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| Titel |
Secondary organic aerosol formation and primary organic aerosol oxidation from biomass-burning smoke in a flow reactor during FLAME-3 |
| VerfasserIn |
A. M. Ortega, D. A. Day, M. J. Cubison, W. H. Brune, D. Bon, J. A. de Gouw, J. L. Jimenez |
| 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. 22 ; Nr. 13, no. 22 (2013-11-28), S.11551-11571 |
| Datensatznummer |
250085842
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| Publikation (Nr.) |
 copernicus.org/acp-13-11551-2013.pdf |
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| Zusammenfassung |
| We report the physical and chemical effects of
photochemically aging dilute biomass-burning smoke. A "potential aerosol
mass" (PAM) flow reactor was used with analysis by a high-resolution aerosol
mass spectrometer and a proton-transfer-reaction ion-trap mass spectrometer
during the FLAME-3 campaign. Hydroxyl (OH) radical concentrations in the
reactor reached up to ~1000 times average tropospheric
levels, producing effective OH exposures equivalent to up to 5 days of aging in
the atmosphere, and allowing for us to extend the investigation of smoke aging
beyond the oxidation levels achieved in traditional smog chambers. Volatile organic
compound (VOC) observations show aromatics and terpenes decrease with aging, while formic
acid and other unidentified oxidation products increase. Unidentified
gas-phase oxidation products, previously observed in atmospheric and
laboratory measurements, were observed here, including evidence of multiple
generations of photochemistry. Substantial new organic aerosol (OA) mass
("net SOA"; secondary OA) was observed from aging biomass-burning smoke,
resulting in total OA average of 1.42 ± 0.36 times the initial primary
OA (POA) after oxidation. This study confirms that the net-SOA-to-POA ratio
of biomass-burning smoke is far lower on average than that observed for
urban emissions. Although most fuels were very reproducible, significant
differences were observed among the biomasses, with some fuels resulting in
a doubling of the OA mass, while for others a very small increase or even a
decrease was observed. Net SOA formation in the photochemical reactor
increased with OH exposure (OHexp), typically peaking around three days
of equivalent atmospheric photochemical age (OHexp~3.9 × 1011 molecules cm−3 s), then leveling off at higher
exposures. The amount of additional OA mass added from aging is positively
correlated with initial POA concentration, but not with the total VOC
concentration or the concentration of known SOA precursors. The mass of SOA formed often exceeded the mass of
the known VOC precursors, indicating the likely importance of primary
semivolatile/intermediate volatility species, and possibly of
unidentified VOCs as SOA precursors in biomass burning smoke. Chemical transformations continued even after mass concentration stabilized. Changes in the biomass-burning tracer f60 ranged from
substantially decreasing to remaining constant with increased aging. With
increased OHexp, oxidation was always detected (as indicated by
f44 and O/C). POA O/C ranged from 0.15 to 0.5, while aged OA O/C reached up to
0.87. The rate of oxidation and maximum O/C achieved differs for each
biomass, and appears to increase with the initial O/C of the POA. |
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