Most of the fine, breathable summer dust in the southern U.S. Great Plains comes from the Sahara Desert, say UC Davis researchers, and the dustiest site in the U.S. national park system is in the Virgin Islands. Saharan dust, which has a distinctive "fingerprint," moves across the ocean, through the Caribbean, through the "dust bowl" states of Texas, Oklahoma and Kansas -- sometimes reaching as far as Maine and over the Atlantic, says Tom Cahill, head of the UC Davis Air Quality Group. The findings were presented recently at a meeting of the American Geophysical Union. In another study, the group showed evidence that industrial pollution from mainland China reaches Hawaii, possibly affecting observatory measurements at Mauna Loa that are key to global climate research, says Cahill, a professor emeritus of physics. For nearly 20 years, the group has been measuring air quality at national parks and monuments. The program has expanded internationally. Now, the group is coordinating 20 other research groups to create a seasonal map of fine sulfate aerosols, according to another AGU paper. Sulfate pollution may slow the rate of global warming, Cahill says, so the new data may reconcile climate models with the 1945-95 temperature records.