|
|
Thread Tools | Display Modes |
#1
|
|||
|
|||
Do NASA's engines destroy the Ozone Layer
Just to comment, freon is not used to cool rocket engines. Don't know where
the original poster got that idea. Rocket engines are typically cooled by the fuel or oxidizer brought used to propel the craft. There's little enough mass margin as is, they can't waste any on what would be an ineffective coolant. Freon is used to cool the shuttle itself: http://www.cnn.com/2002/TECH/space/0...oblem/?related It is not true that ground relesed freon is "too heavy" to reach the ozone layer: http://rpuchalsky.home.att.net/sci_env/dixy_1.txt 1.: Vertical distribution of atmospheric gases p. 35: "How does CFC rise when its molecules are four to eight times heavier than air? All experience with freon and related CFCs shows that they are non-volatile and so heavy that you can pour CFCs from a container and if some of them spill, they will collect at the lowest point on the ground where soil bacteria will decompose them. Of course, some molecules will be caught in upward air eddies or otherwise carried upwards, but this is a very small fraction of the total." This seemingly plausible objection merely demonstrates that the authors [Dixy Lee Ray and Lou Guzzo] do not understand the mechanisms of vertical transport in the atmosphere. It has long been known [Wallace and Hobbs] that gases do not segregate by weight in the first 80 km of the atmosphere, an altitude range that extends well above the ozone layer. Molecular weight is entirely irrelevant for determining the chemical composition in the troposphere and stratosphere. The mixing of atmospheric gases takes place by turbulent processes that do not distinguish molecular masses - the rare heavy particles are carried along by the much more numerous light ones. Thus, for example, the ratio of oxygen to nitrogen is constant up to ~100 km (the ozone layer lies between 15 and 50 km.) Now one might argue that CFC's are quite a bit heavier than most molecules in the atmosphere; perhaps the mixing mechanisms are strong enough to keep the O2/N2 ratio constant, but not to sustain the heavier CFC molecules. Rowland and Molina considered this point carefully in their 1975 review [Rowland and Molina]. At that time CFC's had not yet been measured in the stratosphere, so they examined data on atmospheric concentrations of heavy inert gases. These data showed that the relative proportions of Krypton (mass 84), Argon (mass 40) and Neon (mass 20) between 40 and 60 km were within 0.5% of those measured at ground level. Shortly thereafter, direct measurements of CFC's themselves as a function of altitude began; the very first such measurements showed that the CFC mole fraction is virtually independent of altitude up through the troposphere and lower stratosphere, then drops off suddenly at altitudes in which the molecules are exposed to UV radiation. It is a molecule's UV absorption spectrum, not its weight, that determines its distribution in the atmosphere. Even more revealing are measurements of the fluorocarbon CF4. This extraordinarily persistent molecule is not dissociated by the UV wavelengths that are abundant in the stratosphere, and thus serves as a tracer for vertical motion. The mole fraction of CF4 has been measured and found to be essentially independent of altitude all the way up to the top of the stratosphere at 55 km. [Fabian et al.] [Zander et al. 1992] =========================== Anti-environmental myths http://info-pollution.com/myths.htm Practical skepticism http://info-pollution.com/skeptic.htm |
Thread Tools | |
Display Modes | |
|
|