The WMO/GAW X2006 SF_{6} scale was updated to X2014 on 18 September 2014. The X2014 scale supercedes the X2006 scale.

The X2014 SF_{6} scale is defined by 17 primary standards over the range 2-20 pmol mol^{-1} (ppt), prepared by static gravimetric dilution in 5.9-L aluminum cylinders. Assigned values were determined by fitting a 2nd order polynomial to the response of each standard (relative to a 8.25 ppt natural air secondary standard) measured using an HP6890 GC with electron capture detection (GC-ECD). Analysis repeatability (precision) was typically less than 0.3% (one standard deviation).

Conversion from X2006 to X2014:

For SF_{6} > 2 ppt:

The conversion is: Y = a*X^{2} + b*X + c
Where Y = SF_{6} on the X2014 scale, X is SF_{6} on the X2006 scale.
a = 2.6821·10^{-3}, b=9.7748·10^{-1}, c = 3.5831·10^{-2}

The conversion has an uncertainty of ± 0.01 ppt.
Please use caution applying this equation to SF_{6} > 10 ppt. Results will only be approximate.

Table 1: Comparison of X2006 to X2014 SF_{6} scales over the range 1-12 pmol mol^{-1} (ppt).

X2006 (ppt)

X2014 (ppt)

X2014–X2006 (ppt)

1.0

1.00

0.00

2.0

2.00

0.00

3.0

2.99

-0.01

4.0

3.99

-0.01

5.0

4.99

-0.01

6.0

6.00

0.00

7.0

7.01

0.01

8.0

8.03

0.03

9.0

9.05

0.05

10.0

10.08

0.08

*11.0

11.11

0.11

*12.0

12.15

0.15

*Values above 10 ppt are included for illustration purposes, but are beyond the range of the X2006 scale.

Table 2: Primary Standards that define the X2014 SF_{6} scale. Uncertainties associated with prepared mole fractions are approximately one standard deviation. Mole fractions assignments are based on GC-ECD analysis, using a 2nd order polynomial response function.