Future Air Quality in Danish cities

English Summary

Future Air Quality in Danish cities

Background and Objectives

Background

The EU Commission has in co-operation with the European Auto- and Oil industry carried out the Auto-Oil Programme. The aim of the programme was to identify cost effective measures to comply to future EU air quality standards in cities in 2010 according to the new EU directive "Council directive 1999/30/EC of 22 April 1999 relating to limit values for sulphur dioxide, nitrogen dioxide and oxides of nitrogen, particulate matter and lead in ambient air". Based on the study, EU directives have been proposed and partly approved to regulate vehicle emissions and fuel qualities.

Objectives

The aim of the present project is to evaluate the impact on the future air quality in selected Danish cities of the new EU directives and proposals on vehicle emissions and fuel qualities. Furthermore, the objective is to compare the estimated future air quality with air quality limit values for protection of human health approved or proposed by EU as well as air quality guidelines by WHO and the Danish EPA.

Overall Approach, Applied Models and Main Assumptions

Overall Methodology

The assessment is carried out for the reference year 1995 and the scenario years: 2000, 2005, 2010, 2015 and 2020. Modelled substances include health related substances: NO₂ (NO_x), O_3, CO and benzene. Predictions for particles are based on expert judgement. Future air quality levels are predicted in a selected street named Jagtvej in the central part of Copenhagen that represent a near worst case. Jagtvej has an average daily traffic of about 24.000 vehicles, the street width is 25 meters with 3-5 storeyed buildings. Traffic loads and vehicle composition are assumed to be constant 1995-2020 in the street of Jagtvej which is in accordance with assessments of traffic development by local authorities. Air quality levels in the street is modelled by nested modelling taking into account emissions in the street, urban background levels and regional background levels. Interactions between the street air, the urban background air and the regional background air together with chemical transformations are modelled.

Additionally, calculations are carried out with less detailed input data for 103 other streets in the Copenhagen area with a wide range of traffic loads and street configurations to be able to generalise and relate the results to general traffic conditions in urban areas.

Danish Eulerian Model (DEM)

Regional background levels are predicted by the Danish Eulerian Model (DEM), a large-scale transport model based on 50 x 50 km² emission grids for all Europe and meteorology on a 150 x 150 km² grid. Development in European emissions is based on proposals for the new ECE protocols on regulation of trans-boundary air pollution to be met in 2010. Development in European emissions is determined by development in emission factors for each activity and development in the activities (industry, energy, transport etc.). National emission ceilings include all these sources. Expected increases in e.g. transport are therefore included.

Danish Urban Background Model (UBM) and Urban Emission Model (UBE)

The urban background levels are modelled by the Danish Urban Background Model (UBM) based on a 2 x 2 km² emission grid for the Greater Copenhagen urban area covering 151 km². Grid emissions are determined by a Urban Emission Model (UEM) that takes into account the traffic levels on the road network. Other sources are not considered as traffic is the dominating source in larger urban areas. Validation studies of the UBM model show a good agreement between modelled and measured levels when just considering traffic as source indicating that other sources play a minor role. Traffic is expected to increase by 17% on main roads in the urban road network during 1995-2010 corresponding to a general traffic increase of 10% in the road network. Development in traffic emission factors is based on the EU COPERT III emission model, proposed emission reductions and prediction of the development of the age profile of the Danish car fleet.

Danish Operational Street Pollution Model (OSPM)

Air pollution levels in the street of Jagtvej in Copenhagen are modelled by the Danish Operational Street Pollution Model (OSPM) as a contribution from the direct traffic emission in the street and a contribution from the modelled urban background. Vehicle emission factors are also based on COPERT III.

Predicted Future Air Quality

Vehicle Emission Reduction

Vehicle emission reductions during 1995-2010 are determined to about 70%, 75% and 85% for NO_x, CO and benzene, respectively. The impact on future air quality levels has been modelled and compared with limit values.

Importance of Regional and Urban Background Concentrations

The relation between air quality levels in the street of Jagtvej in Copenhagen has been related to concentration levels in the urban background of Copenhagen and the regional background outside Copenhagen, see Table 1. In 1995, urban background and regional background NO₂ levels are about 50% and 25% of the levels in the street, respectively. For CO and benzene, it is about 25% and 10%, respectively. Urban and regional NO₂ levels are relatively high compared to the street levels because NO₂ is mainly a secondary pollutant formed in reactions between NO and ozone. For ozone, concentration levels in the regional background, the urban background and at street level will narrow down from 1995 to 2010. For non-reactive species like CO and benzene, urban and regional levels are relatively low compared to the street levels.

Direct Vehicle Emissions -Decrease in Importance in Determining Street Levels

Table 1
The Relation Between Air Quality at Street Level and in the Urban and Regional Background (Index)

It is also seen that the regional and urban background will play a relatively larger role in determining street levels in 2010 compared to 1995, most profound for CO and benzene, and less for NO₂. In other words, the direct vehicle emission in the street will decrease in importance in determining air quality levels, although still dominating.

