The US Environmental Protection Agency (EPA) is once again under fire for ignoring its science advisers — this time in setting a new air-quality standard for ozone, a primary component of smog.

The agency's decision on 13 March will reduce the current regulatory limit on ground-level ozone concentrations, set in 1997, from a maximum of 84 parts per billion (p.p.b.) to 75 p.p.b.. An agency advisory panel had recommended a range of 60 to 70 p.p.b..

Environmentalists also criticized what they saw as White House interference. In a 6 March memorandum, a top White House regulatory official, Susan Dudley, urged the EPA not to set a secondary “welfare” standard at a lower level to protect against other environmental problems, including potential damage to crops and other vegetation. In the end, the EPA set the primary and secondary standards at the same level.

The air quality in an estimated 345 municipalities and counties could be in violation when the new standards come into effect in 2010.