Abstract
Abstract. We present first eddy covariance flux measurements with the PTR3-TOF-MS, a novel proton transfer time of flight reaction mass spectrometer. During 3 weeks in spring 2016, the instrument recorded 10 Hz data of biogenic volatile organic compounds above a boreal forest, on top of a measurement tower at the SMEAR (Station for Measuring Ecosystem –Atmosphere Relations) II station in Hyytiälä, Finland. Flux and concentration data of isoprene, monoterpenes, and sesquiterpenes were compared to the literature. Due to the improved instrument sensitivity and a customized wall-less inlet design, we could detect fluxes of semi-volatile and low-volatility organic compounds with less than single-digit picomol per square meter per second (pmolm-2s-1) values for the first time. These compounds include sesquiterpene oxidation products and diterpenes. Daytime diterpene fluxes were in the range of 0.05 to 0.15 pmolm-2s-1, which amounts to about 0.25 % to 0.5 % of the daytime sesquiterpene flux above canopy.
Highlights
More than 1000 Tg of organic carbon, excluding methane, is emitted from terrestrial ecosystems into the atmosphere per year as biogenic volatile organic compounds (BVOCs; Guenther et al, 2012)
Guenther et al (2012) stress the need for instrumentation able to measure BVOCs with low vapor pressures, and semi-volatile organic compounds (SVOCs), in order to refine current emission models. This aim goes in line with monitoring highly oxidized organic molecules (HOMs), which are important for new particle formation (NPF) and secondary organic aerosol (SOA) formation
Accurate quantification of concentrations and fluxes of VOCs and SVOCs is a crucial component for understanding the formation and evolution of SOA
Summary
More than 1000 Tg (teragrams) of organic carbon, excluding methane, is emitted from terrestrial ecosystems into the atmosphere per year as biogenic volatile organic compounds (BVOCs; Guenther et al, 2012). Proton transfer reaction mass spectrometry (PTR-MS; Hansel et al, 1995) can detect the majority of volatile organic carbon in ambient air (Hunter et al, 2017) It is a well-established technique for direct emission measurements of VOC (Karl et al, 2001; Müller et al, 2010) and was used successfully in gradient and eddy covariance flux measurements (e.g., Millet et al, 2018; Karl et al, 2018; Rinne et al, 2007; Ruuskanen et al, 2011). Guenther et al (2012) stress the need for instrumentation able to measure BVOCs with low vapor pressures, and semi-volatile organic compounds (SVOCs), in order to refine current emission models. This aim goes in line with monitoring highly oxidized organic molecules (HOMs), which are important for NPF and SOA formation. Similar progress was made in the meantime with the benzene cluster cation chemical ionization mass spectrometer, as reported by Lavi et al (2018)
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