Experimental and theoretical investigation of nucleation and growth of atmospheric aerosols

摘要

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 wellunderstood. In this work, laboratory and theoretical studies have been performed toinvestigate the formation and growth of atmospheric particles. The first two parts of thedissertation are a laboratory investigation of new particle formation and growth, and atheoretical study of atmospheric molecular complexes and clusters. The nucleation ratewas considerably enhanced in the presence of cis-pinonic acid and ammonia. Thecomposition of the critical cluster was estimated from the dependence of the nucleationrate on the precursor concentration and the time evolution of the clusters was thensimulated using molecular dynamic simulations. Results from quantum chemicalcalculations and quantum theory of atoms in molecules (QTAIM) reveal that formationof strong hydrogen bonding between an organic acid and sulfuric acid is likelyresponsible for a reduction of the nucleation barrier by modifying the hydrophobicproperties 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 thenucleation in the atmosphere.The last part of this dissertation is the laboratory investigation of heterogeneousinteractions of atmospheric carbonyls with sulfuric acid. Direct measurement has beenperformed to investigate the heterogeneous uptake of atmospheric carbonyls on sulfuricacid. Important parameters have been obtained from the time-dependent or timeindependentuptake profiles. The results indicated that the acid-catalyzed reactions oflarger aldehydes (e.g. octanal and 2, 4-hexadienal) in sulfuric acid solution wereattributed to aldol condensation in high acidity. However such reactions do notcontribute much to secondary organic aerosol (SOA) formation due to the low acidityunder tropospheric conditions. On the other hand, heterogeneous reactions of lightdicarbonyl such as methylglyoxal likely contribute to SOA formation in slightly acidicmedia. The reactions of methylglyoxal in the atmospheric aerosol-phase involvehydration and subsequent polymerization, which are dependent on the hygroscopicity,rather than the acidity of the aerosols.