Farming is the biggest single cause of the worst air pollution in Europe, a new study has found, as nitrogen compounds from fertilisers and animal waste drift over industrial regions.
When the nitrogen compounds are mixed with air already polluted from industry, they combine to form solid particles that can stick in the fine lung tissue of children and adults, causing breathing difficulties, impaired lungs and heart function, and eventually even premature death.
The compounds come from nitrogen-rich fertilisers, which have been in common use for decades. Nitrogen, the major content of the air we breathe, is essential for plant growth, and enhancing that growth has led to a massive industry in putting nitrogen – already naturally present in soils – back into the ground in greater quantities.
Ammonia, whose chemical composition is nitrogen and hydrogen (NH3), is a byproduct both of fertilised fields and of animal waste, as it can come from the breakdown of livestock excretions.
Links between fine particulate pollution and ammonia from agricultural sources have been slow to be firmly established, but an increasing body of research suggests that this is now a leading source of air pollution.
Europe, much of the US, Russia and China have been found to suffer from the problem, in the latest research from the Earth Institute at Columbia University, in the US, published in the journal Geophysical Research Letters.
When ammonia in the atmosphere reaches areas of industry, the pollutants from combustion, which include nitrogen oxides produced by diesel vehicles, and sulphur compounds from power plants and some other industrial processes, the chemicals combine to create very small particles, about 2.5 micrometres across.