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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Atmos. Chem. Phys., 10, 8761-8781, 2010
© Author(s) 2010. This work is distributed
under the Creative Commons Attribution 3.0 License.
17 Sep 2010
Observations of elevated formaldehyde over a forest canopy suggest missing sources from rapid oxidation of arboreal hydrocarbons
W. Choi1, I. C. Faloona1, N. C. Bouvier-Brown2,*, M. McKay2,**, A. H. Goldstein2, J. Mao3,***, W. H. Brune3, B. W. LaFranchi4,****, R. C. Cohen4,5, G. M. Wolfe6, J. A. Thornton7, D. M. Sonnenfroh8, and D. B. Millet9
1University of California, Davis, Dept. of Land, Air, and Water Resources, Davis, California, USA
2University of California, Berkeley, Dept. of Environmental Science, Policy & Management, Berkeley, California, USA
3Pennsylvania State University, Dept. of Meteorology, University Park, Pennsylvania, USA
4University of California, Berkeley, Dept. of Chemistry, Berkeley, California, USA
5University of California, Berkeley, Dept. of Earth and Planetary Science, Berkeley, California, USA
6University of Washington, Dept. of Chemistry, Seattle, Washington, USA
7University of Washington, Dept. of Atmospheric Sciences, Seattle, Washington, USA
8Physical Sciences Inc., Atmospheric Sciences group, Andover, Massachusetts, USA
9University of Minnesota, Dept. of Soil, Water, and Climate, St. Paul, Minnesota, USA
*now at: Loyola Marymount University, Dept. of Chemistry and Biochemistry, Los Angeles, California, USA
**now at: California Air Resources Board, Sacramento, California, USA
***now at: Harvard University, School of Engineering and Applied Sciences, Cambridge, Massachustte, USA
****now at: Lawrence Livermore National Lab, Center for Accelerator Mass Spectrometry, Livermore, California, USA

Abstract. To better understand the processing of biogenic VOCs (BVOCs) in the pine forests of the US Sierra Nevada, we measured HCHO at Blodgett Research Station using Quantum Cascade Laser Spectroscopy (QCLS) during the Biosphere Effects on Aerosols and Photochemistry Experiment (BEARPEX) of late summer 2007. Four days of the experiment exhibited particularly copious HCHO, with midday peaks between 15–20 ppbv, while the other days developed delayed maxima between 8–14 ppbv in the early evening. From the expansive photochemical data set, we attempt to explain the observed HCHO concentrations by quantifying the various known photochemical production and loss terms in its chemical budget. Overall, known chemistry predicts a factor of 3–5 times less HCHO than observed. By examining diurnal patterns of the various budget terms we conclude that, during the high HCHO period, local, highly reactive oxidation chemistry produces an abundance of formaldehyde at the site. The results support the hypothesis of previous work at Blodgett Forest suggesting that large quantities of oxidation products, observed directly above the ponderosa pine canopy, are evidence of profuse emissions of very reactive volatile organic compounds (VR-VOCs) from the forest. However, on the majority of days, under generally cooler and more moist conditions, lower levels of HCHO develop primarily influenced by the influx of precursors transported into the region along with the Sacramento plume.

Citation: Choi, W., Faloona, I. C., Bouvier-Brown, N. C., McKay, M., Goldstein, A. H., Mao, J., Brune, W. H., LaFranchi, B. W., Cohen, R. C., Wolfe, G. M., Thornton, J. A., Sonnenfroh, D. M., and Millet, D. B.: Observations of elevated formaldehyde over a forest canopy suggest missing sources from rapid oxidation of arboreal hydrocarbons, Atmos. Chem. Phys., 10, 8761-8781, doi:10.5194/acp-10-8761-2010, 2010.
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