Most of mobile ad revenue comes from interstitial ads
Interstitial ads refers to ads that occur at logical breakpoints during the app flow, overtaking the entire screen, as opposed to taking up a portion of the screen real estate. Other data suggests that interstitial ads can have a much higher conversion rate than ever-present banner ads.
This is because users are forced to look at them. On the surface, forcing users to view an ad may sound somewhat intrusive, but it is no less intrusive than a TV commercial or a YouTube pre-roll ad. In fact, displaying ads in this manner gives you the opportunity to present the rest of your app ad-free.