Derivation of a series of annual values for CFC-12 The series is derived from the Reconstructed histories of the annual mean atmospheric mole fractions for the halocarbons CFC-11, CFC-12, CFC-113 and Carbon Tetrachloride (http://gaslab.ucsd.edu/pub/cfchist/) described in: Walker, S. J., R. F. Weiss and P. K. Salameh, Reconstructed histories of the annual mean atmospheric mole fractions for the halocarbons CFC-11, CFC-12, CFC-113 and carbon tetrachloride. Journal of Geophysical Research, 105, C6, 14,285-14,296, 2000 The annual CFC-12 global concentration values computed from the northern hemisphere and southern hemisphere concentrations given in the file http://gaslab.ucsd.edu/pub/cfchist/cfc12atmhist98.m have been used up to 1990, and completed by zero values from 1900 to 1930 For the period 2000 to 2100 the CFC-12 at 5-yearly resolution are taken from the report: UNEP/WMO Scientific Assessment of Ozone Depletion: 1998 Chapter 11: Halocarbon scenarios for the future ozone layer and related consequences, Guus Velders (RIVM) and Sasha Madronich (NCAR), Version 5, June 3, 1998, Calculations by John Daniel and Guus Velders Guus.Velders@rivm.nl & jdaniel@al.noaa.gov The two datasets have been joined together in a dataset F12_for_fit.dat and imported into the xmgrace package A series of annual values is generated using the function Data| Transformations | Interpolation/splines | Method: Cubic spline, Sampling: Linear mesh, Start at: 1900 Stop at: 2100 Length: 201 The resulting series is then written to file F12_fit.dat using Data| Export | ASCII | Format: %12.2f Values before 1936 have been set to zero to suppress small oscillations around zero generated by the cubic spline interpolation (To make it clear that the series represent annual mean, that is central values, for the year in question, 0.49 is added to the year before writing the series. In this way a rounding of the year when writing it in integer form rounds the year to the correct integer)