Impacts of the long-range transport of global pollutants and precursors on the U.S. air quality in the present and future climate conditions

Human health and the natural environment are significantly impacted by air pollution problems such as elevated tropospheric ozone and aerosols. U.S. air quality is determined by chemical processes and emissions on local to regional scales, long-range transport of global pollutants and precursors originating from global emissions, and global and regional climate changes and variability. The rapid economic growth of regions such as Asia had increased the long-range transport of pollutants and their precursors into North America. Therefore, the future U.S. air quality could be significantly affected by emissions changes due to the global economic growth coupled with climate change. To understand the impact of the long-range transport on U.S. air quality in present and future climates, a state-of-the-art integrated modeling system that includes a global chemical transport model (CTM), a regional climate model (RCM), an air quality model, and an emissions model is used in this study. This system is used to quantify the influence of the long-range transport of pollutants and their precursors on U.S. air quality in the present and future climate conditions as driven by the global circulation model simulations. Two IPCC (A1Fi and B1) emissions scenarios are used for projecting future emissions from the 1999 U.S. EPA National Emission Inventory, National Pollutant Release Inventory, and the Big Bend Regional Aerosol and Visibility Observational Study inventory, and the adjusted Emission Database for Global Atmospheric Research. The results suggest that the chemical lateral boundary conditions from long-range transport strongly impact U.S. air quality and should be appropriately represented. The long-range transport of global pollutants and precursors from remote areas can elevate U.S. background tropospheric ozone concentration and lead to distinct regional air quality changes.