I have small black dots on almost all surfaces of my home and cannot figure out what they are. I live in Louisville, Kentucky in zone 6-7. I live near an airport and think they may be associated with the jet traffic or are some type of fungus or tree pollen. They will come off with crud cutter, but require quite a bit of scrubbing even then and they often leave a dark brown stain. I would say they are about 1mm diameter. Any help is very appreciated!