Phase I

Ozone (O3) and particulate matter (PM) are not only key criteria pollutants, but also major climate-forcing substances. Recently, a widely discussed study has raised the issue of whether the emissions reduction of non-CO2 gases such as O3 and PM, and black carbon in particular, can be a viable alternative to CO2 reduction in order to curb global warming (Hansen et al., 2000). This study identified the importance of examining the extent to which reductions in air pollution, especially tropospheric O3 and black carbon, could simultaneously benefit regional and local air quality and global climate.

Moreover, another recent study suggested that black carbon could be second only to CO2 in exerting a positive radiative forcing on global climate (Jacobson, 2001). There is also mounting evidence that the long-range transport of criteria pollutants originating from some developing countries, especially the more industrialized nations in Asia such as China and India, could affect air quality in the U.S. in addition to contributing to the global background of climate-forcing substances. This intercontinental transport issue is expected to worsen with the rapid growth in emissions in these regions. For example, recent modeling studies showed that by 2020 Asian emissions could contribute as much as 2-6 ppb of O3 in the western U.S., offsetting the Clean Air Act efforts by up to 25% in that region (Jacob et al., 1999), and could increase the global mean O3 level by up to 10% (Collins et al., 2000); Asian and Saharan dust also appear to contribute a significant amount of PM in the western and southeastern U.S. (Husar, 2001, http://capita.wustl.edu/CAPITA/, Hanna et al., 1999, http://www.cep.unc.edu/empd/projects/MITP

To examine some of these issues, the U.S. EPA recently organized a workshop on “Photo-oxidants, Fine Particles, and Haze across the Arctic and North Atlantic: Transport, Observations and Models,” which included participation by leading experts on global chemistry and regional air quality. The workshop presentations and discussions, based on observational and modeling studies, revealed important aspects of the role of continental emissions in increasing the burden of regional air pollutants in the Northern hemisphere. This burden is further magnified by the intercontinental transport of pollutants associated with large-scale stationary seasonal patterns and the associated synoptic weather conditions (e.g., Hanna et al., 2001). To address the many aspects of intercontinental transport of air pollutants and other climate-forcing substances, the workshop recommended the development of a systematic approach to model evaluation, long-term monitoring, intensive observational studies, and emissions inventory development. The workshop also emphasized the need to improve our understanding of the linkages between regional and global air quality and climate change, and the need to improve the communication between the various scientific communities that are working to address these issues.

The Phase I project is an important step toward understanding the link between climate change and air pollution. EPA identifies various task elements to establish a better scientific foundation to address the connection between climate change and criteria pollutants such as ozone and PM, as well as the issues related to intercontinental transport of these and other climate-forcing substances. Within this goal the following objectives are delineated:

(1) conduct four studies to provide a better understanding of the linkages between climate change and air pollution and issues related to the intercontinental transport of the relevant pollutants;
(2) construct a conceptual model that describes in detail the meteorological, chemical, and emissions processes associated with the linkages between climate change, air pollution, and intercontinental transport;
(3) assess the technical strengths, weaknesses, and feasibility of using available/emerging meteorological, emissions, climate, and air pollution models, and emissions, meteorological, ambient air quality, and satellite databases for simulating these processes;
(4) prepare a modeling protocol describing how to apply modeling tools and databases in an integrated global climate and intercontinental transport assessment; and
(5) organize a panel of experts in the fields of global emissions inventories, air pollution modeling and transport, and climate for advice on completing the task order requirements.

UNC-CEP staff members, in collaboration with Harvard University, Stanford University, and Argonne National Laboratory, have collaborated to fill the project requirements.

Final Report - Phase 1 (Word, PDF)
Development of Future Emission Scenarios for Global Atmospheric Models (Word, PDF)
Appendices (Word, PDF)

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Final Report