In the lab

• By Jim DiPeso
• Nov 01, 2000

Hazy days hamper plants

Regional haze in China's most important agricultural areas may be cutting food production there by as much as one-third. The east coast of the United States has seen a similar problem ? however, China's haze levels are almost twice as bad as the United States'. Haze in other developing countries suggests food production may be similarly reduced in India and African nations.

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 as well as Georgia Institute of Technology. Funds came from U.S. National Aeronautics and Space Administration (NASA). It found that haze in China covers at least one million square kilometers and absorbs solar radiation, thereby substantially reducing the amount of sunlight reaching key rice and winter wheat crops. Plant growth and food production suffers, along with human health.

"In China, there is a significant amount of haze that reduced the sunlight reaching the surface by at least five percent, and perhaps by as much as 30 percent. The optimal yields of crops in China are likely reduced by the same percentage," Dr. William L. Chameides, Smithgall Chair and Regents' Professor in the School of Earth and Atmospheric Sciences said.

The study is believed to be the first work to quantitatively assess the direct impact of regional haze on the yields of these crops. The estimates of crop production losses in the study are based on detailed long-term measurements in Nanjing, 200 miles southwest of Shanghai. The haze comes primarily from power plants and is made up of aerosols.

Chameides found that the regional haze affects approximately 70 percent of crops grown in China and tends to be worst in the eastern part of the country in the most productive and heavily cultivated areas.

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 reduces the sunlight reaching plants. Finally, harm from growth-stunting ozone, acid deposition and other air pollutants also worsens the impact of poor air quality. "Controlling the sources of the haze represents a potential way to increase crop production because the technology exists to control air pollution," Chameides said.

According to Chameides, the work gives policymakers better information to base environmental decisions on. Reductions in crop production tied directly to haze-induced sunlight reductions provide the kind of cause and effect that can be used in balancing production against the costs of improving environmental quality. "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," said Chameides.

For more information, visit www.gtri.gatech.edu/res-news/CHINA-AIR.html

CO₂ goes underground

According to the White House Office of Science and Technology policy, industrialized nations are responsible for 73 percent of carbon dioxide (CO₂) emissions. The United States is solely responsible for 22 percent of the world's emissions ? that's five tons of CO₂ per U.S. citizen per year. One way to possibly eliminate the amount of CO₂ is by sequestering it. A project utilizing this method will take place in Canada while an international team will monitor its progress.

In the United States, some of the structures that natural gas has been taken from are being used to safely store high-pressure gas produced elsewhere. It has been discovered that in many oil wells, pressure and temperatures are high enough that CO₂ becomes a mobile fluid that is miscible with oils having densities of about 0.90 grams per cubic centimeter or less. These liquids tend to move toward lower pressures in production wells, and when CO₂ is injected, an additional 10-15 percent of the oil in an oil field can be recovered. Much of the CO₂ is recycled, but part of it remains in the oil-bearing formations. In the United States in 1998, CO₂ had a major role in producing six percent of domestic crude oil.

A field in Weymouth Sasketchawan, Canada will receive 5000 metric tons of CO₂ per day through a 300-kilometer pipeline. The source will be the Dakota Gasification Company, located in Beulah, North Dakota. During the course of a multi-year injection, 20 million metric tons of CO₂ will be sequestered and an extra 130 million barrels of oil will be produced.

At the Bati Roman field in southeast Turkey, the attempts were not so advantageous. The oil has high-molecular-weight components and only 1.5 percent of the original oil was able to be recovered in an effort to inject CO₂. Injection increased production but total miscibility was not achieved. A large volume of CO₂ dissolved in the oil and its viscosity decreased from 1000 centiposes (cp) to less than 100 cp. A recovery of 6.5 percent is expected.

In addition to petroleum fields, a large amount of CO₂ could be isolated in deep unmineable coal and in depleted natural gas fields. A report commissioned by the International Energy Agency (IEA) and supported in part by the U.S. Department of Energy (DOE) estimates that the ultimate storage capacity of the oil and gas fields equates to over 125 years of total current CO₂ emissions from fossil-fueled power plants.

The gas must be cleaned and pressurized before injection and the total cost of such procedures is roughly $53 per metric ton or more.

For more information, visit www.sciencemag.org.

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This article appeared in Environmental Protection, Volume 11, Number 11, November 2000, Page 10.

This article originally appeared in the 11/01/2000 issue of Environmental Protection.