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Efflorescence of Ammonium Sulfate and Coated Ammonium Sulfate Particles: Evidence for Surface Nucleation

Ciobanu, V. Gabriela and Marcolli, Claudia and Krieger, Ulrich K. and Zuend, Andreas and Peter, Thomas (2010) Efflorescence of Ammonium Sulfate and Coated Ammonium Sulfate Particles: Evidence for Surface Nucleation. Journal of Physical Chemistry A, 114 (35). pp. 9486-9495. ISSN 1089-5639. http://resolver.caltech.edu/CaltechAUTHORS:20100921-152029771

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Abstract

Using optical microscopy, we investigated the efflorescence of ammonium sulfate (AS) in aqueous AS and in aqueous 1:1 and 8:1 (by dry weight) poly(ethylene glycol)-400 (PEG-400)/AS particles deposited on a hydrophobically coated slide. Aqueous PEG-400/AS particles exposed to decreasing relative humidity (RH) exhibit a liquid−liquid phase separation below 90% RH with the PEG-400-rich phase surrounding the aqueous AS inner phase. Pure aqueous AS particles effloresced in the RH range from 36.3% to 43.7%, in agreement with literature data (31−48% RH). In contrast, aqueous 1:1 (by dry weight) PEG-400/AS particles with diameters of the AS phase from 7.2 to 19.2 μm effloresced between 26.8% and 33.9% RH and aqueous 8:1 (by dry weight) PEG-400/AS particles with diameters of the AS phase from 1.8 to 7.3 μm between 24.3% and 29.3% RH. Such low efflorescence relative humidity (ERH) values have never been reached before for AS particles of this size range. We show that these unprecedented low ERHs of AS in PEG-400/AS particles could not possibly be explained by the presence of low amounts of PEG-400 in the aqueous AS phase, by a potential inhibition of water evaporation via anomalously slow diffusion through the PEG coating, or by different time scales between various experimental techniques. High-speed photography of the efflorescence process allowed the development of the AS crystallization fronts within the particles to be monitored with millisecond time resolution. The nucleation sites were inferred from the initial crystal growth sites. Analysis of the probability distribution of initial sites of 31 and 19 efflorescence events for pure AS and 1:1 (by dry weight) PEG-400/AS particles, respectively, showed that the particle volume can be excluded as the preferred nucleation site in the case of pure AS particles. For aqueous 1:1 (by dry weight) PEG-400/AS particles preferential AS nucleation in the PEG phase and at the PEG/AS/substrate contact line can be excluded. On the basis of this probability analysis of efflorescence events together with the AS ERH values of pure aqueous AS and aqueous PEG-400/AS particles aforementioned, we suggest that in pure aqueous AS particles nucleation starts at the surface of the particles and attribute the lower ERH values observed for aqueous PEG-400/AS particles to the suppression of the surface-induced nucleation process. Our results suggest that surface-induced nucleation is likely to also occur during the efflorescence of atmospheric AS aerosol particles, possibly constituting the dominating nucleation pathway.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1021/jp103541wDOIArticle
http://pubs.acs.org/doi/abs/10.1021/jp103541wPublisherArticle
ORCID:
AuthorORCID
Zuend, Andreas0000-0003-3101-8521
Additional Information:© 2010 American Chemical Society. Received: April 20, 2010; Revised Manuscript Received: July 12, 2010. This work was supported by the Swiss National Science Foundation under Contract No. 200020- 103651/1 supporting the Ph.D. work of V.G.C. and under Contract No. PA00P2_126227 for an Advanced Researchers Fellowship of A.Z. This work was also supported by the Competence Center Environment and Sustainability of the ETH Domain (CCES) with Project IMBALANCE supporting A.Z. before receiving his fellowship. We thank Thomas Koop for useful comments.
Funders:
Funding AgencyGrant Number
Swiss National Science Foundation200020- 103651/1
Swiss National Science FoundationPA00P2_126227
Competence Center Environment and Sustainability of the ETH Domain (CCES)Project IMBALANCE
Record Number:CaltechAUTHORS:20100921-152029771
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20100921-152029771
Official Citation:Efflorescence of Ammonium Sulfate and Coated Ammonium Sulfate Particles: Evidence for Surface Nucleation V. Gabriela Ciobanu, Claudia Marcolli, Ulrich K. Krieger, Andreas Zuend, Thomas Peter The Journal of Physical Chemistry A 2010 114 (35), 9486-9495
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:20079
Collection:CaltechAUTHORS
Deposited By: Jason Perez
Deposited On:22 Sep 2010 19:33
Last Modified:06 Apr 2017 20:21

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