Green Roof Study (IMAGE) Portland State University Caption Atmospheric ozone is deposited onto the plants on this Portland, Oregon, commercial roof. The plants help trap and filter some of the ozone as outdoor air is pulled into the building's interior. Credit Portland State University Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.