In polluted cities and towns around the world, it gets harder and harder to breathe.

Cars fill streets with exhaust and tiny particles. Smoke from factories and power plants fills the skies. On some days, sunny summer days especially, particles get converted into dangerous ozone.

All this air pollution — smog, soot, and ozone — does more than choke the lungs of everyone breathing it in. It's also taxing and harming their brains.

According to a study newly published in the journal Proceedings of the National Academy of Sciences, chronic exposure to air pollution appears to cause detrimental effects on cognition that get worse throughout life, potentially increasing risk factors for degenerative diseases like dementia and Alzheimer's.

We already knew that being exposed to bad air cuts lives short and is bad for kids, harming their developing bodies and brains, according to the study's authors. But the new study shows for the first time that the effect doesn't stop, but instead gets worse as people age, with an especially strong effect on less-educated men.

As the study authors note, this could be making dealing with end-of-life brain illnesses even more expensive, and could ultimately make care for the elderly more complex for society.

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Bad air throughout life

For this latest study, the research team examined data from a national survey that was conducted in 162 random counties throughout China between 2010 and 2014, and compared these results with official air quality data.

By using multiple years of data, the researchers were able to see how particularly polluted times affected verbal and math test scores (Hot summer days tend to have particularly bad pollution, for example). They were also able to see how living in a polluted area changed test scores over time. This cumulative effect was significant.

Image: PNAS

All in all, the study authors found that air pollution takes a bigger toll on verbal test scores than on math scores, though it has an effect on both. There's also a bigger effect on men than on women. The authors attribute this to the fact that air pollution tends to have a stronger effect on areas of brain that are relied on in verbal tests, which the authors wrote tend to be better-developed in women in the first place.

Overall, if residents of these cities in China lived in places that met US EPA standards for air pollution, the authors estimate that it would significantly improve their test scores. To show how much better people might do, the authors explain that these improvements would be significant enough to take someone who scored at median (50th percentile levels) to the 58th percentile on math tests and the 63rd percentile on verbal tests. In the most affected groups, like less-educated men over age 64, this change would be even more significant.

China, like many developing countries, has a large number of cities with serious air quality problems. In the study, the authors wrote that 98% of cities with populations above 100,000 in low- and middle-income countries fail to meet World Health Organization air quality guidelines.

That makes these findings applicable to cities with pollution problems around the world.

We know that there are plenty of reasons to be concerned about air pollution in general, ranging from increased likelihood for lung and heart disease to the fact that air pollution helps drive climate change, potentially causing a number of serious health effects.