By Travis Gulbrandson
While most Americans might not think of China as being a country where dust storms take place, the storms do raise a number of health and environment concerns there.
Because of research performed in part by a professor from the University of South Dakota, more is being learned about some of China’s biggest potential dust-emitters.
Mark Sweeney, associate professor of earth sciences at USD, spent two and a half weeks doing research in China this past summer.
“What I’ve seen so far is that in many cases, the amount of dust that’s emitted by these different surfaces in China (is) very similar to what is emitted in similar surfaces of the Mojave Desert,” Sweeney said during a presentation he gave Oct. 17 as part of Earth Science Week.
He traveled to China with Professor Joe Mason of the University of Wisconsin to test the idea that sand dunes could potentially be large emitters of dust.
“Traditionally, sand dunes are not considered big dust-emitters, because they’re mostly sand and they contain five percent less of silt and clay particles,” Sweeney said.
However, Israeli researchers now argue that sand particles can break apart due to wind and other environmental factors, creating dust.
Sweeney, Mason, graduate and undergraduate students performed their research with a Portable In-Situ Wind ERosion Lab (PI-SWERL) on a variety of terrains in China, from the Tengger Desert to dried-out riverbeds.
“(The PI-SWERL) simulates the wind and it generates dust, and then you can measure dust that comes off of different types of soil surfaces at different wind speeds,” Sweeney said.
The PI-SWERL basically looks like “an inverted soup pot” with a blade underneath, he said.
“The blade spins kind of like a fan at different RPMs, and when the blade spins, the PI-SWERL … creates a wind and gets the little particles moving,” Sweeney said. “The reason why people are interested in this type of technology is because it is portable. One person can operate it. It fits on a baby carriage, and it has its own power source, so you can move it over the terrain and measure dust in places where a large wind tunnel could never go.”
The PI-SWERL then measures the amount of dust, and the data is run through a computer.
“We basically plug the data into equations and come up with an emissions flux, which would be how many grams of dust come off of a square meter of ground per second,” Sweeney said.
One of the major research areas was the Chinese Loess Plateau, which Sweeney described as “a very extensive region in central China that basically contains a lot of windblown dust.”
“The dust has been accumulating over millennia, and it covers … 640,000 square kilometers. It’s an enormous area,” he said. “In some cases the dust is over 100 meters thick, so you’ve got over 300 feet of dust that’s been accumulating in some places for 22 million years. Basically, that makes China the king of loess deposits.”
The loess consists mainly of silt and clay particles, stacks well and has good engineering properties.
“Loess is cohesive enough that you can carve caves into it, and people have been living in caves since about 200 BC,” Sweeney said. “There are large metropolises of these cave houses.”
While all of the data collected this summer has not yet been analyzed, that which has been processed shows that coppice dunes – which form around vegetation – are among the largest emitters.
Land use practices could also be a contributing factor, Sweeney said.
“Grazing sheep along the desert margin might destabilize some of these areas where you get coppice dunes forming, (especially) if you get strong winds blowing through there,” he said.
Water shortages also play a role, he said.
Sweeney said the PI-SWERL is the main reason he was asked by Professor Huayu Lu of Nanjing University – who also paid for the entire trip – to come to China in the first place.
“The hope is, after I could show them how useful it was, that they could buy their own and I could potentially come over again for additional collaborative research,” he said.