The background level is calculated as the average of the 2001-2020 time series excluding all years for which abnormal levels of emissions were recorded, i.e. excluding all statistical outliers.
Déantar an leibhéal cúlra a ríomh mar mheán na hamshraithe 2001-2020 ach gan na blianta ar fad ar ina leith a rinneadh leibhéil mhínormálta astaíochtaí a thaifeadadh a áireamh, i.e. gan na hasluitigh uile staidrimh a áireamh.