Asian Pollution Cloud Changing Climate, Study Says

Sharon Guynup
for National Geographic Today
February 10, 2003
When factories, power plants or automobiles spew pollutants into the
air, these emissions take to the wind and travel wherever it blows. A
toxic blend of soot, ash, acids and other airborne particles crosses
borders and oceans—polluting faraway places and affecting climate,
rainfall and causing acid rain.

An international consortium of researchers from three different projects are investigating one of the world's most potent sources of air pollution: the so-called "Asian Express," created over the last decade by rapid Asian industrialization, which is driving changes in the Earth's atmosphere.

A series of recent studies tracked the brown pollution cloud along its annual transpacific migration. Each spring, strong winds blow east from Central China, gathering dust which acts like a sponge, soaking up pollution from East Asia's thick blanket of smog.

Traveling Particulate Stew

This dirty particulate stew most directly threatens Japan, Korea and Taiwan. But this brown cloud can blow eastward across 6,000 miles of ocean to the United States in only four to 10 days—too little time for the air to be cleansed over the sea.

Given the pass-along nature of pollution, however, researchers point out that every region of the world makes its contribution.

"The amount of pollution we get from Asia is probably not dramatically different from what we send to Europe, and Europe sends to Asia," says Barry Joe Huebert, an atmospheric chemist at the University of Hawaii in Honolulu. "We have to think of atmosphere chemistry and its impact on air quality and climate as global issues."

Huebert and other authorities on wind borne pollution presented their findings in December at the annual meeting of American Geophysical Union. Their research identified the major sources of pollution and quantified how much reaches North America.

"The ultimate use of this data will be for setting policy for the use of fossil fuels and other pollutants we put into the atmosphere," said Huebert.

During spring 2001 and 2002, hundreds of scientists from 13 countries joined forces to study air pollution from Asia. The international team tracked and sampled dust plumes from ground stations, aircraft, ships and by satellite.

Atmospheric Aerosols

Huebert headed the research team for the Aerosol Characterization Experiments, or ACE-Asia, which concentrated on aerosols—tiny solid or liquid particles suspended in the atmosphere. Some aerosols come from natural sources like dust from volcanoes and deserts. But most come from human activities like burning wood and coal. Asia is one of the largest sources of aerosols on the Earth.

Aerosols can harm human health by causing asthma and through exposure to the carcinogens they harbor, including arsenic, lead, chromium, selenium and other toxic materials.

Aerosols powerfully affect the environment and climate. They absorb the acids that create acid rain. They reflect sunlight and influence rainfall patterns, affecting weather and global climate change. Understanding the way they affect climate is one of the more perplexing problems for atmospheric scientists.

Atmospheric scientists are puzzling over the interaction of aerosols and other factors like greenhouse gases—carbon dioxide and other gases that trap the sun's heat and warm the Earth's atmosphere.

Altering Climate

"While many parts of Earth are warming up because of greenhouse gases, in places where there are huge concentrations of aerosols, there is actually cooling," said Huebert. In April, for example, the surface cooling effect of aerosols downwind of Asia is 10 percent higher than warming caused by greenhouse gases, Huebert notes.

When you increase temperature differences between places, it may increase the severity of storms, like hurricanes," Huebert says. "One possibility is that this could cause more severe storms, more droughts and more floods."

Although the climatic impact of this cooling is still being assessed, scientists do know that these temperature disparities have great impact on the water cycle. "When air is warmer than the Earth below it, you reduce evaporation and the formation of clouds—which reduces rainfall," explained Huebert.

Good and Bad News

Researchers presented good news as well as bad.

One study, Transport and Chemical Evolution over the Pacific (TRACE-P), "sniffed air coming out of China to learn what was being emitted," says project leader Daniel J. Jacob, an atmospheric chemist from Harvard University in Cambridge, Mass.

Jacob's team tested for about 100 different "species" of pollutants, including greenhouse gases, aerosols and ozone. Although nothing on the list had significantly improved since 1994, "there hasn't been the kind of explosive growth that was predicted," Jacob says.

An exception was soot and carbon, caused by low-tech polluters like wood- and dung-burning stoves and cooking fires, as well as dirty industries. "There was also a lot of biomass burning from forest fires in Cambodia and Thailand," Jacob says.

Asian Ozone Comes to California

Another study examined ozone levels reaching California from across the Pacific and discovered that they are 30 percent higher than levels detected in 1985.

"The increase in ozone is surprising," says David P. Parrish, an atmospheric chemist with the National Oceanic and Atmospheric Administration Aeronomy Lab in Boulder, Colo., and head of the Intercontinental Transport and Chemical Transformation study. "It was larger than we expected. It reduces the room we have to mess up our own air."

"To address the problem, we will need an international consortium of governments willing to make policy based on the best available scientific consensus," Huebert says.

In a world where prevailing winds can push pollution clouds like the Asian Express halfway around the world in a week's time, these new findings underscore how no nation is an island.

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