Energy Indicators for Sustainable Development: Guidelines and Methodologies International Atomic Energy Agency United Nations Department of Economic and Social Affairs International Energy Agency Eurostat European Environment Agency

ENV5: Soil area where acidification exceeds critical load 
Brief Definition 
Soil area where damage could occur due to 
acidification levels that exceed critical loads 
Units 
Square kilometres (km
2
) 
Alternative Definitions 
Soil areas exceeding specific target loads 
Agenda 21 
Chapter 9: Protection of the atmosphere 
POLICY RELEVANCE 
(a) Purpose: This indicator describes the extent of acidification at the national level. 
It is used to monitor the state and trends in the severity of acidification caused by wet 
and dry deposition over time, and to evaluate the environmental performance of 
national air pollution abatement policies. The indicator should show acidification 
attributable to all sources and, where appropriate national data are available, 
acidification due to emissions from the energy sector alone. 
(b) Relevance to Sustainable Development: When both sulphur and nitrogen 
compounds settle out of the atmosphere in the form of wet deposition (acid rain) or 
dry deposition, the resulting acidification of soils and surface waters can have serious 
consequences for both plant life and water fauna. When the soil becomes acidified, its 
essential nutrients are leached out, which reduces the fertility of the soil. The 
acidification process also releases metals that can harm the microorganisms in the soil 
that are responsible for decomposition, as well as birds and mammals higher up in the 
food chain, including humans. The acidifying effects of acid deposition and land use 
must not exceed the limits that can be tolerated by the area in question. 

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Acidification is a priority atmospheric issue considered by Agenda 21 in addressing 
degradation of soil and surface-water resources. Therefore, there should be a 
mechanism for determining the importance of this issue at the national level. Trend 
data over time can indicate the success of response actions. Concrete actions include 
structural changes in energy demand (efficiency improvements and fuel substitution) 
as well as pollution control policies and technical measures.