The Smog That Corn Makes

by Bill Chameides | April 29th, 2010
posted by Erica Rowell (Editor)

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Another black eye for corn and livestock: California smog?

Atmospheric chemists like to refer to the good and the bad ozone (O3).

Good ozone: This ozone is in the stratosphere (the atmospheric layer that starts about 10 miles above the earth’s surface), where among other things it prevents potentially harmful ultraviolet radiation from penetrating the surface.

Bad ozone: Ground-level ozone is a strong oxidant that can trigger a number of health problems when it comes into contact with living tissue like our lungs.

Ground-level ozone is one of the main, noxious components of photochemical smog, produced from reactions between two pollutants — nitrogen oxides (NOx) and reactive organic compounds — in the presence of sunlight.

How We Discovered Ozone’s Contribution to Smog Formation

A quick historical digression: Our basic understanding of how photochemical smog is formed is largely the result of a scientist working in Los Angeles in the 1940s and 1950s: Arie J. Haagen-Smit.

He observed that when exposed in illuminated chambers to various mixtures of air and car exhaust, stretched rubber bands cracked and broke, and reasoned that a strong oxidant like ozone must have been present in the exhaust, causing the deterioration of the rubber. When I met Haagen-Smit as I was a graduate student in the 1970s shortly before his death, he made an impression on me, but little did I know that his seminal work would become the foundation for much of my own scientific research in the decades to follow. (More on Haagen-Smit here [pdf].)

Just Discovered: A Brand New Source of the Ozone That’s Found in Smog

Traditionally, when we think of major sources of the bad-ozone-producing gases, automobiles and power plants come to mind — the main culprits behind much of our urban smog. Now a new paper by Cody Howard, of the University of California, Davis, and colleagues, appearing in this month’s journal Environmental Science & Technolgy, suggests another source: cattle feed.

And that returns us to California (home to the nation’s largest dairy industry [pdf]) — and more specifically the San Joaquin Valley, one of the world’s most productive agricultural regions and the source of almost 10 percent of our homegrown agriculture. It’s also a region that is consistently plagued by very high concentrations of ground-level ozone and, despite decades of air-pollution controls to mitigate the stuff, still ranks high on the country’s smoggiest-regions list.

How This New Discovery Took Place

Why is the smog so bad in the valley? The authors decided to look into the region’s agricultural activities because its population density pales next to urban areas with similar smog problems. Previous searches for a source had landed on cows and their waste, but “direct testing,” the authors write, suggested “that this initial estimate for dairy cattle waste is overstated since animal emissions do not contain [reactive organic compounds] with high ozone formation potential.”

And so, focusing on the area’s big industry of agriculture production, the authors conducted tests using essentially an updated version of Haagen-Smit’s chamber. The very significant difference is that today instead of rubber bands, scientists now use sophisticated sensors that can track a host of different gases and particles with very high precision and accuracy to assess ozone-forming potential. (More details here.)

But how to conduct tests on farming practices? Clearly, you can’t bring the farm into the laboratory. The solution is to go mobile — and bring the laboratory to the farm using miniature (by comparison) portable, smog chambers. And so the authors packed up their mobile smog chamber and visited one of the San Joaquin Valley’s commercial dairy farms, where they tested seven types of feed.

What the Researches Found Down on the Farm

The researchers’ measurements showed that emissions from cattle feed are very effective at producing ozone pollution. (The exposed feed vents reactive organic compounds to the atmosphere either in open trench silos or when the cows sup.)

The authors’ estimates of the total emissions from cattle feed led to a startling conclusion: collectively, cattle feed emissions produce almost twice as much of the San Joaquin Valley’s ground-level ozone as automobile emissions do.

And here’s the punch line. You know how corn has been under attack of late: accusations of unfair and ill-advised subsidies (see here and here), the dangers of high fructose corn syrup, and the environmental evils of corn ethanol (see here, here and here)? So what form of cattle feed do you think is the largest contributor of ozone-forming reactive organic compounds in the San Joaquin Valley? None other than corn silage. And get this: most of the emitted reactive organic compounds are in the form of alcohols. And the primary alcohol in the mix: ethanol. Would it be correct to call that corn ethanol?

Ironically, one of the initial reasons back in the ‘90s for brewing gasoline into ethanol (now a mighty recipient of biofuel subsidies) was that it would lead to less ozone air pollution. But that assertion turned out to be questionable. And now this.

Poor old corn just can’t catch a break. I guess the only way to make up for all this bad corn news is to increase the corn subsidy. In the world of Washington politics it makes a certain sense, don’t you think?

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1 Comment

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  1. Leonard Gianessi
    May 11, 2010

    The impact of agricultural operations on air quality in Caliufornia is under intense scrutiny. One source of airborne respirable dust particles is tillage operations that stir up the soil while removing weeds. A Study by UC-Davis researchers in the San Joaquin Valley determined that respirable dust production is 20% greater from organically grown corn and tomato crops compared to their conventionally grown counterparts. This increase is due to the reliance on tillage to remove weeds instead of herbicides which are used by the conventional growers with no need to stir up the dust. Reference: California Agriculture, Volume 51, Number 2,March-April 1997, p27.

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