Depending on weather conditions, fallout from Japan's crippled nuclear reactors could reach the West Coast within a couple of weeks. But scientists who track other forms of pollution blowing across the Pacific Ocean say the amount of radioactivity should pose no danger to any part of the United States.

McClatchy News Service

CHICAGO — Depending on weather conditions, fallout from Japan's crippled nuclear reactors could reach the West Coast within a couple of weeks. But scientists who track other forms of pollution blowing across the Pacific Ocean say the amount of radioactivity should pose no danger to any part of the United States.

Like other forms of pollution, radioactivity attaches to dust and fine particles that spread through wind, rain and snow and can be breathed or ingested. As the Japan disaster unfolds, the U.S. Environmental Protection Agency is sending extra staff to the West Coast to monitor radiation levels in air, cow's milk and rain, and other agencies, including the Nuclear Regulatory Commission, the National Oceanic and Atmospheric Administration and the Department of Energy, are tracking weather patterns and using computer models to predict how radioactivity from Japan might spread.

But even as government officials step up their monitoring efforts, scientists say it is important to keep the scope of the current crisis in perspective.

"While tragic, this is a single source of radioactivity that will be highly diluted if it crosses the Pacific," said Daniel Jaffe, an atmospheric scientist at the University of Washington who is tracking the fallout from Japan. "It is highly unlikely this would pose any risk to the West Coast ... ."

Jaffe is among a handful of researchers who have documented how noxious pollution from China's growing number of coal-fired power plants is wafting across the ocean to California, Oregon and Washington. "Even that pollution, emitted on a continental scale, is diluted by orders of magnitude by the time it reaches us," Jaffe said.

Experts say it is still too early to estimate how much radioactive material will be released into the atmosphere in Japan. The greatest danger to nearby areas in Japan, experts said, will come if one or more of the reactors completely melts down and contaminant vessels fail to limit the radiation. There also are concerns about large amounts of spent fuel in storage pools that are not shielded as well as the reactors.

Wind and rain will help dictate how far the fallout spreads. Winds could disperse the material over a larger area, where it could be diluted by the Earth's vast atmosphere. Rain or snow would force more of the radioactive debris down to the ground.

Brian Toon, an atmospheric researcher at the University of Colorado at Boulder, said that although reactor cores contain enormous amounts of radioactive material, how far those materials might travel depends in part on the force with which they are released.

An intense fire or a larger explosion could drive the material higher into the air, Toon said, possibly high enough that it would catch the jet stream and travel a considerable distance.

"You can see already in Japan that that material is ... near the surface," Toon said. "Therefore it will probably go right out over the oceans and be washed out quickly and very little radioactive material will go very far."

Many experts predict the health consequences in Japan will pale in comparison to deaths caused by the earthquake and tsunami that set off the nuclear crisis

The closest thing to the situation unfolding now is the 1986 disaster at the Chernobyl nuclear plant in Ukraine, where a reactor blast and fire put 400 times more radioactive material into the atmosphere than the atomic bomb dropped on Hiroshima, according to the International Atomic Energy Agency. Fallout spread around the globe, but years of study have shown the health effects were concentrated in areas near the plant.