Articles | Volume 12, issue 18
Atmos. Chem. Phys., 12, 8829–8849, 2012

Special issue: Community Atmosphere-Biosphere Interactions Experiment 2009...

Atmos. Chem. Phys., 12, 8829–8849, 2012

Research article 28 Sep 2012

Research article | 28 Sep 2012

In-canopy gas-phase chemistry during CABINEX 2009: sensitivity of a 1-D canopy model to vertical mixing and isoprene chemistry

A. M. Bryan1, S. B. Bertman2, M. A. Carroll1, S. Dusanter3,4,5, G. D. Edwards6, R. Forkel7, S. Griffith8, A. B. Guenther9, R. F. Hansen8, D. Helmig10, B. T. Jobson11, F. N. Keutsch12, B. L. Lefer13, S. N. Pressley11, P. B. Shepson14,15, P. S. Stevens8, and A. L. Steiner1 A. M. Bryan et al.
  • 1Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, Ann Arbor, Michigan, 48109, USA
  • 2Department of Chemistry, Western Michigan University, Kalamazoo, Michigan, 49008, USA
  • 3School of Public and Environmental Affairs, Indiana University, Bloomington, Indiana, 47405, USA
  • 4EMDouai, CE, 59508 Douai, France
  • 5Univ Lille Nord de France, 59000, Lille, France
  • 6Department of Chemistry, Eastern Michigan University, Ypsilanti, Michigan, 48197, USA
  • 7Karlsruhe Institute of Technology (KIT), IMK-IFU, 82467 Garmisch-Partenkirchen, Germany
  • 8Department of Chemistry, Indiana University, Bloomington, Indiana, 47405, USA
  • 9Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, Colorado, 80307, USA
  • 10Institute of Arctic and Alpine Research, University of Colorado, Boulder, Colorado, 80309, USA
  • 11Department of Civil & Environmental Engineering, Washington State University, Pullman, Washington, 99164, USA
  • 12Department of Chemistry, University of Wisconsin, Madison, Wisconsin, 53706, USA
  • 13Department of Earth and Atmospheric Sciences, University of Houston, Houston, Texas, 77004, USA
  • 14Department of Chemistry, Purdue University, West Lafayette, Indiana, 47907, USA
  • 15Department of Earth and Atmospheric Sciences, Purdue University, West Lafayette, Indiana, 47907, USA

Abstract. Vegetation emits large quantities of biogenic volatile organic compounds (BVOC). At remote sites, these compounds are the dominant precursors to ozone and secondary organic aerosol (SOA) production, yet current field studies show that atmospheric models have difficulty in capturing the observed HOx cycle and concentrations of BVOC oxidation products. In this manuscript, we simulate BVOC chemistry within a forest canopy using a one-dimensional canopy-chemistry model (Canopy Atmospheric CHemistry Emission model; CACHE) for a mixed deciduous forest in northern Michigan during the CABINEX 2009 campaign. We find that the base-case model, using fully-parameterized mixing and the simplified biogenic chemistry of the Regional Atmospheric Chemistry Model (RACM), underestimates daytime in-canopy vertical mixing by 50–70% and by an order of magnitude at night, leading to discrepancies in the diurnal evolution of HOx, BVOC, and BVOC oxidation products. Implementing observed micrometeorological data from above and within the canopy substantially improves the diurnal cycle of modeled BVOC, particularly at the end of the day, and also improves the observation-model agreement for some BVOC oxidation products and OH reactivity. We compare the RACM mechanism to a version that includes the Mainz isoprene mechanism (RACM-MIM) to test the model sensitivity to enhanced isoprene degradation. RACM-MIM simulates higher concentrations of both primary BVOC (isoprene and monoterpenes) and oxidation products (HCHO, MACR+MVK) compared with RACM simulations. Additionally, the revised mechanism alters the OH concentrations and increases HO2. These changes generally improve agreement with HOx observations yet overestimate BVOC oxidation products, indicating that this isoprene mechanism does not improve the representation of local chemistry at the site. Overall, the revised mechanism yields smaller changes in BVOC and BVOC oxidation product concentrations and gradients than improving the parameterization of vertical mixing with observations, suggesting that uncertainties in vertical mixing parameterizations are an important component in understanding observed BVOC chemistry.

Final-revised paper