Emissions of isoprenoids and oxygenated biogenic volatile organic compounds from a New England mixed forest

Abstract

Abstract. 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 −2 hr −1 in 2005 and 2007, respectively. In comparison, mid-day average fluxes of monoterpenes were 0.21 and 0.15 mg m −2 hr −1 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

Modelling bidirectional fluxes of methanol and acetaldehyde with the FORCAsT canopy exchange model

“…The PTR-TOF-MS captures the entire mass spectrum in each 5 Hz measurement, providing a continuous mixing ratio time series at each mass-to-charge ratio rather than the disjunct time series obtained in previous PTR-MS studies at this site (McKinney et al, 2011). As a result, direct, rather than virtual disjunct, eddy covariances were determined and are reported herein (Mueller et al, 2010).…”

“…up out of the canopy to the atmosphere above) and negative (i.e. downward) fluxes (Park et al, 2013;Karl et al, 2005;McKinney et al, 2011). Several of these compounds, e.g.…”

“…Concentrations and fluxes of bVOCs and their oxidation products have also been measured at the EMS Tower during several summer growing seasons (McKinney et al, 2011;Goldstein et al, 1998Goldstein et al, , 1995, augmenting the AmeriFlux suite of observations. Between 7 June and 24 September 2012, a proton-transfer-reaction time-of-flight mass spectrometer (PTR-TOF-MS 8000, Ionicon Analytik GmbH, Austria) was used to measure the concentrations of volatile organic compounds at the site.…”

“…Ambient air was sampled from an inlet mounted at the top of the 30 m EMS Tower at a total flow rate of 5 slpm using a configuration identical to that used by McKinney et al (2011McKinney et al ( ) in 2007 O + reagent ions were used to selectively ionise organic molecules in the sample air. The instrument was operated with a drift tube temperature of 60 • C and a drift tube pressure of 2.20 mbar.…”

Isoprene emissions from a tundra ecosystem

“…Most field studies of isoprene emissions have focused on temperate ecosystems (e.g., Goldstein et al, 1995;Pressley et al, 2005;McKinney et al, 2011) due to accessibility and tropical ecosystems (e.g., Geron et al, 2002;Rinne et al, 2002;Langford et al, 2010) because warm temperatures, high biomass densities, and long growing seasons drive globally significant fluxes. Other studies have stretched from savannahs (e.g., Guenther et al, 1996;Otter et al, 2003) to boreal forests (e.g., Rinne et al, 2000;Spirig et al, 2004).…”