Articles | Volume 14, issue 9
Atmos. Chem. Phys., 14, 4715–4732, 2014

Special issue: BEACHON Rocky Mountain Organic Carbon Study (ROCS) and Rocky...

Atmos. Chem. Phys., 14, 4715–4732, 2014

Research article 13 May 2014

Research article | 13 May 2014

Missing peroxy radical sources within a summertime ponderosa pine forest

G. M. Wolfe1,a,b, C. Cantrell2,c, S. Kim2,d, R. L. Mauldin III2,3,c, T. Karl2,e, P. Harley2, A. Turnipseed2, W. Zheng2, F. Flocke2, E. C. Apel2, R. S. Hornbrook2, S. R. Hall2, K. Ullmann2, S. B. Henry1, J. P. DiGangi1,f, E. S. Boyle1, L. Kaser4,g, R. Schnitzhofer4, A. Hansel4, M. Graus4,5, Y. Nakashima6,h, Y. Kajii7, A. Guenther2,i, and F. N. Keutsch1 G. M. Wolfe et al.
  • 1Department of Chemistry, University of Wisconsin, Madison, WI, USA
  • 2Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, CO, USA
  • 3Department of Physics, University of Helsinki, Helsinki, Finland
  • 4Institute of Ion Physics and Applied Physics, University of Innsbruck, Innsbruck, Austria
  • 5Chemical Sciences Division, NOAA Earth System Research Laboratory, Boulder, CO, USA
  • 6Division of Applied Chemistry, Faculty of Urban Environmental Sciences, Tokyo Metropolitan University, Tokyo, Japan
  • 7Graduate School of Global Environmental Studies, Kyoto University, Kyoto, Japan
  • anow at: Joint Center for Earth Systems Technology, University of Maryland Baltimore County, Baltimore, MD, USA
  • bnow at: Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD, USA
  • cnow at: Department of Atmospheric and Oceanic Sciences, University of Colorado, Boulder, CO, USA
  • dnow at: Department of Earth System Science, University of California, Irvine, CA, USA
  • enow at: Institute for Meteorology and Geophysics, University of Innsbruck, Innsbruck, Austria
  • fnow at: Department of Civil {&} Environmental Engineering, Princeton University, Princeton, NJ, USA
  • gnow at: Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, CO, USA
  • hnow at: Department of Environmental and Natural Resource Science, Faculty of Agriculture, Tokyo University of Agriculture and Technology, Tokyo, Japan
  • inow at: Atmospheric Sciences and Global Change Division, Pacific Northwest National Laboratory, Richland, WA, USA

Abstract. Organic peroxy (RO2) and hydroperoxy (HO2) radicals are key intermediates in the photochemical processes that generate ozone, secondary organic aerosol and reactive nitrogen reservoirs throughout the troposphere. In regions with ample biogenic hydrocarbons, the richness and complexity of peroxy radical chemistry presents a significant challenge to current-generation models, especially given the scarcity of measurements in such environments. We present peroxy radical observations acquired within a ponderosa pine forest during the summer 2010 Bio-hydro-atmosphere interactions of Energy, Aerosols, Carbon, H2O, Organics and Nitrogen – Rocky Mountain Organic Carbon Study (BEACHON-ROCS). Total peroxy radical mixing ratios reach as high as 180 pptv (parts per trillion by volume) and are among the highest yet recorded. Using the comprehensive measurement suite to constrain a near-explicit 0-D box model, we investigate the sources, sinks and distribution of peroxy radicals below the forest canopy. The base chemical mechanism underestimates total peroxy radicals by as much as a factor of 3. Since primary reaction partners for peroxy radicals are either measured (NO) or underpredicted (HO2 and RO2, i.e., self-reaction), missing sources are the most likely explanation for this result. A close comparison of model output with observations reveals at least two distinct source signatures. The first missing source, characterized by a sharp midday maximum and a strong dependence on solar radiation, is consistent with photolytic production of HO2. The diel profile of the second missing source peaks in the afternoon and suggests a process that generates RO2 independently of sun-driven photochemistry, such as ozonolysis of reactive hydrocarbons. The maximum magnitudes of these missing sources (~120 and 50 pptv min−1, respectively) are consistent with previous observations alluding to unexpectedly intense oxidation within forests. We conclude that a similar mechanism may underlie many such observations.

Final-revised paper