Understanding Climate Change Feedbacks (2003) / Chapter Skim
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6 Atmospheric Chemical Feedbacks
6 Atmospheric Chemical Feedbacks
Pages 76-87
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From page 76... ...
Both tropospheric and stratospheric chemical processes interact with temperature, humidity, circulation, and air composition changes. The oxidizing capacity of the atmosphere and the processes that convert effluents into pollutants may be altered by climate change.
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From page 77... ...
. Atmospheric chemical feedbacks arise when alterations in the surface temperature, precipitation, and other changes in climate interact with air chemistry to alter the abundance or properties of greenhouse gases or aerosols, which then produce an additional climate change.
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From page 78... ...
AN EXAMPLE OF THE MULTIPLE DIMENSIONS OF CLIMATEAIR CHEMISTRY FEEDBACK Methane is the greenhouse gas whose increase since the pre-industrial era provides a climate forcing that is second only to carbon dioxide. Methane is also a chemically active species that affects the abundance of the OH radical, the most important tropospheric oxidizer.
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From page 79... ...
Gas phase production of H2SO4 can lead to a burst of new particles when there are few existing particles, while liquid phase oxidation will only grow existing particles (Seinfeld and Panis, 1998~. The consequences of a larger number of particles are different from the same
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From page 80... ...
Ozone itself is a gas phase oxidant for various olefin organic species and a liquid phase oxidant for many sulfur species, particularly SO2 that is converted into sulfuric acid (Seinfeld and Panis, 1998~. Hence, changes in atmospheric variables can change ozone abundance and drive feedbacks through ozone.
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From page 81... ...
For example, aerosols convert active nitrogen oxides to nitric acid and hence reduce the ability of the atmosphere to photochemically generate ozone. Thus, chemical processing, coupled with the generation of aerosols in the atmosphere, couples atmospheric chemical processes with the important cloud feedback mechanism.
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From page 82... ...
As discussed above, the connection between gas phase oxidation to new particle formation and its coupling to cloud condensation nuclei formation is an example of the coupling between purely chemical processes and other atmospheric feedbacks.
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From page 83... ...
Changes in stratospheric ozone abundances and their future levels can be altered by the changes in stratospheric temperature and water vapor, which are driven by greenhouse gases. Greenhouse warming at the surface and cooling of the stratosphere by increased carbon dioxide, methane, and water vapor may delay the expected recovery of the ozone layer, the ozone hole may persist longer, and Arctic ozone depletions may continue beyond the time currently estimated.
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From page 84... ...
Therefore, requirements for attainment of an air quality standard in a given region or location will be affected by climate change. Factors That Control Chemical Feedbacks Processes that are affected by changes in temperature, water vapor abundance, and other climate variables by means of atmospheric chemical processes are 1.
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From page 85... ...
Many of the atmospheric chemistry feedbacks are identified in principle and have been semi-quantitatively evaluated by their proponents, but reliable quantification awaits a consensus from the community that includes a more accurate treatment of the key processes and their integration into comprehensive models. The first step in dealing with climate-air chemistry feedbacks is to better understand the atmospheric processes responsible for the formation and destruction of the chemical species of interest.
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From page 86... ...
To understand the role of anthropogenic activities in changing the atmospheric burden of the carbonaceous aerosols, speciated measurements of the aerosols at the emission source and in the atmosphere need to be made with the same techniques so that atmospheric burdens can be attributed to specific sources. In addition, absolutely calibrated emissions inventories need to be developed for each species of carbonaceous aerosols so that the atmospheric measurements provide a true test of the global models.
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From page 87... ...
· The key processes that control the abundance of tropospheric ozone need to be quantified, including but not limited to stratospheric influx; natural and anthropogenic emissions of precursor species such as NOx, CO, and VOC; the net export of ozone produced in biomass burning and urban plumes; and the loss of ozone at the surface. Improved characterization is required of the type and magnitude of chemistry-climate feedbacks that would lead to alteration of these processes with future climate change.
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