Tucson “Chemtrails” on December 1, 200...

I'm not too familiar with this conspiracy-theoryesque phenomenon,I've read a bit here and there (abovetopsecret.com, pomoworld.com) on the subject but it still leaves for me many questions 'in the air'. ;) Any thoughts/opinions/theories/info on the matter? Ppl think that this is the government spraying us with chemicals... what type and for what purpous then? I'd also like to know what official explanation the government/airforce gives for these streaks in the air? There could very well be a ...