11.   Government officials have acknowledged that existing policies to limit acidic emissions -- notably of sulphur dioxide -- are inadequate.

12.   The US Environmental Protection Agency has proposed setting up a system by which permits to pollute with sulphur dioxide could be traded among industrial plants.

13.   German technologists have developed a system of filtering out sulphur dioxide and oxides of nitrogen from the flue gases of coal-fired power stations.

14.   He recommended the levying of a pollution tax on emissions of sulphur dioxide from industrial plants and developing low-sulphur coal and other clean energy resources.

15.   They will monitor concentrations of nitrogen oxides, sulphur dioxide, carbon monoxide and low-level ozone, as well as airborne fine dust and hydrocarbons such as benzene.

16.   The basic unit of trade will be the right to emit one ton of sulphur dioxide into the atmosphere each year.

17.   Although RME is more expensive than diesel, it produces no sulphur dioxide and less carbon dioxide, factors which make it particularly suitable for use in urban areas.

18.   Atmospheric levels of sulphur dioxide, an important contributor to acid rain, have begun to fall in Western Europe, but in Eastern Europe remain a severe problem.

19.   Levels of sulphur dioxide, carbon dioxide, lead, airborne dirt and ozone in Mexico City are more than double WHO recommended levels.

20.   The fuel, known as rape methyl ester, emits no sulphur dioxide, halves deposits of particulates and reduces carbon monoxide and nitrogen oxide emissions.