Miljøprojekt, 1021 – Luftforurening med partikler i Danmark

Luftforurening med partikler i Danmark

Summary and conclusions

1.4 What is air pollution with particles?
1.5 Particle pollution and health impacts
1.6 Characterisation of particle pollution

During the last four years, the Danish EPA has carried out a number of studies focusing on air pollution with particles, as part of the Government Environment and Health Efforts. A total of DKK 14 mill. has been used for this purpose.

Major contributions were given by NERI, which has prepared surveys of particle pollution through an extensive monitoring and analysis programme. Moreover, a number of projects have been carried out, focusing on health effects and possible remedial measures.

This report presents the most important results and conclusions achieved during this work.

1.4 What is air pollution with particles?

Air pollution with particles is a result of atmospheric emissions, dispersal and chemical and physical conversion. Low-level sources (for instance transport and local heating of houses) give rise to extensive local air pollution. Therefore, these sources will give rise to relatively high exposure of the residents in urban areas. Pollution from high-level point sources (for instance power plants) is diluted considerably before reaching the surface, and will therefore not cause major exposure of the Danish population. However, it will contribute to the general background pollution in Europe. Similarly, Denmark is largely affected by pollution from other European countries. Finally, there are a number of natural sources of atmospheric particles, for instance earth dust, salt in marine water, and forest fires. Particles from natural sources are generally larger, and are considered to have less health impacts than man-made combustion particles.

Generally we use the terms PM₁₀, i.e. particles up to a diameter of 10 µm (1/1000 mm) and PM_2.5, i.e. particles up to a diameter of 2.5 µm.

Ultrafine particles and nano-particles are particles below 0.1 µm, formed at high temperatures, for instance in combustion engines, power boilers or industrial processes. Some of the ultrafine particles are soot particles, which originate primarily from diesel-powered cars and stoves. Their diameter is typically 0.08-0.1 µm, and they penetrate deeply into the lungs. A number of studies show that – with their content of many different chemical compounds – soot particles are particularly harmful.

Fine particles (below 25 µm) may stay suspended in the air for several weeks and, thus, be transported several hundred thousand kilometres. Due to the physical and chemical processes in the atmosphere, these particles contain large shares of ammonia sulphate and ammonia nitrate. Sulphate and nitrate come mainly from combustion processes (emitted as SO₂ and NO_X), while ammonia comes mainly from releases of ammonia from agriculture.

Recent years have seen a marked decrease in the content of sulphur particles, due to the lower content of sulphur in fuels in Europe, and the introduction of desulphurisation at power plants.

Coarse, airborne particles are typically formed by a number of mechanical processes, for instance dust from the soil and from roads which is whirled up by the wind, during gravelling and salting of slippery roads, salty particles from the sea (drying into salt particles), volcanoes, vegetation (pollen), wear of tyres and road surfaces, traffic-related turbulence in streets, construction and industrial processes. Due to their weight, these particles only remain suspended for a short time, and thus have a short lifetime.

1.5 Particle pollution and health impacts

For a long time we have known that particle pollution is harmful to health, especially in connection with respiratory diseases and cardiovascular diseases. Much indicates that the small particles present the most serious problem to health in relation to air pollution. In connection with efforts within Environment and Health, it was very important to provide more knowledge on exposure and on the health implications for Danish conditions, as well as to increase our understanding of which population groups are especially vulnerable and why.

Up till now, three projects have been completed on these issues, and two projects are still ongoing.

1.5.1 Children with asthma

The project was carried out by the National Institute of Public Health at the University of Copenhagen. The project aimed at studying associations between daily levels of ambient air pollution in the Copenhagen area and daily airway symptoms among 411 children followed from their birth to the age of 18 months. The children all had atopic predisposition for asthma and other hypersensitivity diseases. The study found consistent associations between high levels of air pollution measured at the street stations on Jagtvej and H.C. Andersens Boulevard and incidences of wheezing during the following days by several of the children living in central Copenhagen. Among children living further away from the centre of the city, the associations found between air pollution and symptoms were much less consistent. The respiratory symptoms were related especially to the observed levels of carbon oxide and nitrogen oxides (NO_X), which are generated mostly by traffic. Associations were also found between the recorded levels of PM₁₀ and ultrafine particles, however, to a much smaller degree.

1.5.2 Exposure to ultrafine particles from traffic in Copenhagen

The project was carried out by the National Institute of Public Health at the University of Copenhagen. By means of portable particle counters carried by test subjects, exposure to ultrafine particles was measured in a number of persons taking part in the project in Copenhagen during a period of eight days. In five of the test days, the subjects cycled approx. 20 km along congested streets during rush hours. At the end of each of the days, blood samples were taken to determine the level of DNA damage in lymphocytes. The study shows that elevated exposure to ultrafine particles while bicycling during rush hours in Copenhagen causes significantly increased levels of DNA damage to lymphocytes. Moreover, the study shows that the impact of outdoor traffic-related ultrafine particles on lymphocytes was approx. three-times higher than the associated impact of similar doses of ultrafine particles in indoor environments.

