It’s about time. Google is looking to punish websites that use annoying pop-up ads by lowering their page rank.
For the most part, Google is targeting overlays that gray out the content beneath them to prevent you from reading a website, either for a few seconds or until you find and very carefully tap a little X to dismiss them. These count regardless of whether they load immediately after a page is opened or whether they appear after scrolling a certain distance. On top of that, it sounds like Google will also count ads that create the effect of a pop-up without actually being a pop-up, by taking up most of the page after a site is loaded (you may have seen one of these if you’re reading this article on mobile).
I don’t mind ads as that’s how sites make money, but pop-up ads are just a nuisance.
Read more here.