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Aug. 19, 2011

UI researcher finds link between soil nitrite and atmospheric detergent effect

Yafang Cheng, a University of Iowa post-doctoral researcher, and colleagues at the Max Planck Institute for Chemistry, Mainz, Germany, have found that soil nitrite can be released into the air in the form of nitrous acid (HONO) and indirectly enhance the self-cleansing capacity of the atmosphere.

The study is published in the Aug. 18 online edition of the journal Science (http://www.sciencemag.org/content/early/2011/08/17/science.1207687).

Hydroxyl radicals (OH) have long been known to serve as an atmospheric "detergent," which oxidizes air pollutants and makes them more easily washed out of the air. Atmospheric nitrous acid is an important source of OH, producing up to 30 percent according to field measurement data. However, the major source of HONO has been a mystery -- until now.

In laboratory studies, the researchers showed that soil nitrites -- produced by biogenic conversion of fertilizer -- emit significant amounts of HONO into the atmosphere. The result is a strong increase in the oxidizing capacity of the atmosphere.

The release of HONO from arable soils is particularly important in developing countries because of the increased use of fertilizers and soil acidification.

Cheng said that because eutrophication resulting from the use of farm fertilizers harms the environment in many ways, their research finding should be interpreted as showing that soil nitrite can buffer, in some respects -- but not counteract -- the overall impact of fertilizer application.

"Due to the widespread occurrence of nitrite-producing microbes and natural nitrogen nutrient in soil, the release of nitrous acid from soils may also be influential in natural environments, including forests and boreal regions," said Cheng, the lead author of the paper.

Cheng is a post-doctoral researcher studying under Greg Carmichael, UI professor of chemical and biochemical engineering in the College of Engineering and co-director of the Center for Global and Regional Environmental Research (CGRER).

Cheng's co-authors on the Science paper are: Hang Su, Robert Oswald, Thomas Behrendt, Ivonne Trebs, Franz X. Meixner, Meinrat O. Andreae, Peng Cheng, Yuanhang Zhang and Ulrich Pöschl. The paper is titled, "Soil nitrite as a source of atmospheric HONO and OH radicals."

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MEDIA CONTACT: Gary Galluzzo, 319-384-0009, gary-galluzzo@uiowa.edu