50% of atmospheric mass lies within

The total mean mass of the atmosphere is 5.1480 × 1018 kg with an annual range due to water vapour of 1.2 or 1.5 × 1015 kg depending on whether surface pressure or water vapour data.
50% of the atmospheric mass lies within 5.6 km from the earth’s surface.
About 80% of the total mass lies in the troposphere which is the lowest layer of our atmosphere.