Find what app is causing popups, NOT in notification bar I am getting these popups regularly. They do not appear in the notification center so I can't find out what app is causing them. The only app I can think of that I have installed recently, I have already deleted and they still appear. I am using the Nexus 4 Android 4.2.2. None of the ad detector apps have found anything. 

How can I determine what is causing this?

Here is a screenshot of an ad, and a screenshot of my task manager immediately after. I am not sure if the app would have to be running to show the ad:
If these popups are appearing in front of other apps, look through your installed apps to find any with the "draw over other apps" permission.  Most apps don't have that permission, so this should help to narrow down which one might be the culprit.