When I clean the inside of my car windows, I notice that they are covered with an oily film that leaves a noticeable black residue on the cleaning cloth. There are a lot of plastics used in the manufacture of a car, especially around the inside of the windscreen.
Most plastics contain waxy plasticisers which provide flexibility.
These boil off in the intense heat under the windows and condense as a film on the glass. The films are sticky and attract fine particulate matter from the air intakes. Another effect is that the plastics in a car become brittle with age as plasticisers are lost. The emission of plasticisers causes both the window film, but also the smell of a new car. Old cars that have spent much time in the sunshine do not have this problem because all the plasticisers have been lost.