Copenhagen

Air quality levels in larger cities are elevated due to a combination of high vehicle emission densities, large coherent urban areas, and often poor dispersion conditions due to street canyons. In street canyons, which are common in central parts of European cities, the dispersion is restricted by the building geometry causing elevated air quality levels in these hotspots. At the same time urban areas have high population density and the population exposure to air pollution poses a significant health risk.

Population at risk

Traffic air pollution is the major source of degradation of air quality in larger cities. Human exposure to traffic air pollution in major cities poses a significant public health risk as numerous studies have shown that exposure to air pollution increases risks of developing cancer, respiratory and allergy diseases, and aggravates the condition of people suffering from respiratory or heart diseases. Pollutants of concern are particles, ozone and nitrogen dioxide.
Evaluation of air quality monitoring data by the European Environmental Agency has revealed that air quality limit values and target values for PM10, NO2 and ozone are currently exceeded in many European cities. Furthermore, cross European air quality model studies that have predicted future air quality levels suggest compliance problems in many areas.

EU regulation of air pollution

In a European regulation context the European Union (EU) has established health based air quality limit values or target values for a number of pollutants starting in 1996 with the EU Framework Directives and followed by four daughter directives on assessment and management of ambient air quality. At the same time the European Union has passed a number of directives to reduce air pollution emissions in the form of national emission ceilings targeting country emissions as well as sector emission regulation targeting individual emission sources (e.g. vehicle emission standards). Despite improvements, the adverse health and environmental impacts remain significant. In 2001 the EU Commission initiated the Clean Air for Europe (CAFE) stakeholder programme to provide technical analyses and policy development of a Thematic Strategy on Air Pollution to further improve air quality across Europe. The EU Commission adopted the Thematic Strategy in 2005. The strategy will be implemented in new directives on air quality limit or target values and emission control.

According to the EU directives on assessment and management of ambient air quality, it is a requirement that the national designated institutions prepare an action plan to ensure that limit values set out in the directives are met in the case that measured air quality levels are in excess of the limit levels plus a margin of tolerance. The margin of tolerance is gradually reduced until the attainment date of the limit value. In EU terminology such measures are referred to as non-technical measures as opposed to technical measures (e.g. vehicle emission standards). This means that there is a legal obligation for member states to act in response to observed violation of limit values.
The urban air pollution may be viewed as a contribution from the regional (or rural) background air upwind of the city, the urban emissions affecting the urban background air and vehicle emissions in individual streets that contribute to a further incremental increase in air pollution in the specific street. The regional background air constitutes a boundary condition for the city as it is determined by European (and even global) emissions and long-range transport and transformation of air pollution. The local or city authorities have no means to control the regional contribution.

Regulation of air quality by member states and local authorities

The local authorities can to some extent influence the urban emission contribution and its impact on urban air quality and human exposure. The overall options available for local authorities to regulate transport emissions may be grouped in the following measures: urban and traffic planning, economic measures, and technological measures. Urban and traffic planning influences the amount of traffic, modal split, routing, speed and exposure of the urban inhabitants. Economic measures like toll rings and road pricing (e.g. congestion charging in London and Stockholm) may regulate the amount of traffic and its geographic and temporal distribution. Technological measures may be in the form of environmental zones where certain vehicle emission standards and/or technical requirements have to be fulfilled for a confined geographic area to improve air quality (e.g. Gothenburg, Lund, Malmo and Stockholm in Sweden, and Copenhagen in Denmark). There is also an interplay between the national transport policies and control options of local authorities. National transport policies such as transport infrastructure investment, vehicle registration and fuel taxes, subsidies to public transport influence the transport setting. National legislation may also permit or prohibit local authorities to exploit economic and technological measures.

Case study in Copenhagen

The objectives are to characterise transport related sensitive urban areas in a geographic way in the Copenhagen Area and evaluate transport and emission policy instruments in relation to these sensitive urban areas. The case will focus on health based air quality indicators regulated by the European Union directive on ambient air quality assessment and management.
The city of Copenhagen is characterised by a combination of high population and high vehicle emission density. Copenhagen is located in a coastal area with flat terrain and relatively high average wind speeds that basically provide for favourable air quality conditions. However, the local building topography with many heavy trafficked street canyons restricts the dispersion of emissions and cause degradation of the air quality. Recent scenario studies have shown that a large number of streets in Copenhagen will not be able to comply with European Union air quality limit values for nitrogen dioxide (NO2) in 2010.

This case study will analyse the transport related sensitive areas in relation to urban areas in Copenhagen. The case study will focus on health based air quality indicators regulated by the European Union directive on ambient air quality assessment and management. Selected mitigating transport and emission policy instruments will be assessed in relation to the criteria for the sensitive urban areas and their geographically implications with focus on emissions, air quality, human exposure and health effects. Cost-benefit valuation will be carried out for selected policy instruments. The policy instruments include (a) Municipal measures: new infrastructure, traffic calming etc. (b) Reductions in transport by toll ring or road pricing (c) Cleaner transport technology: accelerated introduction of more stringent emission standards and environmental zone.

In street canyons, which are common in central parts of European cities, the dispersion is restricted by the building geometry causing elevated air quality levels in these hotspots. An example from Jagtvej in Copenhagen.

Example of mapping of NO2 urban background concentration levels in Copenhagen in 2010 based on the Danish Urban Background Model (UBM) on a 1x1 km2 grid. The limit value of 40 μg/m3 in 2010 will not be violated for urban background conditions.

About 80 exceedances of the NO2 limit value in 2010 out of 138 streets are expected in the municipalities of Copenhagen and Frederiksberg. Model results for 138 street canyons with Average Daily Traffic between 10,000-55,000 based on the Danish Operational Street Pollution Model (OSPM).