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Molecular Stages of Atmospheric Particle Formation

Jie Zhong, University of Nebraska - Lincoln


Fine particulate matter (PM) has serious effects on air quality, human health and visibility. Currently, the mechanisms leading to PM formation remain uncertain, which hinders the efforts in developing effective mitigation policies to reduce their adverse impacts. Computational chemistry can assist conventional experiments and gain unique insights of structures, energies and evolution processes of atmospheric particles, which thus can reveal the mechanisms of PM formation from atomic scale. This dissertation presents the results of computational studies on different stages of PM formation, i.e. gas-phase reaction, nucleation and condensation. The dominant gas-phase loss pathway for sulfur trioxide (SO3) is generally believed to be the reaction with water molecules, resulting in sulfuric acid (H2SO4). The latter is viewed as a critical component in the new particle formation (NPF). Herein, a new and competitive loss pathway for SO3 in the presence of abundant ammonia is identified, which produces sulfamic acid. This newly observed product can enhance rate of NPF from sulfuric acid and dimethylamine by about a factor of two. The reaction of Criegee intermediates on water surface might have implications in PM formation during the condensation process. Herein, we find that unlike the simplest Criegee intermediate (CH2OO), the larger Criegee intermediates, syn- and anti-CH3CHOO, (CH3)2COO, syn- and anti-CH2C(CH3)C(H)OO at the air-water interface has less reactivity. Moreover, the Criegee intermediate reaction with hydrogen sulfide at the air/water interface has been studied and the reaction time is observed to occur within a few picoseconds. This reaction provides a novel non-photochemical pathway for formation of a C-S linkage in atmospheric particles. The gas-phase reaction of organic acids with SO3 has been recognized as essential in promoting aerosol particle formation. However, this reaction at the air-water interface is poorly understood. Herein, we find at air-water interface, the reaction of organic acid-SO3 occurs on the picosecond scale, within which the ion pairs of sulphuric-carboxylic anhydride and hydronium form. This reaction at the aqueous surface has important atmospheric implications, e.g., promoting water condensation, uptaking the atmospheric nucleation agents and incorporating “SO4 2-” into organic species in aerosol particles. Therefore, the reaction acts as another path towards aerosol formation.

Subject Area

Atmospheric Chemistry|Molecular chemistry|Physical chemistry

Recommended Citation

Zhong, Jie, "Molecular Stages of Atmospheric Particle Formation" (2019). ETD collection for University of Nebraska-Lincoln. AAI13857916.