In addition, high levels of ozone are going to be found in cities.  It
is formed by the reaction of sunlight and heat with VOCs and NOx from
vehicle emmisions.

Bubbabob's description of blues and blacks fading first is consistent
with ozone fading of dyes.  But I have also had (HP) dye inkjet prints
fade considerably over a period of weeks exposure at home, which I think
was more attributable to UV (high UV levels in NZ - somewhat ironically
the result in part of ozone depletion in the stratosphere, also claimed
to be the result of other man-made pollutants).  Cibachrome prints
mounted behind glass last a few years only in my house.

Ozone fading is apparently worse in high humidity environments.  I
expect that it would also be worse on non gloss papers - as the surface
area of dye exposed is much greater.  It might be reduced by some of the
protective sprays that can be applied to inkjet prints.  For sure,
putting the print behind glass would be a great help.  Don't get too
hung up on the type of glass.  I have read that so-called archival UV
resistant glass is only 10% better than normal stuff.

Canon are aware of the real life limitations of dye - they are releasing
pigment ink based professional printers.  Also, given that the
encapsulation of the dyestuff within the coating on the paper is going
to be critical to the longevity of the print, I am surprised at the
confidence many people seem to have in the expected longevity of their
Canon dye inkjet prints on non OEM papers.  Canon are about as likely to
share the technology behind their ink/paper combinations with third
party paper suppliers, as they have been to share the electronic
technology of their lenses with Sigma.