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| Titel |
In situ submicron organic aerosol characterization at a boreal forest research station during HUMPPA-COPEC 2010 using soft and hard ionization mass spectrometry |
| VerfasserIn |
A. L. Vogel, M. Äijälä, A. L. Corrigan, H. Junninen, M. Ehn, T. Petäjä, D. R. Worsnop, M. Kulmala  , L. M. Russell, J. Williams, T. Hoffmann |
| 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. 21 ; Nr. 13, no. 21 (2013-11-08), S.10933-10950 |
| Datensatznummer |
250085804
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| Publikation (Nr.) |
 copernicus.org/acp-13-10933-2013.pdf |
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| Zusammenfassung |
The chemical composition of submicron aerosol during the comprehensive field
campaign HUMPPA-COPEC 2010 at Hyytiälä, Finland, is presented. The
focus lies on online measurements of organic acids, which were achieved by
using atmospheric pressure chemical ionization (APCI) ion trap mass
spectrometry (IT-MS). These measurements were accompanied by aerosol mass
spectrometry (AMS) measurements and Fourier transform infrared spectroscopy
(FTIR) of filter samples, all showing a high degree of correlation. The soft
ionization mass spectrometer alternated between gas-phase measurements
solely and measuring the sum of gas and particle phase.
The AMS measurements of C, H and O elemental composition show that the
aerosol during the campaign was highly oxidized, which appears reasonable
due to high and prolonged radiation during the boreal summer measurement
period as well as the long transport times of some of the aerosol. In order
to contrast ambient and laboratory aerosol, an average organic acid pattern,
measured by APCI-IT-MS during the campaign, was compared to terpene
ozonolysis products in a laboratory reaction chamber. Identification of
single organic acid species remains a major challenge due to the complexity
of the boreal forest aerosol. Unambiguous online species identification was
attempted by the combinatorial approach of identifying unique fragments in
the MS2 mode of standards, and then comparing these results with
MS2 field spectra. During the campaign, unique fragments of
limonene-derived organic acids (limonic acid and ketolimononic acid) and of the
biomass burning tracer vanillic acid were detected. Other specific fragments
(neutral loss of 28 Da) in the MS2 suggest the occurrence of
semialdehydes.
Furthermore, an approach to determine the average molecular weight of the
aerosol is presented. The campaign average organic molecular weight was
determined to be 300 g mol−1. However, a plume of aged biomass burning
aerosol, arriving at Hyytiälä from Russia, contained organic
compounds up to 800 Da (MWom≈450 g mol−1), showing that the average molecular weight can vary
significantly. The high measurement frequency of both AMS and APCI-IT-MS
enabled the partitioning of selected organic acids between gas and
particle phase as a function of the total particulate mass to be quantified.
Surprisingly high fractions of the higher molecular weight organic acids were
observed to reside in the gas phase. These observations might be a
consequence of large equilibration timescales for semi-solid boreal forest
aerosol, as has been recently hypothesized by Shiraiwa and Seinfeld
(2012). |
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