Aarhus Universitets segl

No. 467: Air quality 2020

Thomas Ellermann, Claus Nordstrøm, Jørgen Brandt, Jesper Christensen, Matthias  Ketzel, Andreas Massling, Rossana Bossi, Lise Marie Frohn, Camilla Geels, Steen Solvang Jensen, Ole-Kenneth Nielsen, Morten Winther, Maria Bech Poulsen, Christian Monies og Martin Bjært Sørensen. 2022. Luftkvalitet 2020. Status for den nationale luftkvalitetsovervågning. Aarhus Universitet, DCE – Nationalt Center for Miljø og Energi, 144 s. - Videnskabelig rapport nr. 467. dce2.au.dk/pub/SR467.pdf


This report presents results for 2020 from the Danish monitoring of air quality with focus on the health related effects of air pollution. The air quality monitoring program covers the entire Denmark. However, the monitoring program has special focus on cities, where air pollution and population density are highest. DCE – the Danish Center for Environment and Energy at Aarhus University carries out the monitoring program on behalf of the Danish Ministry of Environment in cooperation with the municipalities of Copenhagen, Odense, Aarhus and Aalborg.

The aim of the monitoring program is to:

  • document the state of the air quality in relation to EU’s air quality limit and target values,
  • determine the long-term trends for the air quality in order to evaluate the impact of the Danish and international measures taken to reduce air pollution,
  • warn the Danish public when EU’s warning thresholds are exceeded. In Danish context this is only relevant for ozone, and
  • determine the health effects and external costs of air pollution in Denmark and detailed model calculations of the emission sources leading to air quality related health effects and external costs (additionally financed by the Danish Ministry for the Environment).

The monitoring of air quality is based on an integration of measurements and model calculations. The measurements are carried out at nine monitoring stations in the four largest cities in Denmark, one suburban monitoring station in Hvidovre and four regional background monitoring stations placed on the countryside. The model calculations are carried out using DCE’s suite of internationally recognised air quality models.

The monitoring program covers the most relevant air pollutants that have impact on human health and those that are covered by the EU air quality directives (EU, 2004; EU, 2008). The program includes measurements of sulphur dioxide (SO2), nitrogen oxides (NOx/NO2), particles with diameters less than 10 and 2.5 micrometers respectively (PM10 and PM2.5), particle number, elementary carbon (EC), organic carbon (OC), benzene (C6H6), toluene (C7H8), carbon monoxide (CO), ozone (O3), polycyclic aromatic hydrocarbons (PAHs), a number of heavy metals including lead (Pb), arsenic (As), cadmium (Cd), mercury (Hg), nickel (Ni), and finally a number of volatile organic compounds (VOCs) that are precursors to formation of ozone.

Emission inventories

This report presents an overview of the emissions of air pollutants from Danish and European sources. This overview includes 2019 emissions, which is the most recent reporting year. An overview of the long-term trends of the emissions is likewise covered. The aim of this overview is to facilitate the interpretation of monitoring results, i.e. explaining the spatial variability and long-term trends of the different air pollutants.

Data on emissions from Danish sources are obtained from the official national emission inventories prepared by DCE for the Danish Ministry of Environment (Nielsen et al., 2021). Emission data from the remaining EU member states are obtained from the European emission database (EMEP) (CEIP, 2021).

The sources of emissions of air pollutants vary considerably among pollutants. Figure 1 and 2 present the contributions from the different main categories of emission sources for different air pollutants. The emission inventories only cover the directly emitted particles and not particles formed via chemical reactions in the atmosphere.

Since 1990, there have been significant reductions in the Danish emissions for most air pollutants. The largest reductions are for the emissions of lead and sulphur dioxide that have been reduced with about 90%. Arsenic, nickel and chromium emissions have been reduced with 70-85%. Nitrogen oxides, black carbon and carbon monoxide emissions have been reduced with 65-70%, while emissions of fine particles (PM2.5), benzo[a]pyrene, non-methane volatile organic compounds and cadmium have been reduced with 45-50%. Emissions of larger particles (particles between 2.5 and 10 µm) and zinc have only been reduced slightly and for copper there has been an increase of about 30% in the emissions. The long-term trends reflect the measures that have been taken to reduce the various emissions as well as changes in the activities that are responsible for the emissions.

For benzo[a]pyrene, it is worth noting that the updated emission inventory now reflects new data on energy consumption in Denmark from the Danish Energy Agency (Energistyrelsen, 2021). These new data shows that the use of wood burning in households has decreased with 35% in the period from 2016 to 2019. 

State and long-term trends of the air quality

The EU air quality directives establish air quality limit and target values for the most critical air pollutants (EU, 2008; EU, 2004). A detailed description of these can be found in the statutory order from the Ministry of Environment and Food Production (Miljø- og Fødevareministeriet, 2017). In addition, WHO published in September 2021 new air quality guidelines for the most critical air pollutants in relation to human health (WHO, 2021a). In this report the monitoring results are compared with EU limit and target values and the new WHO guidelines.  

