Abstract
Abstract. We present a 60-year record of the stable isotopes of atmospheric carbon monoxide (CO) from firn air samples collected under the framework of the North Greenland Eemian Ice Drilling (NEEM) project. CO concentration, δ13C, and δ18O of CO were measured by gas chromatography/isotope ratio mass spectrometry (gc-IRMS) from trapped gases in the firn. We applied LGGE-GIPSA firn air models (Witrant et al., 2011) to correlate gas age with firn air depth and then reconstructed the trend of atmospheric CO and its stable isotopic composition at high northern latitudes since 1950. The most probable firn air model scenarios show that δ13C decreased slightly from −25.8‰ in 1950 to −26.4‰ in 2000, then decreased more significantly to −27.2‰ in 2008. δ18O decreased more regularly from 9.8‰ in 1950 to 7.1‰ in 2008. Those same scenarios show CO concentration increased gradually from 1950 and peaked in the late 1970s, followed by a gradual decrease to present day values (Petrenko et al., 2012). Results from an isotope mass balance model indicate that a slight increase, followed by a large reduction, in CO derived from fossil fuel combustion has occurred since 1950. The reduction of CO emission from fossil fuel combustion after the mid-1970s is the most plausible mechanism for the drop of CO concentration during this time. Fossil fuel CO emissions decreased as a result of the implementation of catalytic converters and the relative growth of diesel engines, in spite of the global vehicle fleet size having grown several fold over the same time period.
Highlights
The importance and interest for measuring atmospheric carbon monoxide (CO) arises from its significant role in the chemistry of the troposphere, since CO is a major sink for hydroxyl radical (OH)
We present a 60-year record of the stable isotopes of atmospheric carbon monoxide (CO) from firn air samples collected under the framework of the North Greenland Eemian Ice Drilling (NEEM) project
The importance and interest for measuring atmospheric CO arises from its significant role in the chemistry of the troposphere, since CO is a major sink for hydroxyl radical (OH)
Summary
The importance and interest for measuring atmospheric CO arises from its significant role in the chemistry of the troposphere, since CO is a major sink for hydroxyl radical (OH). Measuring the stable isotopes of CO from firn and ice cores would help constrain relative source strengths in the past. A recent study based on firn air analyses provided a reconstruction of atmospheric CO from Berkner Island, Antarctica, roughly covering the last four decades, which is important for understanding the past CO budget in the Southern Hemisphere (Assonov et al, 2007). The only available firn air CO measurements from the Northern Hemisphere are from samples collected from the summit of Devon Island Ice Cap, Nunavut, Canada (75◦20 N; 82◦08 W; 1929 m a.s.l.) in April 1998 (Clark et al, 2007). Measurements of CO concentration and stable isotopic ratios are carried out on Greenland firn air samples to provide the longest CO isotope records for the Northern Hemisphere. The evolving CO budget over the last 50 years at high northern latitudes is calculated based on measurements of CO concentration, δ13C, δ18O and an isotope mass balance model (Wang et al, 2010; Mak and Kra, 1999)
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