Trace Organic Gas Analyzer
Website: https://www2.acom.ucar.edu/voc-measurements/measurement-instrumentation
TOGA is a fast gas chromatograph combined with a mass spectrometer (MS). Its main components are: Pump box, clean air generator/calibrator (CAG), electronics box, MS electronics/flow controllers, MS chamber and high vacuum pumps, and LN2 dewar assembly. These are shown below in the rack schematic and photograph:
TOGA provides atmospheric mixing ratios of an extensive and growing list of gas-phase organic species. The list includes alkanes, alkenes, alkynes, chlorofluorocarbons, halons, plus reactive oxygenated species such as alcohols, ketones, esters, and acids. Typically, a subset of some 40 different trace gases are measured, all at sensitivity to levels that occur in the atmosphere. The following table lists most, though not all, the compounds TOGA is capable of measuring:
TOGA is contained in a standard HIAPER rack, weighs less than 200 kg, and consumes ~1 kW of power.
The inlet is a constant mass flow design to mitigate the intrusion of aerosols and allow for calibrations and system blanks through the inlet and associated tubing.
A cryogenic preconcentrator, consisting of a custom-built dewar and a system of traps, is used for water removal, sample enrichment and cryofocusing of trace constituents. Flow switching between traps is done via a heated (50C) Valco 10-port valve. TOGA's flow system is diagrammed in the following figure:
A quadrupole mass spectrometer operating in selected ion monitoring mode is used to quantify individual compounds. High speed electronics allow the simultaneous measurement of several peaks with ~ 1 second peak width.
System calibrations and blanks are performed using a catalytic-clean air generator/dynamic dilution system with accurate (±1%) and precise (±1%) calibration gas delivery. The system operates continuously, allowing for frequent calibrations and zeros during flight.
Measurement Characteristics:
- Overall estimate of uncertainty: 15% or better.
- Response time: 40s on a 2-minute cycle.
- Precision: 3% or less.
Example(s) of Measurement: Below is an example of a TOGA time series, together with the flight profile, from DC3-Test:
