SHANGHAI--Smog-prone regions near Beijing and Shanghai posted big improvements in air quality in late 2019, but pollution in other parts of China worsened as dirty industries were relocated rather than shut down, researchers said on Thursday.

China’s Premier Li Keqiang launched a “war on pollution” in 2014, but its main focus has been on clearing the skies in the heavily industrialized and politically sensitive Beijing-Tianjin-Hebei and Yangtze river delta regions where smog levels are much higher than the national standard.

The two regions were on track to meet their target of cutting average concentrations of hazardous airborne particles, known as PM2.5, by 4 percent and 2 percent respectively over the six months to March 2020, the Center for Research on Energy and Clean Air (CREA) said.

However, China’s average PM2.5 was unchanged in the final quarter of 2019 after double-digit increases in provinces like Heilongjiang, Jiangxi and Guangdong, according to analysis of government data by the Helsinki-based research group.

“The rest of the country outside the Beijing and Shanghai priority regions made little to no progress amid continued increases in coal and oil consumption,” said Lauri Myllyvirta, CREA’s lead analyst.

In Beijing, PM2.5 fell 18 percent from October to December 2019, while the surrounding province of Hebei--China’s top steel producer and its most polluted region--also recorded an 18 percent fall in concentrations from a year earlier.

Polluting industrial output moved elsewhere, CREA said, with Hebei cutting steel production by 14 percent and cement by 7 percent in October and November even as nationwide output increased.

CREA said China is on track to meet its 2016-2020 air quality goals after cutting PM2.5 by more than a quarter and sulfur dioxide by more than half in four years.

However, nitrogen oxide emissions declined by a slower rate while ground-level ozone--another major health risk--actually increased.

It warned China’s war on pollution is increasingly subject to diminishing returns, after relying too much on the installation of control technology rather than cuts in fossil fuel use.

“Progress on air quality has relied entirely on better filters, and moving industrial production away from priority areas,” said Myllyvirta, adding that China must now “accelerate the clean energy transition.”

According to China’s Ministry of Ecology and Environment, average nationwide PM2.5 concentrations fell 2.9 percent to 34 micrograms per cubic meter from January to November 2019. It has not published calculations for the whole year. China’s interim national standard is 35 micrograms.

Environment minister Li Ganjie told a meeting earlier this week that anti-pollution efforts would be stepped up in “non-core regions” in 2020.