A new multicenter study at Columbia University links long-term exposure to air pollution, especially ozone, to development of emphysema.

Long-term exposure to outdoor air pollutants, especially the pollutant ozone, accelerates the development of emphysema and age-related decline in lung function, even among people who have never smoked, according to a study published in the Journal of the American Medical Association.

The findings may help explain why emphysema is relatively common in nonsmokers.

Chronic lower respiratory disease is the fourth-leading cause of death in the US and third-leading cause of death worldwide. Short-term exposure to air pollutants is a major risk factor for poor lung health. But the long-term effects of air pollutants on the lungs are not well understood.

The study, the largest and longest of its kind, looked at whether exposures to four major pollutants–ground-level ozone, fine particulate matter (PM), nitrogen oxide, and black carbon–were associated with the development of emphysema, measured by CT scan, and decline in lung function, measured by spirometry. (Ground-level ozone harms human health, but ozone high in the atmosphere ozone protects against the sun’s harmful ultraviolet rays.)

The study included more than 7,000 adults (ages 45 to 84) living in Chicago, Los Angeles, Baltimore, St. Paul, New York City, and Winston-Salem, who were taking part in the Multi-Ethnic Study of Atherosclerosis Air Pollution (MESA Air) and MESA Lung studies. Participants were followed for a median of 10 years. Air pollutant levels were estimated at each participant’s home address.

The researchers found that exposure to each of the pollutants at the beginning of the study was independently linked to the development of emphysema during the study period. The strongest association was seen with ozone. Only ozone, at baseline and during follow-up, was associated with a decline in lung function.

Ambient concentrations of fine particulates and nitrous oxide, but not ozone, decreased significantly over the study period.

“The increase in emphysema we observed was relatively large, similar to the lung damage caused by 29 pack-years of smoking and 3 years of aging,”said R. Graham Barr, MD, DrPH, the Hamilton Southworth Professor of Medicine and Epidemiology at Columbia University Irving Medical Center and a senior author of the paper. (One pack-year is equal to smoking a pack a day for a year.)

“These findings matter since ground-level ozone levels are rising, and the amount of emphysema on CT scans predicts hospitalization from and deaths due to chronic lower respiratory disease,” says Barr.

“Ground-level ozone is produced when UV light reacts with pollutants from fossil fuels,” adds Barr. “This process is accelerated by heatwaves, so ground-level ozone will likely continue to increase unless additional steps are taken to reduce fossil fuel emissions and curb climate change. But it’s not clear what level of ozone, if any, is safe for human health.”