The environmental interest in nitrogen (N2), an essential component of the air we breathe, focuses on the conversion of N2 into other chemically reactive forms. Some are vital for life itself and some cause costly and dangerous nitrogen pollution.
“Altogether, humans are producing a cocktail of reactive nitrogen that threatens health, climate and ecosystems, making nitrogen one of the most important pollution issues facing humanity,” the 2018-2019 Frontiers report warns. “Yet the scale of the problem remains largely unknown and unacknowledged outside scientific circles.”
The European Nitrogen Assessment identified five key threats of nitrogen pollution: water quality, air quality, greenhouse-gas balance, ecosystems and biodiversity.
Growing demand on the agriculture, transport, industry and energy sectors has led to a sharp growth in the levels of nitrogen pollution and related greenhouse gas emissions. Nitrous oxide (N2O) from industry and combustion, for example, is 300 times more powerful than carbon dioxide as a greenhouse gas.
“Human nitrogen additions to the soil, in the form of fertilizers, reinforce the greenhouse effect: around 60 per cent of nitrous oxide is emitted from fertilized fields, manures and other agricultural sources,” says Mahesh Pradhan, a nutrient pollution expert with the UN Environment Programme (UNEP).
Fertilizer run-off can also cause algal blooms in lakes and waterways. Algal blooms emit greenhouse gases.
Fossil fuel and biomass combustion processes release nitric oxide (NO) and nitrogen dioxide (NO2),collectively called NOx.While major efforts have been made to reduce NOx from vehicles and energy generation, emissions are still escalating in rapidly developing parts of the world. NOx is an indirect greenhouse gas, because the deposition of emitted NOx results in otherwise natural ecosystems emitting more nitrous oxide.
“It is just the same with ammonia (NH3) emissions from agriculture, which ultimately reach natural ecosystems, further increasing emissions of the greenhouse gas nitrous oxide, while degrading the biodiversity,” says Mark Sutton, an international expert on nitrogen at the United Kingdom Centre for Ecology & Hydrology in Edinburgh, Scotland.
“Ammonia reacts with the products of NOx to form secondary particulate matter (PM2.5). The resulting PM2.5 actually has a cooling effect on climate, as it scatters light and promotes cloud formation. We cannot count on this effect, however, because of the adverse effects of PM2.5 on human health, which exacerbate respiratory and coronary diseases,” says Sutton.
While relatively little research has been done specifically on how improved management of the nitrogen cycle can have beneficial effects in terms of mitigating global heating, experts believe practical steps are possible.
Changing attitudes to nitrogen in Scotland
“There are multiple pollution threats resulting from anthropogenic reactive nitrogen with adverse effects on the terrestrial freshwater and marine environment contributing to air pollution and greenhouse gas emissions,” says Sutton. “What is needed now is practical policies, and Scotland in the United Kingdom is one of a small number of countries taking up the challenge,” he adds.
“Scotland is one of the first countries to include a nitrogen budget in its 2019 Climate Change Bill,” says Keesje Avis, Senior Policy Officer with Nourish Scotland, a charity that has been raising awareness on this issue. “The Bill’s goal is to reduce Scotland’s net greenhouse gas emissions to net zero by 2045.”
Attitudes to nitrogen use in Scotland are changing as stakeholders realize its wider impacts. Nitrous oxide made up 7.9 per cent of Scotland’s greenhouse gas emissions in 2017, 81 per cent of which is from agriculture.
Half of the nitrogen applied in Scotland is being lost to the wider environment because it is unused. This is a waste of resources and farmers’ money.
According to Avis, “in Scotland, nitrogen-related emissions haven’t changed much since 2007, which shows that purely voluntary policies are not enough to create change.” He believes that trust is key: trust in individuals, the science and the desired outcomes—not just to tick boxes. Individuals are really important, too: there needs to be passion for the subject and to do what is right, not what is easy. He also advocates for the use of existing coalitions or organizations because there will already be trust there. A key message is that diffuse pollution is a loss to the system. Farmers want to be seen to be good at what they do—they don’t want to be losing nutrients and money unnecessarily.
“Recognizing the importance—and limitations—of nitrogen to our agricultural and environmental systems is crucial for the success of our farmers and to combat climate change,” says Avis.
“Change is always difficult but if you have the science and the will and finally trust in the policies, it can make for real change. But it does take time. Pressure also needs to come from a variety of places. Many of the actors involved in change in Scotland came from different places with a common goal. The bigger the variety of actors with a simple message, the greater the chance of success,” she says.