By Kate Galbraith, December 25, 2013
When China’s skies darken with pollution, it is not the only nation to suffer.
Soot, ozone-forming compounds and other pollutants from China can blow east to Korea and Japan. Ultimately, some even reach the west coast of the United States, scientists say.
Other nations generate pollution too, of course, so the wafting of bad air from China adds to local problems. China’s emissions worry countries in the path of the plumes, but in a region where political tensions often run high, international solutions are largely elusive.
“The countries most directly affected by air pollution from China are its nearest neighbors,” Paul Harris, the chair professor of global and environmental studies at the Hong Kong Institute of Education, said in an email. “As with every other aspect of relations with China, there is a limit to what they can do about it.”
China’s coal plants and vehicles emit a suite of emissions, including sulfur dioxide, nitrogen oxides, carbon dioxide, mercury and small particles (soot). Some pollutants, including carbon dioxide, contribute to the worldwide problem of climate change. Others stir more immediate health concerns for China’s neighbors, as well as for China itself. Mercury can fall to earth with rain, harming the ocean and fish. Ozone and fine particles, sometimes found far from their sources, pose problems because breathing too much of them can lead to lung damage.
Recent research in Japan suggests that China’s contribution to average annual fine-particle pollution ranges from 40 percent in the Tokyo area to 60 percent in Kyushu, which is closer to China, according to Hiroshi Tanimoto, who heads the global atmospheric chemistry section at Japan’s National Institute for Environmental Studies. On average, about 10 percent to 20 percent of Japan’s springtime ozone comes from Chinese emissions, he said.
“Transport of air pollutants from China enhances the background level entering into Japan,” Dr. Tanimoto said in an email. The impact to effect on Korea is even greater, he added.
Much depends on wind patterns. Often, the haze over Chinese cities is a product of stagnant air and therefore the pollutants may not travel vast distances, said Michael Prather, a professor of earth system science at the University of California, Irvine. The small particles that reach the United States often come from wind-propelled dust storms in the Gobi Desert, he said. China’s main effect on pollution in the United States, however, involves ozone, scientists say.
The transporting of pollutants across the Pacific Ocean takes at least four or five days, and they ride west-to-east winds at heights of 6,000 feet to 20,000 feet, according to Dan Jaffe, a professor of atmospheric and environmental chemistry at the University of Washington-Bothell. He works at a station 9,000 feet high on a mountain in Oregon because it is easier to measure pollutants from Asia there than at sea level.
“People living at higher elevations are definitely getting greater exposure” to pollutants coming from Asia, said Mr. Jaffe. His team uses several tools to identify pollutants that have traveled across the Pacific, including the ratios of pollutants, the amount of mercury, satellite data and computer models.
Scientists say the Chinese contribution to United States pollution is relatively small, dwarfed by domestic sources.
All countries emit pollutants that affect their neighbors. Europe, downwind of North America, receives some American pollution, for example. The big issue, Dr. Prather said, is the “large-scale building up of this stuff in the Northern Hemisphere,” as well as growing emissions in the Southern Hemisphere from fast-developing economies like Brazil.
The emissions from China and elsewhere in Asia have implications for the Pacific Ocean. Traditionally, the Pacific “was a pristine environment,” Dr. Prather said, in contrast to the more polluted North Atlantic. Now, he said, Pacific pollution will increase.
China, which accounts for more than half of the world’s coal consumption, is trying to reduce its pollution for the sake of its worried citizens. It has cut its emissions of sulfur dioxide, which can lead to acid rain and fine-particle creation; it is rapidly building clean- energy plants and setting some limits on coal; and it orders reduced car travel on days of bad smog. But its fast-growing economy makes the pollution problem hard to solve.
Other Asian nations are engaged, too. Dr. Tanimoto said scientists and officials from Japan, China and South Korea had discussed a joint observation and modeling system. Another promising area is the sharing of pollution control technologies, a subject discussed this month in a meeting of representatives of the three countries. Japan has experience to offer, having reduced its own awful air pollution a few decades ago.
But regional cooperation can be hard.
Whereas Europe had success in working to reduce cross-border air pollution in the 1970s and ’80s, “there’s really been no history of that regional cooperation in Asia,” said Loren Cass, an associate professor of political science at the College of the Holy Cross in Massachusetts.