The project resulted in the development of a new method to assess personal exposure to ultrafine particles, and clarification of the situations causing the subjects to be exposed to ultrafine particles on a daily basis. Further, the study found a relevant bio-marker in the form of DNA damage to lymphocytes in connection with short-term exposure. The project is the first of its kind, also at international level.

DNA damage to the blood cannot be considered harmful to health by itself, and the project can therefore not be used in connection with risk assessments proper. However, the effects on the blood indicate that ultrafine particles generate a biological response, and that this may influence the known effects of ultrafine particles on health.

1.5.3 PAH in outdoor and indoor air

The National Institute of Occupational Health at Copenhagen carried out a project to measure different particle sizes and levels of PAH (tar substances) in ambient air in Copenhagen. Measurements were made for 15 weeks in an urban background environment and at a busy road (Jagtvej). Moreover, in order to compare levels in indoor and outdoor air, indoor air was monitored during similar periods, at Jagtvej in an empty apartment on the third floor.

The results demonstrate a relationship between outdoor and indoor levels. The outdoor level of tars at the apartment affects the indoor levels, which are, however, also affected by indoor sources.

Using the latest dose-response associations for particles found in foreign population studies on this material relating to outdoor measurements, it is assessed that, at the levels indicated particle pollution may cause 780 excess deaths per year, thus reducing mean life expectancies by approx. 6 months. Moreover, particle pollution causes approx. 1560 excess hospitalisations because of cardiovascular diseases and respiratory symptoms per 1 mill. inhabitants in Copenhagen. This corresponds to earlier assessments. Note also that on an average, only 5-10 per cent of the particle pollution affecting residents in Copenhagen, originates from Danish sources.

On the basis of PAH levels, measured as B(a)P, 10 excess cancer cases per 1 mill. inhabitants in Copenhagen are expected over a 70-year period, and the content of tars is, by itself, considered to play only a modest role in the carcinogenic effects of the particles.

The project increased our knowledge of the importance of variations of outdoor particle levels at the apartment and in the urban background to indoor exposure of the population. The more detailed knowledge on tar levels in indoor as well as outdoor air is new. The calculated harmful effects confirm previous calculations regarding the magnitude of effects.

1.6 Characterisation of particle pollution

The following gives a summary of the measurements and analyses made by NERI.

Contributions from transport to particle emissions in Denmark are significant. Other mobile sources that are also large contributors are mainly tractors and agricultural and contractor's equipment. Also trains, ferries in domestic routes, fishing boats and other domestic vessels are included in this category. Another important contributor is heating at individual houses, where almost 90 per cent is estimated to originate from woodburning stoves.

The air in Denmark is also affected by sources elsewhere in Europe. Total emissions in Europe are about 100 times larger than Danish emissions, and will therefore have a huge impact on Danish air quality.

1.6.1 Traffic-related particle pollution

NERI has carried out comprehensive studies of traffic-related particle pollution, aiming at determining the contributions from transport, and forming the basis for calculations of the population's exposure to particles.

The contribution from traffic to PM_2.5 is due mainly to soot particles in the exhaust gases from diesel vehicles. However, in step with the introduction of stricter environmental requirements for diesel vehicles, particles from frictional sources, i.e. tyres and brakes, from all types of vehicles are playing an increasing role.

Ordinary petrol-driven cars also contribute to PM_2.5 with particles from wear of brakes, as well as of tyres and road surfaces. Particles from brakes are much larger than soot particles, but still penetrate deeply into the lungs. Moreover, they have a large content of metals of varying toxicity.

Together, particles from brakes and exhaust gases contribute approx. one-third of PM₁₀ from traffic in the street H.C. Andersens Boulevard. The rest originates from road dust (incl. dust from wear of tyres), road salt, and background pollution.

From 1985 to 2002, emissions of exhaust particles from road transport were reduced by 30 per cent, while emissions of particles caused by wear increased by 43 per cent in the same period, in step with increasing traffic intensity. Emissions from vans and lorries and from heavy vehicles have fallen markedly since the mid-1990s, due to stricter emission standards in the EU and, thus, in Denmark. The contribution from wear-related particles is expected to increase further in the future, because of increasing traffic intensity. Moreover, the increase in sales of diesel-powered passenger cars has caused total emissions of particles from passenger cars to increase.

Measurements of particle numbers show that particles in the range < 0.1 µm (ultrafine particles) are predominant. Some of the particles are soot particles. The smallest – which also occur in the largest number – are condensates of sulphuric acid and semi-volatile compounds, for instance fuel and lubricating oil, which also contribute to metal-containing ash particles. Nano-particles (<
0.03 µm), emitted from diesel vehicles as well as old petrol-driven cars, contribute significantly to particle numbers, but their contribution to PM₁₀/ PM_2.5 is very small. For modern diesel vehicles with oxidising catalytic converters (for instance taxies), the contribution to PM₁₀/PM_2.5 is small because the particles are much smaller than in similar diesel vehicles without catalytic converters.

