Deriving critical loads for Asia

Abstract

Critical loads have been computed and mapped in Southeast Asia, comprising China, Korea, Japan, The Philippines, Indo-China, Indonesia and the Indian subcontinent. The methodology involved the Steady-State Mass Balance (SSMB) method, originally developed for Europe. In contrast to Europe, where critical loads were computed for forest soils and surface waters, in Asia critical loads for 31 different vegetation types have been computed. Critical chemical limits as well as soil stability criteria were derived for each of these vegetation types, which include both natural and managed ecosystems. Results show that low critical loads in Asia occur in Bangla-Desh, Indo-China, Indonesia and the southern part of China. Uncertainties of the results are mainly due to uncertainties in base cation deposition. The critical loads are part of the impact module of the Asian version of the Regional Air pollution INformation and Simulation model (RAINS-Asia), a model used to assess abatement strategies for sulfur emissions which are rapidly increasing in this part of the world. The difference in the level of detail between European and Asian critical load maps enables different applications. In Europe, critical loads for sulphur were used in comparison to actual sulphur deposition with the aim of decreasing the excess of sulphur deposition over critical loads through optimal emission abatement. In Asia in general and China in particular the geographical distribution of critical loads of sensitive ecosystems, with some emphasis on crops, is likely to be used as a basis for future emission (re-)allocation.