1. Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA.
2. Department of Atmospheric Sciences, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA.
3. Aerodyne Research Inc., Billerica, Massachusetts, USA.
4. Department of Chemistry, Boston College, Chestnut Hill, Massachusetts, USA.
5. Environmental and Climate Sciences Department, Brookhaven National Laboratory, Upton, New York, USA.