Pre-industrial ethane levels inferred from polar ice cores

Abstract:

Ethane is an abundant hydrocarbon in the atmosphere and it is a precursor to tropospheric ozone formation. Ethane also impacts the atmosphere’s oxidative capacity through its reaction with OH, the primary loss pathway. Today, the primary sources of atmospheric ethane are from anthropogenic fossil fuel use, mainly from evaporative emissions associated with the production, processing and transmission of fossil fuels. Ethane also has significant emissions from biomass burning and biofuel use, and minor emissions from oceanic, biogenic, and possibly geologic sources. The mean annual atmospheric lifetime of ethane is about 2 months. Reconstructions from polar firn air and surface flask data show a significant rise in the global levels of atmospheric ethane during the twentieth century, followed by a peak and a decline from 1980-2010. However, to date, no ice core measurements of paleo-atmospheric ethane have been reported. A pre-industrial ethane record would provide information about the magnitude and natural variability of ethane from biomass-burning and geologic emissions and would contribute to our understanding of the variability in atmospheric methane over long timescales.

In this study, we discuss analytical methods for the extraction of ethane from polar ice cores. Ethane measurements were made in shallow, dry-drilled ice cores from the West Antarctic Ice Sheet Divide and the South Pole, and in Greenland ice cores from the Greenland Ice Sheet Project. Samples were analyzed by both dry and wet extraction procedures, with analysis by high-resolution mass spectrometry with isotope dilution. The results from both methods will be compared. Preliminary estimates of pre-industrial ethane levels will be discussed, as well as the feasibility of reconstructing long-term records of atmospheric ethane.