ETC/ATNI Report 16/2019: Air Quality Trends in Europe: 2000-2017. Assessment for surface SO2, NO2, Ozone, PM10 and PM2.5.

The European network of regulatory air quality monitoring stations is now dense enough to explore long term terms. We combine the Airbase data base for the years 2000 to 2012 and AQ e-reporting after 2013. Trends are computed for SO2, NO2, O3, PM10 and PM2.5, including various metrics and indicators. Quantitative information if provided for the evolution of all these compounds and, when relevant, put in perspective with the trend in air pollutant emissions.

20 Jan 2021

Prepared by:

Augustin Colette, Laurence Rouïl (INERIS)

We present an assessment of observed air quality trends in Europe aimed at making the most of the regulatory monitoring network to document and explain the effectiveness of air pollution mitigation policies. The focus is on the 2000-2017 time period and surface SO2, NO2, ozone, PM10 and PM2.5, for which we can rely on more than 10,000 stations. Data related to 3,500 stations complied with the requirements, in terms of completeness and representativeness for long-term trend assessments. Such long-term records are only available for countries of the European Union, with one exception for Norway.

Substantial improvements are found for all air pollutants. We assess in detail the absolute and relative trends for a wide range of air pollutant indicators and also discuss the spatial variability of the trends as well as changes in monthly, weekly and hourly variability. These changes are put in perspective with emission reductions in Europe in order to point out the pollutants where a potential mismatch may occur between expected and observed improvements in air pollutant concentration.

The relative change in SO2 concentrations lies in the 70 to 85% range. This reduction is lower but still in line with the reported emission decrease in Europe (-89%). There is however a slight mismatch between emissions and concentrations in the aftermath of the 2008 economic crisis. Such a mismatch after 2008 also appears for NO2. But on the contrary to SO2, this mismatch has a more substantial impact on the overall trend as reduction in concentrations is 30% which is lower than expected given the 53% reduction in emission over the same time period.

The magnitude of ozone peaks (as the fourth highest annual daily maximum of 8hr running mean) decreases by 10% and the number of days exceeding the long-term objective of daily maximum hourly ozone above 120µg/m3 is reduced by 30 to 50%. Annual ozone mean however increases, especially at urban sites. The increase is less pronounced at rural sites, suggesting that it is mainly related to lower NOx titration effect rather than hemispheric changes. Annual mean ozone increase also contributes to higher health exposure, with median SOMO35 and SOMO10 increasing by 1.3% and 13.4%, respectively at urban stations. This needs however to be considered with respect to the NO2 reduction in order to understand the net impact on health, for instance by looking at Ox (sum of NO2 and O3) which decreases.

Particulate matter annual mean concentrations decrease by 25 to 45%, depending on station typology. The reductions are similar for PM10 and PM2.5 when comparing collocated measurements. The highest peaks of particulate matter exhibit less relative reduction than the average, showing that episodes of high PM would deserve more focus. PM concentrations decrease faster than primary PM emissions (-30% for primary PM10 and -18% for primary PM2.5), thanks to the additional impact of the reduction of precursors of secondary PM, such as SOx, NOx and NH3.

The air quality index over Europe was computed for the whole time period. It gradually improves over the 2000-2017 time period. But most of the improvement concern days in the “moderate” air quality category, whereas the number of days classified as “poor” for air quality remain quite constant. This observation raises specific concern for future improvement of high air pollution episodes.