From: felton@phoenix.Princeton.EDU (phil. Felton) Organization: Princeton Univ. Date: 01 Jun 96 16:32:35 References: 1 2 3 4 5
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In article <airliners.1996.820@ohare.Chicago.COM>, firstname.lastname@example.org (Larry Stone) wrote: > In article <airliners.1996.805@ohare.Chicago.COM>, > felton@phoenix.Princeton.EDU (phil. Felton) wrote: > > >This is incorrect, the altitudes that are flown by commercial airlines are > ><40000 feet. The atmosphere up to the tropopause is well mixed and therefore > >the altitude of emission is irrelevant, SSTs on the other hand fly higher and > >NOx emissions there are of more concern. (deleted) > Two problems: 1) As Karl has already stated, many modern jets do go above > 40,000. A week ago, I was on a 767 that cruised at 43,000. 2) I believe at > certain times of the year, the tropopasue can be down as low as the > low-30's putting a large percentage of jets cruising above the tropopause. Firstly, I won't argue over an extra 3,000 feet! Secondly, the tropopause does get down to about 30,000 feet over the poles in winter but I would suggest that this is a far cry from "a large percentage of jets...... above the T." Note that total emission by jet aircraft of NOx is 0.25 TgN/yr, which has a lifetime in the troposphere of about 1-7 days (removed rapidly as acid rain). Compare this with 8 TgN/yr produced by lightning, 8 TgN/yr from soil and 20 TgN/yr from fossil fuel combustion. Most of the NOx in the stratosphere comes from the reaction of oxygen atoms with N2O (very stable in the tropo- sphere, lifetime >100yrs). The sources of N2O are mainly biological and lead to 10 TgN/yr being destroyed in the stratosphere resulting in 1 TgN/yr of NOx being formed in the stratosphere, which can decrease the ozone concentration. >From these figures it can be seen that direct production of NOx above the tropopause by jet aircraft is not significant at present. Phil.