ETC/ATNI Report 9/2021: Long-term trends of air pollutants at national level 2005-2019.

Trend calculations of air pollutants for the periods 2005-2019 have been applied. Sulphur dioxide shows the largest decrease of all pollutants with a reduction of the order of 60-70 %. The agreement between reported emission data and measured concentrations are quite good. 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 45 %, the measured NO2 data indicate a decline of the order of 30 %. 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.

31 Jan 2022

Sverre Solberg, Augustin Colette, Blandine Raux, Sam-Erik Walker, Cristina Guerreiro

Prepared by:

Sverre Solberg (NILU), Augustin Colette (INERIS), Blandine Raux (INERIS), Sam-Erik Walker (NILU),
Cristina Guerreiro (NILU)

Trend calculations of air pollutants for the periods 2005-2019 have been applied. Sulphur dioxide shows the largest decrease of all pollutants with a reduction of the order of 60-70 %. The agreement between reported emission data and measured concentrations are quite good. 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 45 %, the measured NO2 data indicate a decline of the order of 30 % 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 of the order of 30-38 % is found during 2005-2019 while the direct emissions give a reduction that is 5-10 percentage units smaller. Similar results are found for PM2.5, but these findings are uncertain due to the less amount of long-term data.  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%.