Scientists watched closely last spring as a haze of pollution, which had been tracked by s

atellite as it crossed the Pacific Ocean, settled over a large swath of North America from Calgary, Canada, into Arizona. Now it appears that, for the first time, researchers on both sides of the Pacific took detailed measurements of the same plume, a cloud that contained Gobi desert dust as well as hydrocarbons from industrial pollution.

Heather Price, a University of Washington doctoral student in chemistry, found that the amount of light reflected by the particles in the air was more than 550 percent greater than normal for that time of year. The mass of Asian air contained elevated levels of ail pollutants measured. Price said, "but the only thing that came close to being alarming was the level of particulate matter."

The haze that settled across the western part of the country was widely reported by the news media, and it was measured as far inland as the ski slopes of Aspen, Colo.

Readings on the western side of the Pacific came from the Aerosol Characterization Experiments, a project aimed at understanding how particles in the atmosphere affect Earth's climate. Additional measurements were taken in the same region at the same time under a project sponsored by the National Aeronautics and Space Administration.

Knowing the pollution was approaching Washington state, Price loaded sensing equipment aboard a rented Beechcraft on April 14 and flew to Neah Bay on the state's Northwest coast. Taking samples at various levels from 15,000 feet to 20, 000 feet in altitude, she monitored quantities of dust, ozone, carbon monoxide and hydrocarbons. "From my copilot's seat. the dust was thick enough to see with the naked eye." Price said.

Now she is trying to correlate her findings with those of the two research teams operating on the other side of the Pacific, where at one point the pollution plume was larger than Japan. The huge size of the cloud showed up clearly in satellite images that gave Price plenty of warning the haze was on its way. "You can see these two blobs coming out of the deserts of Mongolia and growing over Asia, then getting swept out over the ocean and finally setting over North America," she said. She intends to continue measuring air samples off the Washington coast and will be looking for air masses with evidence of pollution originating somewhere other than Asia. "We'd like to see if we can get a signature of pollution coming from Europe because computer models suggest that European sources also can be transported across the Pacific," she said. "However, we expect that sources in Europe will contribute less than Asian sources."

The haze of pollution mentioned in the first paragraph is a cloud ______.

A．of moisture over Calgary, Canada

B．developing over Pacific Ocean

C．of industrial pollutants

D．of desert dust and hydrocarbons