Properties of particulate matter related to health: concerted European research action (COST)

March 19, 2002

Brussels, 18 March 2002

European Cooperation in the field of Scientific and Technical Research - COST Secretariat. Memorandum of Understanding for the implementation of a concerted European research action designated as COST Action 633 "Particulate Matter: Properties Related to Health Effects." Brussels, 15 March 2002 (document COST 225/02). Full text

Delegations will find attached hereto the text of the abovementioned Memorandum signed in Brussels on 6 March 2002 by Austria, Finland, Germany and Greece and on 13 March 2002 by Lithuania and the United Kingdom.

The Signatories to this Memorandum of Understanding, declaring their common intention to participate in the concerted Action referred to above and described in the Technical Annex to the Memorandum, have reached the following understanding:

1. The Action will be carried out in accordance with the provisions of document COST 400/01 "Rules and Procedures for Implementing COST Actions", the contents of which the Signatories are fully aware of.

2. The main objective of the Action is to increase the information on the particulate matter (PM) characteristics throughout Europe, describing the PM-system with respect to geographical and meteorological conditions, particle formation processes and their transport. The results will be used for setting environmental standards in Europe and for defining measures to reduce the particle emission.

3. The economic dimension of the activities carried out under the Action has been estimated, on the basis of information available during the planning of the Action, at Euro 30 million in 2001 prices.

4. The Memorandum of Understanding will take effect on being signed by at least five Signatories.

5. The Memorandum of Understanding will remain in force for a period of five years, calculated from the date of first meeting of the Management Committee, unless the duration of the Action is modified according to the provisions of Chapter 6 of the document referred to in Point 1 above.

A. GENERAL BACKGROUND

Atmospheric particles or dust (particulate matter, PM) have been always considered a major component of air pollution. Epidemiological studies in the recent years gave a strong hint on extended morbidity and mortality even due to relatively low PM burdens (e.g. Dockery et al, 1993).

The understanding of the corresponding causal chains of various parameters describing PM exposure and the health effects is still very weak. Many research projects on PM-exposure and health related effects due to particles have been initiated in the last years, mainly in the United States but also in Europe and other areas of the world. Consequently, ambient air quality standards for particulate matter are being established or revised in many countries. Several workshops on research priorities within this field (EU, USEPA, HEI) indicated extensive needs for additional information.

In many European as well as other countries extensive monitoring programs focused on PM and special parameters like carbon, acidity, semivolatile components, ultrafine particles and so on are carried out. The research goals of these studies are not always the same in detail, but generally particle properties with respect to effects on the environment and in particular on human health are addressed. Furthermore, epidemiological studies focused on different health endpoints and high risk groups are conducted. Since most of these studies are being done independently at present, intensive exchange of experiences among the participating groups from the exposure as well as from the effects research side would be of great benefit to all participants. A harmonisation of the results available is highly desirable. Therefore, this COST Action is to co-ordinate and promote the research going on in Europe on these issues.

Status of the research in the field: The atmospheric aerosol is a disperse system of solid and/or liquid particles of different size, shape, chemical composition and reactivity. Even the chemical composition of a single particle is not necessarily uniform. Among other heterogeneities the aggregation of soot, the formation of electric double layers, and surface layers of organic compounds may play an important role in the chemistry of a particle, and in the evolution of the aerosol. During their life the aerosol particles are continuously influenced by physical and chemical processes resulting in a permanent change of quality and/or quantity of their parameters.

Basically, the size distribution of atmospheric aerosol reflects the processes of particle formation to quite some extent. The so called coarse range with a maximum at around 10 µm contains particles that are produced by mechanical effects (e.g. erosion, abrasion, disintegration of bulk material). The so called nuclei range with a maximum between 0.01 and 0.1 µm contains particles formed primarily by condensation of supersaturated vapours (Fig.1). Combustion products occur in this size range primarily.

