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| Titel |
Evaluating the degree of oxygenation of organic aerosol during foggy and hazy days in Hong Kong using high-resolution time-of-flight aerosol mass spectrometry (HR-ToF-AMS) |
| VerfasserIn |
Y. J. Li, B. Y. L. Lee, J. Z. Yu, N. L. Ng, 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 ; 13, no. 17 ; Nr. 13, no. 17 (2013-09-03), S.8739-8753 |
| Datensatznummer |
250085668
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| Publikation (Nr.) |
 copernicus.org/acp-13-8739-2013.pdf |
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| Zusammenfassung |
| The chemical characteristics of organic aerosol (OA) are still poorly
constrained. Here we present observation results of the degree of
oxygenation of OA based on high-resolution time-of-flight aerosol mass
spectrometry (HR-ToF-AMS) measurements made at a coastal site in Hong Kong
from late April to the end of May in 2011. Two foggy periods and one hazy
period were chosen for detailed analysis to compare the changes in the
degree of oxygenation of OA due to different processes. Using HR-ToF-AMS
measured inorganic species as input, the Extended Aerosol Inorganic Model
(E-AIM) predicted a fine-particle liquid water content (LWCfp) up to 85 μg m−3 during the foggy days. Particle concentration as measured
by HR-ToF-AMS was up to 60 μg m−3 during the hazy days and up to
30 μg m−3 during the foggy days. The degree of oxygenation of OA,
as indicated by several parameters including the fraction of m/z 44 in organic
mass spectra (f44), the elemental ratio of oxygen to carbon (O : C), and
the carbon oxidation state (OSc), was
evaluated against the odd oxygen (Ox) concentration, LWCfp, ionic
strength (IS), and in situ pH (pHis). Observations suggest that the
high concentration of OA (on average 11 μg m−3) and the high
degree of oxygenation (f44 = 0.15, O : C = 0.51, and OSc = −0.31) during the hazy period were mainly
due to gas-phase oxidation. During the foggy periods with low photochemical
activities, the degree of oxygenation of OA was almost as high as that on
the hazy days, and significantly higher than that during non-foggy/non-hazy
days. However, the OA evolved quite differently in the two foggy periods.
The first foggy period in late April saw a larger LWCfp and a lower
Ox concentration and the OA were made up of ~ 20 %
semi-volatile oxygenated organic aerosol (SVOOA) as resolved by positive
matrix factorization (PMF). In the second foggy period in mid-May, higher
Ox concentration and lower LWCfp were observed, and the OA were
found to contain > 50 % low-volatility oxygenated organic
aerosols (LVOOA). An examination of the particle characteristics (pHis,
IS, and LWCfp) suggests that partitioning may have been the dominating
process through which oxygenated species were incorporated into the particle
phase during the first foggy period, while oxidation in the aqueous phase
dominated over gas-phase processes during the second foggy period. |
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