Both population and living standards are increasing in many parts of the world; often, so are the resulting pollutant emissions. At the same time, air quality standards are being tightened in response to studies that demonstrate adverse health consequences at ever lower exposures. Other studies document unwelcome impacts of air pollutants on crop yields and the viability of forests, grasslands, and other natural ecosystems. Still other studies are unveiling the interplay between air pollution levels and climate change on scales ranging from regional to global. All of these concerns have led to increasing international efforts to recognize and measure long-range transport of pollutants. They have also spurred attempts to predict how expected changes in population; in production of food, energy, and goods; and in climate will impact future pollutant transport and air quality.
Federal, state, and local agencies are faced with the need to understand and manage the current impact of long-range transport of pollution on health and well-being (relative to the impacts of local pollution sources), as well as the need to develop measurement methods and models to track pollution transport trends and project their future levels and impacts. Agencies with environmental regulatory responsibilities need to better understand how, when, and where long-range transport may lead to National Ambient Air Quality Standard (NAAQS) violations or pollutant levels that exceed other regulatory guidelines. Agencies with atmospheric research portfolios are interested in knowing what gaps in knowledge and capability weaken our understanding of current long-range transport of pollutants, as well as those that reduce our abilities to measure trends and predict future activity and its impacts. They would also like to envision how our atmospheric observational capabilities and diagnostic and predictive models can be improved to close these gaps.
In response to these challenges the Environmental Protection Agency (EPA), the National Oceanic and Atmospheric Administration (NOAA), the National Aeronautics and Space Administration (NASA), and the National Science Foundation (NSF) have cosponsored this National Research Council (NRC) Committee to explore these issues for four specific pollutant classes: ozone and it precursors (O3), fine particulate matter and its precursors (PM), atomic and molecular mercury (Hg), and persistent organic pollutants (POPs).1 Specifically, the Committee was asked to consider the impacts of long-range pollution transport on air quality, pollutant deposition, and radia-