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Parameterization of Thermal Properties of Aging Secondary Organic Aerosol Produced by Photo-Oxidation of Selected Terpene Mixtures

Journal article
Authors Eva U. Emanuelsson
T. F. Mentel
Ågot Watne
C. Spindler
B. Bohn
T. Brauers
H. P. Dorn
Åsa M. Hallquist
R. Haseler
A. Kiendler-Scharr
K. P. Muller
Håkan Pleijel
F. Rohrer
F. Rubach
E. Schlosser
R. Tillmann
Mattias Hallquist
Published in Environmental Science and Technology
Volume 48
Issue 11
Pages 6168-6176
ISSN 0013-936X
Publication year 2014
Published at Department of Biological and Environmental Sciences
Department of Chemistry and Molecular Biology
Pages 6168-6176
Language en
Links dx.doi.org/10.1021/es405412p
Subject categories Other Engineering and Technologies

Abstract

Formation and evolution of secondary organic aerosols (SOA) from biogenic VOCs influences the Earth's radiative balance. We have examined the photo-oxidation and aging of boreal terpene mixtures in the SAPHIR simulation chamber. Changes in thermal properties and chemical composition, deduced from mass spectrometric measurements, were providing information on the aging of biogenic SOA produced under ambient solar conditions. Effects of precursor mixture, concentration, and photochemical oxidation levels (OH exposure) were evaluated. OH exposure was found to be the major driver in the long term photochemical transformations, i.e., reaction times of several hours up to days, of SOA and its thermal properties, whereas the initial concentrations and terpenoid mixtures had only minor influence. The volatility distributions were parametrized using a sigmoidal function to determine T-VFR0.5 (the temperature yielding a 50% particle volume fraction remaining) and the steepness of the volatility distribution. T-VFR0.5 increased by 0.3 +/- 0.1% (ca. 1 K), while the steepness increased by 0.9 +/- 0.3% per hour of 1 x 10(6) cm(-3) OH exposure. Thus, aging reduces volatility and increases homogeneity of the vapor pressure distribution, presumably because highly volatile fractions become increasingly susceptible to gas phase oxidation, while less volatile fractions are less reactive with gas phase OH.

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