Export of reactive nitrogen from coal‐fired power plants in the U.S.: Estimates from a plume‐in‐grid modeling study

The export of reactive nitrogen (nitrogen oxides and their oxidation products, collectively referred to as NO y ) from coal‐fired power plants in the U.S. to the rest of the world could have a significant global contribution to ozone. Traditional Eulerian gridded air quality models cannot characterize accurately the chemistry and transport of plumes from elevated point sources such as power plant stacks. A state‐of‐the‐science plume‐in‐grid (PinG) air quality model, a reactive plume model embedded in an Eulerian gridded model, is used to estimate the export of NO y from 25 large coal‐fired power plants in the U.S. (in terms of NO x and SO 2 emissions) in July 2001 to the global atmosphere. The PinG model used is the Community Multiscale Air Quality Model with Advanced Plume Treatment (CMAQ‐APT). A benchmark simulation with only the gridded model, CMAQ, is also conducted for comparison purposes. The simulations with and without advanced plume treatment show differences in the calculated export of NO y from the 25 plants considered reflecting the effect of using a detailed and explicit treatment of plume transport and chemistry. The advanced plume treatment results in 31% greater simulated export of NO y compared to the purely grid‐based modeling approach. The export efficiency of NO y (the fraction of NO y emitted that is exported) is predicted to be 21% without APT and 27% with APT. When considering only export through the eastern boundary across the Atlantic, CMAQ‐APT predicts that the export efficiency is 24% and that 2% of NO y is exported as NO x , 49% as inorganic nitrate, and 25% as PAN. These results are in reasonably good agreement with an analysis reported in the literature of aircraft measurements over the North Atlantic.