Did you need another reason to visit the Grand Canyon? Are you a big national parks fan? Well here you are. Grand Canyon has cleaner air than other national parks. A study carried out by Iowa State and Cornell Universities found the Grand Canyon national park has the cleanest air of all the national parks. Based on how often a national park has a day of unhealthy ozone levels, Grand Canyon came in with the cleanest air record. Take a look here for the story.