Using air quality modeling to study source-receptor relationships between nitrogen oxides emissions and ozone exposures over the United States

摘要

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 (NO_x) emissions and population exposure to ambient O_3 in 48 states over the continental United States. By removing NO_x 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 NO_x 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 NO_x 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 NO_x is equal. In this study, the average O_3 exposures caused by one ton of NO_x emissions ranges from -2.0 to 2.3 ppm-people-hours depending on the state. The actual damage caused by one ton of NO_x emissions varies considerably over space.