Journal of Geophysical Research: Atmospheres

Isocyanic acid in a global chemistry transport model: Tropospheric distribution, budget, and identification of regions with potential health impacts

Authors

  • Paul. J. Young,

    Corresponding author
    1. Cooperative Institute for Research in the Environmental Sciences, University of Colorado Boulder, Boulder, Colorado, USA
    2. Chemical Sciences Division, Earth System Research Laboratory, NOAA, Boulder, Colorado, USA
      Corresponding author: P. J. Young, Chemical Sciences Division, Earth System Research Laboratory, NOAA, Boulder, CO 80305, USA. (paul.j.young@noaa.gov)
    Search for more papers by this author
  • Louisa K. Emmons,

    1. National Center for Atmospheric Research, Boulder, Colorado, USA
    Search for more papers by this author
  • James M. Roberts,

    1. Chemical Sciences Division, Earth System Research Laboratory, NOAA, Boulder, Colorado, USA
    Search for more papers by this author
  • Jean-François Lamarque,

    1. National Center for Atmospheric Research, Boulder, Colorado, USA
    Search for more papers by this author
  • Christine Wiedinmyer,

    1. National Center for Atmospheric Research, Boulder, Colorado, USA
    Search for more papers by this author
  • Patrick Veres,

    1. Chemical Sciences Division, Earth System Research Laboratory, NOAA, Boulder, Colorado, USA
    2. Department of Chemistry and Biochemistry, University of Colorado Boulder, Boulder, Colorado, USA
    3. Now at Max Planck Institute for Chemistry, Mainz, Germany
    Search for more papers by this author
  • Trevor C. VandenBoer

    1. Department of Chemistry, University of Toronto, Toronto, Ontario, Canada
    Search for more papers by this author

Corresponding author: P. J. Young, Chemical Sciences Division, Earth System Research Laboratory, NOAA, Boulder, CO 80305, USA. (paul.j.young@noaa.gov)

Abstract

[1] This study uses a global chemical transport model to estimate the distribution of isocyanic acid (HNCO). HNCO is toxic, and concentrations exceeding 1 ppbv have been suggested to have negative health effects. Based on fire studies, HNCO emissions were scaled to those of hydrogen cyanide (30%), resulting in yearly total emissions of 1.5 Tg for 2008, from both anthropogenic and biomass burning sources. Loss processes included heterogeneous uptake (pH dependent), dry deposition (like formic acid), and reaction with the OH radical (k = 1 × 10−15 molecule−1 cm3 s−1). Annual mean surface HNCO concentrations were highest over parts of China (maximum of 470 pptv), but episodic fire emissions gave much higher levels, exceeding 4 ppbv in tropical Africa and the Amazon, and exceeding 10 ppbv in Southeast Asia and Siberia. This suggests that large biomass burning events could result in deleterious health effects for populations in these regions. For the tropospheric budget, using the model-calculated pH the HNCO lifetime was 37 days, with the split between dry deposition and heterogeneous loss being 95%:5%. Fixing the heterogeneous loss rate at pH = 7 meant that this process dominated, accounting for ∼70% of the total loss, giving a lifetime of 6 days, and resulting in upper tropospheric concentrations that were essentially zero. However, changing the pH does not notably impact the high concentrations found in biomass burning regions. More observational data is needed to evaluate the model, as well as a better representation of the likely underestimated biofuel emissions, which could mean more populations exposed to elevated HNCO concentrations.