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| Titel |
Chemical aging of single and multicomponent biomass burning aerosol surrogate particles by OH: implications for cloud condensation nucleus activity |
| VerfasserIn |
J. H. Slade, R. Thalman, J. Wang, D. A. Knopf |
| 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. 17 ; Nr. 15, no. 17 (2015-09-14), S.10183-10201 |
| Datensatznummer |
250120030
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| Publikation (Nr.) |
 copernicus.org/acp-15-10183-2015.pdf |
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| Zusammenfassung |
| Multiphase OH and O3 oxidation reactions with atmospheric
organic aerosol (OA) can influence particle physicochemical
properties including composition, morphology, and lifetime. Chemical
aging of initially insoluble or low-soluble single-component OA by
OH and O3 can increase their water solubility and
hygroscopicity, making them more active as cloud condensation nuclei
(CCN) and susceptible to wet deposition. However, an outstanding
problem is whether the effects of chemical aging on their CCN
activity are preserved when mixed with other organic or inorganic
compounds exhibiting greater water solubility. In this work, the CCN
activity of laboratory-generated biomass burning aerosol (BBA)
surrogate particles exposed to OH and O3 is evaluated by
determining the hygroscopicity parameter, κ, as a function of
particle type, mixing state, and OH and O3 exposure applying
a CCN counter (CCNc) coupled to an aerosol flow reactor
(AFR). Levoglucosan (LEV), 4-methyl-5-nitrocatechol (MNC), and
potassium sulfate (KS) serve as representative BBA compounds that
exhibit different hygroscopicity, water solubility, chemical
functionalities, and reactivity with OH radicals, and thus exemplify
the complexity of mixed inorganic/organic aerosol in the
atmosphere. The CCN activities of all of the particles were
unaffected by O3 exposure. Following exposure to OH,
κ of MNC was enhanced by an order of magnitude, from 0.009 to
~ 0.1, indicating that chemically aged MNC particles are better
CCN and more prone to wet deposition than pure MNC particles. No
significant enhancement in κ was observed for pure LEV
particles following OH exposure. κ of the internally mixed
particles was not affected by OH oxidation. Furthermore, the CCN
activity of OH-exposed MNC-coated KS particles is similar to the OH
unexposed atomized 1 : 1 by mass MNC : KS binary-component
particles. Our results strongly suggest that when OA is dominated by
water-soluble organic carbon (WSOC) or inorganic ions, chemical
aging has no significant impact on OA hygroscopicity. The organic
compounds exhibiting low solubility behave as if they are infinitely
soluble when mixed with a sufficient number of water-soluble
compounds. At and beyond this point, the particles' CCN activity is
governed entirely by the water-soluble fraction and is not influenced
by the oxidized organic fraction. Our results have important
implications for heterogeneous oxidation and its impact on cloud
formation given that atmospheric aerosol is a complex mixture of
organic and inorganic compounds exhibiting a wide range of
solubilities. |
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