TOGA: The Trace Organic Gas Analyzer

Our research group has been deploying fast online gas chromatograph/mass spectrometers (GC/MS) since the 1990s, and the most recent generation, the Trace Organic Gas Analyzer (TOGA) was completed in 2012 and is certified for deployment on the NSF/NCAR Gulfstream V. The TOGA provides continuous real-time atmospheric mixing ratios of an extensive list of volatile organic compounds (VOCs), including saturated and unsaturated hydrocarbons, oxygenated VOCs, halogenated VOCs, biogenic VOCs, and sulfur- and nitrogen-containing trace gases.

The primary components of the TOGA are the pump box, clean air generator/calibrator (CAG), electronics box, mass spectometer (MS) electronics/flow controllers, MS chamber and high vacuum pumps, and LN2 Dewar assembly. These are shown in Figure 1 in the rack schematic and photograph.

TOGA page schematic

Figure 1. Diagram of the TOGA (left) and a photo of the TOGA installed on the NSF/NCAR G-V (right)

TOGA provides atmospheric mixing ratios of an extensive and growing list of compounds, nearly any organic species in the C2-C10 molecular structure range. The list includes alkanes, alkenes, alkynes, chlorofluorocarbons, halons, nitrates, nitriles, sulfides, alcohols, ketones, aldehydes and ethers. Typically, a subset of some 60 different trace gases are measured, all at sensitivity to levels that occur in the atmosphere.

TOGA is contained in a standard HIAPER rack and consumes ~1 kW of power.

The TOGA 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 (50°C) Valco 10-port valve. TOGA's flow system is diagrammed in Figure 2.

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: VOC dependent, typically 20%.
Precision: 3% or less.
Response time: 35s on a 2-minute cycle.

 TOGA instrument collage

Left to right: the interior of the TOGA mass spectrometer; sampling inlets on the belly of the NSF/NCAR C-130 during FRAPPÉ; Alan Hills fills the TOGA LN2 dewar on the NSF/NCAR C-130 before a flight.




ACOM | Atmospheric Chemistry Observations & Modeling