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Volume 15, issue 16
Atmos. Chem. Phys., 15, 9327–9343, 2015
https://doi.org/10.5194/acp-15-9327-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
Atmos. Chem. Phys., 15, 9327–9343, 2015
https://doi.org/10.5194/acp-15-9327-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 21 Aug 2015

Research article | 21 Aug 2015

The influences of mass loading and rapid dilution of secondary organic aerosol on particle volatility

K. R. Kolesar1, C. Chen1,a, D. Johnson1,b, and C. D. Cappa1 K. R. Kolesar et al.
  • 1Department of Civil and Environmental Engineering, University of California, Davis, One Shields Avenue, Davis, California 95616, USA
  • anow at: Sustainable Energy Initiative, Santa Clara University, 500 El Camino Real, Santa Clara, California 95053, USA
  • bnow at: Advanced Light Source, Lawrence Berkeley National Laboratory, 1 Cyclotron Rd, Berkeley, California 94720, USA

Abstract. The thermally induced evaporation of secondary organic aerosol (SOA) has been characterized for SOA formed from the dark ozonolysis of α-pinene at initial mass concentrations ranging from 1 to 800 μg m−3. Temperature-dependent particle size distributions were measured using a thermodenuder and the resulting mass thermograms were compared between the SOA formed at the various SOA mass concentrations. Negligible differences were observed between the mass thermograms for SOA concentrations < 300 μg m−3. At higher SOA concentrations, the observed mass thermograms indicated the SOA was actually slightly less volatile than the SOA at lower concentrations; this is likely an artifact due to either saturation of the gas phase or to recondensation during cooling. The thermograms observed when the SOA was formed at high concentrations (> 380 μg m−3) and then rapidly isothermally diluted to low concentrations (1–20 μg m−3) were identical to those for the SOA that was initially formed at low concentrations. The experimental results were compared to a kinetic model that simulates particle evaporation upon heating in a thermodenuder for a given input volatility distribution and particle composition. Three cases were considered: (1) the SOA was composed of semi-volatile monomer species with a volatility distribution based on that derived previously from consideration of SOA growth experiments; (2) the initial SOA was composed almost entirely of non-volatile dimers that decompose upon heating into their semi-volatile monomer units, which can then evaporate; and (3) where a volatility distribution was derived by fitting the model to the observed mass thermograms. It was found that good agreement is obtained between model predictions and the observations when the particle composition is dominated by either compounds of low volatility or by dimers. These same models were used to simulate isothermal evaporation of the SOA and were found to be broadly consistent with literature observations that indicate that SOA evaporation occurs with multiple timescales. The use of the semi-volatile monomer volatility distribution fails to reproduce the observed evaporation. The presence of dimers and larger oligomers in secondary organic aerosol formed from products of the reaction of α-pinene and O3 has been well established in laboratory studies. However, the timescale and relative importance of the formation of oligomers or low-volatility compounds in the growth and evaporation of SOA has been debated. This study provides further support that low-volatility compounds and oligomers are formed in α-pinene + O3 in high abundances and suggests that their formation occurs rapidly upon particle formation.

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Secondary organic aerosol from the dark ozonolysis of α‑pinene was formed at a range of mass loadings from 1 to 800μg m-3. The amount of mass loss during evaporation in a thermodenuder was found to be independent of mass loading. A kinetic model of evaporation was fit to the observations and good agreement was obtained when the particle was either composed of dimers that decompose into semi-volatile monomers or when it was composed of low-volatility compounds that evaporate directly.
Secondary organic aerosol from the dark ozonolysis of α‑pinene was formed at a range of mass...
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