World’s Soil Resources

are however strongly dependent on the neutralisation mechanisms considered in the analysis, for example,
the inclusion or exclusion of sulphate adsorption (Rodríguez-Lado, Montanarella and Macías, 2007). Spatial
differences in soil sensitivity − commonly defined by the ‘critical load’ − and in pollutant deposition result in
an uneven global distribution of impacted soils (Figure 4.10). For instance, global emissions of sulphur and
nitrogen have increased 3–10 fold since the pre-industrial period (van Aardenne et al., 2001), yet critical loads
for acidification are only exceeded in 7–17 percent of the global natural terrestrial ecosystems area (Bouwman
et al., 2002).
4.4.2 | Main atmospheric pollutants: Synopsis of current state of knowledge
Since the 1980s, emissions of pollutants, notably sulphur, across Europe and North America have declined.
The decline is due to the establishment of protocols under the 1979 Convention on Long-range Transboundary
Air Pollution (LRTAP) and the 1990 United States Clean Air Act Amendments (CAAA) (Greaver et al., 2012; Reis et
al., 2012; EEA, 2014). Conversely, emissions in South and East Asia, sub-Saharan Africa and South America are
likely to increase in response to industrial and agricultural development (Kuylenstierna et al., 2001; Dentener
et al., 2006). Further emission increases are also occurring in remote areas due to mining activity, such as oil
sands extraction in Canada (Kelly et al., 2010; Whitfield et al., 2010).
Sulphur deposition
Sulphur emissions primarily result from combustion of coal and oil and are typically associated with power
generation and heavy industry. In 2001, deposition exceedances of 20 kg S ha -1 yr -1 were detected in regions
of China and Republic of Korea, Western Europe and eastern North America (Vet et al., 2014; Figure 4.10.(a)).
Deposition in unaffected ecosystems is