on source attribution applications. An expert group should be established to help design this source-attribution network (e.g., suggesting parameters to be measured, identifying appropriate monitoring sites, developing an embedded research program). These efforts should consider the need for international cooperation with opportunities to collaborate existing international efforts, such as the World Meteorological Organization’s International Global Atmospheric Chemistry Observation program.

CONCLUDING THOUGHTS

The pollutants discussed in this study do not represent all species of concern, but they do illustrate the variability of pollutant composition and behavior and provide focused examples for analyzing the phenomenon of long-range pollutant transport. Present global socioeconomic scenarios predict that adverse air quality impacts from distant sources of pollution are likely to grow and cause increasing concern in the United States and other nations that are determined to provide clean air for their citizens and their ecosystems. Enhancing atmospheric observations, chemical transport models, trend analyses, the understanding of pollutant chemical and physical transformations, and emission inventories and projections will all be critically important to better quantify such effects.

The Committee wishes to emphasize that our atmosphere connects all regions of the globe, and pollution emissions within any country can affect populations, ecosystems, and climate properties well beyond national borders. Likewise, measures taken to decrease emissions in any region can have benefits that are distributed across the Northern Hemisphere. The United States, as both a source and receptor of long-range pollution, has an interest in remaining actively engaged in this issue, including support of more extensive international cooperation in research, assessment, and ultimately, emissions control efforts.

It is clear that local pollution can be affected by global sources, although in most cases air quality violations are driven by local emissions. Regardless of where the pollution originates, protecting human and ecological systems from dangerous levels of pollution should be the policymakers’ primary objective. Meeting this objective will require strengthening domestic pollution control efforts to whatever levels are required to ensure that a population’s total pollution exposure (from local, regional, and distant sources) does not exceed safe levels. Reducing the impacts of distant emissions on local air quality cannot be achieved by domestic efforts alone. Cooperative international action needs to be pursued vigorously to advance our understanding of long-range transport of pollution and its impacts, and to use that understanding to effectively control emissions from both domestic and foreign sources.



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