sensitive to bulk chemistry; they are affected mostly by surface chemistry. The atmospheric-science community has made progress in analyzing the bulk composition of PM, either by using collected samples or single-particle analysis. However, little (if any) progress is being made in the atmospheric-science or health-science community in understanding PM surface composition or interactions between PM surface composition and biologic fluids.

Whether or not a specific priority-setting was intended, the order of the five recommendations and their subrecommendations will suggest priorities to the reader. Thus, the order is important and should be the same everywhere it is discussed (that is, on page 11–1, in the tables, in Section 11.1, and in the synthesis of key issues). Likewise, the same wording should be used everywhere the recommendations are presented. Because priorities are useful for decision-makers, the committee recommends that NARSTO attempt to assign priorities to the recommendations for future research in terms of when each activity needs to be undertaken and what should receive more funding. The committee recognizes the difficulty in assigning uniform priorities for all countries and situations. Thus, based on the basis of the level of understanding in different areas, regional priorities may be appropriate.

The committee also identified a number of specific problems with the recommendations themselves. Recommendation 2.8 should mention the relationships between sources and health effects, rather than only constituents and health effects. A recommendation for continued and enhanced laboratory studies of aerosol atmospheric chemistry and microphysics is missing. And there is no recommendation for a better understanding of PM surface area and surface composition, which may be more closely associated with health effects.