Debris from nuclear tests still present in upper atmosphere

BBC : When nuclear weapons were being tested during the 20th century, researchers thought that the amount of radioactive debris left in the atmosphere would be negligible after a relatively short amount of time. A study by Jose Corcho Alvarado of the Institute of Radiation Physics at Lausanne University Hospital in Switzerland and his colleagues has revealed that while the presence of debris in the troposphere is minimal, detectable levels of debris remain in the stratosphere. In the troposphere, the lowest level of the atmosphere, the debris is removed fairly quickly by precipitation and winds. In the stratosphere, the layer between 10 and 90 km above Earth, levels of radioactive debris were 1000 to 1500 times higher than those in the troposphere. The levels measured are not dangerous to humans, however, and their continued presence can help further understanding of the atmosphere’s behavior. Alvarado’s team measured only the air over Switzerland but believes similar concentrations will be found globally. The researchers also noted that volcanic eruptions contribute to the presence and spread of radioactive particles; after the 2010 eruption of Eyjafjallajökull, an increase in plutonium was detected in the troposphere.