Global Air Quality and Health Co-Benefits of Mitigating Near-Term Climate Change through Methane and Black Carbon Emission Controls

Anenberg, Susan C., Schwartz, Joel, Shindell, Drew, Amann, Markus, Faluvegi, Greg, Klimont, Zbigniew, Janssens-Maenhout, Greet, Pozzoli, Luca, Van Dingenen, Rita, Vignati, Elisabetta, Emberson, Lisa, Muller, Nicholas Z., West, J. Jason, Williams, Martin, Demkine, Volodymyr, Hicks, W. Kevin, Kuylenstiema, Johan, Raes, Frank, Ramanathan, Veerabhadran, Environmental Health Perspectives

BACKGROUND: Tropospheric ozone and black carbon (BC), a component of fine particulate matter (PM [less than or equal to] 2.5 pin in aerodynamic diameter; [PM.sub.2.5]), are associated with premature mortality and they disrupt global and regional climate.

OBJECTIVES: We examined the air quality and health benefits of 14 specific emission control measures targeting BC and methane, an ozone precursor, that were selected because of their potential to reduce the rate of climate change over the next 20-40 years.

METHODS: We simulated the impacts of mitigation measures on outdoor concentrations of [PM.sub.2.5] and ozone using two composition-climate models, and calculated associated changes in premature [PM.sub.2.5]-and ozone-related deaths using epidemiologically derived concentration-response functions.

RESULTS: We estimated that, for [PM.sub.2.5] and ozone, respectively, fully implementing these measures could reduce global population-weighted average surface concentrations by 23-34% and 7-17% and avoid 0.6-4.4 and 0.04-0.52 million annual premature deaths globally in 2030. More than 80% of the health benefits are estimated to occur in Asia. We estimated that BC mitigation measures would achieve approximately 98% of the deaths that would be avoided if all BC and methane mitigation measures were implemented, due to reduced BC and associated reductions of non-methane ozone precursor and organic carbon emissions as well as stronger mortality relationships for [PM.sub.2.5] relative to ozone. Although subject to large uncertainty, these estimates and conclusions are not strongly dependent on assumptions for the concentration--response function.

CONCLUSIONS: In addition to climate benefits, our findings indicate that the methane and BC emission control measures would have substantial co-benefits for air quality and public health worldwide, potentially reversing trends of increasing air pollution concentrations and mortality in Africa and South, West, and Central Asia. These projected benefits are independent of carbon dioxide mitigation measures. Benefits of BC measures are underestimated because we did not account for benefits from reduced indoor exposures and because outdoor exposure estimates were limited by model spatial resolution.

KEY WORDS: air quality, climate change, health impact analysis, outdoor air, particulate matter. Environ Health Perspect 120:831-839 (2012). http://dx.doi.org/10.1289/ehp.1104301 [Online 14 March 2012].

Tropospheric ozone and black carbon (BC), a component of fine particulate matter (PM [less than or equal to] 2.5 pm in aerodynamic diameter; PM2.5), have been associated with deleterious effects on human health (e.g., Jerrett et al. 2009; Laden et al. 2006; Pope et al. 2002), agriculture (e.g., Ashmore 2005), and climate (e.g., Ramanathan and Carmichael 2008). Methane, a relatively short-lived greenhouse gas (residence time 8-10 years), is an ozone precursor that affects background ozone concentrations. Controlling methane emissions may be a promising means of simultaneously mitigating climate change and reducing global ozone concentrations, compared with controlling shorter-lived ozone precursors [nitrogen oxides (N[O.sub.x]), carbon monoxide (CO), and non-methane volatile organic compounds (NMVOCs)] (West et al. 2006, 2007). The latter may have larger and more immediate air quality and health benefits near the areas with emission reductions but smaller benefits (CO, NMVOC) or net disbenefits (N[0.sub.x]) for climate. Major anthropogenic sources of methane include fossil fuel production and distribution, landfills, livestock, rice cultivation, and wastewater treatment. BC is a product of incomplete combustion from sources such as biomass burning, transportation (mainly diesel vehicles), residential combustion, and industry, and is coemitted with other pollutants, including N[0.sub.x], NMVOCs, CO, sulfur dioxide (S[O.sub.2]), and organic carbon.

