This type of transport involves air pollutants in the atmosphere. If the pollutants are light enough---such as gases or low density particles---or are propelled high enough in the atmosphere, they may be picked up in horizontal winds and transported long distances. If the air pollutants travel within the moving air mass greater than 100 kilometers, than this is considered long range transport. In the spring of 2011, after the nuclear accident following the March 2011 9. 0 magnitude earthquake off the Japanese coast, radioactive particles released from the Tokyo Electric Power nuclear reactor complex in the Fukushima Prefecture, Japan were detected on the east coast of the United States at levels that were slightly above background.