A recent balloon flight by Explorers post 632, instrumented with Futurlec.com gas sensors (also available from SparkFun) appears to have detected jet fuel gases in a contrail. I did not expect these sensors to be sensitive enough to detect anything. I’m pleased to be wrong, and will need to start figuring out how to use them. Perhaps a small suite of Ozone, CO2, Air Quality, and Humidity? would be useful to fly regularly.