Cars in Traffic (IMAGE) George Mason University Caption The study found that primary pollutants, such as those emitted from car exhaust, were associated with emergency department visits for cardiovascular and respiratory diseases. Credit Photo by Alexander Popov on Unsplash: <a target="_blank" href="https://unsplash.com/photos/Xbh_OGLRfUM">https://unsplash.com/photos/Xbh_OGLRfUM</a>. Usage Restrictions <p>All photos published on Unsplash can be used for free. You can use them for commercial and noncommercial purposes. You do not need to ask permission from or provide credit to the photographer or Unsplash, although it is appreciated when possible. <p>More precisely, Unsplash grants you an irrevocable, nonexclusive, worldwide copyright license to download, copy, modify, distribute, perform, and use photos from Unsplash for free, including for commercial purposes, without permission from or attributing the photographer or Unsplash. This license does not include the right to compile photos from Unsplash to replicate a similar or competing service. 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.