Tips for QCL Carbonyl Sulfide 
Measurements

Many researchers use a quantum cascade laser (QCL) to make high frequency/high precision measurements of carbonyl sulfide.  

When using a QCL to detect ambient level OCS, two things should be taken into account: 
temperature should be as stable as possible and
moisture should not build up in the sample cell.

While having an air-conditioned room to house the QCL is a first step, further problems can arise with air vents blowing onto the lab bench or temperature fluctuations from opening and closing doors.

Other researchers report ambient pressure effects for some QCL systems.

L. Kooijmans has used a separate CO2 analyzer to find a leak in the sample cell of the QCL by monitoring the analyzer exhaust.

W. Sun suggests using a buffer volume when doing chamber measurements in the canopy, because turbulence may cause ambient COS concentration to fluctuate rapidly.
  

Methods of measurement
NOAA and many Scripps data are produced using the GC-MS method. Small aliquots of samples are pre-concentrated on a cryo-trap before being introduced into the GC.
If you are altering an existing set up used primarily for other compounds (e.g. CFCs), often there is an ascarite trap in the sample handing system to prevent CO2 interference with chromatography. Ascarite partially absorbs OCS. Removal of the ascarite trap and some careful methods development can yield consistent measurements.

Four companies make commercially available QCL units that have been deployed in the field:
Aerodyne (Wingate, Commane, Seibt, Maseyk, Berry, Yakir, Wohlfahrt, Kooijmans)
MIRO Analytics (no published data yet). New competitor to Aerodyne.
Los Gatos Research (Still, Berkelhammer, LaFranchi) These units are less expensive than Aerodyne or MIRO, but the product line does not appear to be actively improved.
Aeris Technologies (Meredith, Commane, Whelan). This last one is much less expensive but has yet to produce presentable data and operators have run into many problems.