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The Effect of Surface Active Organic Molecules on the Water Uptake, Shape and Density of Hygroscopic Particles of Atmospheric Importance


EMSL Project ID
25636

Abstract

This proposal is a continuation of research under EMSL User Proposal #16741. Field measurements of aerosol compositions consistently reveal that organics make up a significant fraction of the aerosol mass. The presence of organics in particles that are composed of hygroscopic substances can significantly alter their hygroscopic properties. Since the particles' optical properties and ability to act as cloud condensation nuclei are strongly dependent on their hygroscopicity it is important to accurately take the effect of organics. Organics is a term that encompasses a wide range of compounds with a broad set of properties. Of the many types of organic particles that are found in particles surfactants represent an interesting and potentially important class. Because surfactants tend to migrate to the surface of hygroscopic particles a monolayer coating is sufficient to change the appearance of the particle to the atmosphere. It has even been suggested that such a coating could prevent the particles from absorbing or releasing any water in response to changes of the atmospheric relative humidity. Within the past year we have conducted a number of measurements jointly with Dr. Zelenyuk using her unparalleled single particle mass spectrometer, SPLAT, on surfactant coated particles and showed that when the surfactant is water soluble, the particles do respond to changes in RH and that the surfactant effect can be explained in the basis of the high resolution density data obtained with SPLAT. How applicable are these results to other surfactants and salts remains to be tested. Also it is important to keep in mind that the organic layer is susceptible to oxidation reactions with ozone and OH. Since these reactions are expected to change their hygroscopic properties it is essential for us to conduct measurements to quantify the properties of particles coated with surfactants as a function of time.

Project Details

Project type
Large-Scale EMSL Research
Start Date
2007-06-06
End Date
2009-09-30
Status
Closed

Team

Principal Investigator

Gayfree Ellison
Institution
University of Colorado at Boulder

Team Members

Timothy Vaden
Institution
Pacific Northwest National Laboratory

Juan Yang
Institution
Pacific Northwest National Laboratory

Luis Cuadra-Rodriguez
Institution
University of Colorado at Boulder

Alla Zelenyuk-Imre
Institution
Pacific Northwest National Laboratory

Related Publications

Alla Zelenyuk, Dan Imre, Luis A. Cuadra-Rodriguez, and Barney Ellison, “Measurements and interpretation of the effect of a soluble organic surfactant on the density, shape and water uptake of hygroscopic particles”, J. Aerosol Sci., 38, 903-923 (2007).