Long-term exposure to air pollution, especially ground-level ozone, is like smoking about a pack of cigarettes a day for many years, a new study says, and like smoking, it can can lead to emphysema.
The study, published Tuesday in the medical journal JAMA, is the largest of its kind. It looked at exposure to air pollution -- specifically to ground-level ozone, fine particulate matter, nitrogen oxide and black carbon. The study looked at more than 7,000 adults ages 45 to 84 for over a decade in six US metropolitan areas -- Baltimore, Chicago, Los Angeles,â€¯ New York City, St. Paul, Minnesota, and Winston-Salem, North Carolina.
Using a CT scan, researchers were able to see that that exposure to each of the pollutants was associated with the development of emphysema, a lung condition that causes shortness of breath, and is usually associated with cigarette smoking. It's a debilitating chronic disease that shrinks the amount of oxygen that reaches your bloodstream.
Scientists were able to show a decline in lung function with a spirometry, a simple test that measures how much air you can breathe out in one forced breath.
The patients were all healthy when they started the study, and researchers controlled for factors that could compromise lung health, including age and whether the person was a smoker or was regularly exposed to secondhand smoke.
The strongest association between a pollutant and emphysema was seen with exposure to ozone, which was the only pollutant associated with an additional decline in lung function.
Exposure to ozone irritates and inflames the lining of our lungs when we breathe it in. It can leave us winded, cause asthma attacks, make us more susceptible to infection.
Ground-level ozone is the part of smog that you can't see. It's colorless and it comes from the photochemical transformation that occurs when pollutants interact with sunlight.
"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," saidâ€¯Dr. R. Graham Barr, â€¯the Hamilton Southworthâ€¯professor ofâ€¯medicine andâ€¯epidemiology at Columbia Universityâ€¯Irvingâ€¯Medical Centerâ€¯and a senior author of the paper. One pack-year means smoking a pack of cigarettes a day for a year.
Air pollution levels were estimated at the home addresses of the participants. They were taking part inâ€¯theâ€¯Multi-Ethnic Study of Atherosclerosis Air Pollution (MESA Air)â€¯andâ€¯MESA Lungâ€¯studies.
Ambient concentrations of fine particulates and nitrous oxide, but not ozone, decreased significantly over the study period, the researchers said.
"These findings matter since ground-level ozone levels are rising, andâ€¯the amount ofâ€¯emphysemaâ€¯on CT scansâ€¯predicts hospitalization from and deaths due toâ€¯chronicâ€¯lower respiratory disease," said Barr.
With the climate crisis, there could be much higher levels of ground-level ozone in the future.
"Ground-level ozone is produced when UV light reacts with pollutants from fossil fuels," added Barr. "This process is accelerated by heatwaves, soâ€¯ground-level ozone will likely continue to increaseâ€¯unless additional steps are taken to reduce fossil fuel emissions and curb climate change.â€¯But it's not clear what level of ozone, if any, is safe for human health."
Stephen Holgate, a special adviser on air quality at the Royal College of Physicians in the UK, said that while it had been known for some time that air pollution and cigarette smoking accelerates the development of emphysema in those who are genetically susceptible to it, this study showed that the same was true in the general population. Holgate was not involved in the research.
"This important study adds to the massive evidence base that air pollution, in this case specifically ozone, is harming people, especially those who are vulnerable with co-existent lung disease," he told the Science Media Centre in the UK.
Holgate noted that the study did have some limitations, including the fact that it didn't measure air pollution indoors, where most people spend their time.
"That is the challenge of this kind of research," said study co-author Dr. Joel Kaufman, physician epidemiologist and faculty member at University of Washington.
Studies like this essentially measure pollution as if you spent all your time on your front porch, he said. It doesn't take into account the time you spend in your house or your office, but it's a good general measure that shows exposure to pollution increases lung problems in the general population.
Kaufman says he hopes people will look at research like this and will use it to encourage their leaders to work on better environmental policies and pay attention to their fossil fuel consumption.
Earlier studies predicted exposure to ground-level ozone concentrations could lead to millions more acute respiratory problems and would cost the United States billions of dollars. Exposure to air pollution caused more than 107,000 premature deaths in the United States in 2011 alone, research has found.
"The big surprise was the magnitude of this, putting pollution in the same league as cigarette smoking," said Kaufman. "Cigarette smoking is by far the best known cause of emphysema. The fact that ozone is in the same league was definitely a surprise."