Characterizing CO and NO Sources and Relative Ambient Ratios in the Baltimore Area Using Ambient Measurements and Source Attribution Modeling.
Heather Simon, Luke C Valin, Kirk R Baker, Barron H Henderson, James H Crawford, Sally E Pusede, James T Kelly, Kristen M Foley, R Chris Owen, Ronald C Cohen, Brian Timin, Andrew J Weinheimer, Norm Possiel, Chris Misenis, Glenn S Diskin, Alan Fried
Author Information
Heather Simon: Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency, Research Triangle Park, NC, USA. ORCID
Luke C Valin: National Exposure Research Laboratory, U.S. Environmental Protection Agency, Research Triangle Park, NC, USA. ORCID
Kirk R Baker: Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency, Research Triangle Park, NC, USA.
Barron H Henderson: Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency, Research Triangle Park, NC, USA. ORCID
James H Crawford: NASA Langley Research Center, Hampton, VA, USA. ORCID
Sally E Pusede: Department of Environmental Sciences, University of Virginia, Charlottesville, VA, USA.
James T Kelly: Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency, Research Triangle Park, NC, USA. ORCID
Kristen M Foley: National Exposure Research Laboratory, U.S. Environmental Protection Agency, Research Triangle Park, NC, USA. ORCID
R Chris Owen: Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency, Research Triangle Park, NC, USA.
Ronald C Cohen: Department of Chemistry, University of California, Berkeley, CA, USA. ORCID
Brian Timin: Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency, Research Triangle Park, NC, USA.
Andrew J Weinheimer: National Center for Atmospheric Research, Boulder, CO, USA. ORCID
Norm Possiel: Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency, Research Triangle Park, NC, USA.
Chris Misenis: Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency, Research Triangle Park, NC, USA.
Glenn S Diskin: NASA Langley Research Center, Hampton, VA, USA. ORCID
Alan Fried: Institute of Arctic and Alpine Research, University of Colorado Boulder, Boulder, CO, USA. ORCID
Modeled source attribution information from the Community Multiscale Air Quality model was coupled with ambient data from the 2011 Deriving Information on Surface conditions from Column and Vertically Resolved Observations Relevant to Air Quality Baltimore field study. We assess source contributions and evaluate the utility of using aircraft measured CO and NO relationships to constrain emission inventories. We derive ambient and modeled ΔCO:ΔNO ratios that have previously been interpreted to represent CO:NO ratios in emissions from local sources. Modeled and measured ΔCO:ΔNO are similar; however, measured ΔCO:ΔNO has much more daily variability than modeled values. Sector-based tagging shows that regional transport, on-road gasoline vehicles, and nonroad equipment are the major contributors to modeled CO mixing ratios in the Baltimore area. In addition to those sources, on-road diesel vehicles, soil emissions, and power plants also contribute substantially to modeled NO in the area. The sector mix is important because emitted CO:NO ratios vary by several orders of magnitude among the emission sources. The model-predicted gasoline/diesel split remains constant across all measurement locations in this study. Comparison of ΔCO:ΔNO to emitted CO:NO is challenged by ambient and modeled evidence that free tropospheric entrainment, and atmospheric processing elevates ambient ΔCO:ΔNO above emitted ratios. Specifically, modeled ΔCO:ΔNO from tagged mobile source emissions is enhanced 5-50% above the emitted ratios at times and locations of aircraft measurements. We also find a correlation between ambient formaldehyde concentrations and measured ΔCO:ΔNO suggesting that secondary CO formation plays a role in these elevated ratios. This analysis suggests that ambient urban daytime ΔCO:ΔNO values are not reflective of emitted ratios from individual sources.
