Black dust on windowsills?

[Nialmu]

Noticed that in the past few weeks, black "dust" has started to appear on the windowsills and along the window frames after I've aired out the room.

Vacuumed the floor and wiped the windowsills 2-3 times just this week, but the "dust" keeps coming back?

Got new windows installed a few weeks ago but cleaned everything. Have never experienced this before. Anyone with the same problem and what could it be then?

 

[tompax]

Noticed that in the last few weeks, black "dust" has started to appear on the windowsills and along the window frames after airing out.

Vacuumed the floor and wiped down the windowsills 2-3 times just this week, but the "dust" comes back?

Got new windows installed a few weeks ago but cleaned everything. Never experienced this before. Anyone having the same problem and what could it be if so?

You seem to have a cable there, I guess it goes to a thermometer?
It might be that there's a gap allowing some sand to blow in, especially if it's been windy lately.
Remove the cable, clean the windows, close them and see if the problem persists.

Otherwise, it could be sand from the construction company that installed the windows, as they might have had them placed in sand, causing the sand to get behind sealing strips, etc.