posted 08-27-2001 01:02 PM            

I responded to a post in the "other trails" section of this forum regarding my company's proposed new aircraft, the Sonic Cruiser. The thrust of the article cited in this post was that there was increased chance of ozone depletion with the new, higher-flying aircraft (which, btw, has not yet been completely designed).

I figured that I should really post me article here, since this seems to be the one place on this forum where such a thread might get a reasoned response. My posts starts here:

Here are some resources that might provide more information about the ozone layer and the role of halocarbons, etc., in exacerbating its thinning.

WARNING: These resources are not exciting; factual information rarely is. But if you're interested in the facts and latest scientific thought regarding the ozone layer, some of this data may prove of benefit.

An excellent primer on the ozone layer and the history of activities taken to maintain it can be found at http://www.ogp.noaa.gov/library/rtnf92.htm , NOAA's "Reports to the Nation on Our Changing Planet: Our Ozone Shield" Note that, although the report seems to identify CFCs and other halocarbons as the main culprit, it does say:

"Experts are exploring several unanswered questions, including: [snip] Does a proposed new class of high-altitude aircraft threaten the ozone layer?"

Another report, this one at http://www.nas.nasa.gov/About/Education/Ozone/depletion.html , discusses ozone depletion, differentiating between stratospheric ozone (the good stuff) and tropospheric ozone (the bad stuff that make smog). The report mentions that the vast majority of chlorofluorocarbons (CFCs) are very non-reactive in the troposphere, which means they make it up to the stratosphere and can remain there - doing their dirty deeds - for over fifty years. However, aircraft emissions have negligible levels of CFCs.

Aircraft emissions are, of course, primarily hydrocarbons. Here is what the EPA says about hydrocarbons:

"Hydrocarbon (HC): a compound consisting of carbon and hydrogen. Hydrocarbons include methane, ethane, propane, cyclopropane, butane, and cyclopentane. Although they are highly flammable, HCs may offer advantages as ODS substitutes because they are inexpensive to produce and they have zero ozone depletion potential, very low global warming potential (GWP), and low toxicity. HCs are numbered according to a standard scheme." ( http://www.epa.gov/ozone/defns.html#ods )

I have spoken with Ms. Stacy Benfer (415) 744-1161, with the Education Section at the Environmental Protection Agency (EPA). Neither she, nor any of the Internet resources I have seen, can direct me to discussions of correlations between the altitude of an aircraft and the effect of its emissions on stratospheric ozone. Common sense tells me that if an aircraft moves into the stratosphere, its exhaust has an increased effect on the ambient environment. If you accept this, and use straight-line extrapolation, then an assumption might be that an aircraft that produces 1X amount of CFCs at 33,000 feet will produce 1.36 X the amount at 45,000 feet over the same time period.

But inasmuch as the proposed Sonic Cruiser will be flying the same routes in about 70 percent of the time (given its increased inherent speed and the ability to dial in higher jet-stream speeds) then the potential amount of CFCs, instead of being (present) X (1.36), would be (present) X (0.95) - a net decrease in CFC pollution over the duration of the flight.

Near as I can see, then, (given the fact that airplane exhaust is not proven to be a player in the ozone depletion equation and that if it were, there'd be less pollution per flight with the Sonic Cruiser) the whole brouhaha is just a red herring.

Regrds,

posted 03-18-2002 11:13 PM            

I'll be the first to admit that I know very little about the boosters, except that the propellant is an aluminum + ammonium perchlorate in a polymer binder.

Here is what the same site mentioned about the potential for Space Shuttle impacting the ozone layer:

“Space shuttle and other high altitude flights:
In the early 1970's it was suggested than chlorine from solid rocket boosters might have a significant effect on the ozone layer.

A study by Cicerone and Steadman,1974, found the resulting contribution of chlorine to be relatively small as have many studies since then. The most current article on the issue calculates that the shuttle program has relatively little effect on the stratospheric chlorine levels, although it does raise some concern about the particles of aluminum that the solid-booster engine sprays into the atmosphere.

Each shuttle launch produces about 68 tons of HCl, most of that released in the troposphere. Ten launches per year would amount to less than 0.06% of the yearly chlorofluorcarbons released which was 1.2 million tons per year in the 1980's.(18)"

However, that is merely one set of data. I would very much like to see your correlation of ozone layer thinning and space flights. I cannot, of course, tell whether it might be causal rather than casual unless I see, but I would be very interested in finding out.

Bear in mind that I am not a chemical engineer, so you should take all my inputs with a large grain of salt!

Regards,