In-situ Halocarbon trace-gas concentrations measured by the Dirac GC-ECD during the SIPEX II voyage of the Aurora Australis, 2012

Brief description

The current data set contains in-situ halocarbon atmospheric measurements of CH3CCl3, CH2Br2, CHBr3, CHCl3, C2Cl4 made using a Gas Chromatograph - Electron Capture Detector (GC-ECD) known as the micro- DIRAC.

Instrument description and setup details:
GC-ECD
Instrument Description:
"micro-Dirac: an autonomous instrument for halocarbon measurements"
B. Gostlow, A. D. Robinson, N. R. P. Harris, L. M. O'Brien, D. E. Oram, G. P. Mills, H. M. Newton, S. E. Yong, and J. A Pyle Atmos. Meas. Tech., 3, 507-521, 2010

Instrument Setup:
This instrument is sampling from a weather protected inlet positioned ~2 m off the front port side of the Monkey Deck of the Aurora Australis, directly above the bridge. The end of the Teflon sample line is bare (with an inserted glass wool filter) and contained within the "Ned Kelly", a large (~30 cm diameter) stainless steel can which protects against rain, snow, sea spray and major impacts. The quarter inch teflon sample line runs 60m (2 x 30m with 1 join) down to the GC-ECD which was located in a modified shipping container located on the foredeck. Ultra high purity He (99.995% purity) and N2 (99.998% purity) were fed ~ 6m into the instrument container via stainless steel 1/16" tubing from a smaller adjacent container containing a number of other gas cylinders (primarily He, N2 and H2). A cylinder of calibrated air is located within the instrument container to perform regular calibrations.

Inlet flow rate of 1 L/min; sampling rate - about 20 samples per day.
Method description: a sample volume of 20 ml is passed through the adsorbent tube which quantitatively traps the compounds of interest. The tube is mounted across a 6 port 2 position valco valve. The adsorbent bed is then purged with helium to remove oxygen and the valco valve is switched to the 'inject' position. The tube is heated to 180 C, releasing the compounds of interest into a carrier flow of helium onto the separation column. The column is heated first isothermally at 35 C for 5 minutes before heating at 8 C/min to 145 C. The target compounds are separated according to boiling point and pass through the ECD. The chromatogram takes ~30 minutes to complete. After the bromoform peak has appeared the column is cooled back to 35 C, the valco valve is switched to the 'load' position and the next sample can be injected.