Table 3.   Column amounts to raise grey opacity of a doubled terrestrial atmosphere to 3; lifetimes in present terrestrial atmosphere Gas Suggested column per m2 Lifetime against photolysis, yr CF3CF2CF3 1.1  × 1022 >1 × 108 CF3SCF2CF3 1.4  × 1022 8950 SF6 5.2  × 1021 3200* SF5CF3 1.0  × 1022 4050 SF4(CF3)2 8.0  × 1021 3070 * Includes reaction with mesophere's free electrons.