1. Department of Environmental Sciences and Engineering, Gillings School of Global Public Health, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27514, United States
2. Aerodyne Research Inc., Billerica, Massachusetts 01821, United States
3. Department of Environmental Health Sciences, School of Public Health, University of Michigan, Ann Arbor, Michigan 48109, United States
4. Department of Chemistry, College of Literature Sciences and the Arts, University of Michigan, Ann Arbor, Michigan 48109, United States
5. Earth System Science Programme, Faculty of Science, The Chinese University of Hong Kong, Hong Kong 100872, China
6. Department of Chemistry, College of Arts and Sciences, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States