CLOUD experiment

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From NASA and from data from multiple satellites compiled representation of the earth. a. with cloud cover, vegetation and increased aerosol concentration over Africa (due to sandstorms and fires).

CLOUD ( acronym for English Cosmics Leaving OUtdoor Droplets ) is a project in which with laboratory methods in nuclear research facility CERN , the influence of ions on the nucleation of aerosols under atmospheric is investigated conditions. Due to the support from the pot cooperation of the 7th Framework Program of the EU (2007 to 2013) 106 scientists from 18 institutes from nine mostly European countries are involved (as of 2013). Further funds come from the CERN budget and national research funding in Germany, Switzerland and Finland.

The background to this is the controversial explanation of the long-suspected influence of solar activity on the lower layers of the earth's atmosphere through corresponding fluctuations in cosmic radiation, the rate of nucleation and cloud cover, propagated in 1997 by the Danish scientists Henrik Svensmark and Eigil Friis-Christensen ; See Global Warming Controversy for more details .

First results showed that under environmental conditions different substances contribute competitively to nucleation and that under some conditions ions play an important role.

Planning and implementation

The experiment was conceived in 1998 and is currently directed by particle physicist Jasper Kirkby . EU funding from 2007 was approved in 2006. A first prototype ( Mk1 prototype with 2 × 2 × 2 m 3 volume) was tested from the end of 2006. After three years of design and construction, the CLOUD chamber ( Mk2 prototype , 26 m 3 ) was built in the second half of 2009. At the end of 2009, the international teams were able to start measurement campaigns .

After two to three years of experience with the second chamber, an even larger third chamber should be built (as of 2008), but this has not yet been implemented (as of 2014).

Experimental setup

The CLOUD experiment is housed in the East Area of ​​the Proton Synchrotron (PS) at CERN .

CLOUD chamber
( Mk2 prototype )
Link to the schematic structure ( Memento from December 12, 2012 in the Internet Archive )
Link to the overall structure at CERN
( note copyrights! )

The so-called CLOUD chamber in the east hall of the CERN Proton Synchrotron (PS) currently ( Mk2 prototype ) consists of an electropolished stainless steel cylinder with a diameter of 3 m and a capacity of 26.1 m 3 in a climatic chamber for initially −30 up to 40 ° C, now upgraded down to −65 ° C. A gas mixing system doses artificial air from liquid nitrogen, liquid oxygen and deionized, purified water. This is the only way to achieve a sufficiently low level of contamination. Ozone is generated in part of the oxygen flow by an ozonizer when required . Other trace gases are added from steel cylinders in which the substances for manageable substance flows are in high dilution.

For experiments in ionized air, air showers are generated whose primary particles are high-energy protons from the storage ring. They are decoupled in packages upon request. Mainly pions get into the chamber and ionize air molecules there . The thermalized electrons preferentially attach to the sulfuric acid molecule used in the experiments . The ions can be withdrawn within a second by building up an electrical field strength of 10 kV / m between two grid-shaped electrodes above and below . To stimulate photochemistry , irradiation with UV light (250–400 nm) is possible via light guides that end evenly distributed in the lid. Fans in the chamber ensure that the dosed mixture, ions and reaction products are evenly distributed.

Through finger-thick Teflon tubes that protrude into the side of the chamber, sample streams from the artificial atmosphere are continuously and quickly passed past the analysis devices in order to keep falsifications to a minimum. For many analyzes it is important that the hoses do not have a different temperature outside the climatic chamber. For this purpose, they are thermally connected to the climatic chamber via copper wires and are well insulated. The instruments include several ( time-of-flight ) mass spectrometers with different interfaces (CI, chemical ionization , PTR, proton transfer , APi, Atmospheric Pressure Interface ) for measuring neutral and charged molecules and particles up to about two nanometers in diameter, and condensation particle counters down to two three nanometers, differential mobility analyzers, a spectrophotometer with long-path absorption cell (LOPAP) and humidity sensors.

