Better air quality in Oslo

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Norwegian Institute for Air Research (NILU) has performed trend analysis of exposure to air pollution for Oslo, the capital city of Norway, in the period 1995 – 2001. In this period, the number of persons exposed to concentrations of PM10 above the Norwegian guideline for good air quality, were reduced with approx. 100 000 (31%).

Similar, the reduction related to NO2 was 45 000 (77%). The improved impact of air pollution was mainly due to reduced use of studded tyres (PM10) and more cars using 3-way catalytic converter (NO2).

The NILU developed air quality management system AirQUIS has been used to calculate hour by hour concentrations and exposure fields in Oslo in 1995, 1998 and 2001 for selected source categories such as industry, traffic and private consumption of fossil fuels and indoor wood burning.

The impact of air pollution is divided into user specified source categories and the exposure calculation can be performed in specified building points or as average for a grid square. The results has been compared to recommended Norwegian air quality guidelines of nitrogen dioxide (NO2) and particles (PM10).

Better air quality in Oslo

Emissions to air

The main sources to emissions to air of PM10 and NO2 in Norwegian cities are traffic and indoor wood burning. Other sources such as industry, public buildings and harbour activities are limited. In some few specific regions also industrial areas might impact urban areas

Traffic

The number of vehicle driven kilometres in Oslo has increased by 22% from 1995 to 2001. In the same period, the fraction of cars using studded tyres have been reduced from approx. 70% to 20% due to implementation of taxes for using studded tyres in Oslo. This has lead to about 60% reduction of resuspended particles caused by vehicle driven turbulence. Emission of nitrogen oxides from traffic have been reduced by approx. 33% due to increased use of 3-way catalytic converters in the cars.

Indoor wood combustion

The private use of wood for heating in stoves or open fire places is commonly used in Norwegian houses during the winter period. Next to traffic, this is the major source to emission to air of particles. The emissions to air from wood burning has been reduced by approx. 33% due to a combination of reduced use of wood burning and improved technology in the stoves.

Other sources

Other sources of emissions to air such as industry, public buildings, harbour activities and heating by fossil fuels are limited and only small changes have occurred in the period.

Norwegian recommended air quality guidelines
The recommended Norwegian air quality guidelines of PM10 and NO2 are based on the same concept as the EU Directives. These are:

  • NO2: 150 µg/m3 as 8. highest hourly averaged value
  • PM10: 50 µg/m3 as 7. highest daily averaged value

Concentration distributions

The results of the dispersion calculations for Oslo from 1995 – 2001 shows reduced concentrations levels for both NO2 and PM10, giving the highest reductions for PM10. The 8. highest daily average concentration distribution of PM10 for the year 1995 and 2001 is given in figure below.

Better air quality in Oslo

Exposure

Personal exposure of NO2 and PM10 has been calculated by a combination of exposure calculations in building points along major roads and for each model grid square. The number of persons exposed to exceedances of the recommended guidelines for 1995 and 2001 is given in figure 2, respectively.

Better air quality in Oslo

These gives that the number of persons exposed to exceedances of PM10 is reduced from 320 000 persons to 220 000 persons, while the reduction for NO2 was from 58 500 persons to 13 500 persons.

Source contribution

The situations where exceedances of recommended air quality guidelines occur are related to cold, calm days with atmospheric inversions and poor dispersion conditions.

The typical source contribution of the main source classes to the impact of NO2 and PM10 according to the guidelines is given in figure 5 and 6. This clearly shows that the major source category for emissions to air of nitrogen oxides during these episodes are traffic with approx. 90% of the emissions. Similar, the main source categories to emissions of PM10 in the centre of Oslo are wood burning and traffic with approx. 60% and 30%, respectively.

Conclusions and recommendations

The situations where exceedances of recommended Norwegian air quality guidelines occur are related to cold, calm days with atmospheric inversions and poor dispersion conditions.

The major source to the impact of NO2 according to the guidelines are traffic with approx. 90% of the NOx-emissions. Similar, the main source categories to emissions of PM10 in the centre of Oslo are wood burning and traffic with approx. 60% and 30%, respectively.

Better air quality in Oslo

The trend analysis of air pollution impact in Oslo in the period 1995 – 2001 shows a reduction in number of people exposed to exceedances of recommended air quality guidelines for PM10 and NO2 by 100 000 and 45 000, respectively. The main reason for this is reduced use of studded tyres and wood for house heating and the introduction of 3-way catalytic converter in cars.

NILU would like to thank The Norwegian Pollution Control Authority for funding this project and The Department of Public Health, Oslo, for important collaboration.

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