Published Sept. 29, 2007

The California Air Resources Board banned popular in-home ozone air purifiers this week, saying studies have found that they can worsen conditions such as asthma that marketers claim they help prevent.

The regulation, which the board said is the first of its kind, will require testing and certification of all types of air purifiers. Any that emit more than a tiny amount of ozone will have to be pulled from the California market.

An estimated 2 percent of the state's households have one of the ozone air purifiers, according to research, and the staff estimated that more than 500,000 people had been exposed to levels of ozone above federally recognized health standards as a result. More than 2-million California residents have some sort of air purifier, and other types can be safe and effective, the board said.