Methodology

Each measurement record used to derive GLOBALVIEW-CH4 was edited and selected by the organization or institution contributing the observations. The measurement records are accumulated at NOAA ESRL along with documentation and references. Wherever possible, NOAA ESRL attempts to reproduce the selected data set based on methods described in the literature by the contributor. Selected measurements are then compared to other measurement records that are nearby in latitude as an additional assessment of potential calibration or sampling problems. Occasionally, two or more organizations make observations at the same location providing an opportunity to directly compare independent measurement programs [Masarie et al., 2001].

Standard Scale

Each participating laboratory provides either measurements calibrated with the NOAA 2004 scale (the WMO GAW CH4 mole fraction scale; [Dlugokencky et al., 2005]) or a multiplicative adjustment factor based on intercomparisons of their scale with the NOAA 2004 scale. We encourage all laboratories participating in the WMO Global Atmosphere Watch program to report CH4 mole fractions on the NOAA 2004 scale.

Table 1. Identifies the standard scale used by participating measurement laboratories. A multiplier factor is used to adjust CH4 values to a common scale (see text for details).
LABORATORY [lab #] STANDARD SCALE MULTIPLIER FACTOR (1 std. error)
ESRL [01] NOAA 2004 1.0
CSIRO [02] NOAA 2004 1.0
EC [06] NOAA 2004 1.0
LSCE [11] CMDL83 1.0124
NIWA [15] NOAA 2004 1.0
JMA [19] NOAA 2004 1.0
NIES [20] NIES Gravimetric 0.997 (0.0001)
AEMET [27] NOAA 2004 1.0
ENEA [28] CMDL83 1.0124
CMA [33] NOAA 2004 1.0
SAWS [37] NOAA 2004 1.0
AGAGE [43] TU 1.0003

PLEASE NOTE: The GLOBALVIEW-CH4 data product includes these adjustments; no adjustments by the user are required.

Some laboratories have not yet intercompared their scales with the CMDL83 or the NOAA 2004 scales. Data from these programs will be included in a future release of this product once an adjustment factor can be determined.