Respiratory Hospitalization Study Implicates Ozone


As many as 10% of the tens of thousands of people in Los Angeles County who seek medical care for serious respiratory ailments wind up in hospitals because of breathing ozone, Harvard University researchers and the American Lung Assn. report in a study made public today.

In an analysis of 13 large metropolitan areas, including Los Angeles and San Diego, the researchers estimate that the potent pollutant--the main ingredient of smog--may be responsible for about 50,000 emergency room visits overall during the smoggiest months of the year. The estimate was based on hospital visits in the 13 cities in either 1993 or 1994.

Los Angeles County--which has by far the nation’s worst smog--showed the highest increase in hospitalizations on smoggy days. The Los Angeles data were gathered from February through November 1993.

Of 132,000 people treated in Los Angeles County emergency rooms for respiratory ailments during that time, 8,500 to 13,000 may have contracted them from ozone, the researchers estimate.


Of 44,005 actually admitted to Los Angeles-area hospitals for treatment, the researchers attribute from 2,856 to 4,371 of the admissions to the air pollutant.

The patients in the study went to hospitals suffering from asthma attacks, pneumonia, influenza, bronchitis or chronic obstructive pulmonary disease.

“Our study finally brings to life the reality of smog on the health of people’s lives,” said Dr. Vanessa Tatum, a pulmonologist with the lung association. “These are real people with health problems caused by air pollution. Smog is not simply an inconvenience.”

The researchers did not review each individual’s medical records to determine what caused the sickness. Instead, they came up with their estimates by projecting from four earlier published studies that compared hospital visits on high- and low-smog days in moderately polluted cities. Depending on the amount of pollution, those earlier studies showed emergency room visits jumping by 5% to 43%.

A separate study last month estimated that thousands of people in Greater Los Angeles die prematurely each year from another widespread air pollutant, the particulates that come mostly from cars and diesel vehicles.

Although many health experts say the studies are scientifically valid, they say the work is intended in part to influence national policies to curb pollution.

Health groups such as the American Lung Assn. and environmentalists have stepped up their campaigns because the U.S. Environmental Protection Agency plans to propose new national health standards for ozone and particulates by the end of this year.

The EPA is expected to set tougher limits on ozone because research has shown it affects health when present at lower levels than the current standard, especially among asthmatics and others with chronic respiratory ailments.


For years, health experts have believed that ozone--a colorless gas that forms when pollutants react to sunlight--can cause shortness of breath and aggravate respiratory infections and diseases.

The Harvard-Lung Assn. study for the first time attempts to quantify ozone’s impact on health in cities with the smoggiest air, among them New York, Washington, Dallas, Detroit and Philadelphia.

The rate of hospital visits linked to smog was lower in the other cities than in Los Angeles, where ozone levels are much more severe. In the worst-case scenario presented in the report, the hospital visits blamed on ozone elsewhere varied from a low of 7.6% in Detroit and Milwaukee to 9.6% in Baltimore. San Diego was near the middle, with 8.8%.

Researchers from the Harvard School of Public Health say they would expect to see similar hospitalization rates in other regions where ozone levels exceed health standards. In California, that would include Orange, Riverside, San Bernardino and Ventura counties, the San Joaquin Valley and Sacramento.


Although ozone levels typically rise in months with high temperatures and high pollen counts, the Harvard researchers discounted hospitalizations linked to those causes. Because the overall visits on smoggy days jumped so drastically, most medical experts believe ozone is the reason.

In recent years, ozone levels have declined in most U.S. metropolitan areas, especially the Los Angeles Basin, largely because of emission controls on cars, cleaner-burning fuels and rules targeting various industries.

But in the United States, about 90 million people still live in areas that violate the national health standard for ozone. In the Los Angeles region, ozone levels exceeded the health standard on more than 90 days last year.