Open AccessDevelopment of analytical methods and measurements of 13 C/ 12 C in atmospheric CH 4 from the NOAA Climate Monitoring and Diagnostics Laboratory Global Air Sampling Network
Author(s) -
Miller John B.,
Mack Kenneth A.,
Dissly Richard,
White James W. C.,
Dlugokencky Edward J.,
Tans Pieter P.
Publication year - 2002
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2001jd000630
Subject(s) - environmental science , southern hemisphere , atmospheric sciences , air mass (solar energy) , sampling (signal processing) , northern hemisphere , atmosphere (unit) , mixing ratio , atmospheric chemistry , accelerator mass spectrometry , ozone , meteorology , climatology , geology , radiocarbon dating , physics , paleontology , boundary layer , detector , optics , thermodynamics
We describe the development of an automated gas chromatography‐isotope ratio mass spectrometry (GC‐IRMS) system capable of measuring the carbon isotopic composition of atmospheric methane (δ 13 CH 4 ) with a precision of better than 0.1‰. The system requires 200 mL of air and completes a single analysis in 15 min. The combination of small sample size, fast analysis time, and high precision has allowed us to measure background variations in atmospheric δ 13 CH 4 through the NOAA Climate Monitoring and Diagnostics Laboratory Cooperative Air Sampling Network. We then present a record of δ 13 CH 4 obtained from six surface sites of the network between January 1998 and December 1999. The sites are Barrow, Alaska (71°N); Niwot Ridge, Colorado (40°N); Mauna Loa, Hawaii (20°N); American Samoa (14°S); Cape Grim, Tasmania (41°S); and the South Pole (90°S). For the years 1998 and 1999, the globally averaged surface δ 13 C value was −47.1‰, and the average difference between Barrow and the South Pole was 0.6‰. Consistent seasonal variations were seen only in the Northern Hemisphere, especially at Barrow, where the average amplitude was 0.5‰. Seasonal variations in 1998, however, were evident at all sites, the cause of which is unknown. We also use a two‐box model to examine the extent to which annual average δ 13 C and CH 4 mole fraction measurements can constrain broad categories of source emissions. We find that the biggest sources of error are not the atmospheric δ 13 C measurements but instead the radiocarbon‐derived fossil fuel emission estimates, rate coefficients for methane destruction, and isotopic ratios of source emissions.