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No. 25: Assessment of air quality in low emission zones in Copenhagen

Jensen, S.S., Ketzel, M., Brandt, J., Winther, M. 2012: Luftkvalitetsvurdering af ren-luftzone i København. Aarhus Universitet, DCE – Nationalt Center for Miljø og Energi, 86 s. - Videnskabelig rapport fra DCE - Nationalt Center for Miljø og Energi nr. 25. http://www.dmu.dk/Pub/SR25.pdf

Summary 

Background and objectives

According to the government agreement from 2011 improved low emission zones have been identified as a measure to improve the air quality in greater Danish cities, and to ensure compliance with air quality limit values for NO2 of 40 µg/m3 as an annual mean. The limit value is violated at H.C. Andersens Boulevard in Copenhagen which is one of the busiest urban streets in Denmark and a fixed air quality monitor station is also located in the street. Air quality model calculations also shows that some other busy streets in Copenhagen violate the annual air quality limit values for NO2.

The objective of the project is to assess the impacts of a number of improved low emission zone measures in Copenhagen regarding emissions and air quality with focus on NO2. The extent of the existing low emission zone is equal to the extent of the Municipality of Copenhagen and Municipality of Frederiksberg.

The existing low emission zones (LEZ) in the cities of Copenhagen, Aarhus, Odense and Aalborg were fully implemented in 2010 and regulates older buses and trucks. Buses and trucks over 3.5 tons should comply with the Euro 4 emission standard or be equipped with a particle filter. Evaluation of the existing low emission zones have shown a reduction i particle and NOx emissions and improvements in air quality (Jensen et al. 2011).

Scenarios

Euro emission standards regulate emissions of air pollutants from vehicles and set limit values for emissions defined in relation to a driving cycle under laboratory conditions. Vehicles have to comply with these limit values to obtain type approvals. See Euro emission standards Euro 0-6 in Appendix 2. The limit values have been continuously strengthened during the years. Therefore, banning of e.g. Euro 0-3 (older cars) in a LEZ and replacement by newer cars (Euro 4-6) will lead to reduction in emissions.

There are two types of base scenarios. The first base scenario (1A) assumes that the car fleet is as expected with the existing LEZ and the second base scenario (1B) assumes that Euro 6 will be promoted through various incentives resulting in more Euro 6 passenger cars and vans. Therefore, scenario 1B will have lower emissions that scenario 1A.

The van scenario (2A/2B) assumes that diesel-powered vans older or equal to Euro 3 and petrol-powered vans older or equal to Euro 1 are banned from the LEZ. This regulation is almost similar to the German LEZ requirements although a little more stringent as German LEZ allows Euro 1 petrol-powered vans.

The combined passenger cars and vans scenario (3A/3B) have the same requirements to vans as 2A/2B and further requires that diesel-powered passenger cars older or equal to Euro 3 and petrol-powered passenger cars older or equal to Euro 1 are banned from the LEZ. This regulation is a little more stringent for passenger cars compared to German LEZ as German LEZ allows Euro 1 petrol-powered passenger cars.

Scenario 4A/4B are variants of scenario 2 and 3 that assumes either Euro 0 or Euro 2 instead of Euro 1 for petrol-powered passenger cars or vans.

Scenario 4 also includes scenarios where SCR (Selective Catalyst Reduction) are assumed to be retro-fitted on coaches, urban buses and trucks that are older or equal to Euro 3. These NOx catalysts are assumed to reduce NOx emissions by 80 %. Scenario 4 also includes a scenario that assumes that all urban buses are Euro 6.

Scenario 4 also includes a scenario that assumes that new sales of diesel-powered passenger cars are reduces during the years 2013-15 by 5 procentpoints, that is, from 48 % to 43 % of all passenger cars. As a result the diesel share of the car fleet of passenger cars is reduced from 34.1 % to 33.2 % in 2015.

