The Environmental Protection Agency announced last week that the country’s anti-smog standard does not sufficiently protect Americans’ lungs and will be tightened, a move that irked groups on both sides of the debate.

The decision comes after years of wrangling over the national limit for ozone, the lung-damaging gas in smog.

The EPA said it decided to lower the legal ceiling on the amount of ozone permitted in the air from 75 parts per billion to 70, citing "extensive scientific evidence about ozone’s effects on public health and welfare."

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After the EPA proposed a threshold in the range of 65 to 70 parts per billion last year, clean-air and health groups had urged the agency to rein in ozone more significantly. Earthjustice, an environmental law firm involved in a 2013 lawsuit that forced the agency to act, was among them.

“This weak-kneed action leaves children, seniors, and asthmatics without the protection doctors say they need from this dangerous pollutant,” David Baron, managing attorney at Earthjustice, said in a statement Thursday. “It will allow thousands of deaths, hospitalizations, asthma attacks, and missed school and work days that would be prevented by the much stronger standard supported by medical experts.”

The National Association of Manufacturers, which lobbied hard to leave the limit unchanged, called the decision to tighten the standard “a punch in the gut” because of the cost and economic ripple effects its members fear from tighter pollution controls.

“After an unprecedented level of outreach by manufacturers and other stakeholders, the worst-case scenario was avoided,” Jay Timmons, the trade group’s president and CEO, said in a statement. “However, make no mistake: The new ozone standard will inflict pain on companies that build things in America — and destroy job opportunities for American workers.”

The EPA’s independent scientific advisory committee of researchers and doctors has said since 2006 that the standard is too lenient. But when the EPA last lowered the limit, in 2008, officials did not set it within the 60-to-70 parts per billion range its panel recommended. President Barack Obama told the EPA to hold off in 2011, when the agency was on the verge of trying again.

This time, the EPA faced a court-ordered deadline to make a decision. The American Lung Association and three environmental groups sued in 2013 when the agency had yet to take up the matter as required.

The EPA isn’t permitted to consider cost when it sets the ozone standard, only the effect on public health. Figuring out the most cost-effective way to control smog is supposed to come after the threshold is set.

But you wouldn’t know that by listening to the ozone debates.

Opponents of anti-smog efforts have long argued that stricter rules would wreck the economy, as described in a Center for Public Integrity investigation into the 44-year history of ozone regulation.

When an area is out of compliance with the standard, state officials must come up with a plan to control the pollutants that form ground-level ozone, which is subject to EPA approval. Industry groups fear these ozone-reducing efforts will make daily business more expensive and expansions difficult or impossible.

An economic consulting group hired by the National Association of Manufacturers said in February that the rule would cost the U.S. economy $140 billion a year, with higher compliance costs rippling outward in lost jobs, higher electricity rates and other problems.

Clean-air advocates and the EPA said the dire predictions of economic disaster have never come true, and they doubt this time would be an exception. In September, an economic consulting group hired by Earthjustice contended that the manufacturers’ ozone-rule analysis “grossly inflated the cost” — in part due to what it called a $70 billion math error — while ignoring the economic value of better health.

The cost of failing to control ozone is measured in medical bills, lost work days and shortened lives, according to the EPA. Health groups urging the standard be tightened, including the American Academy of Pediatrics and the American Medical Association, pointed to studies that find respiratory problems such as asthma attacks at ozone levels below the 75 parts-per-billion threshold set in 2008. Evidence is also mounting that ozone has problematic effects on the heart, they say.

Ozone-causing pollutants come from a variety of sources, including factories, vehicles, power plants and refineries. But not all are man-made or locally produced. That’s a particular issue for areas in the West dealing with ozone-worsening wildfires and pollution wafting in from Asia.

A new NASA-led study found that only a quarter of the ozone in California and Nevada in the summer of 2008, a period rife with wildfires, was both local and man-made.

Industry groups have pointed to such “background” ozone when arguing against tightening the standard. Health advocates note that states can ask for an exemption if they are able to demonstrate that their air-quality violations were triggered by causes such as wildfires; the EPA has said it will coordinate with states to work through these issues.

Efforts to influence the EPA’s decision on the ozone standard ramped up to a fever pitch in recent weeks.

At least 21 groups, some for and some against a stricter standard, met with the White House’s Office of Management and Budget in September to try to sway officials at that agency, which has the power to change proposed rules.

Both the lung and manufacturers associations released poll results to suggest that Americans are on their side. The two groups also launched dueling ad campaigns, though not exactly on the same playing field: The lung association’s static ads appeared on websites in the Washington area for a cost the group characterized as “low six figures,” while the manufacturers’ multimillion-dollar effort put ads on television in Washington, D.C., and eight states.

One of the manufacturers’ ads focuses on ozone-forming pollutants that travel from China to the western United States. Tighter ozone rules won’t hurt China, the announcer says, “but they could cost our country more than a trillion dollars” — that’s the group’s estimate when tallying up the effect through 2040 — “and kill more than a million jobs per year.” RELATED: How China Is Helping Reduce Pollution in the United States “We reserve this kind of advocacy for the kind of issues that matter a lot to our members, and this is one of them,” said Ross Eisenberg, vice president of energy and resources policy at the National Association of Manufacturers. “It’s not just us — it’s governors, it’s mayors, it’s other business associations, it’s unions and public officials all speaking up, Republicans, Democrats … that this is probably the wrong rule at the wrong time.” Paul G. Billings, senior vice president for advocacy and education at the American Lung Association, said his group’s polling in August suggests that more Americans want stricter ozone standards now than last year, despite the TV ads. “I think the public understands that the vast majority of air pollution is unfortunately homegrown,” he said. “We have the law on our side, we have the science on our side and we have the credibility of health and medical leaders supporting a much more protective standard. What industry is left with is distractions.”

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