Hi Stephen>I don't know a great deal about the alleged environmental
>impact of air traffic. Could someone tell me exactly how
>polluting large commercial aircraft are and whether or not
>environmental damage is a legitimate reason for people to
>oppose the construction of new runways and the additional
>traffic they bring to an airport?
I can't say I know a great deal on the subject either, but there's not much argument (by engineers, at least) that modern high-bypass turbofan engines are amongst the most fuel-efficient internal combustion engines ever produced. More of the energy of the fuel is converted to useful work than in other types of engine.
Furthermore, the combustion process in such an engine is very much more complete than in piston engines. From the chemist's theoretical point of view, jet fuel (essentially kerosene) burns to produce nothing but carbon dioxide and water. It's only when incomplete combustion occurs, that you get carbon monoxide, as in car engine exhaust. There's practically no carbon monoxide in jet exhausts, I think.
One of my friends from university days is an aircraft propulsion specialist. Unfortunately, he's in Saudi Arabia, and after the events in Riyadh recently, he's gone very quiet - keeping his head down hopefully - so I can't really quiz him on details.
I seem to remember that the fuel consumption mpg figures of jet airliners are better than for cars (per passenger, that is)
Alan