The importance of gas-aerosol interactions in policy making

In current emission comparisons, the most cost effective method is one which employs multicomponent climate change mitigation strategies. These strategies involve analyzing both the direct and indirect effects of various linked emissions. However, the information of indirect effects between most gaseous pollutants and aerosols is absent. Shindell et al. (2009) took two approaches to calculate the impact of emissions on aerosols and the influence of these on radiative forcing. They found that the global warming potential (GWP) is substantially larger when the direct effects of aerosol interactions are considered and increases further when aerosol-cloud interactions are taken into account. Therefore, as atmospheric chemistry links methane, ozone, and aerosols, the policies regarding multigas mitigation should take gas-aerosol interactions into consideration.  Alyson Stark
Shindell, D., Faluvegi, G., Koch, D., Schmidt, G., Unger, N., Bauer, S., 2009. Improved Attribution of Climate Forcing to Emissions. Science 326: 716-718.

Shindell et al. relied heavily on averaged radiative forcing (RF) to compare various emissions and to estimate GWP. To find the response of atmospheric composition to both the collective and individual effects of emissions, the researchers calculated abundance based RF, which measured the effects of all emissions changing concurrently, and emissions based forcing, which instead attributed the response to a specific pollutant. Using these two techniques, Shindell et al. estimated several 100-year GWPs. These computations demonstrated that, with the absence of aerosol responses, the results were similar to previous studies. However, once the radiative effects are regarded, the GWP becomes larger in both methane and carbon monoxide (CO). Compared to the initial situation with no aerosol, the possible methane emission range increases, from approximately 25 to a range of 25-40 over a 100 year horizon. Similarly, the CO emissions initially begin at a 1-3 range and increases to a 3-8 range.  However,  the accuracy of these values is essential, and it there still remains much uncertainty in the predictions. For example, increases in these values also increases carbon dioxide, which perpetuates higher GWPs, and leads to more uncertain policymaking. 

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