Obama administration tightens rules on smog pollution

• EPA cuts standard for US smog levels to 70 parts per billion
• Campaigners on both sides of debate frustrated by new figure

New national rules to reduce smog pollution in the US were announced on Thursday, in a long-awaited environmental move by the Obama administration.

The Environmental Protection Agency administrator, Gina McCarthy, announced that the new standard for smog levels in the US will be 70 parts per billion (ppb), tightening the rules from the previous limit of 75 ppb agreed in 2008 by the previous Republican government.