*(12): add any other gases that might be significant
in this spectral range
(from rfm.log it can be seen that it chooses
to add CH4, F22 (HCFC-22), F11 (CFC-11) and CO2).
Although N2O is included because it was explicitly specified by the user,
the RFM wouldn't have added it itself.
Since this is a plane parallel atmosphere calculation, the path is
specified by sec(zenith angle), the value 1.0 defining the vertical path
(1.0 = 1/cos(0°))