Volatile organic compound speciation above and within a Douglas fir forest

Mixing ratios and fluxes of volatile organic compounds (VOCs) were measured by PTR-MS (and GC-MS) and virtual disjunct eddy covariance during a three-week field campaign in summer 2009 within and above a Douglas fir (Pseudotsuga menziesii) forest in Speulderbos, the Netherlands. Measurements included the first non-terpenoid species fluxes and mixing ratios for Douglas fir canopy. Above-canopy emissions of monoterpenes were comparable to previous studies of P. menziesii, with estimated standard emission factors for the first and second halves of the campaign of 0.8 +/- 0.4 and 0.8 +/- 0.3 mu g g(dw)(-1) h(-1), and temperature coefficients of 0.19 +/- 0.06 and 0.08 +/- 0.05 degrees C-1, respectively. Estimated isoprene standard emission factors for the two halves of the campaign were 0.09 +/- 0.12 and 0.16 +/- 0.18 mu g g(dw)(-1) h(-1). Fluxes of several non-terpenoid VOCs were significant, with maximum fluxes greater than has been measured for other coniferous species. alpha-Pinene was the dominant monoterpene within and above the canopy. Within-canopy mixing ratios of individual species were generally greatest in early evening consistent with reduced vertical mixing and continued temperature-dependent emissions. Acetaldehyde, acetone and monoterpenes had elevated mixing ratios toward the bottom of the canopy (5-10 m) with assumed contribution from the large quantities of forest-floor leaf litter. MBO (2-methyl-3-buten-2-ol) and estragole had peak mixing ratios at the top of the canopy and are known to have coniferous sources. MVK + MACR (methyl vinyl ketone and methacrolein) also had highest mixing ratios at the top of the canopy consistent with formation from in-canopy oxidation of isoprene. The work highlights the importance of quantifying a wider variety of VOCs from biogenic sources than isoprene and monoterpenes. (C) 2014 Elsevier Ltd. All rights reserved.