While Baltimore's air is healthier to breathe than it used to be, at least one environmental group thinks it could be cleaner still. 

The Sierra Club released a report this week contending that two power plants in the area - C.P. Crane in Baltimore County, and H.A. Wager in Anne Arundel County - are releasing four times as much potentially harmful sulfur dioxide as the Environmental Protection Agency now deems safe. 

The group, which is campaigning to end or at least reduce coal use, is calling on the Maryland Department of the Environment to step up and require tighter and potentially costly pollution controls at the two facilities.

Sulfur dioxide can cause breathing problems, including asthma attacks. Children, the elderly and those suffering from chronic respiratory diseases are especially vulnerable.  Baltimore leads the state in asthma deaths, and has one of the nation's highest rates of hospitalizing children with asthma, according to the city health department

Crane and Wagner are the last two coal-burning power plants in the Mid-Atlantic region that have neither installed nor plan to install pollution "scrubbers" to reduce harmful emissions, according to the Sierra report.

Maryland's six-year-old Healthy Air Act required the state's largest coal power plants to put in scrubbers, which have greatly reduced their output of harmful pollutants like sulfur dioxide, mercury and particulates.  But these two plants managed to avoid such costly control requirements, which ran up to $1 billion or more on each of the larger plants.

In an attempt to be more protective of vulnerable populations, the EPA recently lowered the acceptable limits on sulfur dioxide in the air. Sierra's report notes that Crane and Wagner are currently permitted to release far more than the new standard permits, and maps indicate that plumes from the plant's smokestacks drift across a huge swath of the region, potentially affecting the air around more than 100 schools, as well as parks and playgrounds. 

Crane and Wagner were owned for years by Constellation but are now being sold by Exelon to Raven Power Holdings LLC, a subsidiary of the New York-based private equity firm Riverstone Holdings.  The Sierra Club wants the state to step in and impose stricter new emission limits on the two plants. It's attempting to generate public pressure on the plant's owners and the state, putting up a billboard along Interstate 95 and developing online ads calling for the two plants to be retired.

Exelon Power spokeswoman Valencia McClure emailed that the plants meet the state's Healthy Air Act and testing has demonstrated they can meet additional pollution reductions being required under the state law.

Jay Apperson, spokesman for the Department of the Environment, said regulators have met with Sierra Club representatives and are discussing with the plant's owners the need for them to take a harder look at their emissions.

But the MDE spokesman noted that air monitoring to date has shown no exceedances in the Baltimore area of EPA's strictur sulfur dioxide limits.  It would be premature, he said, to impose new controls on the plants until these and other questions are answered.