Laser-based carbon dioxide monitoring instrument testing during a 30-day controlled underground carbon release field experiment

The performance of two laser-based instruments for carbon dioxide (CO2) monitoring was tested during a controlled release experiment performed at the zero emissions research and technology (ZERT) controlled release facility. The first instrument measures path-integrated CO2 concentrations above ground in two orthogonal directions using a continuous-wave, temperature-tunable, distributed feedback (DFB) diode laser with a center wavelength of 2.003 μm. The second instrument also uses a continuous-wave temperature-tunable DFB laser to deliver light via fiber optics to three underground sensors. Two underground sensors utilize absorption cells of 0.3 and 1 m lengths that are buried 1 m apart approximate 0.75 m above the underground release pipe. The third underground sensor utilizes a photonic bandgap (PBG) fiber as part of a fiber optic sensor. A 0.3 tCO2/day controlled release was conducted from July 9 to August 7, 2008. The two instruments were able to distinguish the elevated CO2 concentration associated with the CO2 injection.