2006 Sonata Observation, any corroboration?

Been noticing an accumulation of dirt over and on the bumper area in
the rear. Was driving behind one the other day in the cold and I
noticed that the exhaust vapor kind of gets trapped in a dead air space
behing the car at lower speeds, curls up and seems to get trapped up in
that area. Now certianly this may just be drainage and general road
grime due to the onset of winter, but it does look like on the top
bumper surface that a fine layer of dirt/grime is being deposted by
some process other than rain or road spritz, anybody else notice
this?.....Doc

 

Doc,

That area of the car is a low-pressure area, and anything from the
exhaust or general road grime from the rear gets sucked into that area.
It's quite normal. One of the reasons for a small lip or spoiler on
the rear deck is to break up this airflow and help to eliminate this
low-pressure area.

Don