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| Titel |
Light extinction by secondary organic aerosol: an intercomparison of three broadband cavity spectrometers |
| VerfasserIn |
R. M. Varma, S. M. Ball, T. Brauers, H.-P. Dorn, U. Heitmann, R. L. Jones, U. Platt, D. Pöhler, A. A. Ruth, A. J. L. Shillings, J. Thieser, A. Wahner, D. S. Venables |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 6, no. 11 ; Nr. 6, no. 11 (2013-11-19), S.3115-3130 |
| Datensatznummer |
250085109
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| Publikation (Nr.) |
 copernicus.org/amt-6-3115-2013.pdf |
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| Zusammenfassung |
| Broadband optical cavity spectrometers are maturing as a technology for
trace-gas detection, but only recently have they been used to retrieve the
extinction coefficient of aerosols. Sensitive broadband extinction
measurements allow explicit separation of gas and particle phase spectral
contributions, as well as continuous spectral measurements of aerosol
extinction in favourable cases. In this work, we report an intercomparison
study of the aerosol extinction coefficients measured by three such
instruments: a broadband cavity ring-down spectrometer (BBCRDS), a
cavity-enhanced differential optical absorption spectrometer (CE-DOAS), and
an incoherent broadband cavity-enhanced absorption spectrometer (IBBCEAS).
Experiments were carried out in the SAPHIR atmospheric simulation chamber as
part of the NO3Comp campaign to compare the measurement capabilities of
NO3 and N2O5 instrumentation. Aerosol extinction coefficients
between 655 and 690 nm are reported for secondary organic aerosols (SOA)
formed by the NO3 oxidation of β-pinene under dry and humid
conditions. Despite different measurement approaches and spectral analysis
procedures, the three instruments retrieved aerosol extinction coefficients
that were in close agreement. The refractive index of SOA formed from the
β-pinene + NO3 reaction was 1.61, and was not measurably
affected by the chamber humidity or by aging of the aerosol over several
hours. This refractive index is significantly larger than SOA refractive
indices observed in other studies of OH and ozone-initiated terpene
oxidations, and may be caused by the large proportion of organic nitrates in
the particle phase. In an experiment involving ammonium sulfate particles,
the aerosol extinction coefficients as measured by IBBCEAS were found to be
in reasonable agreement with those calculated using the Mie theory. The results
of the study demonstrate the potential of broadband cavity spectrometers for
determining the optical properties of aerosols. |
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