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We present a new instrument, "Boreas", a cryogen-free methane (CH 4 ) preconcentration system coupled to a dual-laser spectrometer for making simultaneous measurements of δ 13 C(CH 4 ) and δ 2 H(CH 4 ) in ambient air. Excluding isotope ratio scale uncertainty, we estimate a typical standard measurement uncertainty for an ambient air sample of 0.07‰ for δ 13 C(CH 4 ) and 0.9‰ for δ 2 H(CH 4 ), which are the lowest reported for a laser spectroscopy-based system and comparable to isotope ratio mass spectrometry. We trap CH 4 (∼1.9 μmol mol -1 ) from ∼5 L of air onto the front end of a packed column, subsequently separating CH 4 from interferences using a controlled temperature ramp with nitrogen (N 2 ) as the carrier gas, before eluting CH 4 at ∼550 μmol mol -1 . This processed sample is then delivered to an infrared laser spectrometer for measuring the amount fractions of 12 CH 4 , 13 CH 4 , and 12 CH 3 D isotopologues. We calibrate the instrument using a set of gravimetrically prepared amount fraction primary reference materials directly into the laser spectrometer that span a range of 500-626 μmol mol -1 (CH 4 in N 2 ) made from a single pure CH 4 source that has been isotopically characterized for δ 13 C(CH 4 ) by IRMS. Under the principle of identical treatment, a compressed ambient air sample is used as a working standard and measured between air samples, from which a final calibrated isotope ratio is calculated. Finally, we make automated measurements of both δ 13 C(CH 4 ) and δ 2 H(CH 4 ) in over 200 ambient air samples and demonstrate the application of Boreas for deployment to atmospheric monitoring sites.

analytical chemistry

Boreas: A Sample Preparation-Coupled Laser Spectrometer System for Simultaneous High-Precision In Situ Analysis of δ<sup>13</sup>C and δ<sup>2</sup>H from Ambient Air Methane

Boreas: A Sample Preparation-Coupled Laser Spectrometer System for Simultaneous High-Precision In Situ Analysis of δ13C and δ2H from Ambient Air Methane

Boreas: A Sample Preparation-Coupled Laser Spectrometer System for Simultaneous High-Precision In Situ Analysis of δ¹³C and δ²H from Ambient Air Methane