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| Titel |
Aqueous-phase photochemical oxidation and direct photolysis of vanillin – a model compound of methoxy phenols from biomass burning |
| VerfasserIn |
Y. J. Li, D. D. Huang, H. Y. Cheung, A. K. Y. Lee, C. K. Chan |
| 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 ; 14, no. 6 ; Nr. 14, no. 6 (2014-03-19), S.2871-2885 |
| Datensatznummer |
250118516
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| Publikation (Nr.) |
 copernicus.org/acp-14-2871-2014.pdf |
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| Zusammenfassung |
| We present here experimental results on aqueous-phase (A) photochemical
oxidation (with UV and OH radicals generated from H2O2 photolysis)
and (B) direct photolysis (with only UV irradiation) of a methoxy phenol,
vanillin (VL), as a model compound from biomass burning. Both on-line
aerosol mass spectrometric (AMS) characterization and off-line chemical
analyses were performed. AMS analyses of dried atomized droplets of the bulk
reacting mixtures showed that VL almost entirely evaporates during the
drying process. Large amounts of organic mass remained in the particle phase
after reactions under both conditions. Under condition (A), AMS measured
organic mass first increased rapidly and then decreased, attributable to the
formation of non-volatile products and subsequent formation of smaller and
volatile products, respectively. The oxygen-to-carbon (O : C) ratio of the
products reached 1.5 after about 80 min, but dropped substantially
thereafter. In contrast, organic mass increased slowly under condition (B).
The O : C ratio reached 1.0 after 180 min. In off-line analyses, small
oxygenates were detected under condition (A), while hydroxylated products
and dimers of VL were detected under condition (B). Particle hygroscopic
growth factor (GF) and cloud condensation nuclei (CCN) activity of the
reacting mixtures were found to depend on both organic volume fraction and
the degree of oxygenation of organics. Results show that (1) aqueous-phase
processes can lead to the retention of a large portion of the organic mass
in the particle phase; (2) once retained, this portion of organic mass
significantly changes the hygroscopicity and CCN activity of the aerosol
particles; (3) intensive photochemical oxidation gave rise to an O : C ratio
as high as 1.5 but the ratio decreased as further oxidation led to smaller
and more volatile products; and (4) polymerization occurred with direct
photolysis, resulting in high-molecular-weight products of a yellowish
color. This study demonstrates that aqueous-phase reactions of a
methoxy phenol can lead to substantial amount of secondary organic aerosol
(SOA) formation. Given the vast amount of biomass burning input globally,
model representation of either the SOA budget or their subsequent effects
would not be adequate if the contribution of SOA formation from
aqueous-phase reactions of methoxy phenols is not considered. |
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