Pollution

I noticed a black smudge on the back of my front door the other day, so today I took a sponge to the door. YUCK. The entire door was covered with a black sheen. And each of the other four doors in the front hall (each room in Germany has a door on it, and most of them have seals around them - airtight). The worst was the kitchen door. The kitchen faces the street. This is pollution making it's way up from the street and into my fifth story (fourth in Germany) apartment. And I'm breathing this in. Yummy. Still, this only what's built up in a year and four months. So I guess the pollution isn't THAT bad. But still, yuck.