There is many different types an reasons for them, lots of different contracts from different companies from cloud seeding to fertilizing. In australia our soil and water is so lacking of mineral content it makes sense they have to spray it in the sky. Problem is like all things the additives needed like emulsifiers Are usually made from something toxic. The sun is so hot here that blocking sun at certain times of year is probably for survival. No doubt so evil intentions are also being camoflaged by these good intentions