Google is about to deal a small blow to some of the most annoying ads on mobile: pop-ups and interstitials. It’s not a stretch to argue that readers don’t like these ads. So Google is making a call that websites that use pop-ups and interstitials are worse search results and may rank them lower because of it.
There are a "hundreds of signals" that go into Google’s search result rankings, so it’s not like every website that uses these ads will feel pressured to remove them overnight. If a site with a pop-up still has the best information, it’s still likely to appear first. But this change ought to benefit one site over another when those two sites appear roughly equal otherwise.
More here: https://www.theverge.com/2016/8/23/12610890/google-search-punish-pop-ups-interstitial-ads