1.6.2 Particles from woodburning stoves

In Denmark the number of woodburning stoves and boilers has increased in recent years, due among other things to the increasing prices of oil and electricity. NERI has carried out a number of studies of the contribution to particle pollution in Denmark from stoves and boilers. The studies focused on emissions of particles from stoves and boilers, and measurements of particle levels in a residential area with many woodburning stoves.

It appeared that burning of wood in households (in stoves and boilers) is a major source of particle emissions in Denmark. Although wood accounts for only approx. 20 per cent of the consumption of fuel in private households, 93 per cent of emissions of fine particles (PM_2.5) from households derive from this source.

From the latest NERI inventories of particle emissions in Denmark it appears that approx. 10,000 tonnes of small particles are emitted as a result of burning of wood in Danish households, i.e. almost half of total emissions of PM_2.5 in Denmark.

Heating by burning of wood generates much more pollution with fine particles than district heating plants as well as small oil and natural-gas-fired boilers. Particle emissions per rated thermal input from burning of wood in households are about 600 times larger than emissions from coal-fired power plants, and about 250 times larger than for CPH plants burning wood and waste.

1.6.3 Measurements of air pollution in residential areas with stoves

In the winters of 2002 and 2003/4, NERI completed two campaigns in an area of terraced houses at the town of Gundsømagle near Copenhagen, with approx. 2,500 inhabitants. This place was chosen because it is a typical residential area with lots of woodburning stoves.

Measurements of particle mass show that the contribution from stoves consists mainly of fine particles PM_2.5. From the measurements in Copenhagen we know that variations follow 24-hour intervals according to daily traffic intensity. In the areas with woodburning stoves, daily variations were different, with higher levels during the evening than evening levels observed in busy streets in Copenhagen, due to local burning in stoves and boilers. The average increased PM_2.5 concentration was approx. 4 µg/m³ in the stove area during the winter. This corresponds to the traffic-related contribution to PM_2.5 on the pavement of a busy street.

The results show that the major contributor to PM_2.5 is long-distance pollution. Contributions to PM_2.5 from traffic is low, with the exception of very few days. Burning of wood contributes slightly to PM_2.5 in the entire period, but during days of cold and calm weather, the contribution is considerable. Calculations also show that the major sources of carbon in the particles (soot particles) in the stove area are woodburning and traffic.

Model calculations show that woodburning stoves contribute only slightly to total PM_2.5 pollution in the air in Denmark (approx. 2 per cent). Stove particles are, however, assumed to represent a larger share of the PM_2.5 that consists of soot and tar particles (carbon/PAHs), which are considered to contribute significantly to the harmful effects of particle pollution.

1.6.4 Exposure to particle pollution

During the project, the NERI air quality and exposure models were developed to include particles, and may for instance be used to clarify the effect of planned emission reduction measures. The models have been used, for instance, to give a preliminary assessment of the effect of introducing environment zones in Copenhagen. Calculations have been made of the quality of the air, in terms of particle number (ultrafine particles), PM_2.5 and PM₁₀ for the situation in 2003 and a scenario assuming particle filters in all trucks in the proposed zone. The calculations assume that the filters will reduce particles from exhaust gases by 80 per cent.

The effect of environment zones is limited for the concentration of PM_2.5 and PM₁₀ in the urban background, since PM_2.5 and PM₁₀ are reduced by a maximum of 2 per cent. As regards the concentration of particle numbers, reductions in the air within the zone in the order of 10-25 per cent are envisaged.

Calculations have also been made for 139 streets, showing that, by introducing particle filters in all heavy-goods vehicles, average reductions are 4 per cent and 6 per cent for PM₁₀ and PM_2.5 and 13 – 20 per cent in the number of particles.

A demonstration project has been carried out, with a macro-economic assessment of the introduction of particle filters in heavy-goods vehicles in the environment zone. The assessment is based on changes in air quality and population exposure following the introduction of particle filters. The study concentrates on PM_2.5, since the health-effect-related parameters are well-documented. The costs of environment zones are estimated at approx. DKK 80 mill./year, and the positive effects on health are calculated at approx. DKK 160 mill./year. The welfare economic surplus is, thus, DKK 80 mill. per year^[2]. The calculation shows that an environment zone can prevent about 90 excess deaths in the metropolitan area on an annual basis.

A complete analysis of the consequences of a possible introduction of environment zones in Copenhagen will be made when the required data and assumptions are available.

Foot note

[2] Using the Ministry of Transport and Energy life-expectancy-based method, the benefits from environment zones are assessed at DKK 114 mill., and a surplus of DKK 34 mill. on an annual basis.