1. U.S. Environmental Protection Agency, National Health and Environmental Effects Research Laboratory, Research Triangle Park, North Carolina, USA
2. Inner Mongolia Center for Endemic Disease Control and Research, Huhhot, Inner Mongolia, China
3. RTI International, Research Triangle Park, North Carolina, USA
4. Ba Men Anti-Epidemic Station, Lin He, Inner Mongolia, China
5. Wake Heart Associates, Raleigh, North Carolina, USA
6. Department of Medicine and
7. Center for Environmental Medicine, Asthma and Lung Biology, University of North Carolina, Chapel Hill, North Carolina, USA