WOW thread your still alive I see.
here is a random reason why "Sulfur Hexafluoride is an approved additive for leak detection in aviation fuel." - Rand, Salvatore J.. Significance of tests for petroleum products. 7th ed. West Conshohocken, PA: ASTM International, 2003. Print.
"What Clouds Are Made Of
Both SO2 (which forms sulfate particles) and soot particles from aircraft exhaust are aerosols—microscopic particles suspended in air. They act like seeds. Water molecules can condense or freeze on them to form cloud particles.
Aircraft exhaust produces contrails—condensation trails in the atmosphere about 5 miles above the Earth's surface. At these high altitudes, contrails and cirrus clouds form depending on the quantity of water vapor and atmospheric conditions.
Contrails and cirrus clouds both reflect sunlight that would otherwise warm the Earth's surface. At the same time, they absorb heat from the ground instead of allowing it to escape. Do they contribute to global warming or global cooling? The scientific community is still trying to answer that question.
Contrails contribute to the phenomenon known as "global change." Right now this effect is small, but it is growing. Although scientists are uncertain about the impact of contrails on global change, they believe that persistent contrails, those that last longer than a few minutes, gradually develop into cirrus clouds. Over the past 40 years, cloudiness seems to have increased. If this is in fact true, then this continual increase in cloudiness may lead to global climate change because it will change the amount of radiation entering and leaving the Earth's atmosphere. This characteristic of aircraft engine exhaust may act in a way similar to the effects produced by greenhouse gases.
What effect, if any, do contrails have on weather? Answering this accurately is difficult because so many factors affect weather. However, many meteorologists believe increased jet traffic and the contrails it produces have altered the weather. They point out that areas of high jet traffic show the greatest change. Although circumstantial, evidence seems to indicate that contrails do affect climate. Glenn's contribution of a new generation of highly efficient, clean-burning aircraft engines will reduce the amount of aerosols in the upper atmosphere, which will in turn lessen the effect of increased air traffic on climate." - Dunbar, Brian. "Safeguarding Our Atmosphere." NASA. NASA, 20 May 2008.
http://www.nasa.gov/centers/glenn/about/fs10grc.html