How stringent is the new limit on ozone?
Republican lawmakers and business groups had urged the EPA to leave the ozone limit at 75 ppb, arguing that a stricter standard will require costly new pollution controls and damage the economy.
What will the new ozone limit mean for California?
The most polluted areas, in Southern California and the San Joaquin Valley, are expected to have until 2037 to meet the standards. That is 12 years longer than the rest of the nation.
To make the required steep cuts in nitrogen oxides and other smog-forming pollutants, the state must undergo full transformation of its transportation sector, including cars, trucks, ships, trains and construction equipment, state regulators say.
How bad is California's ozone pollution?
About one-third of California residents live in communities with pollution that exceeds federal standards, according to estimates by the state Air Resources Board.
Air quality is worst in inland valleys, where pollution from vehicles and factories cook in sunlight to form ozone, which is blown and trapped against the mountains.
The South Coast air basin, which includes Los Angeles, Orange, Riverside and San Bernardino counties, violated the current 75-ppb ozone standard on 92 days in 2014. The highest ozone levels in the nation are in San Bernardino County, which reported a 2012-2014 average of 102 parts per billion.
What are the health consequences?
Ozone is a lung-searing gas that irritates airways and causes respiratory problems such as asthma and bronchitis and worsens heart and lung disease. On high ozone days, hospital visits for asthma rise and the risk of premature deaths increases.
Children, the elderly and people with lung diseases are at greatest risk from ozone. Meeting the new ozone standard by 2025 will prevent hundreds of thousands of asthma attacks and missed school days for children and hundreds of early deaths from cardiovascular disease and other illnesses, according toEPA estimates.
Stricter standards could benefit the health of tens of millions of Americans. More than 40 million people -- or about 1 in 8 people nationwide -- live in counties where air pollution levels exceed the previous ozone standard of 75 ppb, according to EPA data from 2014.
Is smog getting better?
Ozone levels have declined by about one-third nationwide since 1980 as a result of regulations targeting emissions from cars, factories, consumer products and other sources of pollutants, according to the EPA.
In the 1970s and '80s, the Los Angeles region often saw more than 200 bad-air days a year, with ozone levels exceeding 300 parts per billion on the smoggiest summer days. Peak ozone concentrations have dropped to about a third of that, even as the region's population has grown and the number of vehicle miles traveled has doubled.
Why are smog standards changing now?
Scientists, public health experts and environmental groups have pushed to strengthen the nation's ozone standard after years of inaction by the EPA.
Under the Clean Air Act, the EPA is required to review its air quality standards for ozone and other pollutants every five years and adjust them if necessary to reflect the latest health science.
The administration of George W. Bush rejected recommendations for a tougher limit when it adopted the 2008 ozone standard of 75 ppb. The Obama administration vowed to tighten ozone rules, but the president scuttled the proposal four years ago at the start of his reelection bid, leaving the Bush-era limit in place.
A federal court set a deadline of Oct. 1—Thursday—for the EPA to adopt new limits.
What will a new smog standard require?
States will have to impose tighter controls on vehicles, factories, power plants or other emitters of smog-forming pollutants to reduce ozone concentrations over the next decade. The EPA says most counties across the nation are projected to meet the standards by 2025 with only the rules and programs already underway.
Will the new rules hurt the economy?
Business groups and some elected officials have waged a fierce campaign against a stricter ozone standard. The National Assn. of Manufacturers, which has led the opposition and run television ads calling previous rules adequate, has called the ozone rule "the most expensive regulation in U.S. history" and predicts it will stifle economic growth and job creation.
Environmental groups and federal officials say the success of emissions standards that began more than four decades ago is proof they do not cause economic devastation. The Clean Air Act has slashed air pollution by 70% since 1970, while gross domestic product has increased by about 240%, according to the EPA.
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