Ion-induced nucleation of pure biogenic particles

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Kirkby Jasper ; Duplissy Jonathan ; Sengupta Kamalika ; Frege Carla ; Gordon Hamish ; Williamson Christina ; Heinritzi Martin ; Simon Mario ; Yan Chao ; Almeida João ; Tröstl Jasmin ; Nieminen Tuomo ; Ortega Ismael K. ; Wagner Robert ; Adamov Alexey ; Amorim Antonio ; Bernhammer Anne-Kathrin ; Bianchi Federico ; Breitenlechner Martin ; Brilke Sophia ; Chen Xuemeng ; Craven Jill ; Dias Antonio ; Ehrhart Sebastian ; Flagan Richard C. (2016)

Atmospheric aerosols and their effect on clouds are thought to be important for anthropogenic radiative forcing of the climate, yet remain poorly understood. Globally, around half of cloud condensation nuclei originate from nucleation of atmospheric vapours. It is thought that sulfuric acid is essential to initiate most particle formation in the atmosphere and that ions have a relatively minor role. Some laboratory studies, however, have reported organic particle formation without the intentional addition of sulfuric acid, although contamination could not be excluded. Here we present evidence for the formation of aerosol particles from highly oxidized biogenic vapours in the absence of sulfuric acid in a large chamber under atmospheric conditions. The highly oxygenated molecules (HOMs) are produced by ozonolysis of $\alpha$-pinene. We find that ions from Galactic cosmic rays increase the nucleation rate by one to two orders of magnitude compared with neutral nucleation. Our experimental findings are supported by quantum chemical calculations of the cluster binding energies of representative HOMs. Ion-induced nucleation of pure organic particles constitutes a potentially widespread source of aerosol particles in terrestrial environments with low sulfuric acid pollution.