Aerosol nucleation measurements from the CLOUD experiment at CERN
Abstract
Globally, a significant source of cloud condensation nuclei is thought to originate from the nucleation of trace sulphuric acid vapour (H2SO4). Despite an extensive research effort, questions remain about the nucleation mechanism and the influence of cosmic rays. Here we present the first results from the CLOUD experiment at CERN. We find that cosmic ray ionisation substantially increases the nucleation rate of sulphuric acid particles. For mid-tropospheric temperatures, typical atmospheric concentrations of H2SO4 and H2O are sufficient for nucleation to take place via the ion-induced binary mechanism. However, for boundary-layer temperatures, even in the presence of ions, the concentrations of H2SO4 required for nucleation are well above atmospheric values, indicating that additional compounds must be participating in the boundary layer. Our measurements of the growing sulphuric acid clusters reveal that they are stabilised by the stepwise accretion of nitrogen-containing molecules: ammonia, amines or urea. This N-stabilisation mechanism may help explain seemingly conflicting laboratory experiments and atmospheric observations. Our results constitute quantitative measurements of purely-neutral and ion-induced nucleation of sulphuric acid particles. Furthermore, in the CLOUD experiment, chemical composition of the growing clusters and the nucleation mechanism at the molecular level is revealed.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.A32D..03C
- Keywords:
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- 0305 ATMOSPHERIC COMPOSITION AND STRUCTURE / Aerosols and particles;
- 0335 ATMOSPHERIC COMPOSITION AND STRUCTURE / Ion chemistry of the atmosphere;
- 0394 ATMOSPHERIC COMPOSITION AND STRUCTURE / Instruments and techniques;
- 3311 ATMOSPHERIC PROCESSES / Clouds and aerosols