BEIJING — Thick, gray, soupy air used to be synonymous with this sprawling city of 22 million.

No longer.

The Swiss firm IQAir AirVisual said Thursday that the Chinese capital could drop out of the list of the world’s 200 most polluted cities, with concentrations of small particulates falling to their lowest level since record-keeping began in 2008.

The data, pulled from sensors installed by the U.S. Embassy in Beijing and local authorities, confirms what many longtime residents have reported anecdotally: a significant improvement in the city’s air in the past two years as the government clamped down on the burning of coal for heating, shuttered polluting factories and kept heavy trucks outside city limits.

Average annual concentrations of tiny PM2.5 particles have decreased almost 60 percent since 2010, according to IQAir, an air purifier manufacturer that issues worldwide air quality reports in partnership with Greenpeace.

The IQAir AirVisual list in 2018 ranked Beijing at 122 among the most-polluted cities. Gurugram, India, a city bordering New Delhi, was ranked as having the world’s worst air quality last year, followed by another New Delhi neighbor, Ghaziabad, and Faisalabad in western Pakistan.

Despite the improvement in Beijing, however, other regions in China appeared to be moving backward as local authorities sought to stoke growth amid an economic slowdown, said Lauri Myllyvirta of Greenpeace.

Myllyvirta noted that emissions of compounds such as nitrogen oxide in northern China’s industrial heartland ticked up last year as a result of a growth in cement and steel production feeding a government-spurred construction boom.

“Old-fashioned smokestack industries are increasing in share and importance” in regions such as Hebei province, he said. “The pressure to hit GDP targets in the short term is a big part of it.”

A key question now, Myllyvirta said, is whether Chinese provinces will adhere to a coal consumption ceiling the central government set for next year in an effort to move the country toward cleaner energy.

China expects emissions of greenhouse gases to peak as soon as 2022, years ahead of the original target of “around 2030” outlined in the Paris climate agreement that numerous countries reached in 2015, a senior Chinese government researcher told Reuters this week.

The Communist Party has been under pressure for decades from a Chinese public fed up with environmental degradation and has invested heavily to become a leader in green technologies such as solar energy and electric vehicles.

At the same, the story of Beijing’s improved air at the expense of poorer, neighboring industrial regions could eventually be writ large on a global scale.

Researchers worry that China — ruled by a Communist Party in which heavy industries such as coal and steel producers remain influential stakeholders — will simply export polluting industries to developing markets abroad under its massive Belt and Road Initiative, which invests in infrastructure projects worldwide.

A report this month by researchers at Tsinghua University in Beijing tallied up $12 trillion worth of these infrastructure projects that could cumulatively generate emissions far beyond the Paris agreement targets and, in the worst-case scenario, lead to an increase in global warming by 3 degrees Celsius.

For instance, hundreds of coal-fired power plants will be built in countries from Pakistan to the Philippines under agreements struck by China.