In Denmark approximately 3,400 people die annually due to air pollution, according to an article in the national daily newspaper, Morgenavisen Jyllands-Posten on 28 March 2011.

Senior scientist Jørgen Brandt from the National Environmental Research Institute is cited as saying that agriculture is the dominant sector when it comes to the effect of air pollution on human health. He reports that the detrimental health effects due to air pollution from agriculture are twice as high as from traffic.

Agriculture's major contributor to air pollution is emission of ammonia. There is, however, help to be found, according to research by Jørgen E. Olesen from the Department of Agroecology and Environment at Aarhus University.

"There are plenty of technological solutions that can reduce ammonia emissions from agriculture," Professor Olesen.

Several sources of ammonia

Agricultural ammonia comes from animal housing, manure storage and manure application in the field. Denmark has regulations with regard to ammonia emission that apply when the farmer intends to expand or alter his animal production.

Professor Olesen said: "There are maximum levels with regard to how much ammonia an animal farm may emit and these regulations have become increasingly stricter. However, the regulations have been formulated to protect the environment, not human health,"

Suggesting practical solutions to the problem, he said: "Ammonia is emitted from animal houses and manure storage areas and when applying manure. All these sources must be plugged – and it is possible to do so."

Covering the slurry tank is one of the ways in which to limit evaporation of ammonia from agriculture
Photo: Jesper Rais, AU Communication

Sour slurry and floating covers

Professor Olesen continued: "Evaporation of ammonia from animal housing can be reduced by cleaning the ventilation air. This is an expensive solution. Another possibility is to acidify the slurry, which makes a big difference. Maintaining clean surfaces in the animal houses so they are not covered in manure also helps keep ammonia evaporation down, as does cooling the slurry and the floors."

Evaporation can also occur during storage of the manure or slurry. Regulations state that the storage facilities must be covered or, in the case of slurry, have a functional floating cover.

There is also a risk of ammonia evaporation in the field. This occurs when the farmer applies slurry as a crop fertiliser.

Professor Olesen also has a suggestion as to how to reduce ammonia evaporation in the field. He said: "Slurry injection helps but is not good to use in winter crops. Slurry acidification can probably reduce evaporation markedly. The disadvantage of acidification is that it makes it difficult to use the slurry for biogas production but otherwise acidification is a really good and relatively cheap solution."