Pop quiz hot shot! If this were true, every jet aircraft would be spraying chemicals. I was weight and balance certified for several large commercial airplanes. If I didn't account for all the weight and balance it mathematically, the plane would crash, and people would die. The weight to spray chemicals would have to be accounted for or those planes would crash. I have personally fueled these aircraft, which includes testing the burn rate of the fuel before pumping, loading the cargo, or boarding the passengers, sometimes both/ Hell I even emptied and re-filled the poop juice. I account for the Crew's body weight even. If there were a crap load of chemicals on any of my aircraft I would have known. Every picture I have seen touted as evidence is simply people not knowing what they are looking at. Like jet fuel gauges being claimed to be chemical gauges, simulation blasts full of water to simulate passengers when an aircraft is trying to get certified, spray nozzles one fire fighting aircraft of crop dusters. What you are seeing in contrails, and the CO2 they omit is not great for the environment and can block the sun a bit. That are many varying factors on how, when, and where they happen. Good news, though, they have developed ways to great reduce them and will phase that tech in slowly. Then maybe you can all get a new hobby! There is legit weather geoengineering going on but the scale of those experiments are .00001% of flights, and I am being generous. The level of human cooperation it would take to pull off what some of you are talking about goes against human nature and is impossible! In case you have not noticed we don't cooperate very well, especially these days! lol