Increases in air pollution caused by cars, power plants and industry can be directly linked to higher death rates, according to a major study published in this week's issue of the Journal of the American Medical Association.
Reducing such ozone pollution, or smog, by about 35 percent on any given day could save about 4,000 lives a year across the United States, researchers concluded in the study funded in part by the U.S. Environmental Protection Agency.
The risk of death was similar for adults of all ages and slightly higher for people with respiratory or cardiovascular problems, the researchers said, adding that the increase in deaths occurred at ozone levels below EPA standards.
The conclusion came from a look at 95 urban areas where about 40 percent of the U.S. population lives, comparing spikes in ozone pollution there with death rates from 1987 to 2000.
Ground-level ozone typically increases when temperatures rise. While short-term increases have been recognized as causing jumps in hospital admissions, especially among those with chronic respiratory problems, there have been inconsistent results from studies tying them to mortality rates, the authors said.
'Underestimates the total impact'
“By linking day-to-day variations in ambient ozone levels and daily number of deaths in each of the urban areas, and pooling the results across the 95 urban areas, this study provides strong evidence of short-term effects of ozone on mortality,” said Francesca Dominici, an author of the study and researcher at the Johns Hopkins Bloomberg School of Public Health.
“This is one of the largest ozone pollution studies ever conducted,” added Michelle Bell, the lead author. “This actually underestimates the total impact of ozone on mortality, because it only captures the mortality impact associated with high ozone levels in the past few days, not the impact associated with a lifetime exposure to high ozone levels,” she said.
“This reduction of ozone is modest given available technology,” she added. Ozone pollution can be reduced by equipment that captures pollutants or by lowering energy consumption through such things as carpooling and using public transportation.
The American Lung Association called it a "landmark" study.
"This research shows that ozone may indeed kill people," association president John Kirkwood said in a statement. "Early death would join the long litany of harmful effects of ozone exposure: shortness of breath, chest pain, wheezing and coughing and greatly increased risk of respiratory infections, asthma episodes, pulmonary inflammation, and the need for medical treatment and hospitalization for asthma. More may come as new studies are raising the possibility that ozone may cause asthma to develop in children."
Looking at the raw data
The study found that an increase of 10 parts per billion in ozone pollution in the previous week was associated with an increase of 0.52 percent in the daily death rate and specifically with a 0.64 percent increase in cardiovascular and respiratory-related deaths.
People aged 65 to 74 had a slightly higher increase in the death rate, at 0.70 percent.
The 10 parts per billion increase would correspond to an additional 319 annual premature deaths in New York City and 3,767 premature deaths annually for the other urban communities, the study concluded.
The authors said the 10 parts per billion figure chosen a unit for the study has no special significance in itself other than that it helps demonstrate that higher ozone is associated with higher mortality.
While ground-level ozone is considered a hazard, stratospheric ozone is not because it helps protect the Earth from harmful solar rays.
The study follows one published that found similar effects in 19 of 23 European cities reviewed. That study was published in the American Journal of Respiratory and Critical Care Medicine.
EPA urged to do more
Kirkwood said the EPA could and should do more. "In April, EPA issued guidance that gave the states and local governments far too much leeway in meeting the current health-based air pollution standards," he said. "Earlier this year EPA proposed weak, drawn out measures to clean up coal-fired power plants that contribute significantly to the ozone and particle pollution problems in the eastern United States."
"This study comes at a critical time in the fight against air pollution," he added. "Some in Congress and the administration have expressed the desire to ease the 'burden' on polluters by rolling back key provisions of the Clean Air Act and weakening its requirements."
The EPA, for its part, notes that smog levels have improved over the years and counters that its more flexible rules aim to achieve even greater pollution reductions than what would have been the case without them.
"We learned that using collaborations, incentives and a direct focus on results accelerates our efforts to clean the air," EPA chief Michael Leavitt said earlier this year.
Reuters contributed to this report.