Atmos. Chem. Phys. Discuss., 13, 31713-31759, 2013
www.atmos-chem-phys-discuss.net/13/31713/2013/
doi:10.5194/acpd-13-31713-2013
© Author(s) 2013. This work is distributed
under the Creative Commons Attribution 3.0 License.
Review Status
This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Missing peroxy radical sources within a rural forest canopy
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. Graus5, Y. Nakashima6,h, Y. Kajii7, A. Guenther2,i, and F. N. Keutsch1
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 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 under-predicted (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.

Citation: Wolfe, G. M., Cantrell, C., Kim, S., Mauldin III, R. L., Karl, T., Harley, P., Turnipseed, A., Zheng, W., Flocke, F., Apel, E. C., Hornbrook, R. S., Hall, S. R., Ullmann, K., Henry, S. B., DiGangi, J. P., Boyle, E. S., Kaser, L., Schnitzhofer, R., Hansel, A., Graus, M., Nakashima, Y., Kajii, Y., Guenther, A., and Keutsch, F. N.: Missing peroxy radical sources within a rural forest canopy, Atmos. Chem. Phys. Discuss., 13, 31713-31759, doi:10.5194/acpd-13-31713-2013, 2013.
 
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