The gas chromatograph (GC) GhOST-MS (Gas chromatograph for Observational Studies using Tracers – Mass Spectrometer) is a fully automated in-Situ GC for the measurement of trace gases. The measurement device was successfully installed on the research aircraft HALO for several campaigns. GhOST-MS has two separated chromatographic measuring channels.
The first channel can measure SF6 and CF2Cl2 (CFC-12) with a time resolution of one minute by using an Electron Capture Detector (ECD) with a very good precision. Due to the high sensitivity, a direct injection of the atmospheric samples onto the separation column can take place. SF6 can be used to determine the age of the air, CFC-12 is a tracer for the atmospheric transport as well as one of the main source for chlorine in the stratosphere.
The second channel of the GhOST-MS is based on the GC/MS measurement, where an enrichment is necessary before the measurement. For this purpose, external air passed through a cooled sample loop to concentrate the trace gases. Subsequently, the trace gases are desorbed, separated chromatography and quantified with the mass spectrometer. For a particularly high sensitivity, the MS can be operated in the chemical ionization (CI). In the standard configuration, the MS can measure all brominated source gases as well as some chlorinated and iodinated with a time resolution of four minutes. Furthermore, the MS can be operated in the electron ionization (EI). This ionization leads to more fragmentation and therefore more measurable substances. In addition to the brominated source gases, a variety of chlorinated source gases can thus be measured.