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https://doi.org/10.5194/amt-2017-114
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
16 May 2017
Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Atmospheric Measurement Techniques (AMT).
Temperature uniformity in the CERN CLOUD chamber
Antonio Dias1, Sebastian Ehrhart1,2, Alexander Vogel1, Christina Williamson3,4, Joao Almeida1,5, Jasper Kirkby1,5, Serge Mathot1, Samuel Mumford1, and Antti Onnela1 1CERN, CH-1211 Geneva, Switzerland
2Max Planck Institute for Chemistry Atmospheric Chemistry Department Hahn-Meitner-Weg 1, 55128 Mainz, Germany
3CIRES, University of Colorado, Boulder, CO
4Chemical Sciences Division, NOAA Earth System Research Laboratory, Boulder, CO
5Goethe University Frankfurt, Institute for Atmospheric and Environmental Sciences, 60438 Frankfurt am Main, Germany
Abstract. The CLOUD (Cosmics Leaving OUtdoor Droplets) experiment at CERN is studying the nucleation and growth of aerosol particles under atmospheric conditions, and their activation into cloud droplets. A key feature of the CLOUD experiment is precise control of the experimental parameters. Temperature uniformity and stability in the chamber are important since many of the processes under study are sensitive to temperature and also to contaminants that can be released from the stainless steel walls by upward temperature fluctuations. The air enclosed within the 3 m CLOUD chamber is equipped with several arrays (strings) of high precision, fast-response thermometers to measure its temperature. Here we present a study of the air temperature uniformity inside the CLOUD chamber under various experimental conditions. Measurements were performed under calibration conditions and run conditions, which are distinguished by the flow rate of fresh air and trace gases entering the chamber: 20 l/min and up to 210 l/min, respectively. During steady-state calibration runs between −70 °C and +20 °C, the air temperature uniformity is better than +/−0.06 °C in the radial direction and +/−0.1 °C in the vertical direction. Larger non-uniformities are present during experimental runs, depending on the temperature control of the make-up air and trace gases (since some trace gases require elevated temperatures until injection into the chamber). The temperature stability is a few times 0.01 °C over periods of several hours during either calibration or steady-state run conditions. During rapid adiabatic expansions to activate cloud droplets and ice particles, the chamber walls are up to 10 °C warmer than the enclosed air. This results in larger non-uniformities while the air returns to its equilibrium temperature with time constant of about 200 s.

Citation: Dias, A., Ehrhart, S., Vogel, A., Williamson, C., Almeida, J., Kirkby, J., Mathot, S., Mumford, S., and Onnela, A.: Temperature uniformity in the CERN CLOUD chamber, Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2017-114, in review, 2017.
Antonio Dias et al.
Antonio Dias et al.
Antonio Dias et al.

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Short summary
The CERN CLOUD chamber aims to understand different processes of particle formation in the atmosphere. This information can be used by global climate models to update the influence of cloud formation. To provide the most accurate information on these processes, a thorough understanding of the chamber is necessary. Temperature measurements were preformed inside the whole volume of the CLOUD chamber to ensure temperature stability and more accurate estimations of particle formation parameters.
The CERN CLOUD chamber aims to understand different processes of particle formation in the...
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