The following sources of atmospheric releases (emissions) on the CERN sites are monitored:
Ventilation of accelerator installations
Cooling of accelerator installations
Industrial activities
Heating plants
Ventilation of CERN accelerator installations
Ventilation of accelerator installations
Accelerator installations (accelerators, experimental halls, transfer tunnels, etc.) need continuous ventilation and air renewal especially in closed areas like tunnels. The ventilation systems maintain the required air temperature and humidity suitable for operating the installed devices and for removing possible pollutants.
High-energy particle beams may induce two types of pollution:
Radioactivity
Ozone and nitrogen oxides
Radioactivity is either created in air by direct nuclear interactions of high-energy particles, or gets into the air from other targets in the form of fragments, as aerosol (air contamination by dust) or as volatile fraction (tritium, 75Se, radioactive iodine, etc.).
Ozone is created by radiolysis of oxygen molecules resulting from ionising radiation. Ozone can then oxidise nitrogen and produce nitrogen oxides (NO, NO2).
The accelerator ventilation systems work at under-pressure regime: the air supplied from outside, may be conditioned, passes through the installation premises, and is finally released in a controlled way from ventilation outlets. All ventilation outlets are equipped with monitoring stations that measure radioactive emissions.
So far, the CERN monitoring programme which measures ozone and nitrogen oxides has not observed any effect of the CERN accelerators operations on the quality of released air. The concentrations of ozone and nitrogen oxides at the monitoring stations are comparable to those detected at locations far from any accelerators (ROPAG* stations in Meyrin and Passeiry). They, thus, reflect the influence of other sources than accelerators such as sunshine, heating, traffic, etc.
* Réseau d'Observation de la Pollution Atmosphérique à Genéve
CERN air monitoring station (immissions)
Ventilation monitoring station (emissions)
Cooling of accelerator installations
Some of the accelerator installations are cooled in closed circuit with demineralized water that is directly in contact with the devices to be cooled (primary closed circuit). Raw water is used to cool the warm demineralized water (secondary semi-closed circuit). The warmed-up raw water is finally brought back to its initial temperature by passing through cooling towers before it returns into the cooling system. The atmospheric discharges of cooling towers consist solely of water vapour. In conformity with the legislation in force, water in CERN's cooling towers is checked regularly for the Legionella bacteria. Preventive treatments with biocides are regularly carried out.
CERN atmospheric refrigerants towers
Industrial activities
A limited number of industrial-like activities, which may result in the emissions of pollutants mostly via the ventilation systems of various workshops, are carried out on the CERN sites. The main industrial pollutants are: acids and cynides vapours coming from electroplating baths, vapours from baths with solvents (e.g. alcohol, perchloroethylene), gaseous effluents of welding and exhausts of oil vacuum pumps (hydrocarbons). Technical systems are set up to minimize the extent of these emissions.
Ventilation outlet of a workshop
Heating plants
CERN has two heating plants which are operated with natural gas. One is located on the Meyrin site (CH) and has an annual gas consumption of about 8 million m3. The second is located on the Prévessin site (F) and has an annual gas consumption of about 1.5 million m3. Both plants are operated by external companies who carry out the necessary controls and adjustments to keep the emissions of dust, CO, CO2, nitrogen oxides and sulphur oxides within the limits fixed by the Host States regulations.
Ventilation outlet chimney of Meyrin heating plant