The chamber is usually operated in the flow and always kept under a slight overpressure to prevent the ingress of contaminants, e.g. B. via analytics to avoid. In an alternative mode of operation, the mixture is prepared at an increased pressure and then expanded in a short time in order to achieve supersaturation through the associated cooling.

Results

In February 2010 the results of a 4-week test run of the pilot system ( Mk1 prototype ) were presented in October 2006. They indicated an existing connection between ion-induced condensation nucleation and the formation of aerosols. For a precise quantification of the conditions under which this aerosol formation reached a significant size, improvements to the experimental setup were necessary, which were incorporated into the construction of the 2nd CLOUD chamber ( Mk2 prototype ).

The first results with the Mk2 prototype were published in 2011 in the journal Nature (short summaries in naturenews-online and the CERN press release ) and, as CERN Director General Rolf-Dieter Heuer warned, contained clear representations of the test data without any interpretation regarding a possible Climate impact.

A reinforcing effect of the ionizing cosmic radiation on the agglomeration of aerosol particles in the simulated colder layers of the middle troposphere could be clearly demonstrated. The ionized molecule clusters from sulfuric acid showed a 10 times higher nucleation rate than electrically neutral clusters. For the lower atmospheric layers up to 1000 m it could also be shown that the prevailing assumption that sulfuric acid, ammonia and water vapor are the only aerosol particles responsible for the formation of condensation nuclei does not apply . Under the laboratory conditions, only a 10 to 1000 times smaller nucleation rate of condensation nuclei with these components could be registered than is observable overall in these atmospheric layers. The researchers suspected volatile organic compounds (VOC) to be another important ingredient.

Amines were examined first because they bind to sulfuric acid even more strongly than ammonia. However, these substances are found in much lower concentrations in the environment, 3 pptv . Thanks to the high-purity chamber and more sensitive analysis, it was possible to work with such concentrations. In October 2013, results with dimethylamine were published in the science journal Nature . Compared to the previous experiments with ammonia, the rate of nucleation was now in the correct order of magnitude and was hardly dependent on the presence of ions.

The researchers admit that competing nucleation processes with other vapors are more dependent on ionization or that ions intervene directly in cloud physics rather than via nucleation.

Further experiments address the role of the VOC. The model substance used is higher oxidation products of α-pinene , which are generated photochemically in the experiment . Due to their polar character, they are much less volatile than the α-pinene and other monoterpenes that are emitted by plants (especially pine trees ) in summer . The fact that they contribute to aerosol formation has long been known from smog chamber experiments. The extremely low concentrations required for environmentally relevant nucleation rates under controlled conditions, from 0.1 pptv, show that these substances can play an important role regionally in nucleation and growth. A research group produced the lowest concentrations of higher oxidation products of α-pinene by starting from an initial stable oxidation product, pinanediol , which they added. In combination with traces of sulfuric acid, an intensifying influence of ions was shown: In the case of environmentally relevant concentrations of trace gases and ions (lower troposphere), ions were involved in the formation of 60% of the germs. At higher ion concentrations (upper troposphere) it was 70%. The influence (as expected) decreased drastically with higher trace gas concentrations. Another study started out classically from α-pinene, albeit from particularly low concentrations, and observed a very rapid formation of higher oxidation products, which they interpret as an intramolecular chain reaction. At higher concentrations, this would break off prematurely due to bimolecular reactions. The ionization by pions from the storage ring, which was also used in these experiments, was used for analysis, because the simultaneous measurement of positive, negative and neutral clusters (with the above-mentioned inorganic ions) with three high-resolution TOF mass spectrometers improves the differentiation of species with the same mass number.

In a work published in 2016, the authors write that based on the CLOUD experiments, it can be determined that changes in the intensity of cosmic rays have no noticeable influence on current climate events.

