The high-pressure system that has roasted much of the Northeast in recent days brought with it other unpleasant summer visitors: soot and smog. For most of the week, a "Code Orange" alert has been in effect in Maryland as seniors, young children and those with health issues such as asthma that might make them sensitive to polluted air have been advised to stay indoors.

That's because such pollution, known as ground-level ozone — formed when sunlight interacts with certain emissions (chiefly from cars and electric-power generating plants) — can be deadly. It can damage lung tissue, aggravate respiratory and heart disease and cause people to be more susceptible to infection. When ozone levels are high, hospital emergency room visits usually increase correspondingly.

Maryland has taken considerable steps in recent years to reduce the ozone problem, but the state is severely limited in what it is able to do. An estimated 50 percent to 70 percent of the smog on a typical summer day comes from outside Maryland's borders, chiefly from the Midwest.

That's why new rules proposed this week by the U.S. Environmental Protection Agency to curb the sulfur dioxide and nitrogen oxides pouring out of Midwest power plants are so critical to the efforts to improve air quality in downwind states like Maryland. The aging, coal-fired plants are huge contributors to the problem — but beyond the grasp of Maryland's regulatory authority.

The EPA estimates that it could cost $2.8 billion per year to bring the facilities into compliance with the proposed rules but would produce $120 billion in annual health benefits. Already, power plant operators are balking at the requirements, particularly with further regulations (long-term limits on mercury and perhaps tougher ozone standards among them) expected to be proposed by the EPA next year.

Would the proposed limits on pollution lead to brownouts and blackouts or raise electricity costs for millions of people living in dozens of states? The best evidence suggests no. Maryland's efforts to restrict power plant emissions within the state's borders haven't led to higher rates, and environmental officials say state limits are more restrictive than what the EPA has proposed. Plants have simply been forced to invest in readily available technology.

Nevertheless, many of the worst polluters are older, coal-fired plants that simply are no longer viable and need to be retired anyway, particularly if the U.S. is to limit or reduce greenhouse gas emissions that contribute to global warming. Those facilities have been living on borrowed time made possible only because of a much-abused grandfather provision of the Clean Air Act.

The public has a right to breathe clean air and, if anything, the federal government has been too slow to uphold it. The rules are a good step toward protecting the rights of Marylanders and others living in this part of the country who shouldn't have to choke on pollution blowing in from the west. The agency needs to stand firm against what blows in next — the inevitable attempts in Congress or the courts to weaken the regulations.