Contrails usually dissipate within a normal amount of time and the planes are in a traffic pattern. Chemtrails last for 12 hours or more till they disperse and completely obliterate the sky. They are also sprayed in a grid usually. There is plenty of information at
http://www.carnicom.com/ and various others. Just take your pick.
To the one with the comment about air in your home;
Chemtrails have been found to contain aluminum, barium, ethylene dibromide, banned as a pesticide due to causing severe respiratory reactions even at low levels) numerous pathogens, disease causing agents. Thousands of fungi, some previously unknown.
These included Pseudomonas Aeruginosa, which not only causes respiratory infection but also attacks the immune system; Serratia Marcescens, an antibiotic-resistant bacteria which causes pneumonia, endocarditis and meningitis; as well as Streptomyces and molds capable of inducing heart disease. The government has used us time and again for inhumane testing.
Want a better source or many more? Try rense dot com. His site is full of horror stories about the governments high priorities regarding her citizens.
http://www.rense.com/general36/history.htm