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01. Strange Happenings

Strange Happenings

EPA Ozone Info

24 December 1997. Ozone Depletion FAQ
Sample Question--Subject: 1.3) How does the composition of the atmosphere change with altitude? (Or, how can CFC's get up to the stratosphere when they are heavier than air?) Answer: In the earth's troposphere and stratosphere, most _stable_ chemical species are "well-mixed" - their mixing ratios are independent of altitude. If a species' mixing ratio changes with altitude, some kind of physical or chemical transformation is taking place. That last statement may seem surprising - one might expect the heavier molecules to dominate at lower altitudes. The mixing ratio of Krypton (mass 84), then, would decrease with altitude, while that of Helium (mass 4) would increase. In reality, however, molecules do not segregate by weight in the troposphere or stratosphere. The relative proportions of Helium, Nitrogen, and Krypton are unchanged up to about 100 km. Why is this? Vertical transport in the troposphere takes place by convection and turbulent mixing....


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