FAAM CORE TE49C UV Photometric Ozone Analyser
 
The model TE49C is a commercial gas analyser produced by Thermo Scientific. The analyser employs the Beer-Lambert law to relate UV absorption of Ozone at 254nm directly to the concentration of Ozone in the sample air. The TE49C is a dual-cell instrument, simultaneously measuring the different responses from the sample air (intensity I) and reference gas (intensity Io of ozone-scrubbed sample).
 

System Components

Ambient air is drawn into the cabin from the starboard air sample pipe (port #12) along several meters of 1/4" od PFA line using an external sample pump. Air passes through this Full Teflon diaphragm pump (KNF model N726.1.2 FT.18), and through a PTFE buffer volume where excess flow is vented to the cabin. At low altitudes the residence time of this system is negligible because of the very high flow from this pump (>20LPM). At the highest altitudes the residence time is estimated to approach 10s.
 
The sample air is drawn through the TE49C monitor at a capillary controlled nominal flowrate of ~0.7 LPM for each absorption cell, via a particulate filter PFTE membrane (5 μm pore size) using the TE49C internal pump. The analyser has been modified with an internal Perma Pure Nafion drier to limit the known effects caused by water vapour gradients in the atmosphere. The analyser exhaust is connected to one of the aircraft vent pipes.
 

Images



TE49C in Rack
Air Sample Pipe Inlet (open)
Internal Sample Lines

Documentation

 The TE49C user manual is available: icon TE49C Manual (5.78 MB 2009-11-17 10:42:47)
 Core Chemistry Rack Technical Specification
 

Data

The TE49C has been configured so that the sample and reference measurements (I and Io) are made every 4 seconds, the sample/reference cells are then switched to cancel any effects that are cell-specific. Therefore although Ozone data are output within the Core data at 1 Hz, the system only produces independent measurements every 4 seconds, from approximately the last second before the valve switch.
 
The analogue output from the instrument is logged by the aircraft data recording system and scaled accordingly to produce a concentration measurement in ppbv. Instrument calibrations are referenced to this analogue output. Data output by the TE49C are automatically corrected for the analyser's absorption cells temperature and pressure.
 
The TE49C is operated and calibrated throughout the range 0-500 ppbv.
 
The manufacturer estimates the instrument precision and lowest detectable limit to be 1 ppbv, and the response time to be 8s. FAAM have experienced very little calibration drift with this type of analyser, which is periodically referenced by transfering the Ozone standard (over the 0-500 ppbv range) from a TE49C Primary Standard analyser, itself calibrated yearly by the UK National Physical Laboratory. The overall 2σ calibration uncertainty is estimated at ±3% of value above 100 ppbv and ±3 ppbv below this. FAAM believe this to be broadly representative of the overall measurement uncertainty.
 

Publications

Here's a recent paper that uses the TE49C data.
Real, E., Law, K. S., Weinzierl, B., Fiebig, M., Petzold, A., Wild, O., Methven, J., Arnold, S., Stohl, A., Huntrieser, H., Roiger, A., Schlager, H., Stewart, D., Avery, M., Sachse, G., Browell, E., Ferrare, R., Blake, D., Processes influencing ozone levels in Alaskan forest fire plumes during long-range transport over the North Atlantic, J. Geophys. Res. -A, 112 (D10), DOI: 10.1029/2006JD007576, 2007. [link]
 

Further Details

Contact Stéphane Bauguitte at FAAM