Environmental pollution is often expressed in environmental indicators. An environmental indicator totals the effects of the various substances which contribute to a particular kind of environmental pollution and reflects the harmful effects to the environment. The environmental indicator overfertilsation refers to emission of phosphorus (P) and nitrogen (N). The main source of acidifying pollutants are sulphur dioxide (SO2), nitrogen dioxide (NOx) and ammonia (NH3). The chemical compounds carbon dioxide (CO2), dinitrogen oxide (N2O) and methane (CH4) contribute to the greenhouse effect. Ozone depletion is caused by emission of CFCs. Heavy metals dumped into water consist of emissions of copper, chromium, zinc, lead, cadmium, mercury and arsenic.
Emissions of the above substances are calculated on the basis of the environmental accounts definition. In compliance with these definitions, emissions by Dutch residents abroad are also included, e.g. emissions by Dutch tourists abroad.