But few epidemiological studies have analyzed associations between air pollution and cognition in older adults, a team of researchers from France and Britain wrote in a 2014 study in the journal Epidemiology. Their study found that traffic-related pollution in greater London was associated with declining cognitive functions over time among study participants, who had an average age of 66.

In China, which already has the world’s largest population of people with dementia, the number is expected to rise to 75.6 million by 2030, up from about 44.4 million in 2013, according to a report that year by Alzheimer’s Disease International, a nonprofit based in Chicago.

The new study’s findings “imply that the indirect effect on social welfare could be much larger than previously thought,” the authors wrote. “A narrow focus on the negative effect on health may underestimate the total cost of air pollution.”

The study used test scores from the 2010 and 2014 editions of China Family Panel Studies, an interview-based exam given nationwide, as well as air-quality data from readings of three types of pollutants: sulfur dioxide, nitrogen dioxide and particulate matter that is smaller than 10 micrometers in diameter, called PM10.

“Essentially, we compare the same person in two time periods,” said Zhang Xin, the study’s lead author and a pollution expert at Bejing Normal University, referring to the study’s methodology. “The major variation stems from exposure to local air pollution at the date of interview, which is largely random.”

The study found that “accumulative exposure” had a pronounced impact on verbal test scores — especially for older, less-educated men — and that cutting the local concentration of PM10 to levels that meet United States Environmental Protection Agency air quality standards would move people up from the median, or 50th percentile, to the 58th percentile on math test scores and the 63rd percentile on verbal scores.

He Guojun, an economist at the Hong Kong University of Science and Technology who studies pollution in China, said that he hoped the new study would be the first of many to examine apparent links between pollution and cognition in China. “The paper is quite solid, both in terms of data and methodology and results,” said Dr. He, who was not involved in the study.