A new CF-IRMS system for quantifying stable isotopes of carbon monoxide from ice cores and small air samples

Z. Wang,J. E. Mak

doi:10.5194/amt-3-1307-2010

Abstract

Abstract. We present a new analysis technique for stable isotope ratios (δ13C and δ18O) of atmospheric carbon monoxide (CO) from ice core samples. The technique is an online cryogenic vacuum extraction followed by continuous-flow isotope ratio mass spectrometry (CF-IRMS); it can also be used with small air samples. The CO extraction system includes two multi-loop cryogenic cleanup traps, a chemical oxidant for oxidation to CO2, a cryogenic collection trap, a cryofocusing unit, gas chromatography purification, and subsequent injection into a Finnigan Delta Plus IRMS. Analytical precision of 0.2‰ (±1δ) for δ13C and 0.6‰ (±1δ) for δ18O can be obtained for 100 mL (STP) air samples with CO mixing ratios ranging from 60 ppbv to 140 ppbv (~268–625 pmol CO). Six South Pole ice core samples from depths ranging from 133 m to 177 m were processed for CO isotope analysis after wet extraction. To our knowledge, this is the first measurement of stable isotopes of CO in ice core air.

Highlights

Atmospheric carbon monoxide (CO) plays a key role in global atmospheric chemistry as the main sink for hydroxyl radicals (OH), strongly affecting the oxidizing capacity of the atmosphere (Crutzen and Zimmermann, 1991; Logan et al, 1981; Thompson, 1992)
The Schutze blank was measured to be lower than 40 pmol CO (9 ppbv at STP) for a 100 mL air sample with a flow rate of 50 mL/min and a collection time of 2 min
Six South Pole ice core samples were analysed with a new technique using online cryogenic extraction and continuous-flow isotope ratio mass spectrometry (CF-isotope ratio mass spectrometer (IRMS)) analysis for simultaneous measurement of stable isotope ratios (δ13C and δ18O) of atmospheric CO in small air samples

Summary

Introduction

Atmospheric CO plays a key role in global atmospheric chemistry as the main sink for hydroxyl radicals (OH), strongly affecting the oxidizing capacity of the atmosphere (Crutzen and Zimmermann, 1991; Logan et al, 1981; Thompson, 1992). Different sources producing atmospheric CO with distinct ratios of 13C/12C and 18O/16O have been observed (Kato et al, 1999a, b; Stevens et al, 1972; Stevens and Wagner, 1989; Brenninkmeijer and Rockmann, 1997). Stable isotope ratios (δ13C and δ18O) in atmospheric CO help to resolve the contributions of certain sources and, to better estimate the global CO budget (Mak and Kra, 1999; Rockmann et al, 2002; Manning et al, 1997). The stable isotopes from air bubbles trapped in ice cores provide information on CO source strengths in the past. The limited sample size of ice core air makes measuring CO isotope composition challenging

Methods

Results

Conclusion