Ozone is a gas that can be either beneficial or harmful, depending on its location. The good ozone layer starts about six miles above the earth and extends up to 30 miles. This layer protects life on earth from the sun’s damaging ultraviolet rays. Much closer to the earth is a layer referred to as ground-level ozone. This ozone is the main component of urban smog. It is an air pollutant that is harmful to our lungs, as well as trees and other plants.

Ground-level ozone is created by chemical reactions between so-called nitrogen oxides (NOx) and volatile organic compounds (VOC) in the presence of sunlight. Major sources of NOx and VOC include emissions from industrial facilities and electric utilities, automobile exhaust, gasoline vapors, and chemical solvents. Ozone production is greatest in the summer because sunlight and hot weather combine to increase ozone in the air. Exposure to high levels of ground-level ozone increases the risk for respiratory problems, including:

  • Difficulty breathing
  • Coughing and throat irritation
  • Congestion
  • Chest pain
  • Worsening of bronchitis , emphysema , or asthma
  • Decreased lung function
  • Inflammation of the lining of the lungs
  • Permanent scarring of lung tissue

In 1997, the Environmental Protection Agency (EPA) lowered the air quality standard for ozone to a daily eight-hour maximum of 80 parts per billion (ppb). Millions of Americans live in areas where ozone levels are higher than this standard on many days of the year. A group of researchers from the School of Forestry and Environmental Studies at Yale University and Johns Hopkins Bloomberg School of Public Health set out to determine if short-term exposure to ground-level ozone is associated with greater rates of death. Their results, published in the November 17, 2004 issue of the Journal of the American Medical Association , showed that daily and weekly increases in ozone levels are associated with increased mortality for citizens living in the affected cities.

About the Study

The researchers studied ozone levels and mortality rates in 95 large US urban areas from 1987-2000. Their goal was to calculate a national estimate of the risk of death associated with short-term ozone levels. The EPA’s Aerometric Information Retrieval Service (now called Air Quality System Database) provided air pollution data daily mortality counts for the 14 years of the study came from the National Center for Health Statistics. Deaths were divided into cardiovascular and respiratory causes, while deaths due to external causes, such as injury, were excluded. Using their data, researchers first calculated rates of mortality associated with ozone levels over the past week for specific areas. Next, all 95 rates were combined to produce a national estimate of the association between ozone and mortality.

The Findings

Daily ozone concentration varied across the 95 communities, and averaged 26 ppb. A 10 ppb increase in ozone from one week to the next was associated with a 0.52% increase in daily mortality. This translates into 319 premature ozone-related deaths per year in New York City, for example, and 3,767 premature deaths per year across all urban areas studied. Looking only at deaths due to cardiovascular and respiratory diseases, the increase was 0.64% with each 10 ppb increase in ozone concentration. The mortality rate of a given day was most affected by the ozone exposure on that day or the day before. Exposure levels two days prior and earlier had less effect on the mortality rate.

How Does This Affect You?

Ground-level ozone pollution is clearly a public health problem. Until major environment legislation is enacted and enforced to significantly raise air quality in American cities, AIRNOW, a program sponsored by the EPA, recommends the following steps to minimize your exposure, as well as help reduce the creation of ground-level ozone:

  • If you spend time outdoors, check the Air Quality Index (AQI). If the quality is unhealthy, limit your time outside, reduce the intensity of your activity, or reschedule to a different time of day. Ozone levels are highest in mid-afternoon to early evening. Levels are also high on hot days.
  • Conserve energy. Turn off computers, TVs, and appliances you are not using. Use a microwave when possible; they use up to 75% less energy than a stove or oven.
  • Participate in the local utility companies’ energy conservation programs.
  • Use your car less. Carpool, use public transportation, walk, or ride a bicycle. This is especially important in the warm summer months.
  • Reduce pollution from cars, trucks, gas-powered lawn equipment, boats, and similar equipment by keeping them properly maintained and off when not in use.
  • During the summer, fill your gas tank during the cooler evening hours and be careful not to spill gasoline.
  • Use and dispose of household and garden chemicals as directed. Select paints and solvents that are low in VOC.

All people can benefit from these steps. If you have a respiratory illness, talk with your doctor about any extra steps you should take to help protect yourself from ozone exposure.