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Viscosity of alpha-pinene secondary organic material and implications for particle growth and reactivity

TitleViscosity of alpha-pinene secondary organic material and implications for particle growth and reactivity
Publication TypeJournal Article
Year of Publication2013
AuthorsRenbaum-Wolff, L, Grayson, JW, Bateman, AP, Kuwata, M, Sellier, M, Murray, BJ, Shilling, JE, Martin, ST, Bertram, AK
JournalPROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume110
Pagination8014-8019
Date PublishedMAY 14
ISSN0027-8424
Abstract

Particles composed of secondary organic material (SOM) are abundant in the lower troposphere. The viscosity of these particles is a fundamental property that is presently poorly quantified yet required for accurate modeling of their formation, growth, evaporation, and environmental impacts. Using two unique techniques, namely a ``bead-mobility{''} technique and a ``poke-flow{''} technique, in conjunction with simulations of fluid flow, the viscosity of the water-soluble component of SOM produced by alpha-pinene ozonolysis is quantified for 20- to 50-mu m particles at 293-295 K. The viscosity is comparable to that of honey at 90% relative humidity (RH), similar to that of peanut butter at 70% RH, and at least as viscous as bitumen at <= 30% RH, implying that the studied SOM ranges from liquid to semisolid or solid across the range of atmospheric RH. These data combined with simple calculations or previous modeling studies are used to show the following: (i) the growth of SOM by the exchange of organic molecules between gas and particle may be confined to the surface region of the particles for RH <= 30%; (ii) at <= 30% RH, the particle-mass concentrations of semivolatile and low-volatility organic compounds may be overpredicted by an order of magnitude if instantaneous equilibrium partitioning is assumed in the bulk of SOM particles; and (iii) the diffusivity of semireactive atmospheric oxidants such as ozone may decrease by two to five orders of magnitude for a drop in RH from 90% to 30%. These findings have possible consequences for predictions of air quality, visibility, and climate.

DOI10.1073/pnas.1219548110