The worsening air quality of inland cities should be a warning to policymakers that tough anti-smog measures need to be expanded beyond the traditional industrial centres, environmentalists said.
"The smog problem is expanding fast into inland cities, and their residents simply cannot wait another five years," said Huang Wei , a climate and energy campaigner with Greenpeace.
The five-year clean-air plan released by the State Council in September requires only cities within three built-up areas - the Yangtze and Pearl river deltas and the metropolitan cluster including Beijing, Tianjin and Hebei - to cut levels of PM2.5, potentially hazardous particles smaller than 2.5 microns in diameter.
The rest of the country needs only to reduce quantities of the larger and less dangerous PM10 before the plan ends in 2017.
Central authorities decided that air pollution outside of the three main industrial areas was still tolerable and required less immediate action, analysts said. Keeping the air pollution requirements lax in other areas will allow them more freedom to develop their local economies.
But the policy gap between the regions could create a loophole allowing polluting industries to relocate to areas with looser rules as the overall smog problem persists, Huang said.
Beijing, for instance, already imports electricity from surrounding regions, like Inner Mongolia. Guangdong similarly plans to relocate some of its coal-fired power plants to less-developed areas outside the Pearl River Delta, she said.
"These are all worrying signs for pollution transfer as such moves could create new problems before the old ones are solved," Huang said.
With their neighbours left out of the fight, the three major city clusters may also fail to meet their own smog-reduction targets as pollution blows in from outside.
Chai Fahe , vice-president of the Chinese Research Academy of Environmental Sciences, said the data showed that pollution emissions in many regions had exceeded the environment's capacity to absorb them.
"Most of the pollution is locally generated," Chai said. "Still, many of these areas - except for the three regions - do not have obligations to cut PM2.5."