Abstract
Abstract. A new online gas chromatographic method dedicated to biogenic volatile organic compound (BVOC) analysis was developed for the measurement of a 20 BVOC gaseous mixture (isoprene; β-pinene; α-pinene; limonene; ocimene; myrcene; sabinene; Δ3-carene; camphene; 1,8 cineole; terpinolene; linalool; α-phellandrene; nopinone; citral; α-terpinene; β-caryophyllene; p-cymene; γ-terpinene; and 2-carene) at a time resolution of 90 min. The optimized method includes an online Peltier-cooled thermodesorption system sample trap made of Carbopack B coupled to a gas chromatographic system equipped with a 60 m, 0.25 mm internal diameter (i.d.) BPX5 column. Eluent was analysed using flame ionization detection (FID). Potassium iodide was identified as the best ozone scrubber for the 20 BVOC mixture. In order to obtain an accurate quantification of BVOC concentrations, the development of a reliable standard mixture was also required. Quantification of BVOCs was reported with a detection limit ranging from 4 ppt for α-pinene to 19 ppt for sabinene. The main source of uncertainty was the calibration step, stressing the need for certified gaseous standards for a wider panel of BVOCs. This new method was applied for the first time to measure BVOCs in a pine forest during the LANDEX episode 1 field campaign (summer 2017). All target BVOCs were detected at least once during the campaign. The two major monoterpenes observed were β-pinene and α-pinene, representing 60 % of the measured terpenoid concentration on average, while isoprene represented only 17 %. The uncertainties determined were always below 13 % for the six major terpenes.
Highlights
A new online gas chromatographic method dedicated to biogenic volatile organic compound (BVOC) analysis was developed for the measurement of a 20 BVOC gaseous mixture at a time resolution of 90 min
Repeatability – the measurement repeatability was evaluated from seven replicates using a mixture of 3–5 ppb of the target compounds (Table 2) at 50 % relative humidity (RH) under laboratory conditions and from three replicates using the same mixture under field conditions
The memory effect was calculated from Eq (3): Mi where Ari is the peak area of a compound i in the volatile organic compounds (VOCs) mixture, and Ai is the peak area of the same compound i present in zero air
Summary
Emissions of volatile organic compounds (VOCs) can impact both (i) the atmospheric oxidation capacity (Houweling et al, 1998; Lelieveld et al, 2008; Taraborrelli et al, 2012), due to the reactivity of VOCs with atmospheric oxidants such as ozone (O3), hydroxyl (OH), and nitrate (NO3) radicals (Atkinson and Arey, 2003), and (ii) the Earth’s radiative balance (Gauss et al, 2006; GIEC, 2013; Hoffmann et al, 1997; Kazil et al, 2010) through the formation of ozone and secondary organic aerosols (SOAs).Biogenic VOCs (BVOCs) represent the largest fraction of non-methane VOCs emitted in the troposphere, contributing to 75 %–90 % of the total global emissions (Guenther et al, 1995; Lamarque et al, 2010; Sindelarova et al, 2014). Reported measurements of total OH reactivity performed in ambient air have highlighted some gaps in our knowledge regarding OH sinks, especially in forested regions, where the measured OH reactivity is frequently higher than that calculated from concomitant VOC observations (Carslaw et al, 2001; Di Carlo et al, 2004; Dusanter and Stevens, 2017; Edwards et al, 2013; Griffith et al, 2013; Hansen et al, 2014; Hens et al, 2014; Stavrakou et al, 2010; Tan et al, 2001; Wolfe et al, 2014; Zannoni et al, 2017) This difference reveals the presence of unmeasured OH sinks within the forest boundary layer, which may either be attributed to unidentified primary BVOC emissions (Di Carlo et al, 2004; Sinha et al, 2010), oxidation products of BVOCs (Edwards et al, 2013; Hansen et al, 2014; Lou et al, 2010; Mao et al, 2012; Zannoni et al, 2017), or both (Nölscher et al, 2012). Speciated measurements of these compounds are important to improve our understanding of the atmospheric composition and reactivity
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