ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-11-4807-2011 Emissions of isoprenoids and oxygenated biogenic volatile organic compounds from a New England mixed forest McKinney K. A. 1 Lee B. H. 2 Vasta A. 1 Pho T. V. 1 3 Munger J. W. 2 Department of Chemistry, Amherst College, Amherst, Massachusetts, USA Department of Earth and Planetary Sciences and School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA now at: Department of Chemistry and Biochemistry, University of California, Santa Barbara, California, USA 24 05 2011 11 10 4807 4831 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/11/4807/2011/acp-11-4807-2011.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/11/4807/2011/acp-11-4807-2011.pdf

Fluxes of biogenic volatile organic compounds, including isoprene, monoterpenes, and oxygenated VOCs measured above a mixed forest canopy in central Massachusetts during the 2005 and 2007 growing seasons are reported. Mixing ratios were measured using proton transfer reaction mass spectrometry (PTR-MS) and fluxes computed by the disjunct eddy covariance technique. Isoprene was by far the predominant BVOC emitted at this site, with summer mid-day average fluxes of 5.3 and 4.4 mg m<sup>−2</sup> hr<sup>−1</sup> in 2005 and 2007, respectively. In comparison, mid-day average fluxes of monoterpenes were 0.21 and 0.15 mg m<sup>−2</sup> hr<sup>−1</sup> in each of these years. On short times scales (days), the diel pattern in emission rate compared well with a standard emission algorithm for isoprene. The general shape of the seasonal cycle and the observed decrease in isoprene emission rate in early September was, however, not well captured by the model. Monoterpene emission rates exhibited dependence on light as well as temperature, as determined from the improved fit to the observations obtained by including a light-dependent term in the model. The mid-day average flux of methanol from the canopy was 0.14 mg m<sup>−2</sup> hr<sup>−1</sup> in 2005 and 0.19 mg m<sup>−2</sup> hr<sup>−1</sup> in 2007, but the maximum flux was observed in spring (29 May 2007), when the flux reached 1.0 mg m<sup>−2</sup> hr<sup>−1</sup>. This observation is consistent with enhanced methanol production during leaf expansion. Summer mid-day fluxes of acetone were 0.15 mg m<sup>−2</sup> hr<sup>−1</sup> during a short period in 2005, but only 0.03 mg m<sup>−2</sup> h<sup>−1</sup> averaged over 2007. Episodes of negative fluxes of oxygenated VOCs, particularly acetone, were observed periodically, especially in 2007. Thus, deposition within the canopy could help explain the low season-averaged flux of acetone in 2007. Fluxes of species of biogenic origin at mass-to-charge ($m/z$) ratios of 73 (0.05 mg m<sup>−2</sup> hr<sup>−1</sup> in 2005; 0.03 mg m<sup>−2</sup> hr<sup>−1</sup> in 2007) and 153 (5 μg m<sup>−2</sup> hr<sup>−1</sup> in 2007), possibly corresponding to methyl ethyl ketone and an oxygenated terpene or methyl salicylate, respectively, were also observed.

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