The permitted number of exceedances in a year of the diurnal limit value of 50 µg/m3 for PM10 was not exceeded at any monitoring station in the monitoring network in 2020. Likewise, there were no exceedances of the annual limit values for PM10 (40 µg/m3) and PM2.5 (25 µg/m3). Model calculations at 98 selected street segments in Copenhagen and 26 selected street segments in Aalborg in 2020 showed likewise no exceedances for annual average concentrations of PM2.5 and PM10. The average exposure indicator (AEI) determined as a running three-year mean of the average urban background concentration of PM2.5 has decreased with about 30% since 2010 and hence the target (15% reduction) has been reached. The annual average concentrations of PM2.5 and PM10 have decreased with 30-50% since 2007/2008 and 30-45% since 2001, respectively.

This report presents results from a detailed analysis of the chemical contents of PM2.5 in the regional background at Risø/Roskilde, the urban background in Copenhagen and at the most polluted street monitoring station in Denmark (H.C. Andersens Boulevard, Copenhagen). This analysis shows that only about 25% of PM2.5 at H.C. Andersens Boulevard originates from sources in Copenhagen, while about 75% of the concentration of PM2.5 originates from sources in foreign countries and sources in the remaining part of Denmark.

Technical difficulties of recent years with the measurements of particle numbers have now been solved, and hence data from the particle range from 41- 478/550 nm as well as 11-478/550 nm can now be analysed. The number of particles in the range 11-478/550 nm was about 8,900 particles per cm3 at the street measurement station at H.C. Andersens Boulevard. This is about a factor of two higher than at the suburban measurement station in Hvidovre and about a factor of three higher than the urban and rural background measurement stations. Since 2020 the particle numbers for both size fractions have decreased with about 70% and 45% at the street measurement station on H.C. Andersens Boulevard and the urban background measurement station in Copenhagen, respectively. In the rural background at Risø, the particle number has decreased about 40% since 2005 for the fraction 11-478/55 nm and about 50% for the particle fraction 41-478/550 nm.

The limit values for nitrogen dioxide were not exceeded at any of the monitoring stations in Denmark. Model calculations at 98 selected street segments in Copenhagen and 26 selected street segments in Aalborg in 2020 showed likewise no exceedances of the long-term limit value based on the annual average concentration. The annual average concentrations of nitrogen dioxide at the street monitoring stations have been reduced with about 50% since 2005.

The concentrations of Sulphur dioxide and carbon monoxide is very low compared to the limit values and there are no exceedance of these. Since 1990, the concentrations of Sulphur dioxide and carbon monoxide have decreased with about 95% and 80%, respectively, at the street measurement station at H.C. Andersens Boulevard. 

The annual average concentrations of elemental carbon (EC) were about 0.7 µg/m3 at the street measurement station at H.C. Andersens Boulevard while the concentrations were considerably lower in the urban and rural background (0.2-0.3 µg/m3). A large decrease in the concentrations has been measured for elemental carbon. The largest decrease has been measured at the street measurement station at H.C. Andersens Boulevard (about 70%) which is in agreement with the emission data.

In 2020, the annual average ozone concentrations were at the same level as in the previous years. No clear trend is observed for the average ozone concentration during the last years. The target value states that the maximum daily 8-hour mean ozone concentration must not exceed 120 µg/m3 more than 25 times annually on average for three years. The target value was not exceeded at any of the monitoring station, but the long-term objective for this parameter (maximum daily 8-hour mean ozone concentration must not exceed 120 µg/m3) was exceeded at all Danish stations except at the street measurement station on H.C. Andersens Boulevard. The target value entered into force in 2010 while the long-term objective has not entered into force and the date for this has not yet been decided. The information threshold of 180 µg/m3 was not exceeded during 2020.

Measurements of volatile organic compounds at the urban background monitoring station in Copenhagen showed concentration levels between 0.01 µg/m3 and 0.8 µg/m3 for the selected 17 different compounds. Benzene is the only volatile organic compound with a settled air quality limit value (EU, 2008). In 2020 the annual average concentrations were about 10% of the limit value for the two street measurement stations in Copenhagen. Volatile organic compounds can act as precursors for the formation of ozone, and the aim of these measurements is to improve the general understanding of the ozone formation at a European level. The formation of ozone in Denmark is in general small due to moderate solar radiation. Ozone pollution in Denmark is mainly the result of long-range transport of pollutants from other European countries south of Denmark. The annual average concentrations for most of the measured volatile organic compounds have been reduced significantly since 2010.

