A quantum cascade laser infrared spectrometer for CO2 stable isotope analysis: Field implementation at a hydrocarbon contaminated site under bio-remediation

Abstract

Real-time methods to monitor stable isotope ratios of CO2 are needed to identify biogeochemical origins of CO2 emissions from the soil-air interface. An isotope ratio infra-red spectrometer (IRIS) has been developed to measure CO2 mixing ratio with δ(13)C isotopic signature, in addition to mixing ratios of other greenhouse gases (CH4, N2O). The original aspects of the instrument as well as its precision and accuracy for the determination of the isotopic signature δ(13)C of CO2 are discussed. A first application to biodegradation of hydrocarbons is presented, tested on a hydrocarbon contaminated site under aerobic bio-treatment. CO2 flux measurements using closed chamber method is combined with the determination of the isotopic signature δ(13)C of the CO2 emission to propose a non-intrusive method to monitor in situ biodegradation of hydrocarbons. In the contaminated area, high CO2 emissions have been measured with an isotopic signature δ(13)C suggesting that CO2 comes from petroleum hydrocarbon biodegradation. This first field implementation shows that rapid and accurate measurement of isotopic signature of CO2 emissions is particularly useful in assessing the contribution of contaminant degradation to the measured CO2 efflux and is promising as a monitoring tool for aerobic bio-treatment.

The SPIRIT airborne instrument: a three-channel infrared absorption spectrometer with quantum cascade lasers for in situ atmospheric trace-gas measurements

“…This temperature regulation should stabilize the fringe pattern, and thus reduce the standard deviation of the average mixing ratios when combined to regular in-flight calibrations using reference cylinders. This should lower the minimum of the Allan deviation such as experienced in ground measurements by our team, reaching precisions below 0.3‰ [31]. The accuracy of the measured values depends on the calibration strategy deployed and the field constraints.…”

CO<sub>2</sub> and CH<sub>4</sub> budgets and global warming potential modifications in <i>Sphagnum</i>-dominated peat mesocosms invaded by <i>Molinia caerulea</i>

“…An explication of vascular plants to influence the methane fluxes is often reported for their capacity to supply easily available substrates for the methanogenic microbes and with high variability in substrate quality and availability depending on plants species (Ström et al, 2012). While root exudates are a source of acetate and thus suggested to favor acetoclastic methanogenesis (Saarnio et al, 2004), the root exudates also stimulate the decomposition of recalcitrant organic matter, favoring hydrogenotrophic methanogenesis (Hornibrook et al, 1997) and, maybe more than acetates, promoting acetoclastic methanogenesis. A shift from acetoclastic to hydrogenotrophic methanogenesis pathways could explain the increase in the temperature sensitivity observed here.…”

CO<sub>2</sub> and CH<sub>4</sub> budgets and global warming potential modifications in <i>Sphagnum</i>-dominated peat mesocosms invaded by <i>Molinia caerulea</i>

“…The slope of the relationship between CO2 concentration and time allowed fluxes (in μmol CO2 m -2 s -1 ) to be calculated. CH4 emissions were measured using SPIRIT, a portable infrared laser spectrometer (Guimbaud et al, 2016), measuring CH4 concentration in a transparent chamber. Measurements take several to twenty minutes with time resolution of 1.5 s (Guimbaud et al, 2011).…”