Publication

Human exposure to ambient ozone (O-3) has been linked to a variety of adverse health effects. The ozone level at a location is contributed by local production, regional transport, and background ozone. This Study combines detailed emission inventory, air quality modeling, and census data to investigate the source-receptor relationships between nitrogen oxides (NOx) emissions and population exposure to ambient O-3 in 48 states over the continental United States. By removing NOx emissions from each state one at a time, we calculate the change in O-3 exposures by examining the difference between the base and the sensitivity simulations. Based on the 49 simulations, we construct state-level and census region-level source-receptor matrices describing the relationships among these states/regions. We find that, for 43 receptor states, cumulative NOx emissions from upwind states contribute more to O-3 exposures than the state's own emissions. in-state emissions are responsible for less than 15% Of O-3 exposures in 90% of U.S. states. A state's NOx emissions can influence 2 to 40 downwind states by at least a 0.1 ppbv change in population-averaged O-3 exposure. The results suggest that the U.S. generally needs a regional strategy to effectively reduce O-3 exposures. But the current regional emission control program in the U.S. is a cap-and-trade program that assumes the marginal damage of every ton of NOx is equal. In this study, the average O-3 exposures caused by one ton of NOx emissions ranges from -2.0 to 2.3 ppm-people-hours depending on the state. The actual damage caused by one ton of NOx emissions varies considerably over space. (C) 2009 Elsevier Ltd. All rights reserved.