The Atmosphere Composition -About 99%of the clean, dry air in the troposphere consists of(2) gases: Nitrogen(79%)Oxygen (20%) Water vapor accounts for. 01% to 5% Most of the atmosphere is held close to the earth by the pull of gravitational force, thus it gets thinner with increasing distance from the earthThe Atmosphere • Composition - About 99% of the clean, dry air in the troposphere consists of (2) gases: Nitrogen (79%) Oxygen (20%). – Water vapor accounts for .01% to 5%. – Most of the atmosphere is held close to the earth by the pull of gravitational force, thus it gets thinner with increasing distance from the earth