Like smoking, long-term exposure to ground-level ozone can can lead to emphysema.

The study is the largest of its kind, and looked at more than 7,000 adults ages 45 to 84 for over a decade.

CNN reports the patients were all healthy when they started the study. Scientists were able to show a decline in lung function with a spirometer, a simple test that measures how much air you can breathe out in one forced breath. The strongest association between a pollutant and emphysema was seen with exposure to ozone.

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.

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