LiveScience: Yosemite National Park's Rim Fire dashed the plans of many campers over Labor Day weekend. The iconic views of Half Dome and Yosemite Valley's sheer granite walls disappeared behind a sudden influx of thick smoke the night of Aug. 30, just before most visitors arrived for the holiday. The air quality was deemed to be unhealthy for outdoor activities, according to California air quality officials. Smoke from the still-burning fire continues to cause unhealthy air quality levels for sensitive people...