Articles | Volume 12, issue 2
Atmos. Chem. Phys., 12, 1135–1150, 2012

Special issue: POLARCAT (Polar Study using Aircraft, Remote Sensing, Surface...

Atmos. Chem. Phys., 12, 1135–1150, 2012

Research article 27 Jan 2012

Research article | 27 Jan 2012

Impact of the deep convection of isoprene and other reactive trace species on radicals and ozone in the upper troposphere

E. C. Apel1, J. R. Olson3, J. H. Crawford3, R. S. Hornbrook1, A. J. Hills1, C. A. Cantrell1, L. K. Emmons1, D. J. Knapp1, S. Hall1, R. L. Mauldin III1,*,**, A. J. Weinheimer1, A. Fried2,10, D. R. Blake4, J. D. Crounse5, J. M. St. Clair5, P. O. Wennberg5, G. S. Diskin3, H. E. Fuelberg6, A. Wisthaler7, T. Mikoviny7, W. Brune8, and D. D. Riemer9 E. C. Apel et al.
  • 1Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, Colorado, USA
  • 2Earth Observing Laboratory, National Center for Atmospheric Research, Boulder, Colorado, USA
  • 3NASA Langley Research Center, Hampton, Virginia, USA
  • 4School of Physical Sciences, University of California, Irvine, California, USA
  • 5California Institute of Technology, Pasadena, California, USA
  • 6Department of Meteorology, Florida State University, Tallahassee, Florida, USA
  • 7Institut für Ionenphysik & Angewandte Physik, University of Innsbruck, Innsbruck, Austria
  • 8Pennsylvania State University, State College, PA, USA
  • 9Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, Florida, USA
  • 10Institute for Arctic and Alpine Research, University of Colorado, Boulder, CO, USA
  • *now at: Department of Physics, 00014 University of Helsinki, Finland
  • **now at: Department of Atmospheric and Oceanic Sciences, University of Colorado, Boulder, Colorado, USA

Abstract. Observations of a comprehensive suite of inorganic and organic trace gases, including non-methane hydrocarbons (NMHCs), halogenated organics and oxygenated volatile organic compounds (OVOCs), obtained from the NASA DC-8 over Canada during the ARCTAS aircraft campaign in July 2008 illustrate that convection is important for redistributing both long- and short-lived species throughout the troposphere. Convective outflow events were identified by the elevated mixing ratios of organic species in the upper troposphere relative to background conditions. Several dramatic events were observed in which isoprene and its oxidation products were detected at hundreds of pptv at altitudes higher than 8 km. Two events are studied in detail using detailed experimental data and the NASA Langley Research Center (LaRC) box model. One event had no lightning NOx (NO + NO2) associated with it and the other had substantial lightning NOx (LNOx > 1 ppbv). When convective storms transport isoprene from the boundary layer to the upper troposphere and no LNOx is present, OH is reduced due to scavenging by isoprene, which serves to slow the chemistry, resulting in longer lifetimes for species that react with OH. Ozone and PAN production is minimal in this case. In the case where isoprene is convected and LNOx is present, there is a large effect on the expected ensuing chemistry: isoprene exerts a dominant impact on HOx and nitrogen-containing species; the relative contribution from other species to HOx, such as peroxides, is insignificant. The isoprene reacts quickly, resulting in primary and secondary products, including formaldehyde and methyl glyoxal. The model predicts enhanced production of alkyl nitrates (ANs) and peroxyacyl nitrate compounds (PANs). PANs persist because of the cold temperatures of the upper troposphere resulting in a large change in the NOx mixing ratios which, in turn, has a large impact on the HOx chemistry. Ozone production is substantial during the first few hours following the convection to the UT, resulting in a net gain of approximately 10 ppbv compared to the modeled scenario in which LNOx is present but no isoprene is present aloft.

Final-revised paper