Impact of phase state and viscosity of organic aerosol particles on the reactive uptake of carbonyls in secondary organic aerosol (SOA) formation
EMSL Project ID
48431
Abstract
Secondary organic aerosol (SOA) is a major constituent of submicron atmospheric aerosol particles, whose effects on climate and human health remain highly uncertain. Until very recently SOA particles were assumed low viscosity solutions that maintain nearly instantaneous thermodynamic equilibrium with the gas phase by rapid mixing and evaporation/condensation. Moreover, these models do not include chemical reactions in the particle phase, heterogeneous reactions, and uptake of reactive volatile organic compounds, such as carbonyls onto organic particles that can significantly contribute to SOA formation. Recent experimental data show that under low relative humidity (RH) SOA particles are highly viscous semi-solids and that at higher RH particle viscosity decreases. The goal of the proposed research is to investigate the relation between the mechanisms of the reactive uptake of carbonyls and particle viscosity. We will first use the EMSL's single particle mass spectrometer, SPLAT II, to characterize the viscosity of SOA particles as a function of RH. In these experiments, particles will be doped with a trace amount of a volatile compound, whose diffusivity in SOA will be measured by conducting evaporation studies on size-selected particles, characterizing the rate at which the tracer diffuses through SOA and evaporates. Measured diffusivity as a function of RH yields a relation between particle viscosity and RH. Particle bounce studies show that at low RH, nearly 100% of SOA particles bounce and that as the RH is increased the bounce fraction decreased, indicating that there is a relation between bounce fraction and viscosity, whose exact nature is unknown. We will quantify the relationship between particle viscosity and particle bounce, which have recently been used to characterize particle phase.The kinetics of the reactive uptake of carbonyls will be quantified by measuring changes in particle size, composition, and density in conjunction with measurements of changes in particle mobility diameters and mass, all conducted in real time as function of reaction time. We plan to investigate the reactive uptake of a number of carbonyls with different chain length used to represent a range of carbonyl volatility and conduct the study over a range of RH to yield a simple relation between reactive uptake and particle viscosity.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2014-10-01
End Date
2016-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
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