For many people, smog causes wheezing, chest pain and lung inflammation at concentrations well below what is now deemed safe, says a new federal report.
The finding could mean that people in the Baltimore region breathed unhealthful air as many as 79 days last summer, rather than the 11 reported by the state Department of the Environment.
In a review of some 3,000 scientific studies, the Environmental Protection Agency established that repeated or long-term exposure to smog at levels 33 percent below the federal standard can impair breathing and cause potentially harmful changes in the lungs.
Among the more significant findings about health effects during smog episodes:
* The number of people admitted to hospitals with asthma attacks and other breathing problems increased, even when smog remained well within federal limits. A couple of recent studies even suggest that smog may somehow contribute to increased or premature deaths.
* Children at summer camps experienced impaired breathing after playing outdoors in smoggy air. Adults had coughing fits after working or exercising outdoors for prolonged periods, though ozone levels were below the federal standard.
* Even moderate exercise at low levels produced lung inflammation, which some studies suggest may gradually restrict person's breathing, causing a kind of premature aging of the lungs.
Prepared by the EPA's staff scientists, the report summarizes the latest research on how people and plants are affected by ozone, the chief ingredient in the smog that concentrates in Baltimore and 90 other metropolitan areas every summer. Ozone is produced when hydrocarbons from fuel vapors and nitrogen oxides from combustion combine in hot, sunny skies.
The report is the first step by the EPA in a two-year re-evaluation of its ozone pollution standard, unchanged since 1979. That review could prompt the agency next year to propose altering the safety standard, which now says people are at risk when breathing 120 parts of ozone per billion parts air for an hour or more.
Studies in recent years have found that people experience breathing problems and lung inflammation when exposed to air containing as little as 80 parts of ozone per billion, said David J. jTC McKee, a principal author of the EPA report.
Dr. McKee, a biochemist who is overseeing the agency's review of the ozone standard, outlined the research last week to members of the Ozone Transport Commission, a panel representing air-pollution regulators from 12 East Coast states, including Maryland, and the District of Columbia.
Any change in the government's ozone standard could have a major impact on what pollution controls are required of industries, small businesses and motor vehicles.
The report comes at a time when smog appears to be easing in many urban areas, including Baltimore, and ozone-reduction programs are under attack in Congress and in statehouses around the country.
The EPA has reached no conclusions on whether the ozone standard ought to be changed, said Dr. McKee, who works in the agency's Office of Air Quality Planning and Standards in North Carolina.
The report on ozone's effects must first be reviewed by the EPA's panel of scientific advisers, which is scheduled to meet this month.
Of 91 urban areas with smog problems in the late 1980s, 48 did not see ozone levels exceed the current federal limit from 1991 through 1993, according to the EPA. Even in Baltimore, ranked the sixth smoggiest city in the country by the EPA, the average number of days when ozone exceeded the federal limit has declined slightly since the 1980s.
But people still regularly breathe ozone at levels found by recent studies to cause health problems. An American Lung Association review of air quality in Maryland found that, especially in suburban areas such as Edgewood in Harford County and Fort Meade in Anne Arundel County, people are frequently exposed to 80 parts per billion or more of ozone, often for much of the day.
"We have shaved off the peaks, so that air quality looks better right now than it did 10 to 15 years ago, especially in big cities," said Dr. McKee. What hasn't been addressed yet, he added, are long-term exposures to ozone at levels well below the current federal standard.
For most people, the ill effects from breathing smoggy air are relatively minor and reversible once air quality improves, as it often does after a few hours or days in most cities.
But research suggests that from 5 percent to 15 percent of the population is especially sensitive to smog, Dr. McKee said, and relatively low levels of it can cause severe symptoms in those people with what he called "twitchy" airways.
Researchers in Canada and elsewhere have documented increases in hospital admissions for respiratory ailments after air pollution episodes. Dr. McKee said some experts estimate that 10 percent to 20 percent of all East Coast hospital admissions for respiratory problems in the summer are related to smog.
'Over the edge'
Asthmatics and others with chronic breathing problems already are "respiratory cripples" who "can be pushed over the edge" by smog, he said. "There are a lot more of them in this country than people realize."
In Maryland, an estimated 600,000 people have asthma or other breathing problems, according to the American Lung Association.
A few recent studies in cities like Los Angeles and Detroit have linked smog to increased or premature deaths among people with respiratory disease, Dr. McKee said, but he stressed that those findings are still being reviewed.
Lately, scientists have been looking at the subtle, long-term impact of repeated ozone exposure on otherwise healthy people.
Breathing ozone-laden air causes an inflammation of lung tissue, studies say. The inflammation is relatively minor, but animal studies suggest that repeated inflammation can cause scar tissue to form and reduce a person's ability to breathe deeply.
Dr. McKee likened the deterioration to an "accelerated aging" of the lungs.
Lower-level smog also causes widespread but largely unnoticed crop losses, Dr. McKee said. Agricultural studies have found that ozone concentrations below the current standard can cause leaf damage, impair reproduction and increase susceptibility to pests.
Some economists have estimated that ozone-related crop damage costs farmers $2 billion to $3 billion a year, the EPA report says.
For several years, the EPA has been under pressure from environmental groups to tighten the ozone standard.
The federal Clean Air Act requires a tighter ozone standard if scientific evidence shows that the current limit provides no margin of safety for people. In 1979 the standard was relaxed from 80 parts per billion to 120 parts per billion.
But any move to tighten it now may be hampered by regulatory reform legislation passed last week by the House of Representatives. If it becomes law, the measure would forbid federal agencies from issuing new regulations unless the
benefits outweigh the costs.