OREANDA-NEWS. A group of 70 US mayors from 24 states is calling on the Obama administration to strengthen federal air quality standards for smog.

The mayors, from states including California, Pennsylvania, Michigan and Illinois, this week asked President Barack Obama to replace the current federal ozone standard of 75 parts per billion (ppb) with a more stringent limit. The medical community considers the current standard "insufficient" to protect public health, the mayors wrote in a 21 September letter to the president.

Strengthening the federal ozone standard can better protect populations sensitive to air pollution such as the elderly, children and those suffering from asthma, the mayors said. The leaders urged the White House and the US Environmental Protection Agency (EPA) to consider the latest scientific evidence and guidance from the medical community justifying a lower standard.

EPA is under a court order to issue a new standard by 1 October. The agency has proposed setting a new limit in the range of 65-70ppb.

Mayors are on the "front lines of addressing public health challenges" and a stronger standard will allow Americans to spend more time outdoors without having to worry about the quality of the air they breathe, Salt Lake City mayor Ralph Becker (D) said.

Ground-level ozone forms when NOx and volatile organic compounds, emitted from sources such as power plants and automobiles, react in the presence of sunlight. Ozone is the main component of smog, which EPA says can aggravate asthma and other respiratory illnesses.

Mayors from states such as Pennsylvania and Indiana that rely heavily on coal-fired generation signed the letter, including Pittsburgh mayor William Peduto (D) and South Bend, Indiana, mayor Pete Buttigieg (D).