- Last Updated on Wednesday, 05 September 2012 15:51
Associated topic: acidification
Emissions monitoring period: since 1980
Data source: CITEPA / SECTEN format - April 2012
Origin of the indicator
The acid equivalent index (Aeq) has been developed to measure the overall quantity of air emissions that contribute, to a varying extent over time and depending on geographical scales, to acidification on land, in water and in the air.
The index is calculated on the basis of potential fixation of the H+ ion. Only sulphur dioxide (SO2), nitrogen oxides (NOx) and ammonia (NH3) are taken into account, as a quick calculation shows that because emission levels of the other acidifying substances, such as hydrochloric acid (HCl), are low compared to the three substances mentioned above, they contribute only marginally to acidification. The following weighting coefficients are used in the calculations: 0.0313 for SO2, 0.0217 for NOx and 0.0588 for NH3.
Emissions and trends
|Minimum observed:||70 kt in 2010|
|Maximum observed:||182 kt in 1980|
|Emissions in 2010:||70 kt|
Measurement unit: kt (kilotonne)
N.B. : emissions include those from combustion and from processes.
The graphs below show that the relative proportions of the pollutants included in the index (Aeq) have changed over time. In 1980, the majority of Aeq emissions were of SO2 (54%), but in 2010, SO2 emissions only accounted for 12% of the Aeq index value. Conversely, NH3 accounted for only 23% of acid equivalent emissions in 1980, but this had climbed to 54% in 2010.
The changing share of each pollutant in the index is partly due to the fact that emissions of the different pollutants concerned declined unevenly during the monitoring period, and partly to the weighting coefficient used for each pollutant (NH3 has the highest weighting coefficient).