Predicted Future Trends in Air Quality

In Table 2, the predicted regional background, urban background and street air quality levels are shown for the different scenario years.

Table 2
Development in Regional, Urban Background and Street Air Quality Levels (Index and Annual Means)

NO Becomes Limiting Factor in Forming NO₂

Catalyst cars were introduced in Denmark in 1990/91 and reduce NO_x emissions (NO and NO₂). NO₂ observed levels in Jagtvej were more or less constant during 1990-95 indicating that ozone was the limiting factor in forming NO₂ in reactions between NO and ozone. From 1995 to 1998, measurements show a downward trend in NO₂ levels, and this trend is also reproduced by the OSPM model.

During 1995-2010/2020, 98- and 99.8-percentiles of NO₂ are predicted to decrease about 50% and 35%, respectively. The predictions show that NO becomes the limiting factor in forming NO₂ in reactions with ozone in the future due to the steadily decreasing NO_x emissions (NO and NO₂). NO constitutes about 95% of NO_x vehicle emissions.

Ozone

Annual regional ozone levels are only predicted to decrease about 2% in Denmark during 1995-2010 despite European reductions of ozone precursors like NO_x and VOCs of about 40%. However, high ozone levels during spring and summer decreases more. At Danish meteorological conditions, the regional background ozone is dominated by long-range transport as the net production of ozone is small in Denmark. Ozone levels are modelled to increase about 14% during 1995-2010 in the urban background since less NO is available for ozone depletion due to NO_x vehicle emission reductions.

CO and Benzene

CO levels are predicted to decrease by a factor of 4 and benzene levels by a factor of 10 from 1995 to 2010. The predicted downward trends of CO and benzene are also supported by observed levels during 1995-1998.

Comparison with Air Quality Guidelines

Air Quality Guidelines

Modelled street levels in Jagtvej, Copenhagen were compared with EU air quality limit values, WHO guidelines and Danish EPA criteria. The Danish EPA air quality criteria were set up to minimize adverse health effects. The air quality criteria are not administrative limit values but should be regarded as desired long-term objectives (Larsen et al. 1997).

New EU limit values have to be met in 2010. A margin of tolerance has been defined to secure that limit values will be met in 2010. The margin of tolerance given as a percentage in the table refers to the year the directive entries into force. The margin of tolerance is equally stepped down each year to reach 0% in 2010. Member states have to take local action if the margin of tolerance is exceeded.

Ozone

At street levels, the proposed EU limit value for short-term exposure was not exceeded in 1995 nor will it be exceeded in 2010 despite an increase in ozone levels in the street due to a decrease in NO vehicle emissions leaving less NO for depletion of ozone in forming NO₂. However, the sum of NO₂ and O₃ decreases. The urban background is a better indicator for ozone exposure of the population than levels in the streets since ozone levels are influenced by NO emissions. The proposed EU limit value for short-term exposure was not exceeded in the urban background.

NO₂

The EU limit value for NO₂ for long-term exposure was exceeded in 1995 and the limit value for short-term exposure is tangent. However, the margin of tolerance of 50% in 1999 is not exceeded.

The predicted NO₂ levels in 2010 at Jagtvej are about half of the EU limit value in 2010. The Danish EPA criteria for short-term and long-term exposure is exceeded for all scenario years until 2015-2020.

CO

The EU limit value for CO will be between the 98- and 99.8-percentile. The EU limit value for CO was not exceeded in 1995, and the margin of tolerance of 50% will not be exceeded in the expected year of entry into force of the directive (2000). In 2010 the predicted CO levels will be 10-20% of the EU limit value for 2010. The EU limit value and WHO guidelines are identically for CO. The Danish EPA has not suggested criteria for CO.

Benzene

The EU limit value for benzene was exceeded in 1995. The margin of tolerance of 100% will not be exceeded based on modelled levels in 2000, the expected year of entry into force of the proposed directive. The predicted levels in 2010 will be about half of the EU limit value. WHO guidelines and Danish EPA criteria are exceeded for all scenario years.

103 Streets in Copenhagen

Crude calculations of annual levels of NO₂ and benzene for 103 streets in Copenhagen showed that levels were below EU limit values for all streets.

The health impacts of NO₂, benzene and CO are likely to decrease in the future due to improved air quality for these pollutants.

Particulate Matter

Preliminary assessment

A separate assessment was carried out for particulate matter since Danish air quality models for particles are not yet available but under development.

A preliminary assessment of the particle levels of TSP (Total Suspended Particulate Matter) and PM₁₀ (particles less than 10 m m) in selected streets in Denmark was carried out and levels were related to the new EU limit values for PM₁₀. Measurements of ultrafine particles from vehicles in two Danish streets (particles less than 0.2 m m) were also presented.

