Abstract
Abstract. Ternary aerosol nucleation experiments were conducted in the CLOUD chamber at CERN in order to investigate the influence of ions on new particle formation. Neutral and ion-induced nucleation experiments, i.e. without and with the presence of ions, respectively, were carried out under precisely controlled conditions. The sulfuric acid concentration was measured with a chemical ionisation mass spectrometer (CIMS) during the new particle formation experiments. The added ternary trace gases were ammonia (NH3), dimethylamine (DMA, C2H7N) or oxidised products of pinanediol (PD, C10H18O2). When pinanediol was introduced into the chamber, an increase in the mass spectrometric signal used to determine the sulfuric acid concentration (m/z 97, i.e. HSO4−) was observed due to ions from the CLOUD chamber. The enhancement was only observed during ion-induced nucleation measurements by using either galactic cosmic rays (GCRs) or the proton synchrotron (PS) pion beam for the ion generation, respectively. The ion effect typically involved an increase in the apparent sulfuric acid concentration by a factor of ~ 2 to 3 and was qualitatively verified by the ion measurements with an atmospheric-pressure interface-time of flight (APi-TOF) mass spectrometer. By applying a high-voltage (HV) clearing field inside the CLOUD chamber, the ion effect on the CIMS measurement was completely eliminated since, under these conditions, small ions are swept from the chamber in about 1 s. In order to exclude the ion effect and to provide corrected sulfuric acid concentrations during the GCR and PS beam nucleation experiments, a parameterisation was derived that utilises the trace gas concentrations and the UV light intensity as input parameters. Atmospheric sulfuric acid measurements with a CIMS showed an insignificant ion effect.
Highlights
Atmospheric aerosols have an important effect on clouds and climate, with secondary aerosol particles contributing significantly to the global concentration of cloud condensation nuclei (CCN) via new particle formation (Kulmala et al, 2004; Merikanto et al, 2010)
Ternary aerosol nucleation experiments were conducted in the CLOUD chamber at CERN in order to investigate the influence of ions on new particle formation
With the initial experimental conditions established in the chamber with constant SO2 and O3 concentration, temperature (T ), relative humidity (RH) and stable UV lamp operation, a stable sulfuric acid concentration is typically reached within about 15 min after opening the shutter of the UV light source
Summary
Atmospheric aerosols have an important effect on clouds and climate, with secondary aerosol particles contributing significantly to the global concentration of cloud condensation nuclei (CCN) via new particle formation (Kulmala et al, 2004; Merikanto et al, 2010). From both field and laboratory measurements, it has been well established that sulfuric acid (H2SO4) plays a crucial role in atmospheric nucleation (Curtius, 2006; Riipinen et al, 2007; Kuang et al, 2008). One goal of the CLOUD (Cosmics Leaving OUtdoor Droplets) experiment
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