Why are contrails (exaust from airplanes) not fading away like they
used to? (or are they?)

From what I've found out, contrails are supposed to be water vapor
freezing in the sky at high altitudes, then quicly evaporating as the
sun hits it.

There is a video about chemtrails circulating on the net that says
there is a conspiracy to eject material(s) (solids) in the exaust
streams that stay in the sky. I've personally noticed these chemtrails
in many pictures i've taken over the past 4 +years (in Ottawa,
Canada).

My follow up questions are:

1: is there more than just water vapor (and CO2) in the exaust of jet airliners?

2: should the contrails vanish , in any case, in diferent conditions?

3:if there is more than ...(see #1) then what is being left in the sky?

4: what possible reason would there be to do this? (if it is an UN-usual event)

Civil Jet fuel is a kerosine blend.  There are mainly two types, JetA1
and JetA.    There are also additives in the fuel. Tetra-ethyl lead is
one (and remains the only FAA approved one since 1930), which reduces
the 'knock'.  There are also antistatic, anticorrosion, antibacteria,
anti-icing additives.  Note that not all the Jet Fuel will combust and
some of it will exit through the jet engine exhaust (incomplete
combustion).  Of course the contrails are a result of the high
temperature (~600k) jet mixture mixing in a turbulent shear layer in
the cold ambient atmosphere.
In conclusion to your first Question (1:) there is more than water
vapor and C02 in the engine exhaust.

I urge you to pick up a peer-reviewed book on the topic and learn from experts.  

Source: Personal Knowledge.

Best,
Steve =)

Note to Researchers:
 
Conspiracy theories find menace in contrails
http://www.usatoday.com/weather/resources/basics/2001-03-07-contrails.htm
Toxic Contrails Conspiracy
http://leverleyeux.homestead.com/Leverleyeuxhome.html

Here's an entire website devoted to the discussion of chemtrails:

http://www.chemtrailcentral.com