iDirac: a field-portable instrument for long-term autonomous measurements of isoprene and selected VOCs
Abstract. The 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.