ETC HE Report 2023/8: Long-term trends of air pollutants at European and national level 2005-2021

Trend calculations of air pollutants for the periods 2005-2021 have been applied. Sulphur dioxide shows the largest decrease of all pollutants with a concentration reduction of the order of 62-68 %. The agreement between reported emission data and measured concentrations are relatively good up to the year 2008, after which a large mismatch is observed. For NO2, a mismatch between the trend in air concentrations and NOx emissions is found. While the overall NOx emissions are reported to be reduced by 55 %, the measured NO2 data indicate a decline of the order of 38 %. For PM data (PM10 and PM2.5) we find an opposite mismatch, meaning that the PM concentrations show stronger downward trends than the reported emissions. This can be explained by the additional effect of reducing gaseous precursors of secondary PM. For O3, our findings are in line with earlier published studies noting that the annual mean ozone concentration has increased while the high peaks have been reduced. But the reduction of the peaks is now within only a few percent and non-significant.

04 Dec 2023

Talardia Gbangou (INERIS), Augustin Colette (INERIS), Joana Soares, reviewer (NILU), Alberto González Ortiz, reviewer (EEA)

Trend calculations of air pollutants for the periods 2005-2021 have been applied. Sulphur dioxide shows the largest decrease of all pollutants with a concentration reduction of the order of 62-68 %. The agreement between reported emission data and measured concentrations are relatively good up to the year 2008, after which a large mismatch is observed. For NO2, a mismatch between the trend in air concentrations and NOx emissions is found. While the overall NOx emissions are reported to be reduced by 55 %, the measured NO2 data indicate a decline of the order of 38 % although marked differences between the countries are found. This mismatch could not be explained by changes in meteorology as this is accounted for. Possible reasons for the mismatch could be the NO2/NOx ratio of the emissions, changes in baseline hemispheric ozone concentration and natural emissions. For PM data (PM10 and PM2.5) we find an opposite mismatch, meaning that the PM concentrations show stronger downward trends than the reported emissions. This is likely an effect of the importance of secondary aerosols which are mitigated by other activities than the direct PM emissions. An overall reduction in PM10 concentrations of the order of 42% is found during 2005-2021 which is larger than the rate of reduction of primary PM10 emissions (36%), thanks to the additional benefit of the mitigation of other precursor species. A similar feature is found for PM2.5.  For O3, our findings are in line with earlier studies noting that the annual mean ozone concentration has increased while the high peaks have been reduced. But the reduction of the peaks is now within only a few percent and non-significant, while for the 2000-2017 period it was significant and about 10%. An objective clustering revealed countries or zones with outstanding specificities regarding the trend in concentrations and emissions, offering valuable insights to go further with the work and try to learn lessons and improve air quality.