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Xu, Wen (2014-05). Nucleation and Growth of Atmospheric Nanoparticles at Molecular Scale. Doctoral Dissertation. | Thesis individual record
abstract

Atmospheric aerosols are fine liquid droplets or solid particles of various chemical
compositions suspended in the air. They influence the Earth radiation budget, impact cloud
formation, cause or enhance diseases on humans, and change photochemical chemistry and
partitioning of trace gas species. Atmospheric aerosols are classified into two categories, primary
and secondary, on the basis of their formation mechanisms. Although a large portion of
atmospheric aerosols is secondary, the mechanisms for secondary aerosol formation remain
highly uncertain, preventing the development of physically based representations of their
formation in atmospheric models. So far it is known that secondary aerosol formation consists
two consecutive steps, nucleation to form critical nucleus and subsequent growth of freshly
nucleated nanoparticles. Unfortunately, our current knowledge of these two steps is very limited.

In the current study, the dicarboxylic acids (organic acid) assisted nucleation is investigated
both experimentally and theoretically. First, nucleation and partitioning theories are presented as
the theoretical framework for data analysis and explanation. Subsequently, quantum chemistry
calculations are performed to evaluate the hydrogen bonding strength of dicarboxylic acids with
common atmospheric nucleation precursors, including sulfuric acid, water, ammonia, and amines.
Then, succinic acid (dicarboxylic acid) assisted nucleation experiment is carried out to assess the
nucleation enhancement ability of dicarboxylic acids. Next, the growth contributions from
epoxides vapors are determined using a combination of Nano-tandem differential mobility
analyzer (n-TDMA) and thermo desorption ion drift chemical ionization mass spectrometer (TD-ID-
CIMS). Finally, the hygroscopicity and CCN properties of atmospheric polymers are
characterized.

Our results show that dicarboxylic acids bind strongly with sulfuric acid and enhance
nucleation rate by 5-13 times with a concentration of 1 ppb. Dicarboxylic acids also react with
amines under hydration to form non-volatile aminium carboxylate ion pairs, which contribute to
nanoparticles growth. The n-TDMA and TD-ID-CIMS results show that epoxides contribute to
freshly nucleated nanoparticle (sulfuric acid nanoparticles) growth through forming non-volatile
organosulfates and oligomers, which subsequently changes the cloud-forming properties of
aerosols.

etd chair
publication date
2014