Days with unhealthful air will soar unless emissions are slashed, study says

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Smog could worsen across the United States in the coming decades as climate change boosts summer temperatures and makes ozone levels more difficult to control, a new study says.

Americans can expect the number of days with unhealthful air to rise 70 percent by midcentury unless emissions of smog-forming pollutants are slashed, according to a study led by the federally funded National Center for Atmospheric Research in Boulder, Colo.

Higher temperatures accelerate the formation of lung-searing ozone, the main ingredient of smog, and could set back decades of improvements in air quality, the study says. “It will hinder our progress,” said Gabriele Pfister, a scientist at the center and lead author of the study published last week.

Regulators, however, could keep the warming climate from degrading air quality if they adopt stringent emissions controls, the research showed.

To reach their conclusions, scientists used a supercomputer to simulate pollution levels across the nation as the planet warms.

They found a widespread increase in the number of days above federal standards for ozone by 2050 if emissions of smog-forming pollutants remain at their current levels. In that scenario, almost the entire continental U.S. would have at least a few days of unhealthful air a year, and the most heavily polluted metropolitan areas would see ozone levels exceed health standards for most of the summer, the research showed.

Cutting smog-forming emissions by 60 percent to 70 percent, however, would achieve big reductions in ozone pollution even as the climate warms, the analysis found, with the number of days above federal health standards falling below 1 percent of current levels. “If we can really cut back on our local emissions, then we can clean up our air,” Pfister said.

The link between higher temperatures and ozone was already known, but Pfister said it was the first fine-grain analysis of how the warming climate could affect air quality in all regions of the country.

Ozone is a harmful gas that forms when pollutants from vehicles, power plants and factories react in sunlight. Heat speeds up those reactions, so it will be harder to keep ozone levels in check as temperatures rise from the buildup of greenhouse gases in the atmosphere.

Contributing to higher ozone levels globally is methane, a greenhouse gas emitted by oil and gas activity, landfills and livestock. Higher temperatures also cause plants to release more volatile organic compounds, which can boost smog formation when they mix with man-made pollutants.

Ozone can inflame and damage the body’s airways, trigger respiratory problems and aggravate asthma and bronchitis.

Based on robust scientific evidence that ozone is harmful at lower levels than previously thought, the U.S. Environmental Protection Agency is considering stricter health standards that would require state and local regulators to make further emissions cuts.

Recent reports by local air agencies and the American Lung Association have also warned of the effects of climate change on smog, particularly in California, where residents of the greater Los Angeles area and the San Joaquin Valley breathe the dirtiest air in the nation.