1. Center
for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States
2. Department
of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States
3. Department
of Civil and Environmental Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States
4. Aerodyne Research,
Inc., Billerica, Massachusetts 01821, United States