Modeling the role of ions in the formation and detection of atmospheric clusters

Ivo Neefjes

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Sammanfattning

The majority of atmospheric aerosol particles are formed through a gas-to-particle conversion process called new particle formation. Upon their formation, aerosol particles impact the climate both directly, by scattering incoming sunlight, and indirectly, by functioning as cloud condensation nuclei. The effect of atmospheric aerosol particles represents one of the largest uncertainties in current climate models. This uncertainty is mostly caused by a lack of knowledge about the initial stages of new particle formation, where gas-phase compounds undergo sticking collisions to form clusters of 2–3 nm in diameter.

This thesis focuses on the role of ions in the formation and detection of atmospheric clusters. Ions typically have strong long-range interactions with other atmospheric compounds and can, therefore, facilitate the formation of atmospheric clusters. The importance of ion-induced new particle formation pathways is, however, still subject of debate. The relative importance of ion-induced pathways can be determined from their cluster formation rates through dynamical models, such as the Atmospheric Cluster Dynamics Code. These models rely on accurate collision and evaporation rate coefficients. We developed a computational approach to calculate accurate estimates for the collision rate coefficient based on the central field approach with interaction parameters fitted to the potential of mean force obtained from free energy calculations. We also developed an analytical interacting hard-sphere model where collision rate coefficient can be calculated for clusters of arbitrary size with low computational cost.

Evaporation rate coefficients are typically derived from binding free energies calculated through quantum chemistry calculations. We developed a machine learning workflow to more efficiently obtain accurate binding free energies for large clusters and used these to investigate the cluster formation rate dependence on the largest cluster size included in the Atmospheric Cluster Dynamics Code.

Ions also play an important role in the detection of atmospheric clusters in chemical ionization and ion mobility mass spectrometry. Ion mobility mass spectrometry is especially relevant in separating isomers. We performed computational ion mobility calculations to help assign peaks in ion mobility spectra to specific isomers.

The results of these studies can be used to obtain more accurate cluster formation rates and help determine the compounds involved in new particle formation to reduce the uncertainty in the effect of aerosol particles on the climate.
Originalspråkengelska
Tilldelande institution
  • Matematisk-naturvetenskapliga fakulteten
Handledare
  • Vehkamäki, Hanna, Handledare
  • Kurten, Theo, Handledare
  • Reischl, Bernhard, Handledare
Tilldelningsdatum25 maj 2024
UtgivningsortHelsinki
Förlag
Tryckta ISBN978-952-7507-29-2
Elektroniska ISBN978-952-7507-30-8
StatusPublicerad - 13 maj 2024
MoE-publikationstypG5 Doktorsavhandling (artikel)

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  • 116 Kemi

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