Highly Compact CO2 Sensor for Balloon Deployment

Assessment of CO2 exchange between the atmosphere and the biosphere remains one of the largest uncertainties in predicting carbon sequestration by vegetative uptake on a global basis. Distinguishing between photosynthetic uptake and respiratory emission of CO2 is difficult, due to the small differences between two large parameters, but crucial for determining net ecosystem exchange for CO2 between the atmosphere and the biosphere. Carbonyl sulfide (COS) is a surrogate for CO2 uptake by plants during photosynthesis, but COS is not emitted from plants during respiration. COS measurements may be used to provide unique constraints on carbon assimilation by the biosphere that are independent of the influence of respiration. This proposal would develop a highly precise and portable instrument for absolute COS measurements based on newly available continuous wave mid-infrared quantum cascade lasers (QCL). The instrument, with a precision for COS of 1 part-per-trillion (ppt) with 100 s averaging time, would provide continuous measurements of COS both at ground level monitoring sites and from aircraft platforms in order to address the global distribution of COS sources and sinks. A newly acquired QCL was used in a pre-existing laboratory spectrometer to demonstrate detection sensitivity for COS of 5 ppt with 1 s averaging time and 1 ppt in 100 s. The system operated continuously for a period of 5 months sampling roof top ambient air from December to May. Gradual variations in COS due with wind trajectories in the winter contrasted to sharp daily variations due to uptake by soil vegetation with the onset of spring. This data set uniquely demonstrates the power of continuous monitoring for assessing carbon uptake cycles in the biosphere. We will develop detailed optical, thermal, electronic and spectroscopic designs for a Phase II prototype instrument. We will build two versions of the resulting instrument to demonstrate the capabilities both for long term unattended deployments at a local forest research site, and the potential for global COS measurements from aircraft platforms. The instrument will be rigorously tested against existing measurement techniques. Commercial Applications and Other Benefits: The proposed instrument will provide the capability to measure atmospheric abundances of COS in real time in order to better asses CO2 uptake by vegetation. Improved understanding of CO2 uptake will improve our understanding of global warming and help mitigate global climate change. There is a worldwide market for such measurement systems in the environmental and ecological research communities. Potentially larger markets exist in the medical research community where COS measurements in exhaled breath can be used to diagnose cystic fibrosis, liver disease, and lung transplant rejection.