1. a Department of Environmental and Occupational Health Sciences , University of Washington , Seattle , Washington , USA
2. b United States Environmental Protection Agency , Reston , Virginia , USA
3. c Department of Civil and Environmental Engineering , University of Washington , Seattle , Washington , USA
4. d Department of Biostatistics , University of Washington , Seattle , Washington , USA
5. e EPA Northwest Research Center for Particulate Air Pollution and Health , Seattle , Washington , USA