Forget Cars: Cows And Fertilizer Could Be A Big Pollution Problem


At the beginning of the 20th century, two German chemists — Fritz Haber and Carl Bosch — figured out a way to produce ammonia cheaply, and on an industrial scale. Their process, known as the Haber-Bosch process, would go one to win Bosch a Nobel Prize, and completely change the world — it made producing synthetic fertilizers easy and affordable, which in turn helped boost global food production. Without the Haber-Bosch process, it’s estimated that about 40 percent of the human population would not be alive today.

But the use of widely-available fertilizer has also come with some considerable downsides. Fertilizer runoff making its way into streams, rivers, lakes, and oceans has contributed to algal blooms and oxygen-free “dead zones” across the United States, from the Gulf of Mexico to the Great Lakes. In Iowa, the Des Moines Water Works utility filed a federal lawsuit against three farm counties, claiming that the filtration technology required to strip the drinking water of nitrates from excess fertilizer runoff costs the utility between $4,000 and $7,000 a day.

Nobody wants to criticize food production, but we need to think about how we produce food

And it’s not just the water that is being polluted by fertilizer use. A new study published in Geophysical Research Letters found that fertilizer use — as well as animal agriculture — is a significant contributor to air pollution worldwide.


Susanne Bauer, an atmospheric scientist at Columbia University’s Center for Climate Systems Research and the NASA Goddard Institute for Space Studies, told ThinkProgress that she was interested in looking at agricultural air pollution because, unlike car pollution or pollution from combustion engines, it’s a sector that has not been looked at closely, especially on a global scale. Yet with a growing global population, agricultural air pollution — in the form of ammonia from fertilizer and livestock waste — is expected to increase, as farmers race to keep up with the growing demand for food.

“In this study, we wanted to shine a light on a sector that is not talked about a lot,” she said. “Nobody wants to criticize food production, but we need to think about how we produce food.”

When ammonia combines with other gaseous pollutants, like nitrogen oxides and sulfates from vehicles or power plants, it forms tiny particles, no larger than 2.5 micrometers across. These particles can be dangerous to public health, because they are so small that they can penetrate deep into lungs, causing pulmonary and heart disease. According to a 2015 study, some 3.3 million people each year die from these small particles globally.

Previous studies have looked at agricultural pollution, as it relates to these particles, but none have done so on a global scale. The study found that, globally, agricultural pollution becomes a much larger issue when it occurs in places that are already heavily polluted — places like the United States, Europe, and China. In places like Africa, where air pollution is already lower, air pollution from agriculture is less of a problem.

A world map shows main sources of fine-particulate pollution: natural (brown); industrial (red) and agriculture (green). CREDIT: Bauer et al., Geophysical Research Letters, 2016
A world map shows main sources of fine-particulate pollution: natural (brown); industrial (red) and agriculture (green). CREDIT: Bauer et al., Geophysical Research Letters, 2016

Bauer and her colleagues also studied what might happen to air pollution in the future. She said that in most future models, agricultural pollution is the only kind of pollution that is expected to increase — as food production rises to keep up with population growth. Other kinds of pollution — like car exhaust or power plant emissions — are expected to decrease, as technology progresses and policies are put in place to tamp down on pollution.


In modeling future pollution, Bauer thought that agricultural pollution increasing would be a problem. But she was surprised to learn that wasn’t necessarily the case.

“What is expected is that other pollutants go down in the future due to better technology, but agriculture goes up because population goes up,” she said. “I expected that this is becoming a major problem, but the study found the opposite. Yes, the amount of that particle is going up, but it’s not at surface levels [near the ground], it’s at higher levels [in the atmosphere].”

In the future, if technology and policies help decrease pollution from cars or power plants, gaseous ammonia from agricultural pollution won’t have other pollutants to combine with close to the ground, there particles pose the greatest threat to human health. Instead, the gases will combine with other, naturally-occurring gases higher in the atmosphere, which is not a public health threat. Bauer said that this scenario does result in more atmospheric pollution, but noted that that kind of pollution actually has a slightly cooling affect on the planet — though not enough to really put a dent in global warming.

Air Pollution Kills More People Than Malnutrition And Unsafe Sex, Scientists SayClimate by CREDIT: AP Photo/Luis M. Alvarez When Cecilia Salas sees fumes of agricultural burning rising in the horizon…thinkprogress.orgUltimately, Bauer said that the study underscores the need for farmers to be especially precise with the amount of fertilizer they apply to their fields. She noted that the places with the worst agricultural air pollution — countries like the United States or China — are relatively wealthy, and could probably withstand a drop in the amount of fertilizer used in food production.

“One thing that is very obvious is simply stopping the overuse of fertilizers,” she said. “If simply the right amount of fertilizers were to be used, that would be a big step that would improve air quality tomorrow.”

That doesn’t mean that all countries should stop using fertilizer immediately, however. Bauer noted that in places like Africa, where existing air pollution is relatively low, fertilizer could be used to help bolster food production without contributing too much to air pollution.

“This is not against fertilizers, it’s more against using it in very polluted areas, and in excess,” she said.

In the United States, the Department of Agriculture is already taking steps to help farmers become more precise in their application of fertilizer. As one of the ten Building Blocks for Climate Smart Agriculture & Forestry — the USDA’s grand plan to help address agriculture’s contribution to climate change — the department has already pledged $14.8 million to help curb fertilizer overuse in the Midwest. A more precise method of applying fertilizer could also help farmers reduce their overall costs, as they would need to purchase less fertilizer — and less of what they purchased would go to waste.

But stopping fertilizer overuse would not fix air pollution in and of itself, Bauer cautioned.

“We don’t want to pick out one sector and say, if you clean up that, everything is better,” she said. “The truth is that we have to clean up all of them.”