If you were wondering how Google would apply the new interstitial / popup changes to pages, Gary Illyes from Google has confirmed that it is applied on a page level and not a site level.

This isn’t too much of a surprise.  This is how Google originally implemented the mobile friendly ranking boost – the boost was given to each individual page based on whether it met the mobile friendly criteria or not, so the new interstitial and popup criteria will act the same way.

This means if you are prepared for a demotion for a particular page, you can keep an interstitial or popup on that page.

Or you could segment based on referral – referrals from social media get an interstitial while those from Google do not.  But you do need to be aware of potential cloaking issues if you do it this way, and be sure to implement it correctly.

Google announced the change last week that would see sites with an interstitial or obtrusive popup on mobile would be demoted in the search results.  The new change doesn’t go into effect until the new year.