Results from the CERN pilot CLOUD experiment

Abstract

Abstract. During a 4-week run in October-November 2006, a pilot experiment was performed at the CERN Proton Synchrotron in preparation for the Cosmics Leaving OUtdoor Droplets (CLOUD) experiment, whose aim is to study the possible influence of cosmic rays on clouds. The purpose of the pilot experiment was firstly to carry out exploratory measurements of the effect of ionising particle radiation on aerosol formation from trace H 2 SO 4 vapour and secondly to provide technical input for the CLOUD design. A total of 44 nucleation bursts were produced and recorded, with formation rates of particles above the 3 nm detection threshold of between 0.1 and 100 cm −3 s −1 , and growth rates between 2 and 37 nm h −1 . The corresponding H 2 SO 4 conCorrespondence to: J. Duplissy (jonathan.duplissy@cern.ch) centrations were typically around 10 6 cm −3 or less. The experimentally-measured formation rates and H 2 SO 4 concentrations are comparable to those found in the atmosphere, supporting the idea that sulphuric acid is involved in the nucleation of atmospheric aerosols. However, sulphuric acid alone is not able to explain the observed rapid growth rates, which suggests the presence of additional trace vapours in the aerosol chamber, whose identity is unknown. By analysing the charged fraction, a few of the aerosol bursts appear to have a contribution from ion-induced nucleation and ion-ion recombination to form neutral clusters. Some indications were also found for the accelerator beam timing and intensity to influence the aerosol particle formation rate at the highest experimental SO 2 concentrations of 6 ppb, although none was found at lower concentrations. Overall, the exploratory measurements provide suggestive evidence for ion-induced nucleation or ion-ion recombination as sources of aerosol Published by Copernicus Publications on behalf of the European Geosciences Union. particles. However in order to quantify the conditions under which ion processes become significant, improvements are needed in controlling the experimental variables and in the reproducibility of the experiments. Finally, concerning technical aspects, the most important lessons for the CLOUD design include the stringent requirement of internal cleanliness of the aerosol chamber, as well as maintenance of extremely stable temperatures (variations below 0.1 • C).

Thermodynamics of the formation of sulfuric acid dimers in the binary (H<sub>2</sub>SO<sub>4</sub>–H<sub>2</sub>O) and ternary (H<sub>2</sub>SO<sub>4</sub>–H<sub>2</sub>O–NH<sub>3</sub>) system

“…The data were fitted by simple power law fits, and the slopes of p = −1 (at 208 K) and p = −1.6 (at 223 K) indicate that the evaporation rates decrease significantly with increasing RH. Qualitatively this is in agreement with a previous experiment (Hanson and Lovejoy, 2006) and quantum chemical calculations (Ding et al, 2003). However, Hanson and Lovejoy (2006) reported p = −0.5, where the exponent p has an uncertainty of ±100 %.…”

“…In the absence of a clearing field, galactic cosmic rays produce ion pairs at a rate of ∼ 2 cm −3 s −1 . Much higher ion pair production rates can be achieved by illuminating a section of the chamber (approximately 1.5 m × 1.5 m) using a defocused pion beam from CERN's Proton Synchrotron (Duplissy et al, 2010). Ultraclean gas is provided to the chamber by mixing nitrogen and oxygen from cryogenic liquids at a ratio of 79 : 21.…”

Production of ozone and nitrogen oxides by laser filamentation

“…Rather, the observed effect may imply binary nucleation of HNO 3 , [14][15][16] which according to the extended Köhler theory stabilizes the growing droplets of binary mixtures, similar to observations in cloud chambers for binary H 2 SO 4 -H 2 O. 17,18 Assessing this pathway requires a precise knowledge of the physicochemistry of the filaments. In this paper, we measure the generation of three key gases, namely O 3 , NO, and NO 2 by laser filaments.…”

Solar Influence on Global and Regional Climates

“…The best chance of answering objection (1) is the CLOUD experiment at CERN (Duplissy et al 2010), which has just begun to study the ''ion-aerosol clear-air'' mechanism. The first results have just been published (Kirkby et al 2011).…”