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| Titel |
Hygroscopicity of secondary organic aerosols formed by oxidation of cycloalkenes, monoterpenes, sesquiterpenes, and related compounds |
| VerfasserIn |
V. Varutbangkul, F. J. Brechtel, R. Bahreini, N. L. Ng, M. D. Keywood, J. H. Kroll, R. C. Flagan, J. H. Seinfeld, A. Lee, A. H. Goldstein |
| 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 ; 6, no. 9 ; Nr. 6, no. 9 (2006-06-29), S.2367-2388 |
| Datensatznummer |
250003965
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| Publikation (Nr.) |
 copernicus.org/acp-6-2367-2006.pdf |
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| Zusammenfassung |
| A series of experiments has been conducted in the Caltech indoor smog
chamber facility to investigate the water uptake properties of aerosol
formed by oxidation of various organic precursors. Secondary organic aerosol
(SOA) from simple and substituted cycloalkenes (C5-C8) is produced
in dark ozonolysis experiments in a dry chamber (RH~5%). Biogenic
SOA from monoterpenes, sesquiterpenes, and oxygenated terpenes is formed by
photooxidation in a humid chamber (~50% RH). Using the
hygroscopicity tandem differential mobility analyzer (HTDMA), we measure the
diameter-based hygroscopic growth factor (GF) of the SOA as a function of time
and relative humidity. All SOA studied is found to be slightly hygroscopic,
with smaller water uptake than that of typical inorganic aerosol substances.
The aerosol water uptake increases with time early in the experiments for
the cycloalkene SOA, but decreases with time for the sesquiterpene SOA. This
behavior could indicate competing effects between the formation of more
highly oxidized polar compounds (more hygroscopic), and formation of
longer-chained oligomers (less hygroscopic). All SOA also exhibit a smooth
water uptake with RH with no deliquescence or efflorescence. The water
uptake curves are found to be fitted well with an empirical three-parameter
functional form. The measured pure organic GF values at 85% RH are between
1.09–1.16 for SOA from ozonolysis of cycloalkenes, 1.01–1.04 for
sesquiterpene photooxidation SOA, and 1.06–1.10 for the monoterpene and
oxygenated terpene SOA. The GF of pure SOA (GForg) in experiments in which
inorganic seed aerosol is used is determined by assuming volume-weighted
water uptake (Zdanovskii-Stokes-Robinson or "ZSR" approach) and using the
size-resolved organic mass fraction measured by the Aerodyne Aerosol Mass
Spectrometer. Knowing the water content associated with the inorganic
fraction yields GForg values. However, for each precursor, the
GForg values computed from different HTDMA-classified diameters agree
with each other to varying degrees. Comparing growth factors from different precursors, we find that
GForg is inversely proportional to the precursor molecular weight and SOA
yield, which is likely a result of the fact that higher-molecular weight
precursors tend to produce larger and less hygroscopic oxidation products. |
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