The Missouri Department of Natural Resources has requested the U.S. Environmental Protection Agency upgrade Jefferson County's air quality status, now that levels of sulfur dioxide have dropped below the federal limit.

In 2013, the EPA designated Jefferson County as "nonattainment," or not meeting the federal standard for sulfur dioxide, a gas that produces toxic odors and causes respiratory problems. A monitor near the Doe Run lead smelter in Herculaneum detected sulfur dioxide levels above 200 parts per billion, said Kyra Moore, director of the state's air quality control program. After the smelter closed in 2013, levels have dropped well below the 75 parts per billion limit.

However, environmental activists and experts disagree that the air has become cleaner in the county and say that state regulators are ignoring a larger source of pollution in the county.

"The only support for the air being cleaned up is that the smelter has closed and the monitor readings at the smelter are lower," said Maxine Lipeles, director of Washington University's Interdisciplinary Environmental Clinic. "It doesn't address the elephant in the room, which is [Ameren Missouri's] Rush Island [plant]."

Credit Washington University's Interdisciplinary Environmental Clinic A map of expected sulfur dioxide concentrations around the Rush Island Power Plant created from Ameren Missouri's modeling data. The air monitors for sulfur dioxide are indicated by the black triangles.

Lipeles and her colleagues have also argued that the air quality monitors around the Rush Island power plant are placed incorrectly. The three monitors have been placed in areas that are expected to have lower concentrations of sulfur dioxide, according to Ameren's modeling data.

"As a friend of mine used to say, if you ask the wrong question, you get the wrong answer. If you put the monitors in lower concentration areas, that's not going to answer the question [of] are we meeting the standard or not?" said Ken Miller, an environmental scientist who works with Lipeles at Wash U.

The Missouri Sierra Club has also demanded that the air monitors around the Rush Island plant need to be moved and have also pressed the utility to install scrubbers, a pollution control device that removes sulfur dioxide emissions, at the facility.

Steve Whitworth, senior director of environmental policy at Ameren Missouri, said that the company followed the correct procedure in proposing where to place the air monitors and had the locations approved by both the state and the EPA.

"From our perspective, the monitors around the Rush Island facility are appropriately located," Whitworth said.

He added that sulfur dioxide emissions from the plant have decreased by two-thirds since 1990, even as energy consumption rose.

The MDNR is holding a hearing regarding the redesignation on Thursday morning.

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