EUFAR’s joint research activity dedicated to traceability in gas-phase observations (TGOE) seeks to develop robust calibration systems for the core gas-phase chemical measurements currently made on board research aircraft. This in turn, will reduce the uncertainty in these key parameters and will facilitate improved cross platform research by ensuring that the measurement technologies are all tied to a common baseline. Comparison to numerical models and satellite observations will also be critical beneficiaries of the output from TGOE.
Members of the EUFAR TGOE working group have recently been involved in the field deployment during the recent EU funded DACCIWA project over the summer (24 June – 17 July 2016) in Lomé, Togo. During the campaign, a new gas-phase chemistry rack was fitted to the UK BAS Twin Otter aircraft. In addition the French ATR 42 (SAFIRE) and German Falcon 20 (DLR) aircraft were configured for similar measurement parameters. This was done under a framework designed in part through the TGOE contributors (A. Borbon (CNRS), H. Schlager (DLR) & J. Hopkins (Univeristy of York)).
A number of different intercalibration exercises were conducted including “round robin” checks using standard and ‘blind’ standards in high stability gas cylinders.
Table of round-robin exercises made during the DACCIWA campaign
|Species||Descritpion||SAFIRE ATR-42||NERC BAS Twin Otter||DLR Falcon|
|TEI 42 CTL/ BLC NO2||Chemiluminescence /BLC NO2||QCL NO2 (SPIRIT)|
110ppb NO in nitrogen (spectra seal) cylinder (YoU)
100ppb NO2 in nitrogen (spectra seal) cylinder (YoU)
|API-T100U/fluo||TEI 43i (Fluo)||TEI 43i (Fluo)|
|SO2||100 ppbv (Messer) (SAFIRE)||X||X||X|
|BOC 5ppm, 1ppm (DLR?)||X||X|
|CRDS Picarro||CEAS (LGR)||QCL (CO/CH4) SPIRIT|
|CO/CO2/CH4)||ambient air ICOS standards - NOAA scale (SAFIRE)||X||X||X|
|VOCS||NPL-UK NMHC ozone precursors (4ppb)(YoU)||X||X||X|
The stability of these standards has been previously reported through the TGOE reports, and TGOE provides invaluable additional support to the understanding of long-term stability issues in gas cylinders. In particular focussing on the range of stabilities of the different gas phase chemical species, from our work it is clear that there is a range of ‘lifetimes’. The team’s work has also highlighted the importance of rigorous handling and operational protocols for the delivery train between the instrument and the gas cylinder. Post-campaign intercalibration work is continuing now that the aircraft and instruments have returned to their home bases.
The Team from the University of York deployed prototypes of the new design of the glass Whole Air Sampling system (for Volatile Organic Compounds (VOC analysis) for the first time during DACCIWA. Despite some initial problems with the new design, a large number of samples were collected. Data is currently being worked-up now in order to quantify the emissions from different cities in the region. Discussions are already underway about an improved design based on what has been learnt during DACCIWA. Gas phase VOC standards were sampled on the new WAS system alongside the German adsorbent tube sampler and the French PTR-MS (proton transfer reaction mass spectrometer).
As part of DACCIWA, Stephane Bauguitte (FAAM) provided calibrated target gas standards (CO2 and CH4 WMO scales), and Jim McQuaid (University of Leeds), the TGOE activity leader, is currently recertifying this cylinder. Work continues on the linearisation of the BAS Los Gatos Research Greenhouse Gas Analyser (LGR uGGA), in particular the CO2 channel. Further to this, other tests for the LGR uGGA includes:
- evaluation of thermal drift of linearised response to cabin temperature(15 to 40 degrees Celsius)
- check of dry mole fraction accuracy (LGR water correction algorithm) using the method described in O'Shea et al 2013 (AMT). This test was done as part of the checks of greenhouse gas analysers at FAAM.
- conducting tests on the response of the analysers (CO, O3, NOx) to cabin temperature. Click here for more details carried out by the French team (SAFIRE & CNRS).
Cylinder stability trials continue with FAAM now having a one-year record of stability test for carbon monoxide (<500 ppb) standard in Luxfer 10L Hoopwrap cylinder, certified to both NOAA-GMD and by EMPA.
For more information, contact Jim McQuaid (University of Leeds).
French team group photo in front of SAFIRE's ATR-42, in Lomé, Togo
On board SAFIRE's ATR-42 during field experiment
View of pod on board SAFIRE's ATR-42