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

JM Flores, DF Zhao, Lior Segev, P Schlag, A Kiendler-Scharr, Hadar Fuchs, AK Watne, Nir Bluvshtein, TF Mentel, M Hallquist, Yinon Rudich

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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.

Original languageEnglish
Pages (from-to)5793-5806
Number of pages14
JournalAtmospheric Chemistry and Physics
Volume14
Issue number11
DOIs
Publication statusPublished - 11 Jun 2014

Funding

German-Israeli Foundation [1136-26.8/2011]; EUROCHAMP2 transnational access activity [E2-2012-04-22-0072]; Jinich Postdoctoral Fellowship; [FP7-ENV-2010-265148-PEGASOS] This study was partially supported by the German-Israeli Foundation for Scientific Research and Development, research grant no. 1136-26.8/2011, by the EUROCHAMP2 transnational access activity E2-2012-04-22-0072, and by FP7-ENV-2010-265148-PEGASOS. J. M. Flores is supported by a research grant from the Jinich Postdoctoral Fellowship. We thank the SAPHIR team, especially F. Rohrer, B. Bohn, R. Haseler, M. Kaminski, A. Lutz, and I.-H. Acir, for providing helpful data and supporting our measurements. We also thank S. S. Brown and R. Washenfelder for helpful discussions and support with the optical system.

All Science Journal Classification (ASJC) codes

  • Atmospheric Science

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