Any in-app purchase will permanently remove the ads from the game. Please note that the ads don't stop appearing until you have completely quit the game. If you are closing the game by returning to your device's home screen, the game is still in the background and the ads will not be turned off until the game is completely closed and reopened.

If you are unfamiliar with how to completely close an app on your device, you can consult the User Guide for your specific device or access online help for your device's operating system.