1. Department of Environmental Health Sciences, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, USA
2. Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, USA
3. Environmental Health Policy Committee of the American Thoracic Society, Washington, DC, USA
4. RH White Consultants LLC, Silver Spring, Maryland, USA
5. Department of Biostatistics, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, USA