Ground-level ozone levels in the Twin Cities will be high again today, so Minnesota health officials have extended Monday’s air pollution warning.
All of us — but especially children, the elderly and people with respiratory conditions such as asthma and emphysema — are advised by the Minneapolis Pollution Control Agency (MPCA) to limit any outdoor activities that require heavy exertion.
As MPCA’s advice illustrates, the major health concern about ozone pollution (more commonly known as smog) has to do with the respiratory system. Even at relatively low levels, such pollution can irritate and inflame the lungs, leading to coughing, wheezing and breathing difficulties.
But a study published last week in the journal Circulation suggests that ozone pollution poses potential dangers for the cardiovascular system as well. Scientists have long known, from epidemiology studies, that there is an association between ozone and cardiovascular disease, but they believed other particulates in the polluted air were probably responsible for that association. This new study is the first to demonstrate that ozone itself can lead to specific heart-harming physiological changes.
Alterations in biological markers
For the study, researchers at the Environmental Protection Agency in Research Triangle Park, N.C., had 23 young healthy adult volunteers intermittingly exercise in a lab for two hours, first in clean air and then in air containing 0.3 parts per million of ozone. That amount is equal to the ozone a person would be exposed to over seven or eight hours in the average American city.
None of the volunteers, who ranged in age from 19 to 33, complained of any physical symptoms during the experiment. But all developed biological markers during the ozone exposure that could, potentially, harm the heart. Tests showed, for example, that the volunteers’ levels of interleukin-8, a marker for blood vessel inflammation, increased by almost 100 percent, while their levels of plasminogen, an enzyme that helps break down blood clots, fell by 42 percent. There were also subtle changes in their heart’s rhythm.
All the changes were temporary, and thus pose little harm to healthy young adults, such as those in the study. But cardiologists say such changes could cause harm to people with existing heart disease by inflaming plaque, which could then trigger a heart attack or stroke.
‘A credible study’
“It seems to be a very credible study,” said Greg Pratt, a research scientist with MPCA, in a phone interview Monday. “This brings ozone into the realm of having cardiovascular impact.”
Fortunately, he added, Minneapolis-St. Paul has less of an ozone problem than other cities of comparable size, such as St. Louis, Atlanta, Denver, Cleveland and Seattle.
“Our air tends to be cleaner here, and that’s because of our location,” he said. “We’re far to the north, and there are relatively few pollution sources north of us.
Minnesota also has “good winds that blow the pollution that we generate here away,” he added.
For these reasons, Minneapolis-St. Paul meets the national ambient air quality standard for ozone levels, which is based on a three-year average of monitoring data.
The Twin Cities area also meets the standard for fine particular pollution, or soot, which comes from such sources as power plants, diesel engines and wood fires. Last month, however, the EPA announced new, more stringent proposed regulations to reduce the legal limit of soot.
“We may have trouble meeting that new standard here,” said Pratt. It’s also possible, he added, that Minneapolis-St. Paul could one day not meet the ozone standard as well.
Needed: a breath of fresh air
Overall, Pratt said, Minnesota’s air has become much cleaner in recent years, but ozone has stubbornly shown less improvement than other pollutants, with levels “just bumping along.”
And this week those levels are troublesomely high — thus the ozone pollution warning. “When we have a high-pressure system settle in and get a clockwise circulation, the air just sits and spins, bringing up polluted air from the south,” said Pratt. What we need, he added, is a low-pressure system to move in from the north.
In other words, we need a giant breath of fresh air from Canada. It’s predicted to get here by the weekend.