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Earth’s atmosphere: A mixture of several gases: nitrogen (78%), oxygen (21%), argon (1%), carbon dioxide (0.03%) and several trace gases. Water vapor is a variable constituent (up to 4%).
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Tom Skilling is chief meteorologist at WGN-TV. His forecasts can be seen Monday through Friday on WGN-TV News at noon and 9 p.m.
WGN-TV meteorologists Steve Kahn, Richard Koeneman and Paul Dailey plus weather producer Bill Snyder contribute to this page.
