The Environmental Protection Agency's staff concludes that the government needs to tighten smog rules by somewhere between 7 and 20 percent.
In its final recommendation in a 597-page report, the agency staff agrees with EPA's outside scientific advisers that the 6-year-old standard for how much smog is allowed needs to be stricter.
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Since 2008 the standard allows up to 75 parts of ozone per billion parts of air. The staff report recommends between 60 and 70 parts per billion.
The report says it will provide more health protection for higher risk populations including the elderly, very young, outdoor workers and people with asthma and lung disease.
Federal law requires air quality rules be updated every five years. A federal judge ordered the EPA to have a new rule by December.