Nanoparticle growth by particle-phase chemistry

Apsokardu, Michael J.; Johnston, Murray V.

The ability of particle-phase chemistry to alter the molecular composition and enhance the growth rate of nanoparticles in the 2–100 nm 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 20 nm 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 (Dinline-formula5) or ozonolysis of inline-formulaβ-pinene, oligomerization rate constants on the order of 10inline-formula−3 to 10inline-formula−1 Minline-formula−1 sinline-formula−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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Apsokardu, Michael J. / Johnston, Murray V.: Nanoparticle growth by particle-phase chemistry. 2018. Copernicus Publications.

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Rechteinhaber: Michael J. Apsokardu

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