that's the thing, i live minutes from a large, international airport, and the sky is chock full of planes on a daily basis.. it's very easy to spot whether a plane is coming in for a landing or just leaving the airport via the route they're taking, direction of travel, etc, if you pay attention it's simple enough to recognize what sort of pattern any said plane is on at a given time being so close to the airport..
the planes that i took the picture of the other day weren't on some simple flight path, flying from point a to point b, but would rather reach one end of the horizon, and turn around, fly a couple hundred or what ever amount of feet either higher or to the east or west of their last path, and then they'd fly the same pattern again, back from one end of the horizon to the other.. the other plane i saw was flying for thousands of feet in a vertical hold.. no passenger plane i ever witness coming out of the airport goes on such a dramatic ascent.
i understand what contrails are.. i watch formula 1 car racing all of the time, and if the air is moist enough and holding enough water, you can watch the contrails coming right off of the back of the wings, only these contrails evaporate back into the air quite quickly and don't continue to follow the car for extended periods of time, leaving huge trails behind them that linger for sometimes hours, unlike what i see coming off of the back of planes all of the time.
i'm not some conspiracy theory nutjob and don't fall for every little thing i read online, but i don't understand how people don't think this shit is real.. like i said earlier, i won't venture out so far as to make a guess as to what they're spraying as i have no clue, but it should be pretty obvious to anyone who lives in an environment where this happens that it's really happening.