1. a Department of Environmental Sciences , Rutgers University , New Brunswick , NJ , USA
2. b Office of Research and Development, National Exposure Research Laboratory, U.S. Environmental Protection Agency , Las Vegas , NV , USA
3. c School of Public Health, University of Medicine and Dentistry of New Jersey , Piscataway , NJ , USA
4. d Department of Mechanical Engineering , Carnegie Mellon University , Pittsburgh , PA , USA
5. e Droplet Measurement Technologies , Boulder , CO , USA
6. f Department of Civil and Environmental Engineering , University of Southern California , Los Angeles , CA , USA