In China's northernmost province of Heilongjiang, winter heating has become the biggest cause of smog, with coal contributing about 40 percent of overall air pollution, according to the provincial environmental department.
"Heilongjiang has six months of heating due to its prolonged biting cold," according to the department. "Winter heating has the greatest impact on air."
Meanwhile, burning straw has also deteriorated local air quality in the northeast, a region known as "China's granary" for its highly fertile black soil. Local farmers usually dispose of excess straw by burning it after the autumn harvest, which is easy and benefits the soil. But, while farmers take the easy way out, the burning process is being criticized for polluting the air.
Burning straw has contributed greatly to the city's bad air, said the environmental watchdog of Changchun.
As urgency for change mounts, experts say more measures should be taken to tackle the lingering smog.
Zhang Bin said the fundamental way to battle air pollution is changing the current energy structure in China.
"There will be much less smog if China cuts reliance on coal in a large scale," Zhang said. "But it will be a long battle."
Jiang Zhiying, Changchun's city mayor, said while a change in energy structure is necessary, China should tighten grip on the registration of new cars, gradually eliminate vehicles with high emissions and enforce strict bans on straw-burning.
Zheng Hangtian, a teacher with Jilin Communications Polytechnic, said the government should enhance supervision on the law enforcement.
"Related departments should also step up efforts to promote environmental protection to raise public awareness against air pollution," Zheng said.
