Summary and conclusions

NO₂-Virkemiddelkatalog

1.5 Background and objectives
1.6 The study
1.7 Main conclusions
1.8 Project results
- 1.8.1 NO2 in other Danish cities

1.5 Background and objectives

The EU limit value for nitrogen dioxide (NO₂) is exceeded in larger Danish cities and particularly in Copenhagen. NO₂ poses a health risk. The limit value defined as an annual mean of 40 µg/m³ is not to be exceeded in 2010. Until 2010 it must not exceed the sum of 40 µg/m³ and a margin of tolerance. However, measurements of NO₂ at certain street stations in the Danish Air Quality Monitoring Programme show that the limit value plus the margin of tolerance is exceeded. Model calculations also show that a number of busy streets in Copenhagen will exceed the limit value in 2010. Impact assessment studies that have evaluated the effect of various traffic measures and of NO_x catalysts on heavy duty vehicles indicate that these measures are not sufficient to ensure compliance with the NO₂ limit value in busy streets in Copenhagen in 2010. Therefore, it is necessary to evaluate a broader range of measures.

The objective of the present report is to define a catalogue of NO₂ abatement measures and to assess the effectiveness of these measures to reduce NO₂ pollution in larger Danish cities.

1.6 The study

Air quality calculations have been carried out in a two stage process using air quality models developed by the National Environmental Research Institute. Firstly, urban background concentrations have been calculated to represent the general air pollution levels in Copenhagen. The urban background concentrations form a part of the input for calculations of street concentrations. Secondly, air quality calculations are carried for 138 busy streets in the municipalities of Copenhagen and Frederiksberg. These streets represent street canyon conditions with Average Daily Traffic of 15,000 - 60,000 where potential NO₂ compliance problems may occur. Calculations are carried out for the reference year of 2005, and for the scenario years 2010, 2015 and 2020.

Associated impacts on related pollutants have also been assessed but in a less detailed way compared to NO₂. Related air pollutants include particles (PM₁₀ – particles less than 10 micron – and PM_2.5 –particles less than 2.5 micron) and carbon dioxide emissions (CO₂). Particles pose a health risk and CO₂ is a greenhouse gas that contributes to climate change.

9 abatement measures of different types are defined: technology measures in relation to environment zones, traffic management, and economic measures.

1.7 Main conclusions

Road traffic is the main contributor to elevated NO₂ concentrations in busy urban streets.

In recent years, NO₂ concentrations have remained almost constant despite the fact that NO_x emissions have been reduced due to the continuous tightening of emission standards (also offsetting increases in urban traffic). Only a minor part of NO₂ in ambient air has been emitted directly from the sources in the form of NO₂. Most NO₂ is formed in the atmosphere due to reactions between ozone (O₃) in the air and nitrogen monoxide (NO) emissions from vehicles. During the past decade, average ozone concentrations have been more or less constant in Denmark despite reductions in precursor emissions in Europe. In the coming years, ozone concentrations are not assumed to decrease. However, ozone concentrations are expected to decrease in the longer term due to reductions in precursor emissions in Europe.

A decade ago, the directly emitted NO₂ fraction of NO_x (NO₂ and NO) emission from vehicles was about 5-10%. This fraction has increased in recent years and is expected to be about 15-20% in 2010. This is one of the main reasons why NO₂ concentrations have not decreased in urban street despite substantial NO_x emission reductions. The increase in directly emitted NO₂ is mainly due to the increase in the number of mainly diesel-powered passenger cars, but also of diesel-powered vans, that are equipped with oxidative catalysts that oxidise NO to NO₂. Furthermore, certain particle filters also increase the directly emitted NO₂. Most buses in central Copenhagen are equipped with particle filters, and more heavy-duty vehicles are expected to become equipped with particle filters to meet the emission requirements of the environmental zone in Copenhagen. The direct NO₂ fraction is estimated to be 18% in 2010, increasing to 24% in 2015, and then decreasing slightly to 23% i 2020.

