The formulae are identical to those used in the Bern CC Model, which was used to calculate the data given in IPCC-TAR-WG1 Ch6 and SRES appendix. The full set of equations are given in Joos et al 2001 (appendix).
The atmospheric chemistry formulae are derived from the IPCC workshop of Prather et al. These include a simple parameterisation to calculate O3 and OH from CH4, NOx, CO and VOC, and the effect of OH on the lifetime of CH4 and of all the HFCs. The effect of N2O on it's own lifetime is also considered.
The radiative forcing calculation includes the spectral overlap between CH4 and N2O.
For speed, the F-gas concentrations and radiative forcing are calculated using a ramp function over five year intervals, since the original emissions data is also in five-year intervals.
The concentrations of the Montreal gases (CFCs, HCFCs) are prescribed by WMO data, and emissions are estimated by an inverse method.
The formulae for scaling emissions for mitigation scenarios are described under "Other Gas Emissions Menu"