"tendency_of_X" means derivative of X with respect to time. The construction "atmosphere_moles_of_X" means the total number of moles of X in the entire atmosphere, i.e. summed over the atmospheric column and over the entire globe. The chemical formula for halo2402 is C2Br2F4. The IUPAC name for halon2402 is 1,2-dibromo-1,1,2,2-tetrafluoro-ethane.