Study Says Growing Corn Is A Major Contributor To Air Pollution

An aerial view of a combine harvesting corn in a field near Jarrettsville, Md. A new study ties an estimated 4,300 premature deaths a year to the air pollution caused by corn production in the U.S. CREDIT: Edwin Remsburg/Getty Images
An aerial view of a combine harvesting corn in a field near Jarrettsville, Md. A new study ties an estimated 4,300 premature deaths a year to the air pollution caused by corn production in the U.S. CREDIT: Edwin Remsburg/Getty Images

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BY JONATHAN LAMBERT

You’ve probably heard statistics about how our diet affects the health of the planet. Like how a beef hamburger takes considerably more water and land to produce than a veggie burger or that around a quarter of global greenhouse gas emissions stem from food production. In fact, there are websites that can calculate the carbon footprint of specific foods.

But you may not have considered how the food we eat contributes to the quality of the air we breath.

Air pollution is the largest environmental health risk factor in the United States, and agriculture contributes in a number of ways. Fertilizer application, gas use, pesticide production and dust kicked up from tilling all affect air quality. But the sort of accounting done for the carbon footprint of foods hasn’t been done for their air pollution footprint.

That changed Monday with a study published in Nature Sustainability. It modeled how the production of a single crop, corn, contributes to air pollution in the United States. The researchers found that corn production accounts for 4,300 premature deaths related to air pollution every year. Ammonia from fertilizer application was by far the largest contributor to corn’s air pollution footprint.

“If you want to do anything about air pollution, you need to know the cause,” says Susanne Bauer, a climate modeler at the Earth Institute at Columbia University, who was not involved in the study. “This is an important study because instead of just saying air pollution kills people, it’s detailing the specific contributions of different parts of the corn production process to air pollution.”

Corn is the largest agricultural crop in the United States. But you may not immediately associate air pollution with the endless fields of rolling green in Iowa or Illinois. That’s a mistake, according to study author Jason Hill, an engineering professor at the University of Minnesota.

Previous work has found that agricultural practices — like fertilizer production, running tractors and tilling land — account for about 16 percent of all human-caused air pollution of a type called PM2.5. Atmospheric particulate matter with a diameter smaller than 2.5 micrometers (for comparison, a human hair is about 50 micrometers wide) is classified as PM2.5, and exposure has been associated with cardiovascular problems, respiratory illness, diabetes and even birth defects.

Hill and his colleagues wanted to understand how the various stages of corn production fit into this picture. “Does most of the impact from corn production happen on the farm or upstream in the supply chain — the locations that feed activities on the farm?” asks Hill.

To find out, they used a detailed life cycle model that describes the different stages of the corn supply chain. They analyzed every stage of the process — fertilizer production, fuel and electricity use, transportation and distribution, on-farm activity — and calculated which contribute to PM2.5 emissions.

The researchers fed the model with publicly available data on corn yields and manure and synthetic fertilizer usage from corn-producing counties in the U.S., giving them an estimate of the total emissions caused by corn production.

However, not all the emissions it takes to produce a bushel of corn in, say, Stearns County, Minn., are emitted there. “Growing corn in Minnesota results in emissions in Florida, where phosphate fertilizer is produced,” among other places, says Hill. Their model accounts for where the fuel, fertilizer and other upstream processes occur.

With these data in hand, the researchers modeled how corn production emissions contribute to air pollution on a county-by-county basis and mapped those data onto census data to understand who’s exposed to these emissions.

Finally, they used existing research on the health effects of different exposure levels to estimate how many premature deaths per year (out of an estimated 102,000 deathsfrom domestic human-caused emissions in the U.S.) could be ti