Jensen, S.S., Christensen, J.H., Frohn, L.M., Ketzel, M., Nielsen, O.-K., Plejdrup, M.S., 2023. Nationalt program for reduktion af luftforurening (NAPCP) - Udvikling i luftkvalitet og kvælstofafsætning frem til 2030. Aarhus Universitet, DCE – Nationalt Center for Miljø og Energi, 47 s. - Videnskabelig rapport nr. 538. http://dce2.au.dk/pub/SR538.pdf
The purpose of the project is to carry out model calculations of the baseline projection of emissions from 2020 to 2030 for air quality and atmospheric deposition.
The background to the project is requirements set out in the EU Directive from 2016 on National Emission Ceilings (NEC) Directive, including the directive's requirement for the preparation of National Air Pollution Control Programme (NAPCP). Denmark is obliged to continuously assess the development of national emissions, including implementing emission reduction measures to achieve the reduction targets set for Denmark in the NEC Directive.
The NEC directive sets out national commitments for reductions in emissions for 2020 and 2030 for the pollutants: sulphur dioxide (SO2), nitrogen oxides (NOx), non-methane volatile organic compounds (NMVOC), ammonia (NH3), and fine particles (PM2.5 - mass of particulate matter less than 2.5 microns). Emissions of these substances are included in the calculations of air quality of NO2 (nitrogen dioxide), PM2.5, PM10 (mass of particulate matter less than 10 microns), and O3 (ozone). These substances are associated with health effects, and nitrogen deposition is worsening the state of certain sensitive natural habitats.
The baseline of emissions for Denmark is, among others, based on the Danish Energy Agency's baseline projection for 2030. This is a projection based on existing adopted measures, also called "frozen policy" and the baseline projection WM – With Measures. The baseline scenario is described in detail in Nielsen et al. (2023).
The starting point is the national emission inventory for 2020 (Nielsen et al., 2022).
The regional background concentrations are calculated with the Danish Eulerian Hemispheric Model (DEHM) with a geographic resolution of 5.6 km x 5.6 km. The regional background represents the average concentration in rural areas over a larger area. The regional air pollution represents the contribution of long-range transported air pollution from emissions from abroad and from Denmark.
Regional models such as DEHM, which describe background air pollution, tend to underestimate the concentration of PM2.5 when comparing the results of the models with measurements. PM10 is also underestimated, as PM2.5 is part of PM10. In international literature, this is referred to as "the mass closure problem" or "missing mass problem". Results of analysis between measurements and model results for PM2.5 show that the model results need to be revised upwards by 33% to match the measurements when compared with measuring stations in the air quality monitoring programme in Denmark (Ellermann et al., 2022b). This deviation depends on many conditions, and it will also be different over the years. Thus, it is not possible to estimate what the deviation will be in the future, such as in 2030. In this report, we present maps of the concentration from DEHM for 2020 and 2030 (Appendix 1) and DEHM/UBM model results for the same locations as urban background measuring stations in Denmark in 2020 and 2030 (Chapter 5). In Chapter 6, where street concentrations are calculated for 98 streets in Copenhagen based on DEHM/UBM/OSPM, we have adjusted for the above deviation of 33% for both PM2.5 and PM10 for both 2020 and 2030. This is done because of the comparison with limit values and WHO guidelines, and as this also allows direct comparison with results from the monitoring program for 2020 (Ellermann et al., 2022b), where adjustment for the deviation also is done Background concentrations with high resolution
The development in background concentrations with high resolution is calculated with the Urban Background Model (UBM). Urban background pollution represents the average background pollution inside and outside cities calculated with a spatial resolution of 1 km x 1 km. Urban background concentrations correspond in a city to the concentration at roof top level or in a backyard/park. DEHM calculations are input in UBM. For Denmark emissions are available at a spatial resolution of 1 km x 1 km based on the SPREAD model that distributes national emissions based on various geographic variables.
