From:
Google AdSense Program Policies
I italisized the part where I think applies to pop-under Ads since these Ads are launched by a software application that the website visitor did not want to launch IMO.Quote:
Traffic Sources
Google ads may not be placed on pages receiving traffic from certain sources. For example, publishers may not participate in paid-to-click programs, send unwanted emails or display ads as the result of the action of any software application.