The scenario years are 2013, 2015 and 2017 and have been chosen for the following reasons. The Danish Environmental Protection Agency may apply to the EU Commission for an extension of compliance with the NO2 limit value until 2015 but the EU Commission expects compliance to be reach as soon as possible, why 2013 also has been chosen as scenario year. The scenario year 2017 was chosen as the continuous replacement of the car fleet leads to lower emissions, and 2017 illustrates how fast concentrations will decrease after 2015.

Although focus is on compliance with NO2 limit values for air quality the scenarios will also reduce particle emissions and therefore have public health benefits as particle pollution causes health effects.

Methodology

The impact assessment of the different scenarios includes assessment of emissions and air quality. The assessment is carried out in great details for NO2 and to a lesser degree for PM exhaust, PM2.5 and PM10. Since air quality assessment is resource demanding only the main scenarios (2A/2B, 3A/3B) are carried out with the full air quality model whereas the air quality of the scenario variants are assessed based on regression analysis between emissions and air quality in scenarios calculated with the full air quality model.

Emission and air quality assessment is carried out for all scenarios for H.C. Andersens Boulevard where the fixed monitor is located and the annual limit value of NO2 is violated. Furthermore, air quality calculations are carried out for 99 busy streets in Copenhagen. Traffic data originates from the Municipality of Copenhagen and it is assured that the most busy streets are included. Moreover, street canyons are selected to include streets where the highest concentrations can be expected.

Air quality calculations are modelled with a linked air quality model system including a long-range transport chemistry model (DEHM), an urban background model (UBM) and a street model (OSPM) and associated meteorological and emission data.

Calculated NO2 concentrations based on the linked model system have been compared to air quality measurements in urban background (H.C. Ørsted Institute in Copenhagen) and calculations are within a few per cent of the measurements in 2011 after calibration. Modelled street concentrations were also compared to air quality measurements from H.C. Andersens Boulevard and calibrated with measurements from 2007-2009 as the measurement station were influenced by emissions from building construction equipment during 2009-2011. The model represents the trend of NO2 very well for a number of years and the same is true for another street measurement station in Copenhagen (Jagtvej) and the model reproduces measured NO2 within a few per cent for Jagtvej. Therefore, the model system is expected to be able to predict NO2 concentrations in the different scenarios years for the different scenarios.

Main Conclusions

H.C. Andersens Boulevard

Modelled NO2 concentrations decrease from 2011 to 2017 and for H.C. Andersens Boulevard the NO2 concentration decreases from 47.1 to 35.4 µg/m3. The limit value is barely exceeded on H.C. Andersens Boulevard in 2015 (40.54 µg/m3). An exceedance is registered if the value 40.5 is exceeded as the limit is 40 µg/m3 as an integer. The limit value will not be violated in 2017 on H.C. Andersens Boulevard. On the contrary, the analysis shows that it will be very difficult to avoid exceedances in 2013 as the NO2 concentration at H.C. Andersens Boulevard is 44,7 µg/m3 in the reference scenario. All scenarios except base scenario 1A will reduce NO2 concentrations at H.C. Andersens Boulevard leading to no exceedances of the limit value in 2015.

The analysis of the individual measures showed that the impact of the van scenario (2A/2B) was less than expected as it is the regulation of passenger cars that primarily reduces NO2 emissions in the combined passenger cars and vans scenario (3A/3B). Although scenario 3A/3B replaces older diesel vans with newer ones, the newer ones have higher direct NO2 emissions resulting in less reduction in NO2 emissions than may be expected from the overall contribution of diesel vans to NOx emissions. NOx emissions are NO+NO2 emissions and the direct NO2 emission denotes the fraction of NOx that is emitted as NO2. In the atmosphere NO is converted to NO2 in reactions with ozone. The van scenario 2A reduces NOx emissions by 3 % and including promotion of Euro 6 (2B) by 6 %.

