Open AccessConversion of NOAA atmospheric dry air CH 4 mole fractions to a gravimetrically prepared standard scale
Author(s) -
Dlugokencky E. J.,
Myers R. C.,
Lang P. M.,
Masarie K. A.,
Crotwell A. M.,
Thoning K. W.,
Hall B. D.,
Elkins J. W.,
Steele L. P.
Publication year - 2005
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 - 10.1029/2005jd006035
Subject(s) - methane , gravimetric analysis , diluent , atmospheric pressure , repeatability , analytical chemistry (journal) , environmental science , atmosphere (unit) , chemistry , environmental chemistry , meteorology , chromatography , nuclear chemistry , physics , organic chemistry
Sixteen mixtures of methane (CH 4 ) in dry air were prepared using a gravimetric technique to define a CH 4 standard gas scale covering the nominal range 300–2600 nmol mol −1 . It is designed to be suitable for measurements of methane in air ranging from those extracted from glacial ice to contemporary background atmospheric conditions. All standards were prepared in passivated, 5.9 L high‐pressure aluminum cylinders. Methane dry air mole fractions were determined by gas chromatography with flame ionization detection, where the repeatability of the measurement is typically better than 0.1% (≤1.5 nmol mol −1 ) for ambient CH 4 levels. Once a correction was made for 5 nmol mol −1 CH 4 in the diluent air, the scale was used to verify the linearity of our analytical system over the nominal range 300–2600 nmol mol −1 . The gravimetrically prepared standards were analyzed against CH 4 in air standards that define the Climate Monitoring and Diagnostics Laboratory (CMDL) CMDL83 CH 4 in air scale, showing that CH 4 mole fractions in the new scale are a factor of (1.0124 ± 0.0007) greater than those expressed in the CMDL83 scale. All CMDL measurements of atmospheric CH 4 have been adjusted to this new scale, which has also been accepted as the World Meteorological Organization (WMO) CH 4 standard scale; all laboratories participating in the WMO Global Atmosphere Watch program should report atmospheric CH 4 measurements to the world data center on this scale.