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Influence of Humidity, Temperature, and Radicals on the Formation and Thermal Properties of Secondary Organic Aerosol (SOA) from Ozonolysis of β-Pinene

Journal article
Authors Eva U. Emanuelsson
Ågot Watne
Anna Lutz
Evert Ljungström
Mattias Hallquist
Published in Journal of Physical Chemistry A
Volume 117
Issue 40
Pages 10346 - 10358
ISSN 1089-5639
Publication year 2013
Published at Department of Chemistry and Molecular Biology
Pages 10346 - 10358
Language en
Links dx.doi.org/10.1021/jp4010218
Keywords Volatility, Terpenes, Flow reactor, Radical chemistry
Subject categories Chemical Sciences, Analytical Chemistry, Organic Chemistry, Physical organic chemistry, Climate Research, Environmental Sciences, Environmental chemistry, Meteorology and Atmospheric Sciences

Abstract

The influence of water and radicals on SOAs produced by β-pinene ozonolysis was investigated at 298 and 288 K using a laminar flow reactor. A volatility tandem differential mobility analyzer (VTDMA) was used to measure the evaporation of the SOA, enabling the parametrization of its volatility properties. The parameters extracted included the temperature at which 50% of the aerosol had evaporated (TVFR0.5) and the slope factor (SVFR). An increase in SVFR indicates a broader distribution of vapor pressures for the aerosol constituents. Reducing the reaction temperature increased SVFR and decreased TVFR0.5 under humid conditions but had less effect on TVFR0.5 under dry conditions. In general, higher water concentrations gave lower TVFR0.5 values, more negative SVFR values, and a reduction in total SOA production. The radical conditions were changed by introducing OH scavengers to generate systems with and without OH radicals and with different [HO2]/[RO2] ratios. The presence of a scavenger and lower [HO2]/[RO2] ratio reduced SOA production. Observed changes in SVFR values could be linked to the more complex chemistry that occurs in the absence of a scavenger and indicated that additional HO2 chemistry gives products with a wider range of vapor pressures. Updates to existing ozonolysis mechanisms with routes that describe the observed responses to water and radical conditions for monoterpenes with endocyclic and exocyclic double bonds are discussed.

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