China dust storm sweeps to America

Haze hits North America as industrial pollutants from China and Gobi Desert dust drift across the Pacific

DENVER - A dust storm from Mongolia is dispersing dust from the Gobi Desert and industrial pollution from China across a quarter of the mainland United States, strengthening evidence that pollution can drift across continents.

A whitish haze has been seen across Calgary in Canada and Arizona and Aspen in the US, where levels of particulate - the matter that reduces visibility and can cause respiratory problems - quadrupled over last weekend.

Particulate levels measured 58 millionths of a gram per cubic metre of air in Aspen, compared with 14 millionths of a gram a week earlier.

The cloud will reach the east coast of the US, but should dissipate within the next several days.

Air pollution from Asia is generally carried across by strong winds and can take four to 10 days to reach North America.

'This storm is a godsend to pollution researchers. People are realising finally that what they have been saying for years is true. Pollution from Asia is being carried across oceans,' said Mr Russ Schnell of the National Oceanic and Atmospheric Administration in Boulder, Colorado.

He also noted the fact that the pollution this time round was unusual because it had been so visible to the naked eye.

Officials at the Naval Research Laboratory in Monterey, California, and the National Aeronautics and Space Administration (Nasa) confirmed that the haze began as a dust storm over China, the Associated Press reported yesterday.

Mr Gene Feldman of Nasa's Goddard Space Flight Centre in Maryland said aircraft have been monitoring particulate in the dust clouds. 'At one time, this dust cloud was bigger than Japan.'

Health officials have advised people at risk - the elderly, children or those with existing respiratory problems - to stay indoors if they notice any effect from the pollution.

Scientists first presented evidence of transcontinental pollution at a 1998 meeting of the American Geophysical Union.

They showed that dust from the Gobi Desert in Mongolia, riding on a channel of air formed under specific atmospheric conditions - generally in the springtime with strong winds blowing towards the US - had drifted across the Pacific for well over 10,000 km.

Authorities in the state of Colorado are already advising its citizens to take precautions.

'We know that it is having a visible impact across much of the state,' said Mr Chris Dan, spokesman for the air-pollution branch of the state's department of health and environment.

'We had the same kind of haze when Mount St Helen's erupted but the particulate didn't come down to ground level as much,' said Mr Lee Cassin, director of Aspen's environmental health department.

POLLUTION: With the wind

CONDITIONS must be perfect for pollution to cross the Pacific Ocean from Asia to the US. Scientists believe they involve:

• A low-pressure system over the Aleutians and a high-pressure system near Hawaii - a combination of the two sets up an air flow that channels pollutants to North America;
• Winds that blow at heights of between 1,800 m and 3,000 m - they are not of the jet stream type, which is higher.

  In the last major episode of pollution in late April 1998, 140 million tonnes of fine soil particles were thrust into the atmosphere by strong dust storms in China. The dust carried with it portions of arsenic, copper, lead and zinc. NOTE: There is as yet no study on whether pollution is driven in the opposite direction