Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Atmos. Chem. Phys., 16, 9349-9359, 2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
28 Jul 2016
Speciation of OH reactivity above the canopy of an isoprene-dominated forest
J. Kaiser1,a, K. M. Skog1, K. Baumann2, S. B. Bertman3, S. B. Brown4,5, W. H. Brune6, J. D. Crounse7, J. A. de Gouw4,5,8, E. S. Edgerton2, P. A. Feiner6, A. H. Goldstein9,10, A. Koss4,8, P. K. Misztal9, T. B. Nguyen7, K. F. Olson9, J. M. St. Clair7,b,c, A. P. Teng7, S. Toma3, P. O. Wennberg7,11, R. J. Wild4,8, L. Zhang6, and F. N. Keutsch12 1Department of Chemistry, University of Wisconsin-Madison, Madison, WI, USA
2Atmospheric Research & Analysis Inc, Cary, NC, USA
3Department of Chemistry, Western Michigan University, Kalamazoo, MI, USA
4Chemical Sciences Division, NOAA Earth System Research Laboratory, Boulder, CO, USA
5Department of Chemistry, University of Colorado, Boulder, CO, USA
6Department of Meteorology, Pennsylvania State University, University Park, PA, USA
7Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA
8Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, CO, USA
9Department of Environmental Science, Policy, and Management, University of California, Berkeley, CA, USA
10Department of Civil and Environmental Engineering, University of California, Berkeley, CA, USA
11Division of Engineering and Applied Science, California Institute of Technology, Pasadena, CA, USA
12School of Engineering and Applied Sciences and Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, USA
anow at: School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA
bnow at: Joint Center for Earth Systems Technology, University of Maryland Baltimore County, Baltimore, MD, USA
cnow at: Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD, USA
Abstract. Measurements of OH reactivity, the inverse lifetime of the OH radical, can provide a top–down estimate of the total amount of reactive carbon in an air mass. Using a comprehensive measurement suite, we examine the measured and modeled OH reactivity above an isoprene-dominated forest in the southeast United States during the 2013 Southern Oxidant and Aerosol Study (SOAS) field campaign. Measured and modeled species account for the vast majority of average daytime reactivity (80–95 %) and a smaller portion of nighttime and early morning reactivity (68–80 %). The largest contribution to total reactivity consistently comes from primary biogenic emissions, with isoprene contributing ∼  60 % in the afternoon, and ∼  30–40 % at night and monoterpenes contributing ∼  15–25 % at night. By comparing total reactivity to the reactivity stemming from isoprene alone, we find that ∼  20 % of the discrepancy is temporally related to isoprene reactivity, and an additional constant ∼  1 s−1 offset accounts for the remaining portion. The model typically overestimates measured OVOC concentrations, indicating that unmeasured oxidation products are unlikely to influence measured OH reactivity. Instead, we suggest that unmeasured primary emissions may influence the OH reactivity at this site.

Citation: Kaiser, J., Skog, K. M., Baumann, K., Bertman, S. B., Brown, S. B., Brune, W. H., Crounse, J. D., de Gouw, J. A., Edgerton, E. S., Feiner, P. A., Goldstein, A. H., Koss, A., Misztal, P. K., Nguyen, T. B., Olson, K. F., St. Clair, J. M., Teng, A. P., Toma, S., Wennberg, P. O., Wild, R. J., Zhang, L., and Keutsch, F. N.: Speciation of OH reactivity above the canopy of an isoprene-dominated forest, Atmos. Chem. Phys., 16, 9349-9359,, 2016.
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Short summary
OH reactivity can be used to assess the amount of reactive carbon in an air mass. “Missing” reactivity is commonly found in forested environments and is attributed to either direct emissions of unmeasured volatile organic compounds or to unmeasured/underpredicted oxidation products. Using a box model and measurements from the 2013 SOAS campaign, we find only small discrepancies in measured and calculated reactivity. Our results suggest the discrepancies stem from unmeasured direct emissions.
OH reactivity can be used to assess the amount of reactive carbon in an air mass. “Missing”...