models (Daniel and Solomon, 1998), 2-dimensional models (Fuglestvedt et al, 1996;Johnson and Derwent, 1996), or 3-dimensional models (Derwent et al, 2001;Fry et al, 2012Fry et al, , 2013Berntsen et al, 2005;Shindell et al, 2009). Since neither CO nor ozone is well mixed in the atmosphere, the location of the CO perturbation affects its climate impact.…”

Air quality and radiative forcing impacts of anthropogenic volatile organic compound emissions from ten world regions

“…Tropospheric CH 4 and O 3 are the largest greenhouse gas contributors to global anthropogenic radiative climate forcing (RF) behind carbon dioxide (CO 2 ) with abundance-based RFs of 0.48 ± 0.05 W m −2 and 0.35 (−0.1, +0.3) W m −2 , M. M. Fry et al: Air quality and radiative forcing impacts of anthropogenic VOC emissions respectively (Forster et al, 2007). Tropospheric sulfate (SO 2− 4 ) has produced a global net RF of −0.40 ± 0.2 W m −2 (direct effect only) (Forster et al, 2007).…”

“…Tropospheric CH 4 and O 3 are the largest greenhouse gas contributors to global anthropogenic radiative climate forcing (RF) behind carbon dioxide (CO 2 ) with abundance-based RFs of 0.48 ± 0.05 W m −2 and 0.35 (−0.1, +0.3) W m −2 , M. M. Fry et al: Air quality and radiative forcing impacts of anthropogenic VOC emissions respectively (Forster et al, 2007). Tropospheric sulfate (SO 2− 4 ) has produced a global net RF of −0.40 ± 0.2 W m −2 (direct effect only) (Forster et al, 2007). NMVOCs and carbon monoxide (CO) emissions together have contributed an estimated global mean RF of 0.21 ± 0.10 W m −2 due to O 3 and CH 4 (1750 to 1998) (Shindell et al, 2005;Forster et al, 2007) and 0.25 ± 0.04 W m −2 (1750 to 2000) when SO 2− 4 , nitrate (NO − 3 ), and CO 2 impacts are included .…”