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Rising Levels of Ozone Could Reduce Soybean Harvests

A study published in the 14 March online early edition of New Phytologist suggests that rising levels of ozone starting at the Earth’s surface (tropospheric ozone) could reduce soybean harvests. Ozone is formed via the interaction of oxides of nitrogen (NOx) and sunlight.

Mean surface ozone concentration is predicted to increase 23% by 2050. The researchers increased the ozone concentration by 23% from an average daytime ambient 56 ppb to 69 ppb, and found that seed yield decreased by 20%.

FACE set-up for experimentation.

Researchers at the University of Illinois and US Department of Agriculture ARS used free-air gas concentration enrichment (FACE) technology for ozone fumigation of soybean crops over two growing seasons—the first such study using FACE with a foodcrop.

Prior studies on foodcrops have used chamber studies—small greenhouse-like enclosures that create conditions that are too different: warmer, less precipitation, more humid. A FACE study, however, uses a larger area, with no artificial enclosure.

Total above-ground net primary production decreased by 17% without altering dry mass allocation among shoot organs, except seed. Fewer live leaves and decreased photosynthesis in late grain filling appear to drive the ozone-induced losses in production and yield.

The team noted that yield losses with elevated ozone were greater in the second year following a severe hailstorm, suggesting that losses caused by ozone might be exacerbated by extreme climatic events.



Rafael Seidl

The second resource provided illustrates how crop yields increase with increased CO2 and drop with increased surface O3. Both gases are projected to increase, but these increases are not projected to be evenly distributed over the globe. Since CO2 is recognized as a greenhouse gas, its concentration cannot be allowed to rise indefinitely. Otherwise, the ensuining climate changes will cause crops to fail more frequently for the common reasons: drought, floods, storms, blight.

This suggests that concentrations of ozone precursors (VOC, NOx) must not rise indefinitely, either. The primary sources of VOCs are solvents (industrial processes, paints etc.) and ICEs without emissions control equipment. Two-stroke gasoline engines used in small to medium motorcycles, ATVs, jetskis, snowmobiles, leafblowers, chainsaws etc. are particularly gross polluters, but four-stroke motorcycles and light aircraft are also bad. These vehicle categories are presently subject to much higher emissions limits, or none at all.

NOx (i.e. NO, NO2, N20 et al.) is produced in all combustion processes, including caloric power plants, jet aircraft, ICEs, furnaces, wildfires etc.

For lambda=1 systems such as homogeneous gasoline injection, three-way catalysts reduce NOx to N2 and O2 almost completely once they reach operating temperature. Further reductions would be possible by pre-heating the catalyst prior to starting the engine.

For lamda>1 processes (e.g. diesel), volume ignition concepts (HCCI et al.) simply avoid flame fronts and the associated NOx production. Unfortunately. the high heat release rate limits applicability to part load scenarios. HC and CO emissions go up. For flame-based combustion, SCR technology is expensive but effective in reducing engine-out NOx compounds to N2 and O2. Proven in power plants, it is now being applied to new trucks in Europe, with large cars expected to follow soon. The snag is that you have to set up a distribution infrastructure for AdBlue, a 35% aequeous solution of pure urea. The alternative, NOx-store catalysts are not as effective nor do they last as long, which is why they have not made it into series production yet.

Aircraft jet engines release substantial amounts of NOx (chiefly N20, aka laughing gas) into the troposphere, mostly at high altitude. Ground-level emissions can be reduced a little by tractor-pulleys for taxiing (e.g. Frankfurt airport) but take-off and landing (thrust reversal!) account for the lion's share anyhow.

Mark A

Everyone is pushing for the growing our fuels, in place of growing our foods. But its issues such as this one, plus future droughts, floods or, as the article mentions, a sever hailstorm, which should give biodiesels and E85 limited acceptance, due to their unstable production. That, in additional to corn and soybeans only being able to be grown during a portion of the year. (Corn and soybeans do not grow under snow.)

Ethanol and biodiesel are not the final answer, but a small piece of the puzzle in the larger energy picture.


"Ozone is formed via the interaction of oxides of nitrogen (NOx) and sunlight."

Technically, it's NO2 (nitrogen dioxide) that is the ozone precursor form of NOx. NO2 photo-dissociates into nitric oxide (NO) and atomic oxygen (O). The resulting O combines with molecular oxygen (O2) to form ozone (O3). However, the NO that is left over from the initial photo-dissociation immediately reacts with ambient O3 to reform NO2 and O2. Thus there is no net ozone production just from the photo-dissociation of NO2. Volatile Organic Compounds (VOCs) play a significant role in ground-level ozone (GLO) production in that atmospheric decomposition of VOCs produces peroxy radicals (RO2 and HO2). These peroxy radicals oxidize NO into NO2, resulting in more NO2 for O3 formation and less NO for O3 depletion.

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