REUTERS/Go NakamuraCHICAGO, June 30 (Reuters) - Half of the U.S. population was urged on Friday to take precautions when they are outdoors, either due to a relentless heat wave or poor air quality caused by Canadian wildfires ahead of the long Fourth of July weekend. To the north, across the Midwest and East, another 100 million Americans faced another day of smoky skies and poor air quality alerts due to raging wildfires in Canada. The weather service said individuals, especially those who are young, elderly and suffer from respiratory problems, should consider limiting strenuous outdoor activities in those areas. New York and Washington had the second and third worst air quality respectively of any major cities around the globe, according to IQAir.com, which tracks global air pollution. Some people in eastern Illinois and western Indiana faced a hot and humid day of compromised air quality on Friday without electricity after fierce storms on Thursday evening knocked down power lines and trees.

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Persons: Marc Newman, Go Nakamura CHICAGO, Brendan O'Brien, Jonathan Oatis Organizations: REUTERS, National Weather Service, Midwest, Thomson Locations: Houston , Texas, U.S, California, Mississippi, East, Canada, New York, Washington, Illinois, Indiana, Chicago