The skyline of Toronto was masked by pollution on Aug. 12, 2002, when the city was under a smog warning. (Kevin Frayer/CP PHOTO)

Smoggy ozone pollution not only sickens, but long-term exposure can be deadly, according to Canadian and American researchers who conducted a study of the chronic impact of ozone on human health.

"This is the first time we've been able to connect chronic exposure to ozone — one of the most widespread pollutants in the world — with the risk of death, arguably the most important outcome in health impact studies used to justify air quality regulations," said the study's lead author Michael Jerrett, a professor of environmental health sciences at the University of California, Berkeley.

The 23-year study, which appears in Thursday's issue of the New England Journal of Medicine, analyzed the risk of death from two common parts of air pollution — ozone and fine particulate matter —for 450,000 people living in smoggy California to the pristine Midwest.

The researchers found that for every 10 parts-per-billion or ppb increase in ozone level, there was a four per cent increase in risk of death from respiratory causes, mainly pneumonia and chronic pulmonary obstructive pulmonary disease.

Cumulative effect on health

A four per cent increase translates into thousands of excess deaths each year, Jerrett said.

Much of Southern Ontario, parts of Alberta and southern British Columbia face those dangerous levels of the pollutant.

"We see that individuals in high ozone environments are in about a three-fold increase in risk compared to those in the lowest ozone environments," said study author Daniel Krewski of the University of Ottawa.

"What this study says is that to protect the public's health, we can't just reduce the peaks, we must also reduce long-term cumulative exposure," added study author Prof. George Thurston, a professor in environmental medicine at New York University's school of medicine.

The findings show the need to step up the fight against pollution, said respirologist Dr. Gerald Cox of St. Joseph's Hospital in Hamilton, Ont., commenting on the research.

Feels like pounding on the chest

"It changes our standards and changes our focus and changes our target for what we would regards as acceptable ozone exposure," Cox said.

For Debbie Valentini of Toronto, who has had asthma her whole life, the city's smog alerts are unavoidable. Within five minutes of being outside, she said, her chest tightens up.

"I even take my rescue inhaler 15 minutes before I leave the house to prepare myself, but in the heat and really bad smog days, there's nothing I can do," Valentini said.

"It just hits me, and it's just like somebody pounding me right in the chest."

Barring a reduction in air pollution, the only other way for people living in high smog areas to cut their risk of death is to move to rural areas.