1.   It can be placed closer to the exhaust manifold, which heats it up quickly, and can purge exhaust smoke of nitrogen oxides as well as unburned hydrocarbons.

2.   The result was the release of several tons of unburned hydrocarbons, which floated over Robstown, four miles downwind.

3.   This would increase the efficiency with which the converter takes carbon monoxide, unburned hydrocarbons and nitrogen oxides and turns them into carbon dioxide, water and nitrogen.

4.   Unburned hydrocarbons are a source of air pollution.