Residents in 12 regions across the country are breathing unhealthy levels of sulfur dioxide, the Environmental Protection Agency has found.

The agency this week proposed that these 12 areas — in the states of Illinois, Indiana, Louisiana, Maryland, Michigan, Missouri, Oklahoma, and Texas — are violating the federal government’s health standard for sulfur pollution. If this proposal is finalized, these states will have to come up with plans to lower their sulfur emissions.

That’s important, because sulfur is a dangerous pollutant. Short-term exposure — breathing sulfur-polluted air for as little as five minutes — has been linked to an “array of adverse respiratory effects” including exacerbated asthma symptoms and increased emergency room visits. Sulfur oxides can also form small particulate matter when they react with other compounds in the air, and these particulates can aggravate the lungs and cause or exacerbate respiratory diseases.

“SO2 isn’t really about climate. SO2 is about public health,” Zachary Fabish, staff attorney for the Sierra Club, told ThinkProgress. In that way, it’s similar to mercury and ozone — two other forms of pollution that the EPA regulates.

Fabish said the Detroit area was one of the first regions that the EPA identified as having higher-than-healthy levels of sulfur. “I’ve spoken to a lot of folks who live in and around Detroit who have just heartbreaking stories about kids with chronic asthma because the air quality is so bad,” he said. “They miss tons of days of school — I’m not talking about one or two days a semester, but like dozens of days.”

CREDIT: Environmental Protection Agency

Most of the country’s emissions of sulfur dioxide come from big industrial plants — mostly, power plants that burn coal, as well as some chemical facilities and refineries.

“Sulfur dioxide is pretty unique in that something like 90 percent of all the SO2 emitted in this country comes from only a few hundred really large emitters,” Fabish said. “You have a small handful, relatively, of very large emitters of SO2, and that’s where the problem comes from.”

The solution to reducing sulfur from these power plants is pretty simple, however: install a scrubber system, which uses limestone slurry to interact with, and ultimately reduce, SO2 emissions from the plant. Fabish said a good, well-designed scrubber can reduce sulfur emissions in power plants by anywhere from 90 to 97 percent. The problem is, scrubber systems cost money — which is one reason why some plants haven’t yet installed them. Regions out of compliance may need to work with power plants to come up with plans to install scrubbers, or to begin operating their existing scrubbers correctly. Or, in some cases, it may be most cost-effective to shut down aging power plants that aren’t in compliance.

The Sierra Club still wants the EPA to do more on sulfur, however. While the agency identified 12 regions with high levels of sulfur pollution, there are still others, the environmental organization says, that the EPA hasn’t looked at.

“The EPA has failed to include areas with some of the highest levels of sulfur dioxide pollution in the country, places like Jefferson County, Arkansas, and Gibson County, Indiana,” Mary Anne Hitt, the director of the Sierra Club Beyond Coal Campaign, wrote in a recent blog post. “The EPA has the data to identify and crack down on the polluters responsible for creating these conditions, and they need to do just that by designating all areas with high sulfur dioxide pollution levels as being ‘out of compliance’ with clean air standards.”