I've been researching this, definitely planes are diverted to spray particular areas, and the spray can be switched on and off (probably automatically programmed into the autopilot at the same time as the route). I've watched as one after another, planes line the sky with trails, sometimes up to three planes pretty much travelling in unison crossing the sky in the same direction. Then another set, and so on.
I was sitting in the garden enjoying the sun when I noticed they had started spraying...
Northwest England, May this year
One of the planes was throwing out so much stuff, it was literally falling from the trail like a flour bomb. Contrails don't do that. See the vertical streams, that's the particles falling through the air. The actual plane trail is the top broken white line. The trail next to it looks like its doing the same thing, stuff from it falling and being caught on the wind.
Thanks for taking the time to reply Rachel. It's encouraging to see that others are noticing what is happening too. I see similar trails and particles falling through the air down in South West England. Skywatching has become a bit of an obsession with me and the sight of a almost white sky filled with haze that blocks the sun really pisses me off which means I am pissed off quite a lot.
I'm following you now, so I'll look out for your posts on this topic in the future.
Take it easy
Jim