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arXiv · 1309.4202

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

Eva U. Emanuelsson·Ågot K. Watne·Anna Lutz·Evert Ljungström·Mattias Hallquist
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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 parameterization 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. 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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Eva U. Emanuelsson, Ågot K. Watne, Anna Lutz, Evert Ljungström, Mattias Hallquist. 2013-09-17. Influence of Humidity, Temperature and Radicals on the Formation and Thermal Properties of Secondary Organic Aerosol (SOA) from Ozonolysis of β-pinene. https://doi.org/10.1021/jp4010218

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