The critical loads concept emerged in the 1980s during formulation of the landmark UN Economic Commission for Europe (UN/ECE) convention on long-range transboundary air pollution (CLRTAP). The concept draws on the idea that pollution controls should be effects-based, in other words that controls should be designed in the light of quantitative estimates of different regions and ecosystems to tolerate pollution.
In 1990, the UN/ECE launched a programme to make critical loads maps of European countries, measuring direct effects of pollution by sulphur dioxide, nitrogen oxides, ammonia and ozone as well as indirect effects of sulphur and nitrogen compounds. Coordinated from the Netherlands, the programme started with nine European countries but grew rapidly to 15 by 1991 and to 24 now.
The critical loads technique was first applied in policy-making in a 1994 protocol to CLRTAP on sulphur emissions. Since then it has been behind a series of further UN/ECE air pollution protocols, culminating in the sophisticated 1999 "multi-pollutant, multi-effects" protocol. This seeks to reduce acidification, eutrophication and ground-level ozone pollution simultaneously, by setting national emission ceilings for sulphur, nitrogen oxides,volatile organic compounds (VOCs) and ammonia (ENDS Daily 30 November 1999).
Speakers at last week's meeting hosted by the German environmment agency called for further development of critical loads. Dynamic modelling would enable prediction of emission control impacts. Mapping should be extended to cover heavy metals and POPs. New elements should be introduced, including health criteria and problems caused by fine particulates. One speaker called for better integration of freshwater and marine ecosystems, saying this would make critical loads not just a multi-pollutant, multi-effects approach, but a multi-media one too.
German environment agency, tel: +49 30 89031 UN/ECE, tel: +41 22 917 44 44. See also the home page of the CLRTAP and the convention's International Cooperative Programme on Mapping Critical Loads and Levels.
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