CUP Faculty Research


Deliquescence, Efflorescence and Ice Nucleating Ability of NaCl/Hydrated NaCl Particles Under Upper Tropospheric Conditions

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Sea-salt aerosol particles (SSA) are ubiquitous in marine boundary layer and over coastal areas. Therefore SSA have ability to directly and indirectly affect the Earth’s radiation balance. The influence SSA have on the Earth’s radiation balance is related to their water uptake and ice nucleation characteristics. In this study, optical microscopy coupled with Raman spectroscopy was used to determine the deliquescence and efflorescence phase transitions of NaCl particles (a proxy for SSA particles) at temperatures ranging from 233 to 258 K. It was found that NaCl (s) particles deliquesced at 75.7±2.5 % RH and NaCl (aq) particles effloresced at 42.7 ±6.9 % RH. When the temperature of NaCl (aq) particles was held between 236 and 252 K, a mixture of hydrated and non-hydrated particles effloresced. Thus the water uptake characteristics of hydrated NaCl (s) particles were studied. The deliquescence relative humidities (DRH) of hydrated NaCl (s) particles ranged from 75.6 to 94.5 % RH. The DRH values for hydrated NaCl (s) do not agree with the theoretical DRH for the dihydrate form of NaCl (s) particles (the predicted phase using a bulk phase diagram). Additionally, the ice nucleating abilities of NaCl (s) and hydrated NaCl (s) were determined at temperatures ranging from 221 to 230 K. NaCl (s) particles depositionally nucleated ice at an average Sice value of 1.11±0.07. Hydrated NaCl (s) particles depositionally nucleated ice at an average Sice value of 1.01±0.03. When a mixture of hydrated and anhydrous NaCl (s) particles was present in the same sample, ice preferentially nucleated on the hydrated particles 100% of the time. Thus hydrated NaCl (s) particles are better ice nuclei than NaCl (s) particles.


Publication Information.

Wise, M. E., K. J. Baustian, T. Koop, M. Freedman, E.J. Jensen, and M. A. Tolbert, Deliquescence, efflorescence and ice nucleating ability of NaCl/hydrated NaCl particles under upper tropospheric conditions, 2010 American Geophysical Union Meeting, San Francisco, CA, December 2010. Poster A21F-0156.


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