Hygroscopicity, CCN Activity, Phase State and Morphology of Complex Laboratory and Ambient Aerosols with Comparison to SOA Studies

Wednesday, November 10, 2010: 1:06 PM
Grand Ballroom J (Marriott Downtown)
William L. Madry, David Marchese, Laura Cook and Timothy Raymond, Chemical Engineering, Bucknell University, Lewisburg, PA

Many recent studies of cloud condensation nuclei (CCN) activity have been performed at field campaigns and in smog chamber studies around the world. While many studies, such as those looking at complex mixed SOA aerosols, have shown particles to have similar CCN activities, other studies have shown different results. Experiments performed in the Bucknell University Aerosol-Water Interaction Laboratory on complex mixed organic aerosols have shown that CCN activity converges to a narrow range with increasing organic components. This range is often similar to reported smog chamber and ambient CCN studies. Additionally, the Bucknell results have combined individual particle imaging studies which have shown that mixed organics combine to produce liquid-phase aerosols that maintain their liquid state and water content levels at all relative humidities.

CCN activity has been measured along with morphological images of various aerosols and particles in order to investigate appropriate parameters to use for ambient particle modelling and to determine the effects of particle morphology. A Droplet Measurement Technologies (DMT-100) CCNC was used for activity data. This instrument has been used solely for ground-based measurements and is calibrated with ammonium sulphate and sodium chloride aerosols. Measurements were performed at supersaturations between 0.2% and 1.0%.

Particle morphology was determined using atomic force microscopy (AFM) of aerosol particles collected on various substrates. A TSI Nanometer Aerosol Sampler (Model 3089) was used to collect particles via electrostatic attraction in order to maximize the collection of CCN size-relevant particles while minimizing sample interactions such as deformation by impaction.

Expanding on previous studies, we have created even more complex aerosols using tens of different organic compounds typically found in ambient aerosols, several common inorganic salts, and mineral dust components. These components have been mixed in various ways to produce simulated ambient particles and then CCN activity data has been collected simultaneous with aerosol morphology and phase imaging. Additional data has been collected using hygroscopic tandem differential mobility analysis (H-TDMA) and the results are compared to CCN data and related theories.

Finally, the same instrumentation used for the laboratory studies has been deployed to collect ambient aerosol particles from specific sources. These include aerosols from a meat-cooking operation, a busy roadway, and a forest ecosystem. The CCN activity has been measured along with an analysis of a particle phase state and morphology. The results are compared to surrogate laboratory particles, the complex mixtures, and available field campaign and smog chamber studies. General conclusions regarding aerosol phase, morphology and composition will be presented. This work was supported by the National Science Foundation under grant #0746125.


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