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| Titel |
Chemical composition, microstructure, and hygroscopic properties of aerosol particles at the Zotino Tall Tower Observatory (ZOTTO), Siberia, during a summer campaign |
| VerfasserIn |
E. F. Mikhailov, G. N. Mironov, C. Pöhlker, X. Chi, M. L. Krüger, M. Shiraiwa, J.-D. Förster, U. Pöschl, S. S. Vlasenko, T. I. Ryshkevich, M. Weigand, A. L. D. Kilcoyne, M. O. Andreae |
| 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. 15 ; Nr. 15, no. 15 (2015-08-13), S.8847-8869 |
| Datensatznummer |
250119959
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| Publikation (Nr.) |
 copernicus.org/acp-15-8847-2015.pdf |
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| Zusammenfassung |
In this study we describe the hygroscopic properties of accumulation- and
coarse-mode aerosol particles sampled at the Zotino Tall Tower Observatory
(ZOTTO) in central Siberia (61° N, 89° E) from 16 to 21
June 2013. The hygroscopic growth measurements were supplemented with
chemical analyses of the samples, including inorganic ions and
organic/elemental carbon. In addition, the microstructure and chemical
compositions of aerosol particles were analyzed by x-ray micro-spectroscopy
(STXM-NEXAFS) and transmission electron microscopy (TEM). A mass closure
analysis indicates that organic carbon accounted for 61 and 38 % of
particulate matter (PM) in the accumulation mode and coarse mode,
respectively. The water-soluble fraction of organic matter was estimated to
be 52 and 8 % of PM in these modes. Sulfate, predominantly in the form of
ammoniated sulfate, was the dominant inorganic component in both size modes:
~ 34 % in the accumulation mode vs. ~ 47 % in the coarse
mode.
The hygroscopic growth measurements were conducted with a filter-based
differential hygroscopicity analyzer (FDHA) over the range of 5–99.4 %
RH in the hydration and dehydration operation modes. The FDHA study indicates
that both accumulation and coarse modes exhibit pronounced water uptake
approximately at the same relative humidity (RH), starting at
~ 70 %, while efflorescence occurred at different humidities, i.e.,
at ~ 35 % RH for submicron particles vs. ~ 50 % RH for
supermicron particles. This ~ 15 % RH difference was attributed to
higher content of organic material in the submicron particles, which
suppresses water release in the dehydration experiments.
The kappa mass interaction model (KIM) was applied to characterize and
parameterize non-ideal solution behavior and concentration-dependent water
uptake by atmospheric aerosol samples in the 5–99.4 % RH range. Based on
KIM, the volume-based hygroscopicity parameter, κv, was
calculated. The κv,ws value related to the water-soluble
(ws) fraction was estimated to be ~ 0.15 for the accumulation mode
and ~ 0.36 for the coarse mode, respectively. The obtained
κv,ws for the accumulation mode is in good agreement with
earlier data reported for remote sites in the Amazon rain forest (κv ≈ 0.15) and a Colorado mountain forest
(κv ≈ 0.16 ).
We used the Zdanovskii–Stokes–Robinson (ZSR) mixing rule to predict the
chemical composition dependent hygroscopicity, κv,p. The
obtained κv,p values overestimate the experimental
FDHA-KIM-derived κv,ws by factors of 1.8 and 1.5 for the
accumulation and coarse modes, respectively. This divergence can be explained
by incomplete dissolution of the hygroscopic inorganic compounds resulting
from kinetic limitations due to a sparingly soluble organic coating. The TEM
and STXM-NEXAFS results indicate that aged submicron (> 300 nm)
and supermicron aerosol particles possess core–shell structures with an
inorganic core, and are enriched in organic carbon at the mixed particle
surface. The direct FDHA kinetic studies provide a bulk diffusion coefficient
of water of ~ 10−12 cm2 s−1 indicating a semi-solid
state of the organic-rich phase leading to kinetic limitations of water
uptake and release during hydration and dehydration cycles.
Overall, the present ZOTTO data set, obtained in the growing season, has
revealed a strong influence of organic carbon on the hygroscopic properties
of the ambient aerosols. The sparingly soluble organic coating controls
hygroscopic growth, phase transitions, and microstructural rearrangement
processes. The observed kinetic limitations can strongly influence the
outcome of experiments performed on multi-second timescales, such as the
commonly applied HTDMA (Hygroscopicity Tandem Differential Mobility Analyzer)
and CCNC (Cloud Condensation Nuclei Counter) measurements. |
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