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| Titel |
Hygroscopic properties of NaCl and NaNO3 mixture particles as reacted inorganic sea-salt aerosol surrogates |
| VerfasserIn |
D. Gupta, H. Kim, G. Park, X. Li, H.-J. Eom, C.-U. Ro |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 15, no. 6 ; Nr. 15, no. 6 (2015-03-26), S.3379-3393 |
| Datensatznummer |
250119578
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| Publikation (Nr.) |
 copernicus.org/acp-15-3379-2015.pdf |
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| Zusammenfassung |
| NaCl in fresh sea-salt aerosol (SSA) particles can partially or fully react
with atmospheric NOx/HNO3, so internally mixed NaCl and NaNO3
aerosol particles can co-exist over a wide range of mixing ratios.
Laboratory-generated, micrometer-sized NaCl and NaNO3 mixture particles
at 10 mixing ratios (mole fractions of NaCl (XNaCl) = 0.1 to 0.9)
were examined systematically to observe their hygroscopic behavior, derive
experimental phase diagrams for deliquescence and efflorescence, and
understand the efflorescence mechanism. During the humidifying process,
aerosol particles with the eutonic composition (XNaCl = 0.38) showed
only one phase transition at their mutual deliquescence relative humidity
(MDRH) of 67.9 (±0.5)% On the other hand, particles with other
mixing ratios showed two distinct deliquescence transitions; i.e., the
eutonic component dissolved at MDRH, and the remainder in the solid phase
dissolved completely at their DRHs depending on the mixing ratios, resulting
in a phase diagram composed of four different phases, as predicted
thermodynamically. During the dehydration process, NaCl-rich particles
(XNaCl > 0.38) showed a two stage efflorescence transition:
the first stage was purely driven by the homogeneous nucleation of NaCl and
the second stage at the mutual efflorescence RH (MERH) of the eutonic
components, with values in the range of 30.0–35.5%. Interestingly,
aerosol particles with the eutonic composition (XNaCl = 0.38) also
showed two-stage efflorescence, with NaCl crystallizing first followed by
heterogeneous nucleation of the remaining NaNO3 on the NaCl seeds.
NaNO3-rich particles (XNaCl ≤ 0.3) underwent single-stage
efflorescence transitions at ERHs progressively lower than the MERH because
of the homogeneous nucleation of NaCl and the almost simultaneous
heterogeneous nucleation of NaNO3 on the NaCl seeds. SEM/EDX elemental
mapping indicated that the effloresced NaCl–NaNO3 particles at all
mixing ratios were composed of a homogeneously crystallized NaCl moiety in
the center, surrounded either by the eutonic component (for XNaCl
> 0.38) or NaNO3 (for XNaCl ≤ 0.38). During the
humidifying or dehydration process, the amount of eutonic composed part
drives particle/droplet growth or shrinkage at the MDRH or MERH (second
ERH), respectively, and the amount of pure salts (NaCl or NaNO3 in
NaCl- or NaNO3-rich particles, respectively) drives the second DRHs or
first ERHs, respectively. Therefore, their behavior can be a precursor to
the optical properties and direct radiative forcing for these
atmospherically relevant mixture particles representing the coarse, reacted
inorganic SSAs. In addition, the NaCl–NaNO3 mixture aerosol particles
can maintain an aqueous phase over a wider RH range than pure NaCl particles
as SSA surrogate, making their heterogeneous chemistry more probable. |
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