BEIJING • Power plants and household heaters fuelled by "clean" natural gas are contributing to the smog in China, rather than helping to tackle the problem in a country that relies on highly polluting coal for most of its energy needs, according to a retired senior government engineer.

Mr Li Chongxing, a former senior engineer at the Ministry of Water Resources, said burning natural gas for energy releases huge amounts of water vapour that combine with pollutants in the atmosphere to cause smog.

In a research paper first published three years ago, but which went viral on the Internet in recent weeks, he estimated that in Beijing alone, the burning of natural gas was enough to fill a small reservoir with water, reported the South China Morning Post (SCMP).

The Ministry of Environmental Protection has disputed the findings, saying Mr Li's conclusions were flawed.

The controversy generated by the report comes as large parts of China's north have been blanketed in thick smog, much of it caused by power stations fuelling heating systems amid the winter cold.

According to Beijing's municipal government, the city burns more than 100 million cubic metres of natural gas in the winter, making it the third-largest user of the fuel among cities worldwide, behind New York and Moscow.

Mr Li said that the high use of gas could imply that up to a third of the relative humidity in typical Beijing smog might come from the burning of natural gas.

The Ministry of Environmental Protection held a press conference to refute Mr Li's research last week, reported SCMP.