Climate benefits of reducing BC may be partially offset by associated reductions of coemitted pollutants that may have a net cooling effect on climate (and a net warming effect when reduced), either directly (organic carbon) or after chemical transformation in the atmosphere (organic carbon, S[O.sub.2], and N[O.sub.x]). However, all emission reductions leading to reduced ozone and [PM.sub.2.5] concentrations would be expected to have health benefits.

Mitigating ozone and BC may benefit climate and health simultaneously (e.g., Jacobson 2002; Smith et al. 2009; West a al. 2006); because methane and BC are short-lived relative to the long-lived greenhouse gases [e.g., carbon dioxide (C[O.sub.2])], mitigation would reduce the rate of climate change in the near-term (Jackson 2009; Ramanathan and Carmichael 2008). Although a recent series of studies has examined the ancillary health benefits of greenhouse gas mitigation (Haines et al. 2009), the health benefits of mitigating ozone and BC as climate forcers have been studied less extensively. Studies examining the health impacts of all fossil fuel and biofuel emissions (Jacobson 2010), percentage reductions in ozone precursors (West a al. 2006) and BC (Arenberg a al. 2011), and adoption of European vehicle emission standards in the developing world (Shindell et al. 2011) suggest that controlling methane and BC emissions may substantially benefit global public health, particularly in Asia where large populations are exposed to high [PM.sub.2.5] and ozone concentrations (Ramanathan et al. 2008).

The United Nations Environment Programme (UNEP) and the World Meteorological Organization (WMO) therefore initiated an integrated assessment of the potential climate, health, agricultural, and economic benefits that would be achieved by further implementing methane and BC mitigation measures already employed in various parts of the world (UNEP 2011). In the present study, we used emissions scenarios developed for the UNEP/WMO assessment to examine the potential air quality and health benefits of methane and BC mitigation measures in more detail.

Methods

Emission scenarios and modeling. We used five emissions scenarios developed for the UNEP/WMO assessment to examine methane and BC mitigation impacts on air quality and health globally and in five world regions [see Supplemental Material, Figure 1 (http://dx.doi.org/10.1289/ehp.1104301)]. These scenarios include a present-day (2005) reference case, a 2030 reference scenario that incorporates International Energy Agency energy projections (International Energy Agency 2009) and all presently agreed upon (but no additional) policies affecting emissions (see Supplemental Material, Table 2 and Figure 2), and three different policy scenarios in which varying degrees of additional emission controls are implemented by 2030. To isolate the impacts of anthropogenic emission changes, all scenarios assume identical meteorology and natural emissions [including open biomass burning (i.e., wildfires); year 2000]. The emission scenarios and their projected effects on climate are detailed by Shindell et al. (2012) and are summarized in Supplemental Material, pp. 4-9.

We selected the three policy scenarios based on an evaluation of the potential climate impacts of approximately 2,000 mitigation measures defined in the International Institute for Applied Systems Analysis (IIASA) Greenhouse Gas and Air Pollution Interactions and Synergies (GAINS) model (Amann et al. 2011). Climate impacts of each measure were classified according to [CO.sub.2] equivalence, which was calculated based on global warming potential (GWP) over a 100-year time horizon for predicted methane, CO, [SO.sub.2], [NO.sub.x], NMVOCs, BC, organic carbon, and …

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Publication information: Article title: Global Air Quality and Health Co-Benefits of Mitigating Near-Term Climate Change through Methane and Black Carbon Emission Controls. Contributors: Anenberg, Susan C. - Author, Schwartz, Joel - Author, Shindell, Drew - Author, Amann, Markus - Author, Faluvegi, Greg - Author, Klimont, Zbigniew - Author, Janssens-Maenhout, Greet - Author, Pozzoli, Luca - Author, Van Dingenen, Rita - Author, Vignati, Elisabetta - Author, Emberson, Lisa - Author, Muller, Nicholas Z. - Author, West, J. Jason - Author, Williams, Martin - Author, Demkine, Volodymyr - Author, Hicks, W. Kevin - Author, Kuylenstiema, Johan - Author, Raes, Frank - Author, Ramanathan, Veerabhadran - Author. Journal title: Environmental Health Perspectives. Volume: 120. Issue: 6 Publication date: June 2012. Page number: 831+. © 2006 National Institute of Environmental Health Sciences. COPYRIGHT 2012 Gale Group.

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