Ultra-High Precision Laser Isotope Monitor for I3CO2, CO180 and CO170

Greenhouse gas (GHG) emissions are primary drivers of global climate change. Hence there is a crucial need to quantify their sources and sinks. A powerful method to constrain source and sink strengths is the analysis of the relative proportions of isotopic variants of GHG’s in atmospheric samples like those collected globally by NOAA’s Cooperative Air Sampling Network. Measurements that are capable of informing climate science require extremely high precision. The standard technique, isotope ratio mass spectrometry (IRMS), is precise but is limited by laborious sample processing requirements, high capital cost, high maintenance and impracticality of field deployment. We avoid these limitations with an alternative method to measure the isotopic composition of the most important GHG: carbon dioxide. Using Tunable Infrared Laser Direct Absorption Spectroscopy (TILDAS), we demonstrate measurement precision at least as good as IRMS and exceeding that requested until Sub-Topic 8.3.1 for ō13C-CO2 (0.006 vs. 0.01‰_ and ō18O-CO2 (0.007 vs. 0.02‰). During Phase II we will produce and demonstrate a commercial instrument meeting this standard while measuring small discreet air samples (<60 ml). We rely on two innovations: a small volume, high vacuum optical cell and a rapid sample switching method promoting long term signal averaging, without measurement drift.