During coal combustion in a furnace, volatile components burn without much difficulty.

In fact, coal combustion probably was the main factor in the deaths, the researchers said.

Also neglected is the "greenhouse effect," a feared warming of the atmosphere caused by carbon dioxide from coal combustion and burning forests.

Two of the narrow gauge locomotives were later rebuilt to improve coal combustion and reclassified.

Another problem related to coal combustion is the emission of particulates that have a serious impact on public health.

The sulfur dioxide produced in coal combustion poses an immediate threat to the health of China's citizens, contributing to about 400,000 premature deaths a year.

Another 2,000 - 3,000 tons are released by human industrial activities such as coal combustion, metal smelting and cement production.

The coal-derived synthetic gas is much cleaner than conventional coal combustion to begin with, and it is easier to clean to greater extent.

Historically, the term has been used to refer to technologies for reducing emissions of ash, sulfur, and heavy metals from coal combustion.

The byproducts of coal combustion are considerably hazardous to the environment if not properly contained.