Air quality alerts are in place for a large swath of the U.S., with the National Weather Service through the weekend. “When the air quality index starts to get above 50, or even 100, that's when there are health effects of the particles that are in the air,” Shulman said. Wildfire smoke can travel hundreds or even thousands of miles, carrying small particles, or aerosols, dangerous to human health. PHOTOS:If you do have to spend time outdoors on bad air days, an N95 mask can help. If you’re at home during dangerously polluted days, use air purifiers or HEPA filters to create a cleaner "safe room."