Air Pollution as a Climate Forcing: A Workshop

Day 5 Presentations

Multi-Pollutant Strategies and Integrated Assessment

Terry J. Keating
Office of Air and Radiation, US Environmental Protection Agency, Washington, DC. U.S.A.

You may download a PDF version (750 MB) of this presentation.


As demonstrated throughout this workshop, the problems of air quality and climate change are linked together, particularly through the sources and effects of tropospheric ozone and aerosols. A strategy designed to address one of these issues will have implications for the other. Therefore, to design the most cost-effective strategies to address both problems, it is necessary to examine the problems simultaneously using an integrated assessment approach, which links changes in policies to changes in technology, emissions, air quality, deposition, exposure, and health, ecological, and economic impacts.

While air pollution control laws and policies have often been developed on a pollutant-by-pollutant basis, the need to examine multi-pollutant strategies is not new. In 1994, Grennfelt et al. argued that a multi-pollutant approach should be used to address the linked problems of tropospheric ozone and acidifying deposition. Their call was heeded by the countries of Europe and North America in the 1999 Gothenburg Protocol to the Convention on Long Range Transboundary Air Pollution. Developed with the aid of the European RAINS integrated assessment model, this international agreement address the simultaneous control of SO2, NOx, NH3, and volatile organic compounds.

Since the mid-1990's, the U.S. EPA has worked to develop and analyze multi-pollutant strategies for the control of electric power plants, leading up to the proposed Clear Skies Act and similar legislation currently being debated in Congress. Over time, sophisticated modeling tools have been developed to address how the electricity sector will react to different policies (Integrated Planning Model) and to quantify the various health and environmental endpoints of interest (Criteria Air Pollutants Modeling System), in addition to understanding how changes in emissions will effect concentrations and deposition.

Through the Integrated Environmental Strategies (IES) Program, the U.S. EPA has been providing assistance to developing countries to help them identify and implement strategies that simultaneously and efficiently achieve air quality and climate change policy goals. By working with government agencies and research institutions, IES programs have helped to build in-country capacity in Argentina, Brazil, China, Chile, South Korea, India, and Mexico. The results of two IES programs are the subject of two presentations at this workshop (see Chen and Cifuentes on Day 4).

In the last 2 years, the U.S. EPA has launched two efforts to explore the relationships between regional air quality, intercontinental transport, and climate change. The first effort, which is an element of the EPA's Global Change Research Program, seeks to understand the impacts of global change on regional air quality by linking global climate and air quality models to regional air quality models and a health impacts assessment. The second, known as the International transport and Climatic effects of Air Pollutants (ICAP) Project, seeks to understand the climate and transport implications of regional air quality control strategies in the U.S. and abroad.

Thus, while all of the tools necessary to fully address the linkages between air quality and climate change are not yet available, a number of tools have already been developed and are being applied to the linked problems. Some of these applications, such as the analyses of the electric power sector, use a multi-attribute approach in which a variety of impact endpoints are predicted using a variety of complex and simple models. The output of this sort of integrated assessment tends to be a matrix of policy options and impact endpoints, some of which are monetized. Other applications, such as those using the European RAINS model, use a multi-objective approach in which reduced-form models are derived from more complex models and used to drive constrained optimizations. The output of this sort of integrated assessment is a least-cost strategy for achieving a specified set of health and environmental endpoints.

As we consider how to move towards a better understanding of the air quality-climate linkages and how to build upon our existing tools and analyses, we must consider the implications of the different types of integrated assessment and the different ways in which the assessment results may be used. In particular, we need to:

  • Bound the Effects, Feedbacks & Uncertainties. We first need to the direction of the changes produced by different policies. Then we can address the relative magnitude of the impacts. Before developing reduced-form models, we need to know if there are nonlinearities and identify the spatial and temporal scales of the relationships. Recognizing that results will be used to compare one type of impact to another in a risk/risk tradeoff, we need to understand and communicate the relative uncertainties of our predictions of different effects.
  • Differentiate Particles. Health effects researchers are working to differentiate the effects associated with different constituents or characteristics of fine particles. While the results of this research may be a long time off and mass will continue to be the leading metric for characterizing fine particles for some time, we should be working to understand the implications that physical processes and control policies have on other characteristics, including particle number, size distribution, and species composition. Such information can help us to take advantage of new health effects data as it becomes available and to design no regrets strategies that avoid worsening one characteristic of fine particle pollution while trying to improve another.
  • Make Global Effects "Real". The history of international environmental policy suggests that policy makers agree to international action only after they understand that it is in their own national interest. Therefore to inform international policy, it is necessary to develop a better understanding of the climate-air quality linkages at the regional and local scales. Industrialized countries must understand the local impacts of global action, including how global action changes the costs of achieving local environmental goals. Developing countries need to understand that through local actions, they can address local as well as global concerns.

Workshop Homepage * Background
Summaries: Overview, Gases, Aerosols, Tech., Health, Agri./Eco.
Abstracts: Day 1, Day 2, Day 3, Day 4, Day 5 * Participants