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| Titel |
Chemically-resolved aerosol volatility measurements from two megacity field studies |
| VerfasserIn |
J. A. Huffman, K. S. Docherty, A. C. Aiken, M. J. Cubison, I. M. Ulbrich, P. F. DeCarlo, D. Sueper, J. T. Jayne, D. R. Worsnop, P. J. Ziemann, 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 ; 9, no. 18 ; Nr. 9, no. 18 (2009-09-28), S.7161-7182 |
| Datensatznummer |
250007654
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| Publikation (Nr.) |
 copernicus.org/acp-9-7161-2009.pdf |
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| Zusammenfassung |
| The volatilities of different chemical species in ambient aerosols are
important but remain poorly characterized. The coupling of a recently
developed rapid temperature-stepping thermodenuder (TD, operated in the range
54–230°C) with a High-Resolution Time-of-Flight Aerosol Mass
Spectrometer (HR-ToF-AMS) during field studies in two polluted megacities has
enabled the first direct characterization of chemically-resolved urban
particle volatility. Measurements in Riverside, CA and Mexico City are
generally consistent and show ambient nitrate as having the highest
volatility of any AMS standard aerosol species while sulfate showed the
lowest volatility. Total organic aerosol (OA) showed volatility intermediate
between nitrate and sulfate, with an evaporation rate of 0.6%·K−1
near ambient temperature, although OA dominates the residual species at the
highest temperatures. Different types of OA were characterized with marker
ions, diurnal cycles, and positive matrix factorization (PMF) and show
significant differences in volatility. Reduced hydrocarbon-like OA (HOA, a
surrogate for primary OA, POA), oxygenated OA (OOA, a surrogate for secondary
OA, SOA), and biomass-burning OA (BBOA) separated with PMF were all
determined to be semi-volatile. The most aged OOA-1 and its dominant ion,
CO2+, consistently exhibited the lowest volatility, with HOA, BBOA, and
associated ions for each among the highest. The similar or higher volatility
of HOA/POA compared to OOA/SOA contradicts the current representations of OA
volatility in most atmospheric models and has important implications for
aerosol growth and lifetime. A new technique using the AMS background signal
was demonstrated to quantify the fraction of species up to four
orders-of-magnitude less volatile than those detectable in the MS mode, which
for OA represent ~5% of the non-refractory (NR) OA signal. Our results
strongly imply that all OA types should be considered semivolatile in models.
The study in Riverside identified organosulfur species (e.g. CH3HSO3+
ion, likely from methanesulfonic acid), while both studies identified ions
indicative of amines (e.g. C5H12N+) with very different volatility
behaviors than inorganic-dominated ions. The oxygen-to-carbon ratio of OA in
each ambient study was shown to increase both with TD temperature and from
morning to afternoon, while the hydrogen-to-carbon ratio showed the opposite
trend. |
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