1. Rent or purchase an aircraft suitable for intercepting a chemtrail at a safe distance behind a jet creating it.
2. Secure permissions as needed to safely cross a chemtrail without tipping off the authorities as to the true nature of your mission. HIgh altitude parachuting, or some scientific experiments that need to be conducted at the appropriate altitude. Figure something out, and there are admittedly a lot of details and bases to be covered here. Nobody said the FAA was simple.
4. Repeat at least 50 times, preferable 500.
5. Rent a second jet to capture some of the chemtrail your own jet creates.
6. Analyze all of the samples, and publish results
Once the basic science has been done, please get back to me. Discussing cow farts in yonder field without real data from samples as they exit the cow, is poor herdsmanship, and leads to completely speculative ideas, without the necessary experimentation to prove your points.