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CARB Cracks Down on Ozone

The California Air Resources Board (ARB) approved the nation’s most health protective ozone (O3) standard today.  The new 8-hour-average standard of 0.070 parts per million (ppm) (not to be exceeded) is designed to further protect California’s most vulnerable populations from the adverse health effects associated with ground-level ozone, or smog.

The current California ambient air quality standard for ozone is 0.09 ppm averaged over one hour and was set by the Board in 1988.

The genesis of this regulation was the The Children’s Environmental Health Protection Act, passed in 1999, which requires the ARB, in consultation with the Office of Environmental Health Hazard Assessment, to “review all existing health-based ambient air quality standards to determine whether these standards protect public health, including infants and children, with an adequate margin of safety.”

As a result of that requirement, the ARB today adopted the new, stricter 8-hour standard. The 1-hour-average ozone standard is retained at 0.09 ppm, not to be exceeded.

Ozone (O3) Air Quality Standards (ppm)
Regulation1-hour Average8-hour average
US EPA 0.12 0.08
Current CARB 0.09
New CARB 0.09 0.070

CARB recommedned the tougher standard based primarily on the number of studies conducted over the last 15 years, supported by the important health outcomes reported in many of the epidemiologic studies.

In the detailed review of the standard, CARB notes specifically that the new recommended 8-hour average concentration has three rather than two decimal places. This is to protect against rounding conventions that could reduce, say 0.074 ppm to 0.07 ppm. The staff didn’t believe that left enough of a margin of safety.

Among the health risks CARB believes could be avoided via the new standards are:

  • 580 premature deaths for all ages

  • 3,800 hospitalizations due to respiratory diseases for all ages

  • 600 emergency room visits for asthma for children under 18 years of age

  • 3.3 million school absences for children 5 to 17 years of age

  • 2.8 million minor restricted activity days for adults above 18 years of age

(See the full review for details on confidence intervals and methodologies.)

The new standards will go into effect late this year or early next year, after going through California’s review process for new regulations.




And if it goes above 0.070, then what? How can this be enforced? Impose a special fuel tax for filling your tank on Ozone Action days between 7AM and 5PM?


Well, probably just about the way it’s done now, the main difference being the requirements are tighter. All this does is establish a standard. It now is up to local air pollution control or air quality management districts to adopt rules and regulations to control emissions from stationary sources, and to the ARB to revise emission standards and enforecement mechanisms for mobile sources and consumer products.

So that’s all still TBD.

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