effects and sources of the complex mixture of pollutants in urban air are better understood over the long term. At a minimum, these efforts should include

• Active collaborative research design.

• A shift by funding agencies toward giving higher priority to research implemented by truly multidisciplinary teams.

• Adequate research funding for projects to allow the active involvement of a full team, including senior investigators from multiple disciplines, if needed.

• Fellowships or sabbaticals that will enable scientists to spend time with groups outside their disciplines.

• Redoubled efforts of appropriate professional societies to hold joint workshops and meetings and to publish proceedings.

Ultimately these efforts will need to result in fully multidisciplinary review, integration, and synthesis of the science by EPA in the criteria document and staff paper processes.

In 1998, the committee recognized that meeting its research agenda would require a substantial investment as well as the development of new research approaches to address complex scientific questions. In reviewing work carried out since that report, the committee has identified seven scientific challenges that should be a focus of further work to complete the PM research agenda. Of course, there are other challenges, but they are not as critical to moving forward on the full agenda. The next chapter gives the committee’s guidance on strategies to meet these challenges.