plumes emanating from fires in Mexico and extending into Florida, Texas, New Mexico, California, and Wisconsin. Along the Gulf Coast of Texas, a public health alert was issued advising residents to stay indoors to avoid the smoke. Similarly, chemical measurements have documented the import of pollutants transported from the Eurasian continent across the Pacific Ocean into the western part of North America (Jaffe et al. 1999; Wilkening et al. 2000). The rapid industrialization of the Asian continent could conceivably exacerbate this phenomenon.
Pollutant emissions from North America, Europe, and Asia are probably causing an increase in the so-called background concentrations of pollutants in the northern hemisphere. For example, there is evidence that the background concentration of tropospheric (lower atmospheric) O3 in the northern hemisphere has increased by as much as a factor of 3 in the past 100 years, presumably in response to growing pollutant emissions from throughout the hemisphere, including the United States (Volz and Kley 1988; Staehelin et al. 1994). In addition, the mean summer afternoon concentration in rural areas of the United States (Logan 1988) and Europe (Scheel et al. 1997) have grown by a factor of 4 to 6. As standards for PM and O3 become more stringent and the thresholds for health effects from air pollution are found to be lower or nonexistent, the increasing level of background pollution causes difficulty in separating the effects of local and regional air pollution from global problems.
To address these international aspects of air pollution, the AQM system will need to continue to develop, implement, and utilize sophisticated remote-sensing technology to document and track the phenomena. It will also be necessary for the United States to continue to pursue collaborative projects and enter into agreements and treaties with other nations (especially developing nations) to help minimize the emissions of pollutants that can degrade air quality on continental and intercontinental scales. Examples of past initiatives and treaties undertaken by the United States to mitigate atmospheric problems of international concern include the development and implementation of the Montreal Protocol to address stratospheric O3 depletion, the Convention on the Long-Range Transport of Transboundary Air Pollution (CLTRAP) to mitigate a wide range of air quality problems, and NARSTO to develop a coordinated program of research on the causes of and remedies to ground-level O3 and PM pollution in Canada, Mexico, and the United States.
The earth’s climate is warming (IPCC 2001). Although uncertainties exist, the general consensus within the scientific community is that this