Morton Lippmann, Ph.D., is Professor of Environmental Medicine at NYU School of Medicine, where he has been a faculty member since 1967. Much of his research has been focused on exposure to, and the health effects of, particulate matter (PM) in ambient air, and on specific airborne agents, notably ozone, sulfuric acid, and asbestos. Richard B. Schlesinger, Ph.D., is Senior Associate Dean for Academic Affairs and Research in the Dyson College of Arts and Sciences of Pace University, New York, NY, Professor of Biology and Environmental Science, and Executive Director of the Dyson College Institute of Sustainability and the Environment. His research has focused on the toxicology of ambient air pollutants.