Google announced that the mobiles sites showing giant ads will not rank well in the search engine. Basically, the interstitial ads cover significant amount of content on the page. Thus, such pages become worthless for mobile users, i.e. they do not remain mobile friendly.
This action would be started from November 1, 2015.After November 1, mobile web pages will not be considered as mobile-friendly, if there would be an app install interstitial covering a major proportion of content. As an alternative, the browsers must provide different ways to promote the app which will be user-friendly.So, Google Chrome-supported App Install Banners and native Apple-supported Smart Banners are mobile-friendly in Google’s perspective. Only those banners which cover significant portion of content are not mobile-friendly.
Therefore, it is important to use mobile usability test and check whether your web pages pass the mobile-friendly test or not. This will help you identify, if you have any problems with app interstitials and ranking.
Thus, only those app ads which block or cover a major part of content can lead to a decrease in mobile ranking. Other ads that are not for installing apps are fine.