Study Finds Smog Raises Death Rate

Times Staff Writer

On smoggy days, deaths from heart and respiratory ailments and other diseases rise, causing several thousand more people throughout the United States to die each year, according to a study published Tuesday that links air pollution and mortality in 95 urban areas.

Scientists have long known that ozone, the main ingredient of smog, aggravates asthma and other respiratory illnesses and causes hospital visits to surge, particularly in severely polluted areas such as Southern California. But the study in the Journal of the American Medical Assn. is the first major nationwide endeavor that links day-to-day ozone levels with an increased number of deaths.

About 40% of the U.S. population lives in the areas analyzed -- including Los Angeles, Orange, Riverside and San Bernardino counties, which have some of the nation’s worst smog -- according to the authors, from Yale and Johns Hopkins universities.

Other places studied include parts of the Bay Area, the Central Valley and San Diego. Outside California, cities include Chicago, Houston, Phoenix, New York, Atlanta, Detroit, New Orleans, Nashville and Seattle.

Francesca Dominici, a biostatistician at Johns Hopkins Bloomberg School of Public Health and a co-author of the report, said the study “provides strong evidence of short-term effects of ozone on mortality” because it pooled results from a large number of urban areas.


The researchers said they found a link between mortality and ozone even in areas with low pollution, at concentrations less than the current federal health standard. Previous smaller studies reached varying conclusions, some finding an increase in deaths and some not.

Scientists have already documented in several dozen studies around the world that deaths increase when airborne pollutants called particulates, or fine pieces of soot, rise. Particulates come mostly from diesel engines. In contrast, ozone, a colorless gas that develops mostly in summer, is formed when nitrogen and hydrocarbon gases from cars, industries and consumer products react with sunlight.

The Los Angeles basin -- with its large population, pollution-trapping mountains and stagnant, sunny conditions -- is like a smog-forming machine. The region has battled ozone for half a century with state and local controls on cars, businesses and other sources. As a result, levels have declined sharply.

“This is a reminder call for the public and for this agency that ozone still is a pollutant with some very serious health effects and one in which we have to be just as aggressive in reducing as particulates,” said Sam Atwood, a spokesman for the South Coast Air Quality Management District, which regulates air pollution in the Los Angeles basin.

The study found that, when ozone levels increased by a fairly small amount, 10 parts per billion, the daily deaths from noninjury causes over the next few days increased an average of 0.52%. For cardiovascular and respiratory deaths, the increase was slightly higher, 0.64%, and for senior citizens, deaths increased by 0.70%.

“In terms of the overall mortality risk, these changes are small, but they do add up,” said Jean Ospital, the air quality agency’s health effects officer. “Because so many people are exposed, the cumulative effects can be significant.”

In New York, the small increase in ozone caused an additional 319 deaths annually. For the 95 areas nationwide, 3,767 more people died per year when ozone increased by 10 parts per billion. Ozone levels fluctuate greatly, and increases of that magnitude occur routinely. In the Los Angeles region, the current federal health standard, 120 parts per billion, was violated 27 days this year. One day last year, it reached as high as 216 parts per billion, almost double the amount deemed healthful. The worst levels occur in San Bernardino County.

Dr. Henry Gong, a professor of medicine at USC and a leading air pollution researcher, called the increase in deaths “plausible” because ozone was a potent irritant that inflamed airways and triggered asthma attacks and other breathing problems. Recent research also has implicated air pollutants, especially particulates, in heart attacks, based on evidence that they damage the nervous system’s ability to vary the heart rate to handle stress.

“Ozone is still lurking out there, particularly in Southern California during the summer, and there are many sensitive people to it, such as asthmatics,” Gong said.

The study’s lead author, Michelle Bell of Yale University’s School of Forestry and Environmental Studies, and the co-authors said the study underestimated the number of deaths because it only captured those within a few days of high pollution levels, not from lifetime exposure.

“We’ve known for a long time that smog is unhealthy, but this is some of the strongest evidence yet that smog actually kills,” said Nat Mund of the Sierra Club.

John L. Kirkwood, president of the American Lung Assn., said the study, funded by the U.S. Environmental Protection Agency and other federal sources, comes “at a critical time in the fight against air pollution” when the Bush administration and Congress are proposing to ease environmental regulations.