Ozone pollution is linked to asthma, lung damage and other health problems.
The Environmental Protection Agency is calling for a new, lower threshold for ozone pollution of 65 to 70 parts per billion, down from the current standard of 75 parts per billion.
But the EPA is leaving open the possibility it could enact an even lower standard of 60 parts per billion sought by environmental groups.
The California Air Resources Board says if the standard is set at 60 parts per billion that could portentially double the number of non-attainment areas in the state.
Based on 2013 and preliminary 2014 data, at 70 parts per billion California would add five new non-attainment areas, and at 65 parts per billion California would add 13 new non-attainment areas.
Currently one-third of the state's population lives in areas where ozone pollution doesn't meet the federal standard.
The Board says the proposed regulations would primarily affect rural, less-populated areas.
The EPA was under a court-ordered Dec. 1 deadline to issue a new smog standard.
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