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Volume 14, issue 11
Atmos. Chem. Phys., 14, 5793-5806, 2014
https://doi.org/10.5194/acp-14-5793-2014
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue: The Pan European Gas-Aerosols Climate Interaction Study...

Atmos. Chem. Phys., 14, 5793-5806, 2014
https://doi.org/10.5194/acp-14-5793-2014
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 11 Jun 2014

Research article | 11 Jun 2014

Evolution of the complex refractive index in the UV spectral region in ageing secondary organic aerosol

J. M. Flores1, D. F. Zhao2, L. Segev1, P. Schlag2, A. Kiendler-Scharr2, H. Fuchs2, Å. K. Watne3, N. Bluvshtein1, Th. F. Mentel2, M. Hallquist3, and Y. Rudich1 J. M. Flores et al.
  • 1Weizmann Institute of Science, Department of Earth and Planetary Sciences, Rehovot 76100, Israel
  • 2Institut für Energie und Klimaforschung: Troposphäre (IEK-8), Forschungszentrum Jülich, 52425 Jülich, Germany
  • 3Department of Chemistry and Molecular Biology, Atmospheric Science, University of Gothenburg, 41296 Gothenburg, Sweden

Abstract. The chemical and physical properties of secondary organic aerosol (SOA) formed by the photochemical degradation of biogenic and anthropogenic volatile organic compounds (VOC) are as yet still poorly constrained. The evolution of the complex refractive index (RI) of SOA, formed from purely biogenic VOC and mixtures of biogenic and anthropogenic VOC, was studied over a diurnal cycle in the SAPHIR photochemical outdoor chamber in Jülich, Germany. The correlation of RI with SOA chemical and physical properties such as oxidation level and volatility was examined. The RI was retrieved by a newly developed broadband cavity-enhanced spectrometer for aerosol optical extinction measurements in the UV spectral region (360 to 420 nm). Chemical composition and volatility of the particles were monitored by a high-resolution time-of-flight aerosol mass spectrometer, and a volatility tandem differential mobility analyzer. SOA was formed by ozonolysis of either (i) a mixture of biogenic VOC (α-pinene and limonene), (ii) biogenic VOC mixture with subsequent addition of an anthropogenic VOC (p-xylene-d10), or (iii) a mixture of biogenic and anthropogenic VOC. The SOA aged by ozone/OH reactions up to 29.5 h was found to be non-absorbing in all cases. The SOA with p-xylene-d10 showed an increase of the scattering component of the RI correlated with an increase of the O / C ratio and with an increase in the SOA density. There was a greater increase in the scattering component of the RI when the SOA was produced from the mixture of biogenic VOCs and anthropogenic VOC than from the sequential addition of the VOCs after approximately the same ageing time. The increase of the scattering component was inversely correlated with the SOA volatility. Two RI retrievals determined for the pure biogenic SOA showed a constant RI for up to 5 h of ageing. Mass spectral characterization shows the three types of the SOA formed in this study have a significant amount of semivolatile components. The influence of anthropogenic VOCs on the oxygenated organic aerosol as well as the atmospheric implications are discussed.

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