Computer Simulation of Ion-Induced Nucleation in the Presence of Single Ions and Ion Pairs

Atmospheric aerosol particles play an important role in climate and human health. Despite their importance, the mechanisms of their formation are still poorly understood. Ion-induced nucleation may play a role in the process, but details are lacking about how the nucleation rate depends on the size, charge, and number of ions in the cluster. In order to better understand the role that ions might play in new particle formation, we have performed a series of AVUS-HR simulations of the water nucleation in the presence of both single ions and ion pairs. These simulations have shown that the location of the Gibbs free energy minimum on the free energy profile is a key factor controlling the barrier heights for different ions/pairs. When the minimum is located at larger cluster sizes, there is a smaller loss of gas phase entropy between the Gibbs free energy minimum and the critical cluster size (the cluster sizes contributing to the barrier), and the barrier height is usually lower. The location of the Gibbs free energy minimum is generally controlled by the strength of the ion-water interactions, and how quickly they decay with increasing cluster size. However, it is also possible for small differences between two different ionic clusters to persist over a wide range of cluster sizes, adding up to significant differences in the barrier height even when the minima are at similar sizes. We have also found that ion pairs are not as effective at enhancing nucleation as single ions, largely because the long range ion-water interactions are weaker for the ion pair cases, but can still significantly lower the barrier height for nucleation. Furthermore, they may still make a large contribution to atmospheric nucleation due to the much larger concentrations of potential ion-pair forming species compared to single ions.

Name thesis:degree_name

Doctor of Philosophy (PhD)

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Chemistry

Grantor

Chemistry

Year dc:date.available

2010

Author dc:creator

• Keasler, Samuel

• Monte Carlo
• new particle
• atmospheric chemistry
• aerosol

Statement dc:rights

• withheld
• Secure the entire work for patent and/or proprietary purposes for a period of one year. Student has submitted appropriate documentation which states: During this period the copyright owner also agrees not to exercise her/his ownership rights, including public use in works, without prior authorization from LSU. At the end of the one year period, either we or LSU may request an automatic extension for one additional year. At the end of the one year secure period (or its extension, if such is requested), the work will be released for access worldwide.

Identifier

etd-03262010-001926
https://repository.lsu.edu/gradschool_dissertations/1060

OAI identifier oai:identifier

oai:repository.lsu.edu:gradschool_dissertations-2059