Want to know just how badly polluted the air we're breathing is getting? It can be as harmful for your lungs as a pack of cigarettes a day, new research has revealed. The new data might explain why more non-smokers are getting lung problems traditionally associated with smoking.

This latest study looked specifically at emphysema, a condition which destroys the air sacs in the lungs; it can cause wheezing, coughing and shortness of breath, as well as increasing the risk of death.

Researchers found that higher levels of pollutants in city air – ozone in particular – could cause emphysema to progress as quickly as would be expected from smoking an entire pack of cigarettes every day.

"Rates of chronic lung disease in this country are going up and increasingly it is recognised that this disease occurs in non-smokers," says physician-epidemiologist Joel Kaufman, from the University of Washington.

"We really need to understand what's causing chronic lung disease, and it appears that air pollution exposures that are common and hard to avoid might be a major contributor."

This was an extensive study too, covering 7,071 participants between 2000 and 2018 in six metropolitan regions in the US: Chicago, Winston-Salem in North Carolina, Baltimore, Los Angeles, Saint Paul in Minnesota, and New York City. Data was pulled from air and lung analysis in the Multi-Ethnic Study of Atherosclerosis (MESA).

Having an ambient ozone level just 3 parts per billion (ppb) higher than another area, over 10 years, is comparable in terms of emphysema progression to smoking a pack of cigarettes a day for 29 years, the study found. On average, the levels of ozone in the six study areas covered the 10-25 ppb range.

"We were surprised to see how strong air pollution's impact was on the progression of emphysema on lung scans, in the same league as the effects of cigarette smoking, which is by far the best-known cause of emphysema," says Kaufman.

And ground-level ozone is on the rise, produced when fossil fuel pollutants react with ultraviolet light. While ozone is a useful barrier to UV up in the higher atmosphere, it's not something we want to be inhaling down on the ground.

By itself, a link between air pollution and health problems is nothing new – bad air is obviously bad for us – but this particular study really puts into perspective how much damage we can be doing to our bodies just by breathing in the city air.

The researchers say this is the first longitudinal study to look at the long-term effects of air pollutants on percent emphysema, using a large, community-based, multi-ethnic group of people as study participants. The data that went into the study included detailed air pollution readings at many participants' homes, along with more than 15,000 CT scans.

There is a small bit of good news: as the study found in its readings, levels of polluting particulates in the air are actually dropping in the US, though ozone is bucking this trend.

Other statistics are less encouraging, with the World Health Organisation recently reporting that the majority of the world's children are breathing dangerously polluted air, and pollution being linked to a growing number of health problems.

"As temperatures rise with climate change, ground-level ozone will continue to increase unless steps are taken to reduce this pollutant," says epidemiologist Graham Barr, from Columbia University in New York. "But it's not clear what level of the air pollutants, if any, is safe for human health."

The research has been published in JAMA.