Dust on speaker cones.

I have two pair of Aerial Acoustic towers. I prefer the appearance with the grills off. They both don't get used daily but each set does get used multiple times a week.

I recently noticed dust on the lower surface of the speaker cones. Very fine and you have to look close. Just typical house dust. But it wasn't there (I don't think) when I got them 2-3 years ago and 1 year ago respectively. The original owner kept the grills on them.

I'm assuming it doesn't make a lot of difference but do I need to do anything about it? If so, what? I certainly don't want to touch them. I don't think loud volume will do it as it almost looks like it is held in place by static electricity. It is cold and dry hear and everything is staticy. I would be hesitant to use anything to blow air on them.

Open to suggestions  even if it is just to leave them alone.