NO_x source apportionment for selected busy streets in Copenhagen in 2010 show that heavy-duty vehicles (trucks and buses) account for about 30-35% of NO_x emissions but only 3-4% of traffic, taxis for about 7% of NO_x emissions and about 8-9% of traffic, vans for 14-18% of NO_x emissions and 10-12% of traffic, and passenger cars for about 48-54% of NO_x emissions and 77% of traffic. In total, diesel-powered vehicles contribute about 80-85% of NO_x emissions.

Model calculations show that NO_x emissions decrease in the reference scenario from 2010 to 2020 without new abatement measures due to introduction of vehicles that comply with more and more stringent emissions standards. On the other hand, the total amount of directly emitted NO₂ in the reference scenarios increase from 2005 to a maximum in 2015 and then decrease towards 2020 to a level slightly higher than in 2005. The NO₂ fraction shows a similar pattern. The reference scenario includes the requirements of the environmental zone in Copenhagen, requiring all heavy-duty vehicles of Euro 3 or older to be equipped with particle filter. Heavy-duty trucks that comply with Euro 3 are expected to be equipped with particle filters whereas Euro 0-2 are expected to be substituted with new Euro 5 trucks. For buses, Euro 0-1 and 50% of Euro 2 are substituted with Euro 5, 50% of Euro 2 and Euro 3 are equipped with particle filters. The requirements will reduce particle emissions as well as NO_x emissions.

The number of exceedances of the NO₂ limit value i 2010 is about 35 in busy streets in Copenhagen., 15 in 2015 and 2 in 2020. These calculations indicate that the problem of NO₂ exceedances will be solved within a decade, but that new abatement measures are needed to achieve compliance in 2010. Consequently, all the evaluated abatement measures have none or very few exceedances in 2020, as the impact of introduction of more stringent emission standards is dominant. On the other hand, there is profound impact of the different abatement measures in 2010 and 2015.

None of the evaluated abatement measures will solve the problem of exceedances of the NO₂ limit value in 2010, but a number of abatement measures will reduce the number of exceedances significantly, and a combination of abatement measures are likely to be able to eliminate all exceedances. The two most promising abatement measures are the requirements of the German environmental zones, and SCR NO_x catalysts on heavy-duty vehicles.

1.8 Project results

The results of the project are summarized in the table below.

The number of exceedances of the NO₂ limit value in 2010 is shown for the different abatement measures. The table further indicates the ranked performance of the measures, ranked by the number of exceedances, NO_x emissions in the environmental zone, and the directly emitted NO₂ emissions in the environmental zone. The environmental zone is here defined as the geographical extent of the municipalities of Copenhagen and Frederiksberg.

Link til tabel

1.8.1 NO₂ in other Danish cities

It is not within the scope of the present project to carry out detailed model calculations for other cities than Copenhagen. However, it is possible to make a rough assessment of the NO₂ pollution in the three other large cities in Denmark (Odense, Århus and Aalborg) based on urban background concentrations measured within the Danish Air Quality Monitoring Programme, combined with data about traffic flows (Average Daily Traffic (ADT)) and street configuration conditions (street widths and building heights). The urban background concentrations are generally 3-7 µg/m³ lower in these cities compared to Copenhagen with variations from year to year. A busy street in Copenhagen (Jagtvej) with 30,000 ADT has a modelled NO₂ concentration of 42 µg/m³ in 2010. If this street were located in one of the other three cities the limit value of 40 µg/m³ would not – or just marginally – be exceeded, due to the lower urban background levels. Based on information from NERI’s national road and traffic data base that includes all road segments in Denmark, there are no urban street canyons in these three cities that have ADT above 30,000. It is therefore likely that there will be only few exceedances of the NO₂ limit value in 2010 in these three cities.

Within the frame of the Danish Air Quality Monitoring Programme, as part of the integrated monitoring strategy, air quality model calculations with OSPM were performed for the town of Aalborg (Kemp et al. 2008). Urban background concentrations were note modelled in details, but just assumed to be identical to that measured at an urban background monitor station. These calculations show that 3 out of 32 selected busy street canyons in Aalborg exceeded the limit value plus margin of tolerance in 2007. Model calculations were not performed for 2010. Based on the above rough assessment and the calculations for Aalborg it cannot be ruled out that few exceedances of the NO₂ limit value may occur in 2010.