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Haze In China Seen Damaging Crop Production

By Daily University Science News

A new study suggests that cleaning up the air may help to feed the

Published in the November 23 issue of Proceedings of the National
Academy of Sciences, the study found that heavy regional haze in China's
most important agricultural areas may be cutting food production there
by as much as one-third.

Covering a million square kilometers or more, the haze scatters and
absorbs solar radiation, reducing the amount of sunlight reaching key
rice and winter wheat crops. That decreases plant growth and food

"For crops that are irrigated and fertilized, there is often a direct
correlation between how much is grown and how much sunlight reaches
those crops," said Dr. William L. Chameides, professor in the School of
Earth & Atmospheric Sciences at the Georgia Institute of Technology. "In
China there is a significant amount of haze that reduces the sunlight
reaching the surface by at least five percent, and perhaps as much as 30
percent. The optimal yields of crops in China are likely reduced by the
same percentage."

Chameides says the NASA-funded study provides China -- and other nations
with similar issues -- another option in the struggle to feed their
growing populations. It is believed to be the first work quantitatively
to assess the direct impact of regional haze on the yields of these

"China is already losing 10, 20 or even 30 percent of its crop
production to haze," he said. "Controlling the sources of the haze
represents a potential way to increase crop production because the
technology exists to control air pollution."

The estimates of crop production losses are based on detailed long-term
measurements at Nanjing, 200 miles southwest of Shanghai, but are
extrapolated to other areas of China. They consider only the direct
effects of haze on sunlight, and do not include the indirect effects on
sunlight potentially caused by haze interacting with clouds or the toxic
effects of air pollutants that also reduce crop growth.

Extensive studies by agricultural researchers have documented the
relationship between crop production and the sunlight received.

The haze affecting China is made up of aerosols composed of solid and
liquid particles of varying sizes. The aerosols likely result from the
burning of coal, biomass and other fuels, though scientists lack
detailed information on their origins.

Large-scale regional hazes exist in other developing countries,
suggesting food production may be similarly reduced in India and African
nations that are also struggling to feed their people.

"Any economically developing or developed country will have these large
regional hazes associated with burning," Chameides explained. "Burning
fossil fuels, burning wood and burning biomass for clearing fields
causes production of a significant amount of haze that leads to a
reduction in the solar radiation reaching the earth's surface."

The same effect has been measured on the East Coast of the United
States, though China's haze levels are roughly twice as bad. Records
suggest that China's haze problem has worsened over the past 20 years, a
time of massive industrialization.

The study, for which Chameides is the lead investigator, found that the
regional haze affects approximately 70 percent of crops grown in China.
The haze tends to be worst in the eastern part of the country that
includes the most productive and heavily cultivated areas. It can be
measured year-round.

The study produced two different estimates of sunlight reduction, one
based on direct measurements and one based on a model of China's
atmosphere. Data based on direct measurements suggest an even larger
effect than the 5-30 percent crop reduction calculated by the model.

The work gives policymakers better information on which to base
environmental decisions, Chameides said. Researchers have long known
that air pollution harms human health and damages crops, but the
complexity of those factors has made it difficult to quantify the true

Reductions in crop production tied directly to haze-induced sunlight
reductions provide the kind of cause and effect that can be used in
balancing food production against the costs of improving environmental

"In tallying up the balance sheet, policymakers want to make sure they
have everything in each column," he explained. "This is something new
that goes on the side of why it pays to clean up air pollution. In
countries like China, I think this could be quite significant."

Crop reductions predicted by the study provide a lower limit of the
effects caused by air pollution. Adding to the direct effect of reducing
sunlight are indirect effects, such as aerosol-induced cloud cover and
increased reflectivity, which further reduce the sunlight reaching
plants. Finally, harm from growth-stunting ozone, acid deposition and
other air pollutants also worsens the impact of poor air quality.

There are many potential sources for the haze. The coal China uses to
fire much of its industry produces soot and fine particles. Fuel for
cooking and home heating also tends to be dirty. Agricultural practices
involve burning crop debris at the end of the growing season. And China
gets hit each spring with dust from desert regions in the western part
of the country.

The research was done as part of the China-MAP project, supported by the

National Aeronautics and Space Administration (NASA) as part of its
long-term climate studies.

The study was done by a consortium of groups that included the Chinese
Academy of Meteorological Sciences, the U.S. National Center for
Atmospheric Research and the Abdus Salam International Centre for
Theoretical Physics in Italy in addition to Georgia Tech. - By John Toon

[Contact: Dr. William Chameides, John Toon]

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