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Volume 10, issue 18
Atmos. Chem. Phys., 10, 8761–8781, 2010
https://doi.org/10.5194/acp-10-8761-2010
© Author(s) 2010. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue: Biosphere Effects on Aerosols and Photochemistry Experiment:...

Atmos. Chem. Phys., 10, 8761–8781, 2010
https://doi.org/10.5194/acp-10-8761-2010
© Author(s) 2010. This work is distributed under
the Creative Commons Attribution 3.0 License.

  17 Sep 2010

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 W. Choi et al.
  • 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.

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