Optimization of a gas chromatographic unit for measuring biogenic volatile organic compounds in ambient air

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; beta-pinene; alpha-pinene; limonene; ocimene; myrcene; sabinene; Delta(3)-carene; camphene; 1,8 cineole; terpinolene; linalool; alpha-phellandrene; nopinone; citral; alpha-terpinene; beta-caryophyllene; p-cymene; gamma-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 alpha-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 beta-pinene and alpha-pinene, representing 60% of the measured terpenoid concentration on average, while isoprene repre-sented only 17 %. The uncertainties determined were always below 13% for the six major terpenes.