The influence of ions on atmospheric particle growth - flow tube and aerosol chamber studies

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Secondary aerosol formation is a major source of particles in the atmosphere with important implications for climate and human health. This project investigates the role of air ions in secondary aerosol formation both in flow tube and aerosol chamber experiments under controlled laboratory conditions. Despite considerable progress with respect to measuring capabilities for atmospheric nucleation and particle growth, gaps still exist in the understanding of the underlying physical and chemical processes. In particular, the potential impact of ion-particle interactions and ion chemistry on secondary aerosol formation is a topic of scientific discussion. As a complement to existing research efforts, which investigate the role of ions in the initial nucleation step, we propose to study ion-particle interactions in subsequent particle growth with a focus on direct measurements of the charging state, the growth rates and the chemical composition of secondary organic aerosol. To do this, the charging state and growth rates of aerosol populations will be quantified under well-defined conditions in laboratory experiments with a modified mobility particle spectrometer. In a next step, we will fully exploit the novel measuring capabilities of our aerosol mass spectrometer CAChUP, quantifying the contribution of different organic precursor gases at various charging states to the chemical composition of the secondary organic aerosol. Finally, the findings of these experiments will be validated with an aerosol chamber setup studying secondary organic aerosol formation at well-defined ion concentrations. Thus, the proposed research agenda is designed to untangle the potential contributions of ion chemistry to secondary aerosol formation.