Ammonium nitrate goes on the piste
Swiss winter sports event organisers, troubled by unseasonably warm temperatures, have caused an environmental stir by using chemical fertilisers to maintain their precious slopes.
They were praying for snow, but organisers of the Lauberhorn downhill ski race in Switzerland caused a storm of the media variety after it emerged that up to 1.5 tonnes of ammonium nitrate was used to prepare and protect the piste. Environmental researchers are now investigating the extent and effects of this practice.
As with any salt, dissolving ammonium nitrate involves breaking it into its constituent ammonium and nitrate ions, which takes in energy from its surroundings. The formation of new bonds between these ions and surrounding water molecules then releases energy. But since ammonium and nitrate ions are relatively large, the water molecules have relatively weak interactions with their diffuse charges. So with little thermodynamic payback during this bond formation, the immediate effect of adding ammonium nitrate to slushy snow is to cool it down.
Christian Rixen from the Swiss Federal Research Institute told Chemistry World that, since the effect of ammonium nitrate is relatively short-lived, the practice is not used on normal ski runs but reserved specifically for races where wet snow can slow skiers down. But Rixen’s research has highlighted some of the environmental risks of this practice.
’This is a very strong fertilizer. At high elevation, you have alpine meadows with vegetation that lives within nutrient-poor soil. If this is highly fertilized it can have negative effects,’ said Rixen, who explains that fertilisation can help just a few species to dominate the meadows. ’We have already seen that a single application of ammonium nitrate can cause a reduction in biodiversity,’ he said.
The practice has also raised questions about the contamination of waterways. ’It could even be a problem for organic farmers in the area, who are not allowed to use any chemicals at all on their land,’ added Rixen.
He is now working closely with the Swiss Federal office for the environment and says that more information is urgently needed about how widespread this practice is. ’This is a growing concern. Climate change may be creating a need for more of these chemicals to be used,’ he said.
Agricultural use of chemical fertilisers is already subject to detailed guidelines, including regulations barring its use at high altitudes and on snow-covered fields.
Daniel Hartmann from the Swiss Federal Office for the Environment told Chemistry World that, although there is general legislation to govern all use of chemicals, no specific rules exist controlling the use of fertilizers on ski slopes.
’There are many rules to control its agricultural use because farming is such a chemically-intensive practice,’ he explained. ’We need to find out more about how widely these chemicals are used on ski slopes and, if necessary, review the policy and define rules to be put in place to protect the environment.’