Web links

Individual evidence

  1. ↑ Participating Institutes PS215 (CLOUD) . CERN GreyBook.
  2. ↑ Funding. CERN, 2010, archived from the original on September 22, 2013 ; accessed on June 21, 2016 (English).
  3. ↑ B. Fastrup et al. (CLOUD Collaboration): A Study of the link between cosmic rays and clouds with a cloud chamber at the CERN PS. (PDF; 1.5 MB) CERN 2000, CERN-SPSC-2000-021, SPSC-P317, pp. 1–32, arxiv : physics / 0104048 .
  4. ↑ Jasper Kirkby: Beam Measurements of a CLOUD (Cosmics Leaving OUtdoor Droplets) Chamber. CERN 1998, CERN-OPEN-2001-028.
  5. ↑ 2007 PROGRESS REPORT ON PS215 / CLOUD. The CLOUD Collaboration, CERN, Geneva, SPS and PS Experiments Committee, CERN-SPSC-2008-015 / SPSC-SR-032, April 18, 2008 ( PDF )
  6. ↑ 2009 PROGRESS REPORT ON PS215 / CLOUD. The CLOUD Collaboration, CERN, Geneva, SPS and PS Experiments Committee, CERN-SPSC-2010-013 / SPSC-SR-061, April 7, 2010 ( PDF )
  7. ↑ J. Duplissy et al .: Results from the CERN pilot CLOUD experiment. In: Atmospheric Chemistry and Physics. 10, 2010, pp. 1635-1647. ( PDF )
  8. ↑ 2006 PROGRESS REPORT ON PS215 / CLOUD. The CLOUD Collaboration, CERN, Geneva, SPS and PS Experiments Committee, CERN-SPSC-2007-014 / SPSC-SR-019, April 12, 2007 ( PDF )
  9. ↑ Jasper Kirkby et al .: Role of sulfuric acid, ammonia and galactic cosmic rays in atmospheric aerosol nucleation . In: Nature . tape 476 , 2011, p. 429-433 , doi : 10.1038 / nature10343 .
  10. ^ Cloud formation may be linked to cosmic rays. NatureNews Online August 24, 2011.
  11. ↑ CERN's CLOUD experiment provides unprecedented insight into cloud formation. CERN Press Release PR15.11 August 25, 2011.
  12. ↑ How "Illuminati" helped the Cern researchers. Welt Online , July 15, 2011, quote: “I asked my colleagues to present the results clearly but not to interpret them. That would immediately put you in the highly political arena of the climate change discussion. "
  13. ↑ J. Almeida et al. (CLOUD collaboration): Molecular understanding of sulphuric acid-amine particle nucleation in the atmosphere . In: Nature (Letter) . October 6, 2013. ISSN  0028-0836 . doi : 10.1038 / nature12663 .
  14. ↑ CERN Press Office: CERN's CLOUD experiment shines new light on climate change. October 6, 2013.
  15. ↑ Molecular understanding of sulphuric acid-amine particle nucleation in the atmosphere. (pdf; 63 kB) CLOUD Collaboration, October 6, 2013, archived from the original on November 1, 2014 ; accessed on June 21, 2016 (English, Supporting information to press briefing on Nature publication Almeida et al.).
  16. ↑ CLOUD Collaboration: 2011 PROGRESS REPORT ON PS215 / CLOUD . March 2012.
  17. ↑ Francesco Riccobono et al .: Oxidation Products of Biogenic Emissions Contribute to Nucleation of Atmospheric Particles . Science 344, 2014, pp. 717-721, doi : 10.1126 / science.1243527 .
  18. ↑ Arnaud P. Praplan et al .: Elemental composition and clustering behavior of α-pinene oxidation products for different oxidation conditions . Atmos. Chem. Phys. 15, 2015, pp. 4145-4159, doi : 10.5194 / acp-15-4145-2015 .
  19. ↑ EM Dunne, H. Gordon, A. Kurten, J. Almeida, J. Duplissy: Global atmospheric particle formation from CERN CLOUD measurements . In: Science . tape 354 , no. 6316 , December 2, 2016, ISSN  0036-8075 , p. 1119–1124 , doi : 10.1126 / science.aaf2649 ( sciencemag.org [accessed June 12, 2019]).