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

Artikel i vetenskaplig tidskrift
Författare J. M. Flores
D. F. Zhao
L. Segev
P. Schlag
A. Kiendler-Scharr
H. Fuchs
Ågot Watne
N. Bluvshtein
T. F. Mentel
Mattias Hallquist
Y. Rudich
Publicerad i Atmospheric Chemistry and Physics
Volym 14
Nummer/häfte 11
Sidor 5793-5806
ISSN 1680-7316
Publiceringsår 2014
Publicerad vid Institutionen för kemi och molekylärbiologi
Sidor 5793-5806
Språk en
Länkar dx.doi.org/10.5194/acp-14-5793-2014
Ämnesord SIMULATION CHAMBER SAPHIR, HIGH RELATIVE-HUMIDITY, ALPHA-PINENE, HIGH-RESOLUTION, OPTICAL-PROPERTIES, MASS-SPECTROMETRY, BROWN CARBON, CAVITY RING, HYGROSCOPIC GROWTH, SOLAR-RADIATION, Meteorology & Atmospheric Sciences
Ämneskategorier Meteorologi och atmosfärforskning

Sammanfattning

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 Julich, 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 (alpha-pinene and limonene), (ii) biogenic VOC mixture with subsequent addition of an anthropogenic VOC (p-xylene-d(10)), 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-d(10) 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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