Interaction of Particle Phase, Water Uptake and Viscosity Changes Based on Microspectroscopic Observations
Authors
Alexander Laskin — Purdue University
Mary Gilles — Lawrence Berkeley National Laboratory
Sergey Nizkorodov — University of California, Irvine
Bingbing Wang — Pacific Northwest National Laboratory
Category
Secondary Organic Aerosol
Description
Example of variation in the mass and size based growth factors as a function of relative humidity.
To explore phase of atmospheric particles collected in field and laboratory studies we utilized a variety of microscopic and spectroscopic techniques. The optical density is measured using scanning transmission x-ray microscopy/near edge x-ray absorption structure spectroscopy (STXM/NEXAFS) at the carbon edge and plotted versus particle area equivalent diameter. High viscosity/surface tension particles will flatten less upon impaction than less viscous particles, resulting in larger optical densities and a steeper slope. The results from five field campaigns show that the field collected particles deformed less (are more viscous) upon impaction than the laboratory generated SOA.
During the second intensive portion of the DOE GoAmazon campaign we collected samples at the T3 site as well as at the ZF2 site for subsequent single particle and other analyses. Single particle micro-spectroscopy techniques (STXM/NEXAFS & CCSEM/EDX) are used to measure the composition and mixing state of aerosol particles collected at the T3 site during reports of particle “bounce” and “no bounce”. For no-bounce samples (Sept 12th and 19th) 280 particles were analyzed. Samples where “bounce” behavior was reported included Sept. 13 th, 14th, and 20th and a total of 340 particles were analyzed. Although we anticipate that only a small fraction of the total particles “bounce”, the bounce samples contain a slightly higher presence of particles that fall into the organic carbon + elemental carbon mixing state than the no bounce samples. Many of these organic carbon + elemental carbon particles contain substantial sp2 hybridization (C=C bonds), however, there are no obvious soot inclusions.
Work in progress to be presented includes in situ STXM/NEXAFS water vapor uptake experiments on field collected samples (Southern Great Plains ARM Site) to examine the mass based water vapor uptake as well as preliminary data using a quartz crystal microbalance to characterize viscosity, phase changes, and viscosity changes during water vapor uptake.
