Critical Load Approach Challenges and Biogeochemical Fundamentals

1 Critical load approach challenges and biogeochemical fundamentals Political requirements 

The first agreement to control transboundary air pollution was connected with the signing of the United Nations Economic Commission for Europe (UN ECE) Convention on Long-Range Transboundary Air Pollution (LRTAP) by 32 European countries, plus Canada and the USA, in 1979. In a protocol added to this convention in 1985, 

Since 1988 a new concept has been agreed both nationally and internationally to try to improve this situation by optimizing costs and benefits. This is the critical loads/levels approach and it has been adopted as the basis for 1994 UN ECE Second Sulfur Dioxide Protocol, which commits signatories to the Convention on LRTAP to further SO2 reductions up to and beyond the year 2005. Action on this Protocol will produce significant reductions in the emissions of SO2 and sulfate deposition over the next decade, till 2005. 

Over the same period, emissions of nitrogen oxides (NOx) were predicted to remain at current levels or to increase, depending specially on the growth of motor vehicle transport. Such predictions were not initially viewed with any sense of environmental concern because of the accepted nutrient properties of deposited nitrogen and its possible fertilizing action on the terrestrial environment. However, as 

The term critical load refers only to the deposition of pollutants. Threshold gaseous concentration exposures are termed critical levels and are defined as concentrations in the atmosphere above which direct adverse effects on receptors such as plants, ecosystems or materials, may occur according to present knowledge . 

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