of the Energy Department, uses sophisticated models on supercomputers to project the movement of radioactive particles and other toxic substances through the atmosphere.
However, a computer model of atmospheric movements developed by the Belgian Institute for Space Aeronomy shows that the Fukushima plumes could travel across the Pacific, though the levels of radioactivity that could reach the West Coast of the U.S. remain unclear.
It appears that all of the models, however, are not based on measurements of radioactivity at the source and a projection of actual radioactive fallout in the U.S., but rather project a relative scale of radioactivity. Since Japanese authorities have said little about the amount of the releases at Fukushima, nobody can say how much radioactivity will hit California.
The models show that even with prevailing easterly winds, the plumes whip back and forth over a wide area of Japan's east coast, Russia's Kamchatka peninsula and Alaska's Aleutian Islands. It is unknown whether nuclear fallout is hitting the vast wilderness of northeastern Asia.
Of particular concern, however, is radiation emanating from Fukushima's No. 3 reactor. That reactor uses plutonium fuel, which poses a special health risk even in small quantities if the fallout were to reach U.S. shores.
A leading radiological health expert at the Centers for Disease Control and Prevention, speaking on condition of anonymity, said Wednesday that the CDC was still confident that there would be no serious health consequences here. But CDC officials are watching the situation carefully.
"We have a saying: 'Modeling is OK, but measurement is everything,'" he said.
The Environmental Protection Agency said that it was watching the situation closely, but that its Radnet system had not yet detected radioactivity. It has added seven additional portable radiation monitors: two in Guam, three in Alaska and two in Hawaii.