1. Aerodyne Research, Inc. Billerica, Massachusetts 01821, Center of Excellence for Aerospace Particulate Emissions Reduction Center Research, University of Missouri – Rolla, Rolla, Missouri 65409, VOLPE National Transportation Systems Center, Cambridge, Massachusetts 02142, Department of Physics, University of Missouri – Rolla, Rolla, Missouri 65409, and Department of Chemistry, University of Missouri – Rolla, Rolla, Missouri 65409