In the current EU Air Quality Directive (EU Commission, 2008), the Average Exposure Indicator is generally determined as an average over three years for PM2.5 from measured concentrations at urban background stations in cities to reflect the exposure of the population, and the three years are used to take account of variation in meteorological conditions from year to year. The AQ Directive sets targets for 2020 for reducing this exposure indicator compared to 2010. The percentage reduction targets are dependent on the initial concentration in 2010. For Denmark, PM2.5 is measured at urban background stations in Copenhagen, Aarhus and Aalborg, and the average exposure concentration is calculated from these stations. No measurements of PM2.5 are available at the urban background station in Odense. For Denmark, the average exposure concentration must decrease by 15% in the period from 2010 (average of 2008-2010) to 2020 (average of 2018-2020). For all EU countries, the average exposure concentration should not exceed 15 μg/m3 in 2015. Denmark has complied with both of these requirements (Ellermann et al., 2022b).
The new proposal for a revised Air Quality Directive aims to reduce the exposure concentration for PM2.5 by 25% over a ten-year period (European Commission, 2022). The reduction requirement will apply from 2030 and every year thereafter. For example, this means that the exposure concentration in 2030 (average of 2028-2030) should be 25% lower than measured in 2020 (average of 2018-2020). The reduction requirement applies until the average exposure concentration is in line with the proposed exposure concentration target, which for PM2.5 is set at 5 μg/m3, i.e. the same air quality guideline as established by the WHO (WHO, 2021). In 2020, the mean exposure concentration was 10 μg/m3 and should thus be reduced to 7.5 μg/m3 by 2030, and thereafter until the target of 5 μg/m3 is achieved (Ellermann et al., 2022b).
The proposed AQ Directive also suggests an exposure concentration for NO2 (EU Commission, 2022). As for PM2.5, a requirement has been proposed that the exposure concentration for NO2 should decrease by 25% over a ten-year period. The reduction requirement will apply from 2030 until the proposed exposure concentration target is reached. For NO2, a target of 10 μg/m3 has been proposed, i.e. the same air quality guideline as established by the WHO (WHO, 2021). In 2021, the mean exposure concentration was 9.7 μg/m3 (average for 2019-2021) and the target has already been met. NO2 measurements are made at urban background stations in Copenhagen, Odense, Aarhus and Aalborg, and the average exposure concentration is calculated from these stations.
Assessment of air quality in Denmark compared to the objectives of the EU's proposal for a revised Air Quality Directive is described in more detail in a DCE note (Ellermann, 2022a).
The development in street concentrations is calculated with Operational Street Pollution Model (OSPM) for 98 selected streets in Copenhagen. The selected streets in Copenhagen are the same as those included in the Danish Air Quality Monitoring Program. The development in vehicle emissions is based on the Danish emission model for road traffic and other mobile sources implemented into OSPM.
All applied models have been developed at the Department of Environmental Science at Aarhus University.
Air quality calculations of regional concentrations, urban background concentrations and street concentrations are carried out for NO2, PM2.5 and PM10 for 2020 and 2030 for the baseline scenario. The levels are compared to limit values for air quality and WHO air quality guidelines.
Danish emissions of SO2, NOx, NMVOC, NH3 and PM2.5 will be reduced from 2020 to 2030 in the baseline projection, due to changes in the energy mix and measures to reduce agricultural emissions.
The reduction obligations for 2020 in the NEC Directive have been reached for all substances with exception of NH3. For 2030, the emission projection shows that the reduction target will be met for all substances. For NH3, the culling of mink at the end of 2020 and the temporary ban on mink keeping in 2021 and 2022, together with other emission reductions, means that the reduction target for 2020 is expected to be achieved in the final emission inventory for 2022.
European emissions will also be reduced overall from 2020 to 2030 in the baseline projection, reflecting expected compliance with the NEC Directive's emission ceilings for the member states.
Nitrogen deposition to land areas calculated with DEHM is expected to be reduced by 11% from 2020 to 2030 in the baseline scenario as an average for the whole of Denmark. The reductions in nitrogen deposition are a consequence of the reductions in Danish emissions of NOx, but also reductions in NH3 and corresponding foreign emissions.
On average, nitrogen deposition to Danish waters is also expected to be reduced by 11% from 2020 to 2030 in the baseline scenario.
The regional concentrations of PM2.5 calculated with DEHM are expected to be reduced by 12% from 2020 to 2030 in the baseline projection as an average for the whole of Denmark. The corresponding reductions for PM10 and NO2 are 6% and 16%, respectively.
The average background concentrations for the 5 regions in Denmark have also been calculated with DEHM/UBM in 2020 and for the baseline projection in 2030. The calculations are based on a geographical resolution of 1 km x 1 km, i.e. a higher resolution than if only DEHM is included in the calculations.
