The air quality in the Netherlands is not only being determined by Dutch emissions, but also by emitted substances from outside its borders. In the latter case, this concerns air pollutants that can be transported over large distances, such as those that cause acidification and/or eutrophication: sulphur dioxide (SO2), nitrogen oxides (NOx), ammonia (NH3), particulate matter, heavy metals, volatile organic compounds (VOCs) and persistent organic pollutants (POPs). The environmental impact of these substances negatively affects ecosystems, materials and human health.

Air pollution has multiple origins

Large-scale air pollution is caused by a number of substances with large-scale dispersion patterns, which can occur at undesirably high concentration levels. This could lead to health effects, especially from ozone (O3) and particulate matter (PM10), as well as from nitrogen dioxide (NO2). Although nitrogen dioxide is not particularly harmful at its current concentration levels in the atmosphere, it is used as an indicator of traffic-related air pollution - which ís considered damaging to human health.

Acidifying and eutrophying deposition can be harmful

Excessive acid deposition leads to changes in the species composition of vegetation. The excessive deposition of nitrogen, called eutrophication, mainly causes a decline in biodiversity. The ecological effects of eutrophication are currently more prominent than the acidifying effects of sulphur and nitrogen. Because the presence of nitrogen is a decisive factor in the competition between plant species, and because excessive nitrogen input mostly results in additional plant growth, it causes certain plant species to increase at the expense of others. This, in turn, causes a decrease in biodiversity. The overgrowing of heathlands and forests with grasses, as well as the duckweed and algal bloom, are typical examples of the results of eutrophication.

Sources vary greatly

The above named substances originate from various sources. The agricultural sector, for example, is by far the most important source of ammonia. Traffic is largely responsible for nitrogen oxides, closely followed by the industrial and the energy sector. Industry is the largest source of sulphur dioxide emissions, caused by the combustion of fossil fuels, and volatile organic compounds are mainly caused by traffic and industry.

European regulations help to improve environmental quality

One of the European policy targets is to improve air quality. To achieve this, air quality targets have been formulated for a large number of substances, including nitrogen oxides, particulate matter, benzopyrene and some heavy metals. At the same time, according to Natura 2000 and the Birds and Habitats Directives, the biodiversity in the allocated nature areas also needs to be maintained. For the Netherlands, nitrogen deposition remains one of the most limiting factors for biodiversity.

Prevention at the source

In 1991, thirty-one countries, including all EU Member States, agreed on setting an emission ceiling for 2010 in the so-called Gothenburg Protocol. On 23 October 2001, the EU Member States entered into a binding agreement on emission ceilings, in the National Emission Ceilings Directive (NEC Directive). The targets for the Netherlands have been set in the fourth National Environmental Policy Plan. These Dutch targets have been set with narrower margins than those agreed on, internationally. This was done to create a safety margin for dealing with possible setbacks.

The role of the Netherlands Environmental Assessment Agency (PBL)

The PBL is closely involved in the scientific developments around air pollution and acidification. This includes the (European) air quality directives, recent publications such as Ammoniak in Nederland (Ammonia in the Netherlands) and Het ammoniakgat: onderzoek en duiding (The ammonia discrepancy: research and meaning), and the production of the Large-scale concentration maps for air pollution in the Netherlands (GCN maps). PBL houses the Coordination Centre for Effects (CCE) of the Convention on Long-range Transboundary Air Pollution (LRTAP), as well as the European Topic Centre on Air and Climate Change (ETC/ACC). Moreover, the PBL chairs the Task Force on Integrated Assessment Modelling (TFIAM) of the Convention on Long-range Transboundary Air Pollution.