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Urban air quality

Jente
Foto: Christine F. Solbakken, NILU

Good air quality is very important to people’s health and well-being. Most cities in Norway are experiencing population growth and increased urbanisation, which can contribute to more pollution.

In order to meet these challenges, we need more knowledge of how to ensure sustainable urban development and good air quality in the coming years.

NILU contributes to green community development by offering research, services and advice to public administration and industry.

What pollutes Norwegian cities and towns?

Air pollution is a significant health problem worldwide, and it also affects the health of the population in Norwegian cities and towns. The main pollutants in Norwegian cities are nitrogen dioxide (NO2) and particulate matter (PM10 and PM2.5).

Nitrogen oxides (NO and NO2, referred to as NOX) are reactive gases formed by high-temperature combustion. In Norwegian cities, emissions from road traffic (exhaust) are the most important source of NOx. The main health effects of NO2 are impaired pulmonary function and worsening of respiratory diseases, such as asthma and bronchitis.

Particulate matter (PM) refers to particles that are small enough to behave like gas, and are mixed in and transported by air. PM is divided into two size fractions. PM2.5 are the smallest particles, with a diameter less than 2.5 micrometres. PM10 is particles up to 10 micrometres in diameter. PM2.5 comes mainly from combustion (wood burning, car exhaust), while the larger particles derive from suspension of dust from car tyres and road wear. The smallest particles can be transported with the air over great distances, and such long-range transport of air pollutants can also contribute significantly to the concentrations of PM2.5 in Norwegian cities.

Particulate matter can have different health effects depending on the physical and chemical properties of the particles. For example, the size will affect how deep into the respiratory system the particles are inhaled. Surveys from around the world show the correlation between increased levels of PM in the air and the number of hospitalisations and deaths in the population. Exposure to PM can initiate inflammatory reactions that may contribute to the development and worsening of pulmonary and cardiovascular diseases. Research also suggests correlation between PM exposure and effects on foetal development, nervous system and metabolism.

Sources of pollution

The main source of local air pollution in Norwegian cities and towns is road traffic with emissions of exhaust and road dust from studded tyres.

Wood burning in private homes and emissions from industrial and maritime traffic also contribute, as does long-range transported pollution from other European countries.

It is important to note that emissions are not the same as concentration or amount in the air. If the emissions are far from people or high above the ground, they contribute less to the pollution levels where people are than corresponding emissions near the ground in the middle of the city, as is the case for traffic emissions.

Air pollution can vary widely

Several factors affect the pollution level: how much pollution is released from different sources; proximity to pollutant sources; and local meteorological and climatic conditions.

The main sources of air pollution in Norway are emissions from road traffic, wood burning and industry, along with emissions from ships in port. Variations in the amount of emissions from the various sources of pollution over both the day and the year, as well as variations in local meteorological conditions, allow the pollution level locally in cities and towns to vary widely from place to place and over time.

In Norway, air pollution is worse during winter. This is due, among other things, to higher emissions from several sources such as wood burning, road dust from studded car tyres and exhaust emissions from cold engines in cold weather. During the winter, meteorological inversions may also occur, which lead to poorer dispersion. Years with many and long inversion episodes will typically have higher levels of pollution than years with few inversion episodes.