SHANGHAI, Dec. 9 -- The smog that blanketed over 100 cities in half of China last week has rekindled criticism of insufficient efforts in the fight against air pollution.

Among urban residents, severely polluted air has become a main source of complaints and frustration over health concerns.

Late last week, the Air Quality Index (AQI) in dozens of cities in eastern China topped or neared 500. AQI of over 300 cities is defined as "serious pollution."

Many rushed to buy face masks and air purifiers to ward off the choking smog, a result of decades of breakneck economic growth. The dirty air even forced all primary and middle schools in the eastern city of Nanjing to close for two days.

"The smog is everywhere," said Xiong Yuehui, head of the science and technology department of the Ministry of Environmental Protection, at a meeting on Sunday in Shanghai. "If one place is free of smog, then it will be a news," he said.

The world's second-largest economy does not lack the technology and funds needed to clean up the air, but lacks the implementation of concrete efforts, Xiong said.

About 22 million tonnes of sulfur dioxide are emitted into the air untreated each year while the remaining two thirds of the total emissions, or 40 million tonnes, have their sulfur removed, according to data from the ministry.

However, Luo Jianhua, secretary-general of the China Environment Service Industry Association of the All-China Federation of Industry & Commerce, expressed doubt about the authenticity of the sulfur removal rate. He believes that many polluting companies often shut down their pollution treatment facilities to cut costs.

Bian Cheng, chairman of environmental protection equipment manufacturer Keda Industrial Co., Ltd., blamed loose supervision for the smog and called for tough law enforcement.

Wu Xiaoqing, vice minister of environmental protection, said the agency was working to put in place a responsibility system to punish government officials for environmental degradation.

Xiong said the ministry was also working to toughen environmental protection standards. "The new standards approved last week called for some 2,000 cement plants nationwide to improve pollution treatment facilities," the official noted.

Meanwhile, many cities nationwide will enforce limits on emissions of fine particles in mid-2014, forcing many highly polluting plants to upgrade their pollution treatment facilities, according to Xiong.

Many blame China's coal-dominated energy mix for the pollution, and Bian agrees that coal is the main cause of smog. However, he said, China can only go so far in minimizing coal consumption.

It cannot be completely replaced by gas and therefore the current priority is to promote cleaner use of coal. "If coal can be used in a cleaner way, the air quality would then see a dramatic improvement," according to Bian.

Coal can be converted into gas and with high standards on desulfurization and denitrification in place, he added.