NINGBO, China — Environmental protesters in the city of Ningbo, scene of violent weekend demonstrations, went back to work on Monday after the local government made a carefully calculated concession designed to defuse unrest over plans to expand a petrochemical complex.

The Ningbo government took a leaf from the same book as other Chinese cities when faced with protesters whose demands are environmental rather than broadly political: it announced a halt to plans to build a paraxylene facility at a petrochemical plant owned by a subsidiary of Sinopec, China’s biggest oil refiner, in the Zhenhai seaside area near Ningbo.

That concession largely emptied the streets of demonstrators in the eastern port city, leaving only small groups of curious onlookers outside the Ningbo government offices, where a large police presence prevented crowds from forming.

At the Zhenhai chemical industrial area, where a foul odor hung in the air, a handful of angry young men manned a makeshift barricade complaining that the local government had never followed through on a 10-year-old promise to pay a subsidy to local residents because of pollution.

“It’s too smelly here,” says a young man wearing a white face mask over his nose and mouth. “We are here to protect people’s rights,” he says, declining to give his name. His complaint is only tangential to the main protest about the paraxylene plant, but it highlights how unhappiness over an environmental issue can easily spark broader grievances about issues like inequality of income.

The mood in Ningbo highlights a big challenge facing China’s incoming leaders who are set to take power next month: Chinese are more and more willing to take their grievances to the street, particularly for pollution-related issues.

“The time bomb has already been planted,” says Li Bo, environmental activist and board member of Friends of Nature, a Chinese advocacy group. The pollution that has accumulated during China’s decades of rapid growth is now extremely costly and difficult to manage, he says, and environmental concerns are rising.

When Hu Jintao and Wen Jiabao came into office a decade ago, one of the first big domestic crises they faced was a toxic chemical spill on the Songhua river in northern China that contaminated the water supply for millions of people. Since then environmental disasters – and related public protests – have continued.

As a result Wen and Hu have put environmental protection higher on the agenda than any of their predecessors. But environmental degradation has worsened under their watch and remains one of the key sources of social instability.

“The problem is we still have an opaque environmental decision-making system that is not really open to the public,” says Ma Jun, an environment expert and head of the Institute for Public and Environmental Affairs.

Even the humble chemical paraxylene, or PX, the chemical feedstock that was at the centre of the Ningbo protests, has set off multiple large-scale protests across the country.

In 2007, demonstrations against a PX plant in Xiamen succeeded in halting construction there. In 2011, more than 10,000 protesters in Dalian gathered to demand the closure of a PX facility, eliciting a promise from the mayor that he would shut it down.

But local governments do not always follow through on such promises: when the Financial Times visited the PX plant in Dalian, which is owned by Dalian government-backed Dalian Fujia Petrochemical, in June this year, workers, security guards and outside suppliers all said that far from shutting down production the plant had been expanded and was hiring new workers. One western executive of a big petrochemical company in China said the Dalian plant had not stopped production.

The Dalian government and Dalian Fujia Petrochemical declined to comment when asked whether the Dalian plant was still running and why the government had not followed through on its promise to shut it down.

— Financial Times

Yan Zhang contributed to this story.