Minnesota Public Radio slideshow:
MPCA increases air monitoring
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Ozone levels are monitoring only during the summer because thats when high levels are produced by the interaction of ultra violet rays and automotive emissions. (MPR Photo/Dan Gunderson)

Ozone levels are monitoring only during the summer because thats when high levels are produced by the interaction of ultra violet rays and automotive emissions.

(MPR Photo/Dan Gunderson)
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