A QCL-based Carbonyl Sulfide Spectrometer for Environmental Monitoring

Carbonyl sulfide (OCS) is one of the sulfur gases present in the Earth's atmosphere. OCS natural sources are volcanos, hot springs, and oceans. OCS could be produced in forest or biomass burning. This gas is involved in the global sulfur cycle (i.e. in tropospheric and stratospheric regions). OCS also has an important role for biological applications. Here we present first preliminary results of a compact instrument for OCS detection. It will be based on the well known technique of tunable laser absorbtion spectroscopy TLAS. The architecture of such device is based on a low consumption Quantum Cascade Laser around 5 microns. This laser is also resonant with carbon monoxide and carbon dioxed weak transitions. Due to natural lower OCS concentration, the optical path is enhanced by using a 76-m multipass cell. The electronic to control the instrument and for signal acquisition will be based on compact Field Programmable Gate Arrays. This instrument is arranged for both direct absorpiton and second derivative configuration. The setup has been tested in the first configuration with CO2 environmental measuraments evaluating Allan-Werle variance. For the second derivative the instrument has been evaluated with CO and OCS environmental acquisitions. Measurament with an OCS certificated mix are on going.