The nonlinear relationship between temperature and saturation makes it
possible for two unsaturated air samples to mix and form a new
satruated air sample.  Can i get an example that explains this?

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Clarification of Question by waynicemoves-ga on 24 May 2005 11:52 PDT

but can i get an example. a real life example

See the second figure on the webpage at
<http://www.aerospaceweb.org/question/atmosphere/q0111.shtml>, which
discusses this question in the context of the formation of contrails. 
The principle, however, is applicable to the mixing of any two air
masses, regardless of their origin.

Because of the curvature of the saturated water vapor pressure vs
temperature curve, it is possible to pick two air masses with
temperatures and partial pressures of water that are unsaturated
(i.e., lie below the saturation curve), but a mixture of these air
parcels (which must lie on a straight line connecting the two points
in the vapor-pressure vs T plot) can plot *above* the saturation
curve.

As noted in the web page I pointed to in my previous comment,
contrails are an example of this phenomenon.  In terms of weather, the
type of fog known as "mixing fog" or "steam fog" forms by mixing of
warm humid air with cold dry air.  See
<http://amsglossary.allenpress.com/glossary/browse?s=m&p=46> for a
definition.  (The "fog" that forms when you breath out on a cold day
is a micro-version of this.)  Do a web search on "mixing fog" and
you'll find numerous references.