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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 18, issue 3 | Copyright
Atmos. Chem. Phys., 18, 1895-1907, 2018
https://doi.org/10.5194/acp-18-1895-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 09 Feb 2018

Research article | 09 Feb 2018

Nanoparticle growth by particle-phase chemistry

Michael J. Apsokardu and Murray V. Johnston Michael J. Apsokardu and Murray V. Johnston
  • Department of Chemistry and Biochemistry, University of Delaware, Newark, DE, 19716, USA

Abstract. The ability of particle-phase chemistry to alter the molecular composition and enhance the growth rate of nanoparticles in the 2–100nm diameter range is investigated through the use of a kinetic growth model. The molecular components included are sulfuric acid, ammonia, water, a non-volatile organic compound, and a semi-volatile organic compound. Molecular composition and growth rate are compared for particles that grow by partitioning alone vs. those that grow by a combination of partitioning and an accretion reaction in the particle phase between two organic molecules. Particle-phase chemistry causes a change in molecular composition that is particle diameter dependent, and when the reaction involves semi-volatile molecules, the particles grow faster than by partitioning alone. These effects are most pronounced for particles larger than about 20nm in diameter. The modeling results provide a fundamental basis for understanding recent experimental measurements of the molecular composition of secondary organic aerosol showing that accretion reaction product formation increases linearly with increasing aerosol volume-to-surface-area. They also allow initial estimates of the reaction rate constants for these systems. For secondary aerosol produced by either OH oxidation of the cyclic dimethylsiloxane (D5) or ozonolysis of β-pinene, oligomerization rate constants on the order of 10−3 to 10−1M−1s−1 are needed to explain the experimental results. These values are consistent with previously measured rate constants for reactions of hydroperoxides and/or peroxyacids in the condensed phase.

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The ability of particle-phase chemistry to alter the molecular composition and enhance the growth rate of nanoparticles is investigated through the use of a kinetic growth model. The effects of particle-phase chemistry are found to be most pronounced for particles larger than about 20 nm in diameter. The results are discussed in the context of recent experimental measurements of particle-size-dependent molecular composition.
The ability of particle-phase chemistry to alter the molecular composition and enhance the...
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