As expected, the concentrations are higher at the higher resolution. This is because the higher geographical resolution in the emissions better reflects the higher variation in concentrations, where the DEHM calculations due to lower resolution lead to smoother concentrations.
For the baseline projection, high-resolution background concentrations for NO2 are expected to be reduced by 10-28% in 2030 compared to 2020, 9-12% for PM2.5, and 4-9% for PM10. The intervals indicate differences between regions.
The average calculated exposure concentration for NO2 for urban background stations decreases by 32% from 2020 to 2030. The calculated level is 7.1 μg/m3 in 2030 and complies with the target of 10 μg/m3 of the new proposal for the revision of the Air Quality Directive and is also in line with WHO guidelines. As the measurements for 2021 already show that the target of 10 μg/m3 has been met and the projections show a continued decline, it is also very likely that the target will be met by 2030. Concentrations are well below the current limit value of 40 μg/m3.
The average calculated exposure concentration for PM2.5 decreases by 10% from 2020 to 2030, thus not meeting the requirement for a 25% reduction over a 10-year period. The calculated level is 5.8 μg/m3 in 2030 and does not meet the target of 5 μg/m3, which is the same as the WHO guideline. The modelled level of 5.8 μg/m3 in 2030 could have been underestimated as no adjustments have been made for missing mass.
According to the proposal for a new AQ directive (EU Commission, 2022), it is possible to deduct contributions from natural sources such as sea salt and contributions from vegetation, e.g. the formation of SOA (Secondary Organic Aerosols) in the atmosphere from emissions from, for example, terpenes from vegetation. SOA is part of PM2.5. This contribution from natural sources is estimated to be approx. 1.5 μg/m3 based on model calculations (Ellermann et al., 2022b). The combination of a model underestimation of around 0.5-1.3 μg/m3 compared to the measurements, and a deduction of the contribution from natural sources of 1.5 μg/m3 appears to be a level slightly above the target of 5 μg/m3 in 2030. However, there is some uncertainty in this estimate, as there is uncertainty about both the size of missing mass and contributions from natural sources in the future. Concentrations are well below the current limit value of 25 μg/m3.
No average exposure concentration has been established for PM10, but the average for PM10 has been modelled to decrease by 6% from 2020 to 2030. As concentrations for PM10 are expected to continue to decline, it is also likely that the WHO guideline will be met by 2030. The new Air Quality Directive proposal, like the current Directive, allows for deducting PM10 from natural sources and salting roads in winter. This option has not been used in Denmark in recent years, as it has not been necessary for compliance with the existing limit values (Ellermann, 2022a). Concentrations are well below the current limit value of 40 μg/m3.
For NO2, the average street concentration for 98 streets in Copenhagen decreases from 23 μg/m3 in 2020 to 11 μg/m3 in 2030 in the baseline. The reductions in street concentrations are primarily driven by the reduction in emissions from traffic in the street in question, but background concentrations are also reduced. By 2030, it is to be expected that some streets will exceed the WHO guideline of 10 μg/m3, as min. is 8.5 μg/m3 and max. 16 μg/m3. Street concentrations in 2030 are well below the current limit value of 40 μg/m3.
For PM2,5, the average street concentration decreases from 10 μg/m3 in 2020 to 9 μg/m3 in 2030 in the baseline. Almost all streets are expected to exceed the WHO guidelines of 5 μg/m3, as min. is 8.5 μg/m3 and max. 16 μg/m3. Street concentrations in 2030 are well below the current limit value of 25 μg/m3.
For PM10, the average street concentration decreases from 19 μg/m3 in 2020 to 17 μg/m3 in 2030 in the baseline. Some streets are likely to exceed the WHO guideline of 15 μg/m3, as min. is 15 μg/m3 and max. 17 μg/m3. Street concentrations in 2030 are well below the current limit value of 40 μg/m3.
In the above, both PM2.5 and PM10 are adjusted for missing mass, and concentrations are slightly lower if this adjustment is not made.
For PM2.5 and PM10, the percentage reduction is not as large as for NO2, as only exhaust particles are reduced and non-exhaust in the form of road wear, tyre wear and brake wear, which make up a much larger contribution than the exhaust part, is unchanged. Furthermore, background pollution accounts for a much larger proportion for particulate matter than for NO2.
