|MadSci Network: Environment & Ecology|
The air in the troposphere (<10km at middle latitudes) constitutes roughly 95% of the total weight of the atmosphere. Air in the troposphere is relatively well mixed. It takes roughly a few weeks for the breath you exhale today to travel around the globe. Additionally, because in the troposphere, the temperature decreases with increasing altitude (look up adiabatic lapse rate), there is good vertical mixing too (except in winter). Once CFCs are released at ground level, it's inert nature combined with the overall good mixing in the troposphere results in a dispersion of the gas on a global scale. Additionally, diffusion aids dispersing the CFC on a smaller scale. The result is a distribution of the CFC at a constant mixing ratio (e.g. parts per trillion, parts per billion...) throughout the troposphere. Now, as to the question of how the CFC ever gets to the stratosphere, that is a big question in atmospheric physics today. One main theory is that in tropical areas such as Borneo, the high amount of sunlight combined with air holding a lot of water, results in vertical upwellings in turbulent storms. The air is therby "shot" through the tropopause (stratospher-troposphere boundary). Another theory holds that the tropopause elevation in the tropics (equatorial region) allows for horizontal movement of air through the tropopause without going through the barrior of vertical transport. Either way, stratosphere-troposphere exchange is not fully known and the area of study is ripe for future scientists interested in the subject.
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