Measurements of the concentrations of particle bound polycyclic aromatic hydrocarbons were performed at H.C. Andersens Boulevard, Copenhagen and at the suburban monitoring station at Hvidovre. The annual average concentrations of benzo[a]pyrene were 0.13 ng/m3 and 0.14 ng/m3 at H. C. Andersens Boulevard and Hvidovre, respectively. Hence, the target value for benzo[a]pyrene (1 ng/m3) was not exceeded in 2020. The annual average concentrations have been reduced with about 50-60% at H.C. Andersens Boulevard and Hvidovre since 2008 and 2013, respectively.

The levels of heavy metals have decreased for more than two decades, and the concentrations are now far below the limit values. The limit values for benzene and carbon monoxide are not exceeded either, and the levels have been decreasing for the last decades.

Figure 3 gives an overview of the air quality in Denmark in relation to the EU limit and target values. There is no exceedance of limit or target values at the Danish measurement stations. The limit values in relation to the short-term exposures have in the EU directive been defined based on a concentration limit that must not be exceeded more than a specified number of times during a calendar year. As an example, the 24-hour average concentration of PM10 must not be exceeded more than 35 times within a calendar year. The percentage given for PM10 (24-hour average) in Figure 3 corresponds to the 36th highest 24-hour average concentration. For 2020 the 36th highest concentration is 67% of the limit value and hence there is no exceedance of the limit value. Figure 3 presents data for the other short-term limit values in a similar way, although the number of allowed exceedances vary for the different limit values.

In September 2021, WHO published new air quality guidelines for the most critical air pollutants with to respect to human health (WHO, 2021a). Figure 4 presents an overview with a comparison of the concentration levels for nitrogen dioxide, carbon monoxide, sulphur dioxide, ozone and particles (PM2.5 and PM10) relative to the air quality guidelines adopted by WHO. The guidelines in relation to long-term exposure are exceeded for all air pollutants with the highest exceedances for nitrogen dioxide and PM2.5. For short-term exposure there are exceedances for PM2.5, PM10, nitrogen dioxide and ozone. In contrast, the concentration levels are considerably lower than the guidelines for sulphur dioxide and carbon monoxide. It is the air pollutants with the highest impact on human health that show the highest exceedances of the air quality guidelines. This emphasizes the need to reduce the levels of these air pollutants to reduce the impact of air pollution on human health in Denmark (see next paragraph).

Moreover, the model calculations for 98 selected street segments in Copenhagen and 26 selected street segments in Aalborg, give no exceedance of the EU limit values, while the WHO guidelines from 2021 are exceeded for nitrogen dioxide, PM2.5 and PM10 on all street segments in 2020.

Health effects and external economic costs of air pollution in Denmark

Model calculations show that air pollution causes about 4,000 premature deaths in Denmark in 2020 and a large number of other negative health effects. This is about 13% less compared to the reporting for 2019. This lower number of premature deaths are due to updates in the emission inventories, meteorological data and changes in emissions due to the COVID-19 restrictions. Calculations of the entire data series back to 1990 show a decrease in the health effects due to air pollution. In 1990, about 8,200 premature deaths were due to air pollution in Denmark which has decreased with about 51% to around 4,000 premature deaths in 2020.

The total health related external costs of air pollution in Denmark have been calculated to 76 billion DKK for 2020 (in 2016-prices). The cost was about 152 billion DKK as a mean over the years 1988-1990 and hence the cost has decreased with about 50% since 1990.

A detailed analysis of the air emission sources of the health effects and external costs in Denmark have been carried out in connection to this reporting. This analysis shows that about 860 premature deaths are due to emissions of air pollution in Denmark. This corresponds to about 21% of the total number of premature deaths. The remaining 79% are due to emissions outside Denmark. The same pattern is seen for the external costs. The model calculations also show that Danish sources are responsible for about 1,900 premature deaths in foreign countries.

Figure 5 shows the contributions from the main air emission source categories to the number of premature deaths in Demark. The most important Danish air emission source is non-industrial combustion (mainly household warming based on wood burning) responsible for about 280 premature deaths in Denmark corresponding to 32% of the total number of premature deaths due to Danish sources. The Danish non-industrial combustion accounts for about 6% of the total amount of premature deaths in Denmark due to both Danish and international air emission sources.

The uncertainties on the calculations of health effects and external costs are significant. Leading international researchers have estimated that the uncertainties on their calculations are about ±50% (Lelieveld et al., 2019). DCE estimates that the uncertainties on the model calculations of health effects and external costs presented in this report are on the same level.

WHO’s new guidelines (WHO, 2021a) also encompass a thorough review of the international research on the association between exposure to a number of air pollutants and effects on human health. The review documents that the health impacts are larger than previously known and that the impacts on human health are observed at lower concentration levels than preciously documented. These guidelines were published in September 2021 and it has therefore not been possible to include the new knowledge in this annual report. The results presented above are therefore most likely underestimated. It is not possible to estimate the extend of this underestimation before DCE’s model system has been updated with the new consensus knowledge from WHO’s guidelines (WHO, 2021a).