EPA should redirect sufficient resources to undertake immediately carefully designed efforts to develop a biologically based dose model for deposition and fate of particulate matter in the respiratory tract in normal and compromised subjects.

EPA should re-evaluate its current plans for the PM_2.5 monitoring program in light of this report. The agency should consider more fully the possibility that future research results might indicate that the expensive monitoring program is not measuring the most biologically important aspects of particulate matter. Such an inconsistency could undermine the credibility and effectiveness of future control strategies and could underprotect susceptible subpopulations.

EPA's currently planned, university-based centers of excellence for particulate-matter research will require time to develop before producing major results, so EPA should strive to initiate the competitive awards for more of these centers in Fiscal 1998 instead of Fiscal 1999, as currently planned. The centers should augment, not replace, specific investigator-initiated, competitive research grants or competitive cooperative agreements.

In addressing each of these recommendations, EPA should seek a mixture of extramural and intramural investigations that takes maximum advantage of the contributions that extramural scientists can offer, while enhancing the intramural capacity of EPA to address key questions about particulate matter in a timely and credible manner.