Bolas, Conor G.Ferracci, ValerioRobinson, Andrew D.Mead, Mohammed IqbalNadzir, Mohd Shahrul MohdPyle, John A.Jones, Roderic L.Harris, Neil R. P.2020-02-202020-02-202020-02-19Bolas CG, Ferracci V, Robinson AD, et al., (2020) iDirac: a field-portable instrument for long-term autonomous measurements of isoprene and selected VOCs. Atmospheric Measurement Techniques, Volume 13, February 2020, pp. 821-8381867-1381https://doi.org/10.5194/amt-13-821-2020http://dspace.lib.cranfield.ac.uk/handle/1826/15156The iDirac is a new instrument to measure selected hydrocarbons in the remote atmosphere. A robust design is central to its specifications, with portability, power efficiency, low gas consumption and autonomy as the other driving factors in the instrument development. The iDirac is a dual-column isothermal oven gas chromatograph with photoionisation detection (GC-PID). The instrument is designed and built in-house. It features a modular design, with the novel use of open-source technology for accurate instrument control. Currently configured to measure biogenic isoprene, the system is suitable for a range of compounds. For isoprene measurements in the field, the instrument precision (relative standard deviation) is ±10 %, with a limit of detection down to 38 pmol mol−1 (or ppt). The instrument was first tested in the field in 2015 during a ground-based campaign, and has since shown itself suitable for deployment in a variety of environments and platforms. This paper describes the instrument design, operation and performance based on laboratory tests in a controlled environment as well as during deployments in forests in Malaysian Borneo and central England.enAttribution 4.0 InternationalArticle