The Dual Channel Gas Chromatograph with Flame Ionisation Detectors is capable of reporting mixing ratios of a wide range of volatile organic compounds in the atmosphere.

The output includes mixing ratios of a wide range of volatile organic compounds (VOCs). The data from the instrument are split (across three seperate files: -fid1, -fid2, -fid3) according to compound type. The output for -fid1 is Alkanes.

The instrument has variable measurement frequency dependent upon sampling frequency of the Whole Air Sampling (WAS) system.

Samples of air are dried, and then pre-concentrated on a dual-bed adsorbent trap held at sub-ambient temperature (typically -20°C). Sample volumes of up to one litre of air are acquired and then the trap is resistively heated during desorption within a stream of helium (or hydrogen) and injected into the GC oven for analysis. The eluent is split in approximately equal portions between a Na2SO4 deactivated aluminium oxide (Al2O3) porous layer open tubular (PLOT) column (50 m, 0.53 mm id, Varian Netherlands) for analysis of the less polar NMHCs and a LOWOX columns (10 m, 0.53 mm id, Varian Netherlands) for analysis of the more polar VOCs including monoterpenes and oxygenated species. Analytes elute from the GC columns into two flame ionisation detectors for detection. The GC oven has been programmed for optimal separation of all compounds of interest.

There are two near-identical GC instruments for the measurement of Volatile organic compounds. The first is a Perkin Elmer GC with home-built autosampler and flow control box, a home-built preconcentrator and an Ai Qualitek injector. The other is an Agilent GC with a MARKES UNITY2 preconcentrator and CIA Advantage autosampler.

Measurement of VOCs in the atmosphere have been used for a wide range of applications including providing information regarding: quantification of emissions; air mass age; and atmospheric processing during transport.