Wolfe, G. M. and Thornton, J. A. and Bouvier-Brown, N. C. and Goldstein, A. H. and Park, J.-H. and McKay, M. and Matross, D. M. and Mao, J. and Brune, W. H. and LaFranchi, B. W. and Browne, E. C. and Min, K.-E and Wooldridge, P. J. and Cohen, R. C. and Crounse, J. D. and Faloona, I. C. and Gilman, J. B. and Kuster, W. C. and de Gouw, J. A. and Huisman, A. and Keutsch, F. N. (2011) The Chemistry of Atmosphere-Forest Exchange (CAFE) Model – Part 2: Application to BEARPEX-2007 observations. Atmospheric Chemistry and Physics, 11 (3). pp. 1269-1294. ISSN 1680-7316 http://resolver.caltech.edu/CaltechAUTHORS:20110526-143133482
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In a companion paper, we 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 apply CAFE to noontime observations from the 2007 Biosphere Effects on Aerosols and Photochemistry Experiment (BEARPEX-2007). In this work we evaluate the CAFE modeling approach, demonstrate the significance of in-canopy chemistry for forest-atmosphere exchange and identify key shortcomings in the current understanding of intra-canopy processes. CAFE generally reproduces BEARPEX-2007 observations but requires an enhanced radical recycling mechanism to overcome a factor of 6 underestimate of hydroxyl (OH) concentrations observed during a warm (~29 °C) period. Modeled fluxes of acyl peroxy nitrates (APN) are quite sensitive to gradients in chemical production and loss, demonstrating that chemistry may perturb forest-atmosphere exchange even when the chemical timescale is long relative to the canopy mixing timescale. The model underestimates peroxy acetyl nitrate (PAN) fluxes by 50% and the exchange velocity by nearly a factor of three under warmer conditions, suggesting that near-surface APN sinks are underestimated relative to the sources. Nitric acid typically dominates gross dry N deposition at this site, though other reactive nitrogen (NO_y) species can comprise up to 28% of the N deposition budget under cooler conditions. Upward NO_2 fluxes cause the net above-canopy NO_y flux to be ~30% lower than the gross depositional flux. CAFE under-predicts ozone fluxes and exchange velocities by ~20%. Large uncertainty in the parameterization of cuticular and ground deposition precludes conclusive attribution of non-stomatal fluxes to chemistry or surface uptake. Model-measurement comparisons of vertical concentration gradients for several emitted species suggests that the lower canopy airspace may be only weakly coupled with the upper canopy. Future efforts to model forest-atmosphere exchange will require a more mechanistic understanding of non-stomatal deposition and a more thorough characterization of in-canopy mixing processes.
|Additional Information:||© 2011 Author(s). This work is distributed under the Creative Commons Attribution 3.0 License. Published by Copernicus Publications on behalf of the European Geosciences Union. Received: 24 August 2010. Published in Atmos. Chem. Phys. Discuss.: 20 September 2010. Revised: 29 January 2011. Accepted: 1 February 2011. Published: 15 February 2011. The authors acknowledge support from a National Science Foundation grant ATM-0633897. GMW was partially supported by a U.S.-EPA STAR Fellowship Assistance under Agreement No. FP-91698901. This work has not been formally reviewed by EPA. The views expressed in this work are solely those of the authors; EPA and NSF do not endorse any products or commercial services mentioned. The authors also thank F. Paulot for helpful discussions on isoprene oxidation, S. Fares for his insights on ozone fluxes and L. Ganzeveld, T. Karl and an anonymous referee for their critical feedback on both the model and the manuscript. Edited by: J. Lelieveld.|
|Official 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., 11, 1269-1294, doi:10.5194/acp-11-1269-2011, 2011.|
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|Deposited By:||Ruth Sustaita|
|Deposited On:||27 May 2011 16:57|
|Last Modified:||26 Dec 2012 13:16|
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