Kinetic modeling of nucleation experiments involving SO2 and OH: new insights into the underlying nucleation mechanisms

摘要

Nucleation is an important source of atmospheric aerosolswhich have significant climatic and health implications. Despite intensivetheoretical and field studies over the past decades, the dominantnucleation mechanism in the lower troposphere remains to be mysterious.Several recent laboratory studies on atmospheric nucleation may shed lighton this important problem. However, the most interesting finding from thosestudies was based on the derived HSO concentration whoseaccuracy has not yet been evaluated by any other means. Moreover, thethreshold HSO concentration needed to reach the same degree ofnucleation reported by two separate nucleation studies varies by about oneorder of magnitude. In this study, we apply a recently updated kineticnucleation model to study the nucleation phenomena observed in those recentexperiments. We show that the HSO concentration can be estimatedwith a higher level of accuracy with the kinetic model by constraining thesimulated particle size distributions with observed ones. We find that therequired HSO concentrations to achieve the best agreementbetween modeling and measurements are a factor of ~2 to 4 higher thanreported in those experiments. More importantly, by comparing the derivedthermodynamic properties associated with the nucleation process, we concludethat different unknown species may participate in the two separatenucleation experimental studies, which may explain the large difference inthe reported threshold HSO concentration. Although the unknownspecies involved has yet to be identified, the derived values ofthermodynamic properties can serve as a valuable guideline for the search oftheir chemical identities using advanced quantum-chemical approaches.