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| Titel |
Molecular characterization of free tropospheric aerosol collected at the Pico Mountain Observatory: a case study with a long-range transported biomass burning plume |
| VerfasserIn |
K. Dzepina, C. Mazzoleni, P. Fialho, S. China, B. Zhang, R. C. Owen, D. Helmig, J. Hueber, S. Kumar, J. A. Perlinger, L. J. Kramer, M. P. Dziobak, M. T. Ampadu, S. Olsen, D. J. Wuebbles, L. R. Mazzoleni |
| 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 ; 15, no. 9 ; Nr. 15, no. 9 (2015-05-05), S.5047-5068 |
| Datensatznummer |
250119694
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| Publikation (Nr.) |
 copernicus.org/acp-15-5047-2015.pdf |
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| Zusammenfassung |
| Free tropospheric aerosol was sampled at the Pico Mountain Observatory
located at 2225 m above mean sea level on Pico Island of the Azores
archipelago in the North Atlantic. The observatory is located
~ 3900 km east and downwind of North America, which enables
studies of free tropospheric air transported over long distances. Aerosol
samples collected on filters from June to October 2012 were analyzed to
characterize organic carbon, elemental carbon, and inorganic ions. The
average ambient concentration of aerosol was 0.9 ± 0.7 μg m−3. On average, organic aerosol components represent the largest mass
fraction of the total measured aerosol (60 ± 51%), followed by
sulfate (23 ± 28%), nitrate (13 ± 10%), chloride (2 ± 3%), and elemental carbon (2 ± 2%). Water-soluble
organic matter (WSOM) extracted from two aerosol samples (9/24 and 9/25)
collected consecutively during a pollution event were analyzed using
ultrahigh-resolution electrospray ionization Fourier transform ion cyclotron
resonance mass spectrometry. Approximately 4000 molecular formulas were
assigned to each of the mass spectra in the range of m/z 100–1000. The majority
of the assigned molecular formulas had unsaturated structures with CHO and
CHNO elemental compositions. FLEXPART retroplume analyses showed the sampled
air masses were very aged (average plume age > 12 days). These
aged aerosol WSOM compounds had an average O/C ratio of ~ 0.45,
which is relatively low compared to O/C ratios of other aged aerosol.
The increase in aerosol loading during the measurement period of 9/24 was
linked to biomass burning emissions from North America by FLEXPART
retroplume analysis and Moderate Resolution Imaging Spectroradiometer
(MODIS) fire counts. This was confirmed with biomass burning markers
detected in the WSOM and with the morphology and mixing state of particles
as determined by scanning electron microscopy. The presence of markers
characteristic of aqueous-phase reactions of phenolic species suggests that
the aerosol collected at the Pico Mountain Observatory had undergone cloud
processing before reaching the site. Finally, the air masses of 9/25 were
more aged and influenced by marine emissions, as indicated by the presence
of organosulfates and other species characteristic of marine aerosol. The
change in the air masses for the two samples was corroborated by the changes
in ethane, propane, and ozone, morphology of particles, as well as by the
FLEXPART retroplume simulations. This paper presents the first detailed
molecular characterization of free tropospheric aged aerosol intercepted at
a lower free troposphere remote location and provides evidence of low
oxygenation after long-range transport. We hypothesize this is a result of
the selective removal of highly aged and polar species during long-range
transport, because the aerosol underwent a combination of atmospheric
processes during transport facilitating aqueous-phase removal (e.g., clouds
processing) and fragmentation (e.g., photolysis) of components. |
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