Atmos. Chem. Phys. Discuss., 10, 21791-21866, 2010
© Author(s) 2010. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
The Chemistry of Atmosphere-Forest Exchange (CAFE) Model – Part 2: Application to BEARPEX-2007 observations
G. M. Wolfe1,2, J. A. Thornton2, N. C. Bouvier-Brown3,*, A. H. Goldstein3, J.-H. Park3, M. McKay3,**, D. M. Matross3,***, J. Mao4,****, W. H. Brune4, B. W. LaFranchi5,*****, E. C. Browne5, K.-E. Min5, P. J. Wooldridge5, R. C. Cohen5, J. D. Crounse6, I. C. Faloona7, J. B. Gilman8,9, W. C. Kuster8, J. A. de Gouw8,9, A. Huisman10, and F. N. Keutsch10
1Department of Chemistry, University of Washington, Seattle, WA, USA
2Department of Atmospheric Sciences, University of Washington, Seattle, WA, USA
3Department of Environmental Science, Policy, and Management, University of California, Berkeley, CA, USA
4Department of Meteorology, Pennsylvania State University, University Park, PA, USA
5Department of Chemistry, University of California, Berkeley, CA, USA
6Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA, USA
7Department of Land, Air and Water Resources, University of California, Davis, CA, USA
8NOAA Earth System Research Laboratory, Boulder, CO, USA
9Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, USA
10Department of Chemistry, University of Wisconsin, Madison, WI, USA
*now at: Chemistry and Biochemistry Department, Loyola Marymount University, Los Angeles, CA, USA
**now at: California Air Resources Board, Sacramento, CA, USA
***now at: KEMA, Inc., Oakland, CA, USA
****now at: School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA
*****now at: Center for Accelerator Mass Spectrometry (CAMS), Lawrence Livermore National Lab, Livermore, CA, USA

Abstract. In a companion paper, we have introduced the Chemistry of Atmosphere-Forest Exchange (CAFE) model, a vertically-resolved 1-D chemical transport model designed to probe the details of near-surface reactive gas exchange. Here, we use CAFE to interpret noontime observations from the 2007 phase of the Biosphere Effects on Aerosols and Photochemistry Experiment (BEARPEX-2007), conducted at a young Ponderosa pine plantation in the western Sierra Nevada. The model reproduces many features of the BEARPEX-2007 data and offers new insights into the forest-atmosphere exchange of reactive molecules at this location. Nitrogen oxide (NOx = NO + NO2) fluxes are driven by soil emissions of NO, while the partitioning between NO and NO2 fluxes is sensitive to in-canopy photochemical gradients. Enhanced thermolysis at the ground increases downward acyl peroxy nitrate (APN) fluxes by as much as 50%, in general agreement with previous findings. APN fluxes are also influenced by in-canopy chemical production, especially when their formation is tied closely to oxidation of BVOC emissions. Gross dry N deposition is typically dominated by nitric acid, though other reactive nitrogen (NOy) species can comprise up to 28% of the N deposition budget under cooler conditions. Upward NO2 fluxes cause the net above-canopy NOy flux to be ~30% lower than the gross depositional flux. Model-measurement comparison of hydrogen peroxide mixing ratios suggests this molecule deposits at the aerodynamic limit. CAFE under-predicts ozone fluxes by ~20%, which may indicate additional in-canopy chemical losses that are missing from the current model.

Citation: Wolfe, G. M., Thornton, J. A., Bouvier-Brown, N. C., Goldstein, A. H., Park, J.-H., McKay, M., Matross, D. M., Mao, J., Brune, W. H., LaFranchi, B. W., Browne, E. C., Min, K.-E., Wooldridge, P. J., Cohen, R. C., Crounse, J. D., Faloona, I. C., Gilman, J. B., Kuster, W. C., de Gouw, J. A., Huisman, A., and Keutsch, F. N.: The Chemistry of Atmosphere-Forest Exchange (CAFE) Model – Part 2: Application to BEARPEX-2007 observations, Atmos. Chem. Phys. Discuss., 10, 21791-21866, doi:10.5194/acpd-10-21791-2010, 2010.
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