You can't possibly prove chemtrails exist by just "seeing" them. You can't establish they are chemtrails by claiming they "hang around a long time."
Contrails exist due to the way jet engines operate (water vapor is a byproduct of their operation). Contrails vary in numerous ways: whether or not they appear in the first place, how quickly they dissipate (anywhere from less than a second to multiple hours), whether or not they spread and grow, etc. The same variety is true for normal clouds. Guess what? Contrails are basically cirrus clouds and will have the same type of variety as clouds do. Variety is due to variations in atmospheric pressure, temperature, humidity, air currents, etc.
Those claiming chemtrails are true would need to prove it. They are the ones making a claim here. Take air samples. Find the tanks that hold the chemicals on the planes. Find the chemical tank refilling equipment. Find the nozzles that spray it out.
Consider the tens of thousands of people that would have to remain silent: the ground crew that refills the chemical tanks. The maintenance workers who repair the chemtrail equipment. The crews that install the equipment. The pilots who activate the spraying equipment during flight. The staff that works at the companies that manufacture the chemical and sell/ship to airports.
Which is more likely here - you are seeing contrails: a known, proven, and well understood result of jet engines? Or chemtrails: something with no hard evidence, something that would require the silence of 10,000+ individuals in multiple countries and under the jurisdiction of multiple governments?
This will of course be a waste of time, but sometimes I can't help but reply to threads like this.