Google will be reinforcing its emphasis on the mobile search experience by introducing a new ranking factor that will lower the ranking of websites with "intrusive interstitials”on mobile web pages. As Google define interstitial, they are - banners, pop-ups and requests to download third party content. This will take effect from January 10th 2017 and is designed to improve the accessibility of content on the smaller mobile screen.
The following interstitials are features known to Google to make the content of a website less accessible when viewing on mobile:
Showing a popup that covers the main content, either immediately after the user navigates to a page from the search results, or while they are looking through the page.
Displaying a standalone interstitial that the user has to dismiss before accessing the main content.
Using a layout where the above-the-fold portion of the page appears similar to a standalone interstitial, but the original content has been inlined underneath the fold.
Google are however prepared to make exceptions when interstitials are used responsively under the following circumstances:
Interstitials that appear to be in response to a legal obligation, such as for cookie usage or for age verification.
Login dialogues on sites where content is not publicly indexable. For example, this would include private content such as email or unindexable content that is behind a paywall.
Banners that use a reasonable amount of screen space and are easily dismissible. For example, the app install banners provided by Safari and Chrome are examples of banners that use a reasonable amount of screen space.
The introduction of this ranking factor follows Googles attempt to check for interstitials like those that asks a user to instal a map app. Google later realised that a broader approach to all intrusive features would be more appropriate to improving the mobile web experience.
This new factor in ranking is one of the many that contribute to a website's overall position in search results. Great relevant content on a website is still a key defining factor and a website that continues to use these features may still be ranked highly but its overall positions will still be impacted in some way.