TY  - JOUR
AB  - Sea-salt aerosol (SSA) particles are ubiquitous in the 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 climate is
related to their water uptake and ice nucleation characteristics. In this
study, optical microscopy coupled with Raman spectroscopy was used to detect
the formation of a crystalline NaCl hydrate that could form under atmospheric
conditions. NaCl<sub>(s)</sub> particles (~1 to 10 μm in
diameter) deliquesced at 75.7 ± 2.5% RH which agrees well with
values previously established in the literature. NaCl<sub>(aq)</sub> particles
effloresced to a mixture of hydrated and non-hydrated particles at
temperatures between 236 and 252 K. The aqueous particles effloresced into
the non-hydrated form at temperatures warmer than 252 K. At temperatures
colder than 236 K all particles effloresced into the hydrated form. The
deliquescence relative humidities (DRH) of hydrated NaCl<sub>(s)</sub>
particles ranged from 76.6 to 93.2% RH. Based on the measured DRH and
efflorescence relative humidities (ERH), we estimate crystalline NaCl
particles could be in the hydrated form 40–80% of the time in the
troposphere. Additionally, the ice nucleating abilities of NaCl<sub>(s)</sub>
and hydrated NaCl<sub>(s)</sub> were determined at temperatures ranging from
221 to 238 K. Here, depositional ice nucleation is defined as the onset of
ice nucleation and represents the conditions at which the first particle on
the substrate nucleated ice. Thus the values reported here represent the
lower limit of depositional ice nucleation. NaCl<sub>(s)</sub> particles
depositionally nucleated ice at an average <i>S</i><sub>ice</sub> value of
1.11 ± 0.07. Hydrated NaCl<sub>(s)</sub> particles depositionally
nucleated ice at an average <i>S</i><sub>ice</sub> value of 1.02 ± 0.04. When a
mixture of hydrated and anhydrous NaCl<sub>(s)</sub> particles was present in
the same sample, ice preferentially nucleated on the hydrated particles
100% of the time. While both types of particles are efficient ice
nuclei, hydrated NaCl<sub>(s)</sub> particles are better ice nuclei than
NaCl<sub>(s)</sub> particles.
DA  - 2012
DO  - 10.5194/acp-12-1121-2012
LA  - eng
IS  - 2
M2  - 1121
PY  - 2012
SN  - 1680-7324
SP  - 1121-1134
T2  - Atmospheric Chemistry and Physics
TI  - Depositional ice nucleation onto crystalline hydrated NaCl particles: a new mechanism for ice formation in the troposphere
UR  - https://nbn-resolving.org/urn:nbn:de:0070-pub-24636676
Y2  - 2024-11-21T20:33:56
ER  -