Clean air - Danish efforts
Large and small particles
Pollution with particles results in increasing illness, deterioration of general wellbeing and shorter lifetime of persons who are particularly exposed to respiratory diseases.
In contrast to gaseous air pollutants, particles are not a well-defined compound. They occur in varying sizes, shapes and chemical composition. Often the compounds attached to the surface of the particles are important - and not the particles themselves. In addition their size is determining for how long they stay in the atmosphere, and how easy they are deposited in e.g. human lungs.
Roughly, particles are divided into three size groups: coarse (larger then 2.5 µm), fine (smaller than 2.5 µm) and ultrafine (smaller than 1 µm). It appears that the fine and ultrafine particles are most hazardous.
Health impacts
Foreign estimates suggest that the average lifetime is reduced by about half a year per 10 µg/m3 PM10. If this estimate is applied to larger Danish cities, the reduction of the average level by 1/3 will reduce mortality by about 400 per year of 1 mio. inhabitants.
If the smallest particles are the most dangerous, it is because larger particles predominantly consist of worn road surface or compounds from natural sources that are not especially dangerous. Further, a given weight contains a much larger number of particles if they are small than if they are large. And their total surface is larger.
Most countries have established limit values for the mass of particles. Regulation on this basis may therefore be less efficient, because it is not the dangerous part that is directly regulated.
Particles in the air
Particles in the form of soot was, together with sulphur dioxide, the main component in the "classical" urban air pollution, and it was measured by blackening of filter paper. Soot has now largely disappeared from Danish open air due to cleaner fuels and better combustion systems possibly equipped with smoke filters.
Today the main part of the particles in the air is due to traffic - especially diesel cars - and other mobile sources. The rest can be industrial emissions e.g. from cement production or arise from natural sources as soil, vulcanos, forest fires or seaspray.
The total amount of dust (total suspended particulate matter) is measured by weighting filters, and halving of the yearly averages since the beginning of the 1980's has been observed. The amount of particles below 10 µm (PM10) has only been measured for a couple of years, and so far no trend has been observed.
Particles in Danish urban air
Emissions of soot and larger particles have been strongly reduced by the use of
cleaner fuels and improved combustion and purification technology, and their
concentrations in urban air have fallen correspondingly. Very small particles have been
measured for too short a period to show any trend. Soot is measured in the very busy
street Stormgade in Copenhagen, TSP (Total Suspended Particulate Matter) is measured i.a.
in the city of Aalborg. PM10 (the weight of particles below 10 µm) is measured on the
busy street Jagtvej in Copenhagen.
(Sources: HLU and NERI)
Particulate pollution was earlier soot from heating units. It could i.a. make it impossible to dry clothes in the open air, and it may also be the reason why umbrellas were originally black. Today small particles especially from traffic are most important. They are invisible to the naked eye, but they can be inhaled. The particles may have serious effects on human health, and may aggravate the condition of sensitive persons suffering from respiratory and heart diseases. Compounds on the particles can also have a number of impacts, e.g. be carcinogenic.
Danish research
Danish scientists are in the front of the development. Knowledge is still insufficient, but in recent years the basis for decisions has been improved. In the appropriation act funds have been allocated until 2004 to a special research programme on air pollution, especially on particles in the air.
The institutions under the Ministry of the Environment collaborate with a number of other Danish experts. It is expected that the programme will give the Ministry a much better understanding of the health consequences of particles in the air, and where the particles come from - and thus indicate the regulatory measures with the largest reduction potential.