Clear Skies Hide Smoke Danger

ClevelandIts air quality index hit 600, a record since the 1970s.

Sunlight strips brown carbon’s color through oxidation without removing its toxicity, Columbia scientists say, so clear-looking air from over 800 Canadian fires can still carry harmful PM2.5.

Forecasters expect rain over the eastern US, which may temporarily dampen the smoke.

Sources: Yahoo, CNN International, USA Today