TSP/PM₁₀

Measurements show that TSP is approx. 35% higher than PM₁₀, that is, PM₁₀ constitutes on average about 74% of TSP. This relation was used to give an indicative estimation of PM₁₀ levels at selected streets in Denmark where TSP is measured. Estimated PM₁₀ levels in 1998-99 were below the new limit value for 2005 but exceed the limit value for 2010.

Possible Future Development

Denmark has a national objective to reduce particle vehicle emission by 50% in urban areas 1988-2010, and further reductions after 2010. The increase in penetration of catalyst converters reduce particle emissions for petrol powered vehicles due to unleaded petrol. Catalysts become mandatory in 1990. New stringent particulate emission standards for especially diesel powered vehicles will reduce particle emissions. The conversion to diesel with a low content of sulphur will also reduce particulate emissions.

Previous assessments indicate that the total particulate emissions (as mass) from vehicle within the EU will decrease by about 70% 1995-2010 including expected increases in traffic. Based on a few number of European studies, WHO has estimated that the particulate emission from vehicles in urban areas contributes about 40-60% of PM₁₀.

Due to the above mentioned regulation of vehicle particulate emissions it is likely that the PM₁₀ will decrease in the future but it is difficult to estimate how much based on existing knowledge and to estimate if the limit value for 2010 will be met. The above figures indicate that it might be a problem.

Uncertainties and Future Research Needs

COPERT III underestimates emissions

Validation of the Urban Background Model and the OSPM model by comparing modelled and measured concentration levels showed that the models underestimate observed concentrations when using the EU COPERT III emission factors indicating that COPERT III underestimates real world emissions on the road assuming that the air quality models are correct.

A test was carried out that compared the ratio between modelled and measured CO and NO_x in the street of Jagtvej using COPERT III emission factors for CO and NO_x. If the ratio between CO and NO_x emissions is correct then the same ratio will be found in the observed concentrations of CO and NO_x. It was seen that the slope of modelled air quality levels using COPERT III emission factors was very different from the measured ratio between CO and NO_x in the street air. This indicates that the ratio between COPERT III emission factors for CO and NO_x is questionable since it does not comply with the ratio found in the measured street air.

Nevertheless, COPERT III emission factors were applied throughout the study although predicted air quality levels to begin with become underestimated. To compensate, the following approach was applied. For prediction of future concentrations in the urban background or in the street, observed levels have been applied from 1995 as a baseline for calibration, and the modelled trend as an index has been used to estimate future levels to give realistic predicted air quality levels that can be compared to air quality limit values. For reactive species like NO₂ this approach may underestimate future NO₂ levels in the street because of the non-linear relation between NO_x emissions and NO₂ due to interaction with ozone.

A study should be carried out that examines how well COPERT III emission factors correspond to on the road emissions by linking emissions to air quality levels in streets using models and measurements.

Particulate Matter

Particle emissions by mass and probably also by numbers are expected to decrease in the future promising less health impacts due to particulate matter. However, the knowledge about the air pollution with particulate matter is still rather limited. By the new PM₁₀/PM_2.5 methods and measurements of ultrafine particles from traffic, possibilities have opened to obtain valuable data. Systematic measurements, including long time-series, by these methods at representative sites will improve the possibilities for health studies substantially. However, more knowledge is needed about the chemical/physical properties of the particle, e.g. chemical composition, surface properties and morphology. The characterisation of the particles is also important for quantification of the contribution from different sources and parameterisation of the properties of the particles to be included in air quality models. This is necessary for decisions on abatement measures to be taken to reduce the health impacts of particulate air pollution and to evaluate the effects of the measures taken.

Traffic loads

Traffic loads at Jagtvej in Copenhagen was assumed to be constant during the scenario years and traffic loads on the road network in the Copenhagen area was assumed to increase by 17% on main roads during 1995-2010 corresponding to a general traffic increase of 10% in the road network. If these assumptions are too optimistic, air quality levels will be higher than predicted. However, somewhat higher traffic loads will not compromise the downward trend in concentrations due to the profound emission reductions.

Scenarios 2015-2020

Predictions for 2015 and 2020 are indicative. They reflect the penetration of cars that comply to EURO IV for passenger cars and vans (2006-7) and EURO V for lorries and buses (2010). Obviously, these scenarios do not take into account possible future new EU national emission ceilings or vehicle emission regulation.

Other Sources than Traffic

The regional and urban background concentrations gain in importance in relation to the direct vehicle emissions in urban streets in the future. However, traffic will still be the domination source in urban areas but more attention will have to be put on other sources in urban areas to predict concentration levels. In the present study, prediction of the regional background include all source but the Urban Background Model only includes traffic as source. However, it is likely that inclusion of other sources would not have changed predicted urban background levels significantly.

DEM Model

Prediction of CO in the DEM model could be improved by applying better emission data what is available. A feature for predicting benzene levels could be develop.

CO Monitoring

CO is a good indicator for petrol powered vehicles and can be used to estimate other pollutants like benzene. More CO monitoring in regional background is required to get a more complete picture of regional background concentrations, and to get reliable data for validation of the UBM model.