Regional Air Quality Management Aspects of Climate Change: Impact of Climate Mitigation Options on Regional Air Emissions

We investigate the projected impact of six climate mitigation scenarios on U.S. emissions of carbon dioxide (CO<sub>2</sub>), sulfur dioxide (SO<sub>2</sub>), and nitrogen oxides (NO<sub>X</sub>) associated with energy use in major sectors of the U.S. economy (commercial, residential, industrial, electricity generation, and transportation). We use the EPA U.S. 9-region national database with the MARKet Allocation energy system model to project emissions changes over the 2005 to 2050 time frame. The modeled scenarios are two carbon tax, two low carbon transportation, and two biomass fuel choice scenarios. In the lower carbon tax and both biomass fuel choice scenarios, SO<sub>2</sub> and NO<sub>X</sub> achieve reductions largely through pre-existing rules and policies, with only relatively modest additional changes occurring from the climate mitigation measures. The higher carbon tax scenario projects greater declines in CO<sub>2</sub> and SO<sub>2</sub> relative to the 2050 reference case, but electricity sector NO<sub>X</sub> increases. This is a result of reduced investments in power plant NO<sub>X</sub> controls in earlier years in anticipation of accelerated coal power plant retirements, energy penalties associated with carbon capture systems, and shifting of NO<sub>X</sub> emissions in later years from power plants subject to a regional NO<sub>X</sub> cap to those in regions not subject to the cap.