1. Comments on the Research of Dr. Bob Musselman (Atmospheric Deposition Research) Allen S. Lefohn, Ph.D. A.S.L. & Associates Helena, Montana August 10, 2005

2. A Very Important Issue The growing human needs in urban, suburban, and rural settings drive the increasing need for clean air, as well as clean and plentiful water. A very important question to address is the limits of acceptable change in air and water quality.

3. Critical Limits for Change It is necessary to explore the identification of these critical limits to air quality problems by determining the response of terrestrial and aquatic ecosystems to atmospheric deposition, which includes ozone. The research work by Drs. Musselman and Massman is extremely important in developing measures that identify the critical limits to air quality problems.

4. Identifying Critical Limits Currently, the U.S. Environmental Protection Agency is reviewing the state of knowledge of the effects of ozone on human health and welfare (e.g., vegetation) and has published the first draft of its findings in an Ozone Criteria Document (CD) that was released to the public in January 2005. A key section of the CD focuses on effects- based air quality exposure- and dose-response indices that relate ozone to vegetation effects.

5. RMRS Scientists Contribute to the Ozone Criteria Document The section is important because it forms the scientific rationale for the selection of an index that the U.S. EPA may propose as a form for the secondary standard. Dr. Bob Musselman, Dr. Bill Massman, and I co-authored this section. The published research results of Drs. Musselman and Massman played an important role in the conclusions concerning the limitations associated with exposure and flux- based indices for protecting vegetation.

6. Dr. Bob Musselman’s Research Dr. Musselman’s current and past research is extremely valuable in identifying candidate exposure and flux-based indices. Much of Dr. Musselman’s research in the 1980s and 1990s provided valuable information on exposure dynamics as related to vegetation growth. Dr. Musselman’s work emphasized the importance of (1) providing greater weight to the higher hourly average ozone concentrations, while including mid- level values, and (2) nighttime ozone exposures.

7. Dr. Bill Massman’s Research Dr. Massman’s research has provided both the conceptual modeling and the results to show the relative timing of ozone uptake, concentration exposure, and defense mechanisms and how all three interact together to affect vegetation. His research results have been used in highlighting the importance of defense processes when attempting to use flux-based indices to predict vegetation effects.

8. Integrating the Results of Drs. Musselman and Massman Over the past several years, Drs. Musselman, Massman, and I have co-authored peer-review papers that integrated ozone flux modeling with vegetation effects. The integrated work is important for establishing a rational research approach for using dose (i.e., ozone uptake) in assessing possible vegetation effects from ozone. A careful evaluation of plant defense mechanisms is important so that overestimates are avoided when predicting vegetation effects associated with ozone dose/exposure.

9. Who Comprises the Scientific Community in this Area of Research? The contributions of Drs. Musselman and Massman in the exposure- and dose-response scientific area allow for the more efficient application of models to predict the relationship between ozone and vegetation effects.. The results published by Drs. Musselman and Massman provide local, regional, national, and international scientists with the information that is needed to develop scientifically defensible models that relate the relative timing of ozone uptake, concentration exposure, and defense mechanisms with vegetation effects.

10. How Does One Specifically Benefit from the Findings of the RMRS Air Research Program? Drs. Musselman and Massman have demonstrated the capability to provide a bridge between models that are used to relate ambient air quality exposure and pollutant uptake to vegetation. These models are used to estimate safe levels that will protect vegetation from ozone. Academic, government, private sector scientists, and policy makers are utilizing the findings that are associated with the results reported by Drs. Musselman and Massman.

11. Conclusion As indicated in my introductory comments, the identification of critical limits of acceptable change in air and water quality is important in establishing protective standards. The research work by Drs. Musselman and Massman has proven to be extremely important in developing measures that identify some of the critical limits to air quality problems. As development continues to occur across the United States, including the Rocky Mountain area, more and more attention will be focused on the potential for anthropogenic emissions and their chemical reaction products to affect our nation’s resources.