US revives plan to tighten ozone limits Air quality standards that would cut the allowed concentration of smog-creating ozone in the atmosphere have been revived by the Obama administration, after being shelved in 2011 because of concerns about their effect on the economy. On Wednesday morning the Environmental Protection Agency published a proposal to set an upper limit of 65-70 parts per billion for ozone in the atmosphere at ground level, down from the ceiling of 75ppbn set in 2008. Enforcing the lower limit of 65ppbn would be the most costly environmental regulation proposed in the US for 17 years, according to the EPA's own estimates. Ground-level ozone, which results from emissions from power plants, factories and vehicles, causes breathing problems, particularly in children, and can aggravate diseases such as bronchitis and asthma. Oil and manufacturing industry groups indicated they would try to block the rule changes. The standards would not impose direct restrictions on industry but are likely to force some states to create new regulations. Howard Feldman of the American Petroleum Institute, an industry group, said: "Three years ago President [Barack] Obama acted to stop this process because of its effect on the economy. We still think that issue is very germane today. Jay Timmons, president of the National Association of Manufacturers, said the proposed changes would add to the dozens of regulations that threatened US competitiveness and made it "nearly impossible" to increase employment. The EPA argues that the cost of the rules will be limited because other regulations that it has enacted or proposed, including curbs on emissions from power plants and from vehicle exhausts, will have the effect of cutting ozone. The potential cost depends on the precise limit chosen. At 65ppbn, the proposals would have an expected cost of $15bn a year, in 2011 dollars, by 2025, the EPA said. A more lenient standard of 70ppbn would cost $3.9bn a year, it added, while a more stringent limit of 60ppbn, which is also being considered as an option but not formally proposed, would cost $39bn a year. The estimates exclude California, the state with the most severe ozone problem, which would be given longer to reduce it. The costs for California are predicted to be $800m per year for a 70 ppbn limit, or $1.6bn per year for a 65 ppbn limit, but those would be incurred after 2025. However, the agency argues that for either of the two higher limits, the benefits from health improvements would outweigh the costs. Harold Wimmer, president of the American Lung Association, a research and campaign group, welcomed the EPA's move, but said he was "concerned" that it had not included the 60ppbn limit in its proposal, adding that the association would "continue to push the agency to adopt standards based on the scientific evidence." Under the rules, states would be able to choose their own pollution control regulations to cut ozone, which could include changes to road fuel standards or curbs on emissions from coal-fired power plants. The EPA said it expected that by 2025 only nine counties out of about 3,060 outside California would have ozone concentrations higher than 70ppbn, and only 68 would have concentrations above 65ppbn, showing the numbers that would have to take action depending on the final limit that is set. The counties that are expected to have the highest levels of ozone outside California are concentrated in areas of northeast and southeast Texas, and in parts of the north-eastern US including New York state and Connecticut.