Zhao, Jun (2007-12). Experimental and theoretical investigation of nucleation and growth of atmospheric aerosols. Doctoral Dissertation. Thesis uri icon

abstract

  • Aerosol particles have profound impacts on human health, atmospheric radiation, and cloud microphysics and these impacts are strongly dependent on particle sizes. However, formation and growth of atmospheric particles are currently not well understood. In this work, laboratory and theoretical studies have been performed to investigate the formation and growth of atmospheric particles. The first two parts of the dissertation are a laboratory investigation of new particle formation and growth, and a theoretical study of atmospheric molecular complexes and clusters. The nucleation rate was considerably enhanced in the presence of cis-pinonic acid and ammonia. The composition of the critical cluster was estimated from the dependence of the nucleation rate on the precursor concentration and the time evolution of the clusters was then simulated using molecular dynamic simulations. Results from quantum chemical calculations and quantum theory of atoms in molecules (QTAIM) reveal that formation of strong hydrogen bonding between an organic acid and sulfuric acid is likely responsible for a reduction of the nucleation barrier by modifying the hydrophobic properties of the organic acid and allowing further addition of hydrophilic species (e.g., H2SO4, H2O, and possibly NH3) to the hydrophilic side of the clusters. This promotes growth of the nascent cluster to overcome the nucleation barrier and thus enhances the nucleation in the atmosphere. The last part of this dissertation is the laboratory investigation of heterogeneous interactions of atmospheric carbonyls with sulfuric acid. Direct measurement has been performed to investigate the heterogeneous uptake of atmospheric carbonyls on sulfuric acid. Important parameters have been obtained from the time-dependent or timeindependent uptake profiles. The results indicated that the acid-catalyzed reactions of larger aldehydes (e.g. octanal and 2, 4-hexadienal) in sulfuric acid solution were attributed to aldol condensation in high acidity. However such reactions do not contribute much to secondary organic aerosol (SOA) formation due to the low acidity under tropospheric conditions. On the other hand, heterogeneous reactions of light dicarbonyl such as methylglyoxal likely contribute to SOA formation in slightly acidic media. The reactions of methylglyoxal in the atmospheric aerosol-phase involve hydration and subsequent polymerization, which are dependent on the hygroscopicity, rather than the acidity of the aerosols.
  • Aerosol particles have profound impacts on human health, atmospheric radiation,
    and cloud microphysics and these impacts are strongly dependent on particle sizes.
    However, formation and growth of atmospheric particles are currently not well
    understood. In this work, laboratory and theoretical studies have been performed to
    investigate the formation and growth of atmospheric particles. The first two parts of the
    dissertation are a laboratory investigation of new particle formation and growth, and a
    theoretical study of atmospheric molecular complexes and clusters. The nucleation rate
    was considerably enhanced in the presence of cis-pinonic acid and ammonia. The
    composition of the critical cluster was estimated from the dependence of the nucleation
    rate on the precursor concentration and the time evolution of the clusters was then
    simulated using molecular dynamic simulations. Results from quantum chemical
    calculations and quantum theory of atoms in molecules (QTAIM) reveal that formation
    of strong hydrogen bonding between an organic acid and sulfuric acid is likely
    responsible for a reduction of the nucleation barrier by modifying the hydrophobic
    properties of the organic acid and allowing further addition of hydrophilic species (e.g.,
    H2SO4, H2O, and possibly NH3) to the hydrophilic side of the clusters. This promotes growth of the nascent cluster to overcome the nucleation barrier and thus enhances the
    nucleation in the atmosphere.
    The last part of this dissertation is the laboratory investigation of heterogeneous
    interactions of atmospheric carbonyls with sulfuric acid. Direct measurement has been
    performed to investigate the heterogeneous uptake of atmospheric carbonyls on sulfuric
    acid. Important parameters have been obtained from the time-dependent or timeindependent
    uptake profiles. The results indicated that the acid-catalyzed reactions of
    larger aldehydes (e.g. octanal and 2, 4-hexadienal) in sulfuric acid solution were
    attributed to aldol condensation in high acidity. However such reactions do not
    contribute much to secondary organic aerosol (SOA) formation due to the low acidity
    under tropospheric conditions. On the other hand, heterogeneous reactions of light
    dicarbonyl such as methylglyoxal likely contribute to SOA formation in slightly acidic
    media. The reactions of methylglyoxal in the atmospheric aerosol-phase involve
    hydration and subsequent polymerization, which are dependent on the hygroscopicity,
    rather than the acidity of the aerosols.

ETD Chair

publication date

  • December 2007