Dec. 9 (UPI) -- The dangers of smoking are well known, but a new study suggests the habit is likely being made even more hazardous by air pollution.
In a study published Monday in the journal JAMA Internal Medicine, researchers report that long-term exposure to ozone in the atmosphere has significant effects on lung function, particularly among heavy smokers.
Indeed, smokers living in urban or heavily industrialized regions, where ozone levels are generally higher, were more likely to be diagnosed with emphysema and chronic obstructive pulmonary disorders and have more severe disease than non-smokers, they say.
"COPD is known to be caused by exposure to harmful particles and gases, and individuals with existing COPD who are exposed to higher amounts of pollution often have worse disease," study co-author Laura Paulin, assistant professor of pulmonary and critical care medicine at Dartmouth-Hitchcock Medical Center in New Hampshire, told UPI.
The U.S. Clean Air Act was modified in 2015 to strengthen air-quality standards. The change reduced acceptable ozone levels in the air from 75 parts per billion, or ppb, to 70 ppb.
Although dozens have studies have assessed the risk of short-term ozone exposure, few to date have reviewed the risks associated with "historical" exposure, Paulin and her colleagues said.
For their research, they reviewed data from 1,874 current and/or former smokers living in seven cities -- New York City; Baltimore; Los Angeles; Ann Arbor, Michigan; San Francisco; Salt Lake City; and Winston-Salem, North Carolina -- who participated in the Sub-populations and Intermediate Outcome Measures in COPD Study, looking at their lung health following "ambient" ozone exposure over a 10-year period.
The authors predicted two-week mean outdoor concentrations of ozone outside each participant's home using spatio-temporal modeling methods, which incorporated pollutant concentrations previously measured by the Multi-Ethnic Study of Atherosclerosis and Air Pollution Air Study in Baltimore, New York City, Los Angeles, and Winston-Salem; monitoring by the New York City Community Air Study; and regulatory agencies in all seven communities.
Lung function was assessed by multiple methods, including forced expiratory volume in the first second of expiration, or the FEV1, a test used to measure airflow obstruction. It is designed to calculate the amount of air a person can force out of their lungs in one second, with 75 percent considered normal.
In all, more than 65 percent of the study participants had been diagnosed with COPD.
The median two-week ozone concentration of study participants was 25.1 ppb, and ranged from 16.3 ppb in New York City to 29.1 ppb in Salt Lake City. Overall, greater 10-year ozone exposure concentration among current and former smokers was associated with a -2.50 percent lower score on the FEV1.
People "with underlying lung disease and other illnesses who may be more susceptible to the health effects of air pollution exposure should follow publicly available air pollution alerts, available at airnow.gov, and avoid prolonged outdoor exposure on high alert days," Paulin said.
"Minimizing exposure to other known pollutants, such as cigarette smoke and other particulates, is also important in order to reduce overall exposure to harmful air pollution, especially in individuals with COPD," she said.