Deriving critical thresholds for Asia

The critical threshold is a generic term for allowable limits of pollutant loads and concentrations, below which adverse effects on ecosystems and human health do not occur according to current scientific knowledge. Critical loads for acidity have been computed and mapped in Southeast Asia, as part of an Asian version of the Regional Air pollution INformation and Simulation model (RAINS-Asia). The model domain comprises China, Korea, Japan, The Philippines, Indo-China, Indonesia and the Indian subcontinent. The critical load computation methodology involves the Steady-State Mass Balance (SSMB) method applied to 31 different vegetation types. Critical chemical limits as well as soil stability criteria were derived for each of these vegetation types, which include both natural and managed ecosystems. Critical loads for acidity are used in RAINS-Asia to assess alternative sulfur dioxide emission reductions by comparing sulfur deposition to critical loads, and investigating the percentage of the ecosystem area which is at risk of acidification. Results show that low critical loads in Asia occur in Bangla-Desh, Indo-China, Indonesia and the southern part of China, which areas show an excess of critical loads at 1990 sulfur emission levels. Large parts of these areas are subject to multiple impacts due to the excess ofmore » other critical thresholds, including critical air concentrations (i.e. critical levels) of sulfur dioxide. The extent, and the geographical distribution, of the excess of critical loads for acidity is significantly influenced by base cation deposition. However, it is shown that these uncertainties do not relax the assessments of the risk of ecosystem damage expected to be caused by the current economic growth, when no abatement measures are taken.« less