Ultra High Precision Laser Monitor for Oxygen Eddy Flux Measurements

Proposal Technical Abstract: Atmospheric oxygen provides one of the most powerful tracers to study the carbon cycle through its close interaction with carbon dioxide. Keeling and co-workers demonstrated this at the global scale by using small variations in atmospheric oxygen content to disentangle oceanic and terrestrial carbon sinks. It would be very exciting to apply similar ideas at the ecosystem level to improve our understanding of biosphere-atmosphere exchange and our ability to predict the response of the biosphere and atmosphere to climate change. The eddy covariance technique is perhaps the most effective technique available to quantify the exchange of gases between these spheres. Therefore, eddy covariance flux measurements of oxygen would be extremely valuable. However, this requires a fast response (0.1 seconds), high relative precision (0.001% or 10 per meg) oxygen sensor that does not yet exist. We propose to develop such a sensor using a high resolution visible laser to probe the oxygen A-band electronic transition. We have previously demonstrated measurement precision for the isotopes of carbon dioxide and for nitrous oxide at the 10 per meg level even in the mid infrared spectral region. We will use a similar approach in the visible region to achieve the same or better relative performance with less expensive and significantly higher capability optical components. The resulting sensor will enable oxygen flux measurements through next generation eddy covariance measurements as called out in the solicitation. In addition, we will incorporate a second laser to simultaneously determine the fluxes of carbon dioxide and water vapor with the same sampling cell. During Phase I, we will acquire an appropriate laser and detector for oxygen detection and will demonstrate the proof of principle in a bench top experiment. We will also perform more detailed spectral analysis of the target spectral region, will study the effects of water and carbon dioxide variation in the sample matrix, will optimize our spectral analysis methods and will create a conceptual design of the instrument to be produced and demonstrated during Phase II. Commercial applications and other benefits The proposed work will lead to a new class of super precise and low power trace gas monitors that will be useful for a wide variety of trace gases, in both land-based and airborne measurements. These instruments will compliment and lead to improvements in our existing commercially available trace gas instruments. Key Words Carbon cycle, oxygen, carbon dioxide, greenhouse gas emissions, eddy covariance, atmosphere, biosphere, laser spectroscopy. Summary for members of congress This instrument will help quantify the sources and sinks of the gases which primarily drive global climate change.