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Vapor scavenging by atmospheric aerosol particles
Doctoral Committee Chair(s)
Larson, Susan M.
Department of Study
Civil and Environmental Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Physics, Atmospheric Science
Particle growth due to vapor scavenging was studied using both experimental and computational techniques. Vapor scavenging by particles is an important physical process in the atmosphere because it can result in changes to particle properties (e.g., size, shape, composition, and activity) and, thus, influence atmospheric phenomena in which particles play a role, such as cloud formation and long range transport.
In the modelling portion of this thesis, the influence of organic vapor on the evolution of a particle mass size distribution was investigated using a modified version of MAEROS (a multicomponent aerosol dynamics code) (Gelbard and Seinfeld, 1984). The modelling study attempted to identify the sources of organic aerosol observed by Novakov and Penner (1993) in a field study in Puerto Rico. Potential sources were hypothesized to be organic vapor emissions from either forest vegetation near the sampling site or from the ocean's surfactant layer followed by gas-to-particle conversion. Comparison of model parameters with literature values suggested that the observed organic aerosol was formed by nucleation and condensation of terpene vapor emissions onto a preexisting typical marine aerosol size distribution. Organic vapor emissions from the ocean were found to be an unlikely source of the observed organic aerosol.
Experimentally, vapor scavenging and particle growth were investigated using two techniques. The influence of the presence of organic in a particle on the particle's hydroscopicity was investigated using an electrodynamic balance. It was found that, for a Tween80/NaCl system, having organic associated with an inorganic salt particle slowed the deliquescence rate of the particle. Additionally, for the Tween80/NaCl system the deliquescence humidity was lowered due to the presence of organic--suggesting an increase in particle hydroscopicity. It was also shown that the presence of an organic carbon (e.g., azelaic acid, Tween80 or dodecyl sulfate sodium salt) on a carbon block particle made the carbon block particle hygrophilic, while a pure carbon black particle was observed to be hydrophobic. The charge on a particle (which is required for study of a particle in the electrodynamic balance) was investigated theoretically and experimentally. Particle charge was found to have a negligible effect on particle growth in electrodynamic balance studies.
A prototype apparatus--the refractive index thermal diffusion chamber (RITDC)--was developed to study multiple particles in the same environment at the same time. Proof of concept experiments showed that it is possible to determine particle composition with time from changes in particle refractive index measured using the RITDC. Further refinements to the apparatus were suggested.