How much CH4 (in ppm, just give a number) does it take before the absorption ban

How much CH4 (in ppm, just give a number) does it take before the absorption ban

How much CH4 (in ppm, just give a number) does it take before the absorption band begins to saturate like CO2? You’ll have to use your judgement to decide when the CH4 absorption band approaches the coldest Planck curve on the plot.