AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
APM Measured Shape Factor Change of α-pinene SOM and Its Dependence on Relative Humidity
YUE ZHANG, Marianna Santos Sanchez, Claire Douet, Yan Wang, Adam Bateman, Zhaoheng Gong, Mikinori Kuwata, Lindsay Renbaum-Wolff, Pengfei Liu, Bruno Bianchi Sato, Allan Bertram, Franz Geiger, Scot Martin, Harvard University
Abstract Number: 449 Working Group: Aerosol Chemistry
Abstract A flow tube reactor was used to generate α-pinene secondary organic material. The secondary organic material particles were brought to a 9 L flask to enhance coagulation under different relativity humidity (RH) levels. A DMA-APM system was used to measure particle mobility diameter and particle mass, in order to determine particle shape factors. In this study, the particle shape factor was dependent on the particle number concentration, particle size and RH. An optimal particle number concentration was found, which enhanced coagulation of particles with similar diameters and created non-spherical particles under dry (<5% RH) conditions. These non-spherical particles transformed back to spherical particles between 20%-35% RH. The particle shape transition between low and high RH suggests a possible viscosity change rather than a chemical composition change, based on both the APM shape factor and AMS measurement results. This implies that particle viscosity should be within the solid region under 20% RH and within semi-solid to liquid region for RH above 35%. This method provides a new way to estimate particle viscosity through direct aerosol measurement and is applicable under low RH conditions.