This indicator shows emissions of gases that cause acidification and eutrophication and the structure of emissions or particular gases by pollution source in the period 1990–2012. The substances that cause acidification include sulphur oxides (SO_x), nitrogen oxides (NO_x) and ammonia (NH₃). Nitrogen oxides and ammonia contribute to eutrophication as well. The total emissions of substances that cause acidification and eutrophication are expressed as the sum of emissions of the three pollutants multiplied by corresponding acidification factors. The emissions are expressed in tonnes of acidification equivalent.

In 2012, the emissions of gases causing acidification were 74% lower than in 1990, largely due the decrease in sulphur dioxide emissions. Sulphur oxides are formed during the combustion of fuels that contain sulphur. In the observed period, the emissions of sulphur oxides decreased by 95%. The reduction is largely a result of installation of desulphurisation plants at the Šoštanj and Trbovlje thermal power plants, the use of imported low-sulphur coal in the Ljubljana combined heat-and-power Plant, introduction of liquid fuels with a lower sulphur content and the replacement of liquid and solid fuels in industry with natural gas. Recently, emissions from industrial processes have been decreasing which is a consequence of the implementation of the Decree on activities and installations causing large-scale environmental pollution  (IPCC Decree). According to the 2012 data, the largest source of sulphur oxide emissions is the energy supply sector. Electricity and heat generation contributed 64% to total emissions of sulphur oxides at the national level. Total emissions of sulphur oxides in 2012 were 62% below the target value for 2010 onwards. Sulphur oxides represented 14% of the total emissions of gases causing acidification and eutrophication.

In 2012, ammonia represented the largest share of emitted substances causing acidification and eutrophication. The percentage of ammonia in total emissions amounted to 44%. The main source of ammonia is agriculture, which contributes as much as 96% to total ammonia emissions in Slovenia. In 2012, ammonia emissions were 21% lower than in 1990. The reduction in emissions is largely a result of a reduced number of livestock. In 2012, ammonia emissions were 12% below the target value that must not be exceeded from 2010 onwards.

In 2011, the share of nitrogen oxide emissions in total emissions of substances that cause acidification and eutrophication was 42%. According to the 2012 data, the main source of emissions of nitrogen oxides was road transport (53%), followed by energy supply (23%). Compared to 1990, NO_x emissions were reduced by 26%,. This was largely due to stricter emission standards for motor vehicles in the transport sector, implementation of measures in thermal power plants and combined heat-and-power plants and replacement of fuels and improved combustion processes in industry. In 2012, the values of nitrogen oxide emissions were 0.8% above the target value for 2010 onwards. Emissions of nitrogen oxides don’t only depend on the content of nitrogen in fuel but are formed primarily after the reaction of nitrogen and oxygen in the air during combustion at high temperatures.

With 1.2 kilograms per capita, Slovenia is slightly above the EU-28 average in terms of substances that cause acidification and eutrophication. Slovenia was ranked 15^th in the EU-28 in 2011, when the highest emissions per capita were recorded in Bulgaria (3.0 kg/capita) and the lowest in Sweden (075 kg/capita).

In order to meet the target values, measures were adopted in the field of energy efficiency improvement, replacement of solid fossil fuels with natural gas and renewable energy sources, introduction of stricter emission standards for motor vehicles, consistent implementation of environmental legislation, especially in the field of integrated prevention and control of industrial pollution (use of best available technologies) and promotion of good agricultural practices.

Emissions of substances that cause acidification adversely affect human health and water ecosystems, forests, crops and buildings – largely due to corrosion. The negative effects of acidification depend on the acidifying potential of particular pollutants and properties of particular ecosystems and materials. The highest acidifying effect is attributed to ammonia, which also contributes to the eutrophication effect. Excessive accumulation of nutrients in waters (eutrophication) may reduce and change biodiversity.

NO_x emissions also contribute to the formation of ground-level ozone, which is produced in complex photochemical reactions in lower layers of the atmosphere under increased solar radiation during the summer months, causing respiratory diseases.

In addition to acidification and eutrophication, emissions of NO_x, SO_x and NH₃ also cause the formation of dust particles that contribute to increased incidence of respiratory diseases. NO_x, SO_x and NH₃ are secondary solid particles, or precursors to PM₁₀ particles, which are transformed into solid particles with a diameter of 10 μm or smaller as a result of physical-chemical reactions.