Radiation from Japan’s damaged Fukushima nuclear power plant is already reaching the US, and is more difficult to predict than the weather, say University of Maryland atmospheric scientists.
The amount will be affected by the altitude to which radioactive or toxic materials are lifted, wind variability and the removal or dilution of radioactive materials by dispersion, wash-out by rain or contact with the ocean.
But atmospheric science researchers Tim Canty, Jeff Stehr, Russell Dickerson and Ross Salawitch have examined atmospheric patterns this week using the National Oceanic and Atmospheric Administration (NOAA) HYSPLIT model.
Their preliminary findings show that the plumes rising from Fukushima are taking at least five to seven days to reach North America. The majority of the radiation, upon reaching North America, will be at an altitude well above the surface and below the cruising height of commercial airplanes.
And significant amounts of radiation will be removed by precipitation or contact with the ocean, says the team, and concentration levels will be reduced many orders of magnitude by atmospheric mixing.
"Calculations such as those in the dissipation figure are the basis for statements by many scientists that radiation will be diluted, to levels below thresholds of concern for human health, by the time these air masses reach the North America," says Russell Dickerson.
"If there is widespread public concern, airborne measurements of atmospheric radionuclides using small commercial available gamma ray spectrometers, at projected locations of plumes, could be used to verify that the public health risk is minimal."
The figures are being updated daily, here.