Executive summary

Nature of the problem

• The future effects of nitrogen in the environment will depend on the extent of nitrogen use and the practical application techniques of nitrogen in a similar way as in the past. Projections and scenarios are appropriate tools for extrapolating current knowledge into the future. However, these tools will not allow future system turnovers to be predicted.

Approaches

• In principle, scenarios of nitrogen use follow the approaches currently used for air pollution, climate, or ecosystem projections. Short-term projections (to 2030) are developed using a ‘baseline’ path of development, which considers abatement options that are consistent with European policy. For medium-term projections (to 2050) and long-term projections, the European Nitrogen Assessment (ENA) applies a ‘storyline’ approach similar to that used in the IPCC SRES scenarios. Beyond 2050 in particular, such storylines also take into account technological and behavioral shifts.

Key findings/state of knowledge

• The ENA distinguishes between driver-oriented and effect-oriented factors determining nitrogen use. Parameters that cause changes in nitrogen fixation or application are called drivers. In a driver-based approach, it is assumed that any variation of these parameters will also trigger a change in nitrogen pollution. In an effect-based approach, as the adverse effects of nitrogen become evident in the environment, introduction of nitrogen abatement legislation requiring the application of more efficient abatement measures is expected. This approach needs to rely on a target that is likely to be maintained in the future (e.g. human health). Nitrogen abatement legislation based on such targets will aim to counter any growth in adverse environmental effects that occur as a result of increased nitrogen application.

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Air pollution is known to have a range of effects, including those on human health, crop production, soil acidification, visibility and corrosion of materials. This Chapter focuses on the two major impacts of air pollution that have most strongly influenced the development of policies to reduce emissions: those on the natural environment and on human health.

In broad terms, the major impacts of air pollution on the natural environment can be placed into three categories, representing different spatial scales:

• Local impacts of major industrial or urban sources, for example, instances of damage to ecosystems and crop production close to emission sources. Historically, the biggest impacts have been through the direct effects of sulphur dioxide and particles – either around large point sources such as power stations and smelters, or in urban areas with domestic coal burning – and the accumulation of toxic metals in soils around smelters. However, a range of other pollutants from specific local sources can have direct impacts on vegetation.

• Regional impacts of ozone, which is a significant global air pollutant in terms of impacts on vegetation, since high concentrations are found in rural areas.

• Regional impacts of long-Range Transport and deposition of sulphur and nitrogen, which have effects on soil acidity, nutrient availability and water chemistry, and hence on ecosystem composition and function.

The Chapter first considers direct effects of air pollution on vegetation and the visible symptoms of damage that can result, illustrating the spatial variation in damage by reference to national and local studies in the Netherlands.