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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/amt-2019-5
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/amt-2019-5
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 20 Feb 2019

Research article | 20 Feb 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Measurement Techniques (AMT).

Two-wavelength thermo-optical determination of Light Absorbing Carbon in atmospheric aerosols

Dario Massabò1, Alessandro Altomari2, Virginia Vernocchi1, and Paolo Prati1 Dario Massabò et al.
  • 1Dept. of Physics, University of Genoa & INFN, Via Dodecaneso 33, 16146, Genova, Italy
  • 2Dept. of Physics, University of Genoa, Via Dodecaneso 33, 16146, Genova, Italy

Abstract. Thermo-optical analysis is widely adopted for the quantitative determination of Total, TC, Organic, OC, and Elemental, EC, Carbon in atmospheric aerosol sampled by suitable filters. Nevertheless, the methodology suffers of several uncertainties and artefacts as the well-known issue of charring affecting the OC-EC separation. In the standard approach, the effect of the possible presence of Brown Carbon, BrC, in the sample is neglected. BrC is a fraction of OC, usually produced by biomass burning with a thermic behaviour intermediate between OC and EC. BrC is optically active: it shows an increasing absorbance when the wavelength moves to the blue/UV region of the electromagnetic spectrum. Definitively, the thermo-optical characterization of carbonaceous aerosol should be reconsidered to address the possible BrC content in the sample under analysis.

We introduce here a modified Sunset Lab Inc. EC/OC Analyzer. Starting from a standard commercial set-up, the unit has been modified at the Physics Department of the University of Genoa (IT), making possible the alternative use of the standard laser diode at λ = 635 nm and of a new laser diode at λ = 405 nm. In this way, the optical transmittance through the sample can be monitored at both the wavelengths. Since at shorter wavelengths the BrC absorbance is higher, a better sensitivity to this species is gained. The modified set-up also gives the possibility to quantify the BrC concentration in the sample at both the wavelengths. The new unit has been thoroughly tested, with both artificial and real-world samples: the first experiment, in conjunction with the Multi Wavelength Absorbance Analyzer (MWAA, Massabò et al., 2013 and 2015), resulted in the first direct determination of the BrC Mass Absorption Coefficient (MAC) at λ = 405 nm: MAC = 23 ± 1 m2 g−1.

Dario Massabò et al.
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Dario Massabò et al.
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