Ion-induced nucleation of pure biogenic particles

TLDR

Atmospheric aerosols influence cloud formation and climate, yet their role remains poorly understood; roughly half of cloud condensation nuclei arise from vapor nucleation, which is thought to require sulfuric acid, though ions are considered minor, and some laboratory studies have reported organic particle formation without added sulfuric acid, though contamination cannot be ruled out. This study provides evidence that aerosol particles can form from highly oxidized biogenic vapours without sulfuric acid in a large chamber under atmospheric conditions. In the chamber, highly oxidized molecules produced by ozonolysis of α‑pinene were examined, and quantum‑chemical calculations of cluster binding energies supported the nucleation mechanism. Ions from Galactic cosmic rays increased the nucleation rate by one to two orders of magnitude, indicating that ion‑induced nucleation of pure organic particles could be a widespread source in low sulfuric‑acid environments.

Abstract

Abstract Atmospheric aerosols and their effect on clouds are thought to be important for anthropogenic radiative forcing of the climate, yet remain poorly understood 1 . Globally, around half of cloud condensation nuclei originate from nucleation of atmospheric vapours 2 . It is thought that sulfuric acid is essential to initiate most particle formation in the atmosphere 3,4 , and that ions have a relatively minor role 5 . Some laboratory studies, however, have reported organic particle formation without the intentional addition of sulfuric acid, although contamination could not be excluded 6,7 . 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 α-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.