Surface and lightning sources of nitrogen oxides over the United States: Magnitudes, chemical evolution, and outflow

Abstract

[1] 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 NO x . The boundary layer NO x data provide top-down verification of a 50% decrease in power plant and industry NO x emissions over the eastern United States between 1999 and 2004. Observed NO x 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 NO x and increases upper tropospheric ozone by 10 ppbv. Simulating ICARTT upper tropospheric NO x observations with GEOS-Chem requires a factor of 4 increase in modeled NO x 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 NO y -CO correlation analysis of the fraction f of North American NO x emissions vented to the free troposphere as NO y (sum of NO x 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 HNO 3 but at higher altitudes is mostly PAN. The model successfully simulates NO y export efficiency and speciation, supporting previous model estimates of a large U.S. anthropogenic contribution to global tropospheric ozone through PAN export.

Ground‐level nitrogen dioxide concentrations inferred from the satellite‐borne Ozone Monitoring Instrument

“…[13] Several previous studies have used GEOS-Chem to interpret in situ measurements of reactive nitrogen Wang et al, 2004;Hudman et al, 2004Hudman et al, , 2007Martin et al, 2006] as well as observations of tropospheric NO 2 columns from satellite instruments [Martin et al, 2003a[Martin et al, , 2004bJaeglé et al, 2005;Guerova et al, 2006;Sauvage et al, 2007;Wang et al, 2007bWang et al, , 2007aBoersma et al, 2008aBoersma et al, , 2008bBucsela et al, 2008]. GEOS-Chem simulations generally agree to within 30% of measured NO x , HNO 3 , and PAN over eastern North America Hudman et al, 2007;Singh et al, 2007] [15] Figure 1 shows seasonal mean tropospheric NO 2 columns from OMI and GEOS-Chem.…”

“…GEOS-Chem simulations generally agree to within 30% of measured NO x , HNO 3 , and PAN over eastern North America Hudman et al, 2007;Singh et al, 2007] [15] Figure 1 shows seasonal mean tropospheric NO 2 columns from OMI and GEOS-Chem. The high-resolution data in Figure 1 (first row) reveal relatively high values in many urban areas such as Los Angeles, San Francisco, Phoenix, Denver, Houston, Dallas, Chicago, Toronto, and the northeast U.S. corridor.…”

“…Soil NO x emissions are computed using a modified version of the algorithm of Yienger and Levy [1995] with the canopy reduction factors described by Wang et al [1998]. The midlatitude lightning NO x source is 1.6 Tg N yr À1 following Martin et al [2006] and Hudman et al [2007].…”

Intercomparison of SCIAMACHY and OMI tropospheric NO2 columns: Observing the diurnal evolution of chemistry and emissions from space

“…Furthermore, Park et al [2007] found strong biomass burning activity throughout the Southeast and GEOS-Chem does not take into account the diurnal cycle of fires (see next section). In summary, all these NO x sources have a strong afternoon maximum and either their source strength (soils, lightning [Hudman et al, 2007]) or their diurnal cycle (power plants, biomass burning) is underestimated. The observed 1000 -1330 LT ratios <1.0 over the southeastern U.S. appear consistent throughout the summer as we also found them for July 2006 (not shown), while we did not find them for the nonsummer month of October 2004 (not shown).…”

Impact of the assimilation of ozone from the Tropospheric Emission Spectrometer on surface ozone across North America

“…The model includes a detailed description of tropospheric O 3 -NO x -hydrocarbon chemistry. The model has been used in a range of studies, including the analysis of the impact of background O 3 on surface O 3 over North America [e.g., Fiore et al, 2002] and interpretation of in situ aircraft observations from the International Consortium on Atmospheric Transport and Transformation (ICARTT) aircraft campaign over North America [e.g.. Hudman et al, 2007]. We use version v7-02-04 of GEOS-Chem with a horizontal resolution of 2°Â 2.5°and 55 levels in the vertical from the surface to 0.01 hPa, with 5 levels in the PBL.…”