Air Quality Standards for Ozone

In 2005, after an extensive review of the scientific literature, CARB approved an eight-hour standard for ozone (//ww2.arb.ca.gov/resources/fact-sheets/what-ozone) of 0.070 ppm and retained the one-hour 0.09 ppm standard previously established in 1987. Evidence from the reviewed studies indicates that significant harmful health effects could occur among both adults and children if exposed to levels above these standards (//ww2.arb.ca.gov/resources/fact-sheets/health-effects-ozone). On October 1, 2015, the U.S. EPA lowered the national eight-hour standard from 0.075 ppm to 0.070 ppm.

	1-Hour Average	8-Hour Average
National Ambient Air Quality Standard	--	0.070 ppm*
California Ambient Air Quality Standard	0.09 ppm*	0.070 ppm*

* A part per million (ppm) refers to one part of a substance dissolved into a million parts of another substance.

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