Atmospheric New Particle Formation
Atmospheric particles play a significant role in radiative forcing of the Earth, mostly by absorption or scattering of solar radiation, and serving as cloud condensation nuclei (CCN). Ambient studies have shown that some participants of the new particle formation (NPF) processes are sulfuric acid, amines, and oxidized organic molecules. However it is not well understood how they form at the beginning and grow up to effective sizes. Therefore we aim to study NPF processes in sub- to a-few nanometer scale. In particular, to characterize the structures of the clusters, analyze the driving forces, and evaluate some external factors that could enhance NPF processes.
Currently we are using cryogenic ion vibrational predissociation (CIVP) spectroscopy to study the structures of atmospheric clusters. This is an action spectroscopy technique, meaning we are looking at the changes caused by the interaction between a tunable infrared laser beam and the target clusters. The feature of CIVP technique is that it allows us to obtain spectra of gas phase molecules with higher resolution and less perturbation.
The clusters are generated by an electrospray ionization (ESI) source, and then mass-selected and guided toward a cryogenic ion trap by several stages of multipole ion traps. [Link to the instrument page] Inside the cryogenic ion trap, ions are cooled down by colliding with cold helium buffer gas and then physisorb one or more small gas molecules (e.g. He, D2, N2, H2O …) which we call tags.
The current mass spectrometer is a custom-designed and home-built machine on which we have been able to generate atmospheric acid-base clusters that are also observed by the CLOUD chamber.
Another research interest is to investigate impact of acidity and binding type on the affinity of clusters to small molecules that are abundant in the atmosphere, such as H2O, organic acids and bases. This is realized by sending one specific type of ion into the cryo trap with the help of the quadrupole mass filter. Additional ion traps are being made which will allow thermodynamic study of the NPF processes in extended steps and temperature range.
Ref.
1. M. Kulmala et al., Science 339, 943 (2013).
