Excessive reduction of coal combustion might lead to a spurt of demand for scarce natural gas, so coal-to-gas projects should be implemented cautiously and rationally, experts warned.

"Coal consumption has always been blamed as the major culprit of the notorious air pollution, but the reason lies in the utilization technology rather than the coal itself," said Cao Xianghong, a CPPCC member and director of the National Petroleum Products and Lubricants Standardization Technical Committee for more than 10 years.

"Advanced technology enables clean coal to produce very little sulfur content in the emission, and the pollutant discharge of clean coal is on par with natural gas," he said.

According to Cao, China is rich in coal resources but short of natural gas and oil resources. Coal resources have been the major source of energy in the country and will be for the next 30 years, he said.

Replacing coal with cleaner energy like natural gas is a step-by-step process rather than a leap forward, he said.

Cities and regions across the country are shutting down coal-fired boilers and power plants, blamed as one of the major contributors to smog, while replacing coal stoves with natural gas heating to reduce the total amount of coal consumption.

According to the Beijing Environmental Protection Bureau, the capital invested 1.2 billion ($213 million) in the city's coal combustion reduction plan, which aims to cut coal consumption by 600,000 tons a year, sulfur dioxide by 1,680 tons and smoke and dust by 1,392 tons.

The plan also aims to shut down more than 300 polluting companies.

However, Cao said the key lies in the reduction of the total amount of coal consumption as well as use of cleaner coal.

"The coal-to-gas projects should be focused on the maximum emission reduction, and there is no need to replace the coal with natural gas if we can lower the pollutant emission of the coal," he said.

Gas shortage possible

Excessive conversion projects also could cause an abrupt shortage of natural gas and seriously affect the country's energy structure, Cao said.

Regarding large-scale coal consumption companies and enterprises, Cao suggested technologies of denitrification and desulfurization and increasing the proportion of clean coal to fight smog.

The pollutant discharge of a power plant in Zhejiang province, which generates electricity with cleaner coal, is equivalent to that based on natural gas, he said, so there is no need to shut down such plants or replace them with natural gas.

Studies have shown that the sulfur dioxide emission from a ton of coal exceeds the total emission of 100 tons of clean coal consumption, Cao said.

However, for private coal consumers, like small-scale coal-fired boilers and individual coal stoves, replacing coal with natural gas would be the best solution, he said.

According to Cao, heavy users of coal, including medium-size and large thermal power plants, account for about 80 percent of annual coal consumption, while the remaining 20 percent is consumed by individual heating or small-scale coal-fired boilers.

In addition to the use of cleaner coal, experts also suggest that key regions in China adopt the National V fuel standard by the end of this year.

Yang Keng, another CPPCC member, suggested that all municipalities, provincial capitals and cities should adopt the newest standard for fuel, or National V fuel standard, which calls for sulfur content of no more than 10 parts per million.

According to the timetable for fuel quality upgrade nationwide, the National V standard for automobile gasoline and diesel should be implemented nationwide by the end of 2017. Regions including Beijing, Shanghai and Jiangsu have already adopted the new standard.