Even in a mountain wilderness, periods of moderate levels of ozone -- the main ingredient of urban smog -- can decrease active people's lung function, a study led by researchers at Brigham and Women's Hospital and the Harvard School of Public Health has found.
The researchers said their two-year study showed ozone levels common to non-urban parts of the United States were associated with decreases in lung function in adult hikers on Mt. Washington in the White Mountain National Forest in New Hampshire. These declines were more pronounced in hikers with a history of asthma or wheezing.
Their study results are published today in the February issue of Environmental Health Perspectives, the monthly journal of the National Institute of Environmental Health Sciences.
The study evaluated the effects of ozone and other air pollutants, including fine particulate matter and suspended acid droplets, on the lung function of 530 nonsmokers hiking on New Hampshire's Mount Washington during two summers. When ozone went up slightly, lung function decreased, the researchers said.
The hikers ranged from 18 to 64 years of age and hiked an average of eight hours each. During this time, they were exposed to average ozone concentrations from 21 to 74 parts per billion (ppb) per hour. The overall average exposure was 40 ppb, which the researchers called "a relatively low level characteristic of much of the continental United States."
Researchers measured the hikers' forced expiratory volume -- the volume of air they could expel from their lungs in one second -- and forced vital capacity -- the total volume of air expelled from the lungs - before and after their hikes. They found that a 50 ppb increase in ozone concentration was associated with decreased lung function over the course of the hike - an average 2.6 percent decline in forced expiratory volume, and a 2.2 percent decline in forced vital capacity.
The investigators found that hikers with a history of asthma or wheezing had an even greater decline: Their ozone-related changes were approximately four times greater than those of the remaining subjects. The researchers say these effects are important because they occurred among hikers exposed to relatively low ozone concentrations when compared to the recently revised National Ambient Air Quality Standard of 80 ppb over eight hours.
"Physicians, public health officials and the general public should be aware of the potentially negative health impact of relatively low levels of air pollutants, not only among residents of urban and industrial regions, but also among individuals engaged in outdoor recreation in wilderness areas," said lead author Susan Korrick, MD, MPH, an environmental epidemiologist at the Channing Laboratory at Brigham and Women's Hospital, which is in Boston.
The research was funded in part by the National Institute of Environmental Health Sciences, which is a part of the National Institutes of Health; the U.S. Environmental Protection Agency; the Appalachian Mountain Club, and the White Mountain National Forest.
The Brigham and Women's Hospital is a nonprofit teaching affiliate of Harvard Medical School.
Journal
Environmental Health Perspectives