If they added it to the fuel, it would leave "chemtrails" across the entire trip, not just specific areas. That seems counter-productive to controlling rain patterns or dousing civilians with chemicals.

They're produced by heating the cold air, causing the condensation to appear when the air immediately cools back down. They come off wingtips of fast aircraft when they turn or dive, and also when the sound barrier is broken too. They're abundant in WW2 pictures. Were those caused by "Aluminum Oxide nanoparticles too?
Just sayin. It's similar to steam from a boiling kettle.