Changing shapes and implied viscosities of suspended submicron particles
Y. Zhang1,M. S. Sanchez1,2,C. Douet1,3,Y. Wang1,4,A. P. Bateman1,Z. Gong1,M. Kuwata1,5,L. Renbaum-Wolff6,B. B. Sato1,7,P. F. Liu1,A. K. Bertram6,F. M. Geiger8,and S. T. Martin1,9Y. Zhang et al. Y. Zhang1,M. S. Sanchez1,2,C. Douet1,3,Y. Wang1,4,A. P. Bateman1,Z. Gong1,M. Kuwata1,5,L. Renbaum-Wolff6,B. B. Sato1,7,P. F. Liu1,A. K. Bertram6,F. M. Geiger8,and S. T. Martin1,9
1School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA
2Department of Chemical Engineering, University of São Paulo, São Paulo, Brazil
3Department of Energy and Environment, National Institute of Applied Science of Lyon, Villeurbanne, France
4School of Public Health, Harvard University, Boston, Massachusetts, USA
5Earth Observatory of Singapore, School of Physical and Mathematical Sciences, College of Sciences, Nanyang Technological University, Singapore, Singapore
6Department of Chemistry, University of British Columbia, Vancouver, British Columbia, Canada
7Department of Chemical Engineering, Federal University of Sao Carlos, Sao Carlos, São Paulo, Brazil
8Department of Chemistry, Northwestern University, Evanston, Illinois, USA
9Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA
1School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA
2Department of Chemical Engineering, University of São Paulo, São Paulo, Brazil
3Department of Energy and Environment, National Institute of Applied Science of Lyon, Villeurbanne, France
4School of Public Health, Harvard University, Boston, Massachusetts, USA
5Earth Observatory of Singapore, School of Physical and Mathematical Sciences, College of Sciences, Nanyang Technological University, Singapore, Singapore
6Department of Chemistry, University of British Columbia, Vancouver, British Columbia, Canada
7Department of Chemical Engineering, Federal University of Sao Carlos, Sao Carlos, São Paulo, Brazil
8Department of Chemistry, Northwestern University, Evanston, Illinois, USA
9Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA
Correspondence: S. T. Martin (scot_martin@harvard.edu) and F. M. Geiger (geigerf@chem.northwestern.edu)
Received: 26 Jan 2015 – Discussion started: 09 Mar 2015 – Revised: 17 Jun 2015 – Accepted: 29 Jun 2015 – Published: 16 Jul 2015
Abstract. The change in shape of atmospherically relevant organic particles is used to estimate the viscosity of the particle material without the need for removal from aerosol suspension. The dynamic shape factors χ of particles produced by α-pinene ozonolysis in a flow tube reactor, under conditions of particle coagulation, were measured while altering the relative humidity (RH) downstream of the flow tube. As relative humidity was increased, the results showed that χ could change from 1.27 to 1.02, corresponding to a transition from aspherical to nearly spherical shapes. The shape change could occur at elevated RH because the organic material had decreased viscosity and was therefore able to flow to form spherical shapes, as favored by the minimization of surface area. Numerical modeling was used to estimate the particle viscosity associated with this flow. Based on particle diameter and RH exposure time, the viscosity dropped from 10(8.7±2.0) to 10(7.0±2.0) Pa s (two sigma) for an increase in RH from < 5 to 58 % at 293 K. These results imply that the equilibration of the chemical composition of the particle phase with the gas phase can shift from hours at mid-range RH to days at low RH.
The present work estimates the viscosity of submicron organic particles while they are still suspended as an aerosol without further post-processing techniques that can possibly alter the properties of semi-volatile materials. Results imply that atmospheric particles, at least those similar to the ones of this study and for low- to middle-RH regimes, can reach equilibrium or react rather slowly with the surrounding gas phase on time scales even longer than the residence time in the atmosphere.
The present work estimates the viscosity of submicron organic particles while they are still...
