According to a study led by environmental scientists at Rice University's George R. Brown School of Engineering, nitrogen emissions are responsible for a higher proportion of pollutants. Agricultural pollution originates in the prairie, but its economic impact on humans is a concern for cities.
A study led by environmental scientists at Rice University's George R. Brown School of Engineering quantifies the impact of reactive nitrogen species produced in American croplands.
The study, led by associate professor of civil and environmental engineering Daniel Cohan and graduate student Lina Luo, quantifies nitrogen oxide, ammonia, and nitrous oxide emissions from fertilized soils over three years (2011, 2012, and 2017) and compares their impacts on air quality, health, and climate by region.
While seasonal and regional impacts vary by emission type, the study found that total annual damages from ammonia were much higher — $72 billion — than those from nitrogen oxides ($12 billion) and nitrous oxide ($13 billion).
Air pollution damages are measured by increased mortality and morbidity, as well as the monetary value of statistical life, whereas climate change damages include threats to crops, property, ecosystem services, and human health.
On that basis, the researchers discovered that the health impact of ammonia and nitrogen oxides, which react to form particulate matter and ozone, outweighed the climate impact of nitrous oxide in all regions and years.
Agriculture-heavy regions of California, Florida, and the Midwest incurred the highest social costs, as ammonia and nitrogen oxides polluted the air upwind of population centres. Emissions of both pollutants peak in the spring after fertilizers are applied.
The study, published in the American Chemical Society journal Environmental Science & Technology, concludes that future assessments of how farming practices affect reactive nitrogen emissions should take into account air pollution, health, and climate.
"We always talk about how carbon dioxide and methane contribute to greenhouse gases, but nitrous oxide is about 300 times more potent in terms of global warming potential than carbon dioxide," Luo said.
She pointed out that farming practices that reduce greenhouse gas emissions can increase air pollution and vice versa. "We need to see if they can reduce all three nitrogen species — or make some tradeoffs — without reducing crop yield," Luo explained.
Cohan added that nitrogen is essential for crop growth, but the study shows that the importance of controlling agricultural emissions has been largely overlooked by air quality management and climate policy, even as the EPA considers tightening air quality standards and the Biden administration seeks to reduce greenhouse gas emissions.
According to him, federal agencies have focused on reducing transportation and industrial emissions, leaving agriculture as the leading source of harmful nitrogen pollutants in the United States, a problem exacerbated by climate change and increased crop production.
