1. Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA.
2. National Oceanic and Atmospheric Administration Earth System Research Laboratory, Chemical Sciences Division, Boulder, CO 80305, USA.
3. Cooperative Institute for Research in Environmental Science, University of Colorado, Boulder, CO 80309, USA.
4. Institute for Meteorology and Climate Research–Atmospheric Aerosol Research, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany.
5. NASA Ames Research Center, Moffett Field, CA 94035, USA.
6. Department of Civil and Environmental Engineering, Princeton University, Princeton, NJ 08544, USA.
7. School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA.
8. College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331, USA.