Air pollution is one of the largest environmental health risks globally but is often imperceptible to people. Air quality smartphone applications (commonly called apps) provide real-time localized air quality information and have the potential to help people learn about the health effects of air pollution and enable them to take action to protect their health. Hundreds of air quality apps are now available; however, there is scant information on how effective these mobile apps are at educating stakeholders about air pollution and promoting behavioral change to protect their health. In this paper, we test how intrinsic and extrinsic motivations can enhance users' engagement with air quality information through the app, and favor changes in protective behavior. We developed an air quality app, AirForU, with a built-in research study that was downloaded by 2,740 users. We found that engagement was higher for users with intrinsic motivations, such as those who are health conscious, either because they are suffering from heart disease or other conditions aggravated by air pollution, or because they exercise often and want to maintain a healthy lifestyle. Extrinsic motivations such as notifications were also effective. App users stated that they frequently shared air quality with others, learned about the Air Quality Index (AQI), and took measures to protect their health while using the app.