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Surface and lightning sources of nitrogen oxides over the United States: Magnitudes, chemical evolution, and outflow
Department of Earth and Planetary Sciences and Division of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA
Department of Earth and Planetary Sciences and Division of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA
Department of Earth and Planetary Sciences and Division of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA
Department of Earth and Planetary Sciences and Division of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA
Department of Earth and Planetary Sciences and Division of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA
Department of Earth and Planetary Sciences and Division of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA
Air Resources Laboratory, Atmospheric Sciences Modeling Division, NOAA, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, USA
Atmospheric Sciences Division, NASA Langley Research Center, Hampton, Virginia, USA
College of Chemistry, University of California, Berkeley, California, USA
Department of Meteorology, Pennsylvania State University, University Park, Pennsylvania, USA
College of Chemistry, University of California, Berkeley, California, USA
Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, New Hampshire, USA
Earth Observing Laboratory, National Center for Atmospheric Research, Boulder, Colorado, USA
Earth Observing Laboratory, National Center for Atmospheric Research, Boulder, Colorado, USA
Cooperative Institute for Research In Environmental Science, University of Colorado, Boulder, Colorado, USA
Earth System Research Laboratory, NOAA, Boulder, Colorado, USA
Cooperative Institute for Research In Environmental Science, University of Colorado, Boulder, Colorado, USA
Earth System Research Laboratory, NOAA, Boulder, Colorado, USA
Department of Atmospheric Science, Texas A&M University, College Station, Texas, USA
College of Chemistry, University of California, Berkeley, California, USA
Department of Meteorology, Pennsylvania State University, University Park, Pennsylvania, USA
Atmospheric Sciences Division, NASA Langley Research Center, Hampton, Virginia, USA
NASA Ames Research Center, Moffett Field, California, USA
Earth Observing Laboratory, National Center for Atmospheric Research, Boulder, Colorado, USA
Cooperative Institute for Research In Environmental Science, University of Colorado, Boulder, Colorado, USA
Earth System Research Laboratory, NOAA, Boulder, Colorado, USA
College of Chemistry, University of California, Berkeley, California, USA
We use observations from two aircraft during the ICARTT campaign over the eastern United States and North Atlantic during summer 2004, interpreted with a global 3-D model of tropospheric chemistry (GEOS-Chem) to test current understanding of regional sources, chemical evolution, and export of NOx. The boundary layer NOx data provide top-down verification of a 50% decrease in power plant and industry NOx emissions over the eastern United States between 1999 and 2004. Observed NOx concentrations at 8–12 km altitude were 0.55 ± 0.36 ppbv, much larger than in previous U.S. aircraft campaigns (ELCHEM, SUCCESS, SONEX) though consistent with data from the NOXAR program aboard commercial aircraft. We show that regional lightning is the dominant source of this upper tropospheric NOx and increases upper tropospheric ozone by 10 ppbv. Simulating ICARTT upper tropospheric NOx observations with GEOS-Chem requires a factor of 4 increase in modeled NOx yield per flash (to 500 mol/flash). Observed OH concentrations were a factor of 2 lower than can be explained from current photochemical models, for reasons that are unclear. A NOy-CO correlation analysis of the fraction f of North American NOx emissions vented to the free troposphere as NOy (sum of NOx and its oxidation products) shows observed f = 16 ± 10% and modeled f = 14 ± 9%, consistent with previous studies. Export to the lower free troposphere is mostly HNO3 but at higher altitudes is mostly PAN. The model successfully simulates NOy export efficiency and speciation, supporting previous model estimates of a large U.S. anthropogenic contribution to global tropospheric ozone through PAN export.
Received 11 August 2006; accepted 5 January 2007; published 18 April 2007.
Citation: (2007), Surface and lightning sources of nitrogen oxides over the United States: Magnitudes, chemical evolution, and outflow, J. Geophys. Res., 112, D12S05, doi:10.1029/2006JD007912.
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