Both short- and long-term exposure to nitrogen dioxide and particulate matter may cause adverse health effects. Studies have shown that there is a causal relationship between long-term exposure to air pollutants and the development of respiratory illnesses.
The pollution control regulations define minimum requirements for local air quality. In addition, there are health-based air quality criteria defined by the Norwegian Institute of Public Health and the Norwegian Environment Agency. These air quality criteria are stricter than the limit values in the regulations.
Particulate matter consists of small airborne particles commonly differentiated in two size fractions; PM10 includes particles smaller than 10 µm, while PM2.5 includes particles smaller than 2.5 µm. The main sources of PM2.5 are derived from combustion (domestic heating and exhaust from vehicles), while PM10 is derived from the wear and tear of pavement, tyres and brake pads. Construction sites may also contribute to particulate emissions locally.
Limit values for particulate matter have been in effect since 1.1.2005 and the City of Oslo has committed a great deal of resources to finding and implementing measures ensuring compliance. Although this was difficult at first, in more recent years the limit values have largely been met.
The observed decrease in the amount of particulate matter is mostly due to the implementation of fees for studded tyres, environmental speed limits and road dust prevention measures.
In 2016, the limit values for particulate matter were lowered. Consequently, areas with heavy traffic in Oslo risk failing to comply with the new limits unless additional measures are put in place. Exceedances of the daily limit value are most commonly associated with the use of studded tyres and from wood burning during dry and cold periods in the winter.
The limit values define minimum requirements for local air quality and exposure to air pollution below these limits may still have adverse health effects. This is especially true for particulate matter. The City Government’s policy is to set higher standards for air quality in Oslo in line with the Norwegian health authorities' recommendations, and to work for stricter national limit values. However, in order to meet these goals additional measures must be put in place.
Nitrogen dioxide (NO2) is a gas, with the main source in Oslo being derived from exhaust, especially from diesel vehicles.
Annual limit values
Measurements show that annual mean values of NO2 have been steadily decreasing, particularly after 2013. The limit values for NO2 have not been exceeded in Oslo after 2017. However, the risk of exceeding the limit values remains.
The main reason for the observed decrease in NO2 is most likely due to a cleaner vehicle fleet in combination with relatively warm winters. Additionally, since 2017, there has been a slight decrease in the number of cars passing the toll ring (which in turn coincides with the implementation of congestion and environmental tolls). In 2020, measures to prevent covid-19 have also contributed to reduced emissions.
The number of exceedances of the limit value for hourly mean concentrations of NO2 shows a large degree of annual and local variation. The pollution regulations allow for up to 18 hours of concentrations exceeding 200 µg/m3 per year.
Exceedances of the hourly limit values occur most commonly during the winter, particularly on days with low temperatures and little wind. Under these conditions a layer of cold air may trap the polluted air, thus increasing the local concentration of NO2.
Oslo will likely continue to exceed the NO2 limit values on individual years unless more preventive measures are implemented.
The levels of tropospheric ozone in Oslo are low.
The main source of tropospheric (the lowest layer of the earth’s atmosphere) ozone is long-range transport from continental Europe.
The limit value for ozone (the eight hour average ozone concentration) is calculated as an average over a three year period where the concentrations cannot exceed 120 µg/m3 (or 0.07 ppm) during an 8 hour period for more than 25 days a year.
The eight hour average ozone concentration limit is not exceeded in Oslo.