The variant scenarios showed no impact of moving the limit of Euro 1 for petrol-powered vans to either Euro 0 (4A-a and 4B-a) or Euro 2 (4A-b and 4B-b) because there are few petrol-powered vans left in 2015, and they only contribute with 0.27 % of NOx emissions.

There is a minor negative impact of moving the Euro 1 limit to Euro 0 for petrol-powered passenger cars (4A-c and 4B-c) in 2015 since Euro 0 and Euro 1 still contribute to 3.5 % of NOx emissions. The reason is that when Euro 0 and Euro 1 petrol-powered passenger cars are banned they are replaced by petrol- and diesel-powered passenger cars where the diesel cars have higher emissions than the petrol cars.

There is a minor positive impact of moving the limit of Euro 1 to Euro 2 for petrol-powered passenger cars (4A-d and 4B-d) as NOx emissions decrease 2 % and NO2 concentrations decrease 0.3-0.4 µg/m3 in 2015.

The effect of retro-fitting SCR on Euro 3 and older buses (4A-e) is marginal as the NO2 concentration is only reduced by 0.1 µg/m3 for both urban buses and coaches in 2015. The reason for the minor impact is that these buses only contribute to 1.3 % of total NOx emissions in 2015 since the existing LEZ and environmental requirements to urban bus service have reduced their numbers and replaced them with newer vehicles.

There is a moderate positive effect of retro-fitting SCR on Euro 3 and older trucks (4A-g) as NOx emissions are reduced by about 4 % and the NO2 concentration is reduced by 0.9 µg/m3 i 2015.

There is a larger positive effect of the scenario with 100 % Euro 6 urban buses (4A-h) as NOx emissions are reduced by about 9 % and the NO2 concentration is reduced by 1,8 µg/m3 i 2015.

The scenarios also influence particle exhaust emission but non-exhaust is not affected as traffic levels and speed are assumed constant. In the van scenario (2A/2B) particle exhaust emissions are reduced by 15 % and in passenger car and van scenario (3A/3B) by 28 %. However, this leads to marginal changes in the air quality of PM2.5 and PM10 due to large contributions from the regional background, non-exhaust and other sources. Scenario 2A/2B (vans) reduces street concentrations by 0.12 µg/m3 for PM2.5 and also 0.12 µg/m3 for PM10 (respectively 0.6 % and 0.4 % of assumed street concentrations in 2015) and scenario 3A/3B (passenger cars and vans) reduces street concentrations by 0.24 µg/m3 for PM2.5 and also 0.24 µg/m3 for PM10 (respectively 1.3 % and 0.8 % of assumed street concentrations in 2015). The benefits to public health of the scenarios may be larger than these small changes indicate since particle exhaust emission is a strong health risk.

99 selected streets

There are 8 modelled exceedances of the NO2 limit value in 2015 in the base scenario (1A) out of the 99 selected streets with the highest modelled concentration of 44.5 µg/m3.

The base scenario with promotion of Euro 6 (1B) reduces NOx emissions by 3 %, NO2 concentrations by 1,0-1,5 µg/m3 in relation to the base scenario without promotion of euro 6 (1A) and there are 3 exceedances in this case in 2015.

As en example, there would be no exceedances with implementation of the passenger cars and vans scenario (3A) in combination with 100 % Euro 6 on urban buses (4A-h). Each of these scenarios reduces NOx emissions by about 9 % in 2015.

The scenario with passenger cars and vans including promotion of Euro 6 (3B) reduces NOx emission by 13 % (for H.C. Andersens Boulevard) and will just ensure that there are no exceedances on the 99 selected streets in 2015.

Number of affected vehicles

About 2,000-30,000 vans will be affected in the different scenarios, and about 50,000 passenger cars in the main scenario 3A, about 25,000 passenger cars if the limit is shifted from Euro 1 to Euro 0 and about 90,000 passenger cars if the limit is shifted from Euro 1 to Euro 2.