Maryland didn’t mention sulfur-dioxide levels in its latest progress report on air quality. The EPA has issued a preliminary determination that parts of the state have not met federal standards. (Regis Duvignau/Reuters)

Maryland officials left a key pollution measure out of a glowing assessment released this month of the state’s compliance with federal air-quality standards.

An annual report from the state Department of the Environment touted Maryland’s progress in meeting federal guidelines for air pollutants such as nitrous oxide and ground-level ozone. But it neglected to mention sulfur dioxide, which can cause asthma and other breathing problems.

Large swaths of northern Anne Arundel and southern Baltimore counties exceed federal limits on sulfur dioxide, according to a preliminary finding from the U.S. Environmental Protection Agency in February. The state has appealed the determination, and the EPA plans to issue a final designation by July 2.

“We’ve made a lot of great progress on air quality, and we applaud that, but specific communities still have to deal with sulfur-dioxide issues,” said David Smedick, a policy specialist with the Sierra Club environmental group. “We think that needs to be acknowledged in our state reports.”

Jay Apperson, a spokesman for the state agency, said the annual report released this month alluded to sulfur dioxide levels by mentioning that the state met federal standards for “fine particle-pollution” in 2012 and that those levels continue to drop.

“Sulfur dioxide is a precursor to fine-particle pollution,” Apperson said.

Federal guidelines limit sulfur dioxide levels to 75 parts per billion. The state’s analysis shows that the area in question fell slightly below that pollution level, with 71 parts per billion. But the EPA, using Sierra Club measurements, determined that the levels had actually reached 112.3 parts per billion.

Maryland challenged the EPA’s initial finding on grounds that the Sierra Club’s modeling was flawed. The state cited several factors that it believes exaggerated sulfur-dioxide levels in the Sierra Club analysis, including the location of receptors and techniques that analysts used for processing meteorological data and smokestack temperatures.

“These errors in the Sierra Club modeling make it unsuitable for use in the designation process,” the state agency said.

Maryland Secretary of the Environment Ben Grumbles said he is confident in his agency’s finding that sulfur dioxide is within federal limits, adding that the agency “enjoys a national reputation for its expertise in air quality science.”

Smedick, in turn, defended the Sierra Club’s system of measurement, noting that the EPA said in a technical document that the group’s modeling “most closely follows the guidance outlined in EPA’s modeling and is more representative of actual air quality conditions.”

Environmental watchdogs say the Herbert A. Wagner coal power plant, located along the Patapsco River in Anne Arundel County, is the primary contributor to sulfur-dioxide pollution for the area in question. The facility is among the largest single sources of air-pollution on the East Coast, according to the EPA.

If the EPA finalizes its preliminary determination on July 2, Maryland will have to develop a plan to reduce sulfur-dioxide in the area.

Smedick said the Wagner plant should utilize technologies such as “scrubbing” mechanisms that can capture some of the sulfur-dioxide emissions from smokestacks.

State environmental officials say Maryland’s power generators have already invested more than $2 billion in air-pollution controls since 2007.