The critical loads/levels approach to gaseous pollutant emission control

There is increasing pressure to control gaseous acidifying emissions to prevent harmful environmental effects; many governments are looking for a more effective and scientific means of assessing effects and planning emission controls compared with arbitrarily uniform percentage reductions. The critical loads/levels concept may offer the basis for a solution which is acceptable internationally. There is already agreement to map the critical loads and levels for countries in Europe and North America as a first step towards assessment. Recent developments in defining and quantifying critical loads and levels show the approach could be sufficiently adaptable to apply to the effects of different pollutants on a range of environmental receptors. Whilst it is difficult to arrive at an agreed single definition, various international groups have arrived at definitions which suit their own particular purposes. Despite a variety of different approaches to arriving at estimates of critical loads, there is broad agreement at the figures calculated by the different methods. An extension of the concept, the target load/level, provides a practical solution for implementing control strategies to prevent or minimize environmental effects.