In the accumulation range which covers sizes from 0.1 µm to 1 µm, the particles are formed predominantly by coagulation of finer particles, by condensation of products from gaseous aerosol precursors on pre-existing particles, and by products of chemical reactions proceeding on these particles themselves. Most of the material associated with this accumulation aerosol has been formed and transformed in the atmosphere, and is usually briefly called secondary, in contrast to primary aerosol that is emitted into the atmosphere from natural and anthropogenic sources. It must be noted, that the accumulation aerosol would contain some primary aerosol material, whereas coarse particles may contain secondary aerosol material as well...

Compared to the coarse and the nuclei aerosols the accumulation aerosol represents the most stable part of the atmospheric aerosol. Life times are thought to span from a couple of days up to weeks depending on the meteorological situation. Wet deposition is much more effective in removing the accumulation aerosol from the atmosphere than dry deposition. It must be noted however that at least part of the accumulation aerosol is chemically active, so a chemical evolution may lead to notable changes of aerosol parameters during the life time. The chemical evolution poses the problem that life times of the individual particles belonging to an active population may become shorter than the life time of the population. This addresses the dynamics of an aerosol population.

Basic constituents of the accumulation aerosol are sulphates, nitrates, ammonium, organic acids, and other organic compounds soluble and insoluble in water. Many of these components originate from atmospheric trace gases or are at least highly influenced by these gases. The organic material forms a considerable part of the secondary aerosol. On a broader basis, research into the organic part of aerosols has started only recently, so data are scarce and there is a need for stepping up the investigations.

The accumulation aerosol plays a major role in health effects as the toxicologically relevant acidic compounds, various heavy metals as well as organic compounds like PAHs, appear in the accumulation aerosol. In addition, soot particles originating from fossil fuel burning are associated with the secondary aerosol and should be addressed in particular.

Log normal distributions are frequently used to decompose the size distribution of the atmospheric aerosol mathematically. Often a set of a few log normal components describes the size distribution quite well. This is the source of the successful trimodal model of the atmospheric aerosol. However, this model may fail under certain circumstances. Local emissions, mixed aerosols from different atmospheric systems, and relevant large scale changes in the aerosol forming processes during extended sampling periods may cause remarkable deviations.

Recently it has been shown that the accumulation aerosol is better represented by two components or modes. Moreover, two classes of particles with different hygroscopic activity can exist in the accumulation aerosol. Hence, at high relative humidity the accumulation aerosol may split in two submodes with different size and composition. The bimodal structure should be addressed in future research, because of implications to health. Hygroscopic particles are growing within the respiratory tract and thus change their deposition characteristics, compared to non-hygroscopic particles of originally the same size. Moreover, the same aerosol growing to full size already in the atmosphere at high relative humidities may give rise to different health effects because the deposition pattern shifts to the upper parts of the respiratory tract.

Emission of aerosol precursors and evolution of aerosols are regionally very different over Europe.

Especially the profiles met in the Mediterranean as a rather arid and/or maritime zone, must differ from western and central Europe. It is also clear that many of the European profiles do not readily compare to those on the North American continent. Therefore, investigations into regional or even local differences are very important in order to interpret and understand the exposure situation in the European regions.

Health effects assessment of air pollutants depends on a dose-response relation. For PM the dose or the exposure situation is particularly difficult to determine, since a number of parameters must be considered. Ambient air monitoring depends like respirability of particles on wind speed and external air flow patterns. The deposition of inhaled particles is determined by the size of the particles, breathing parameters, type of breathing (mouth or nasal breathing), individual anatomical patterns of the respiratory tract as well as respiratory diseases. The clearance of deposited particles depends on the site of deposition and hence on the particle size, on the shape of the particles, e.g. fibres, on the chemical reactivity (surface) and the functionality of cleaning processes (phagocytosis, ciliary clearance). The chemical composition and reactivity of the particles is not only responsible for the direct chemotoxic effects (e.g. heavy metals) but furthermore determines the fate of the particles in the respiratory tract. Even so called chemically inert particles may cause changes in the lung tissues. Ultrafine particles, i.e. particles with aerodynamic diameters less than 0.1 µm, initiated in animals at high concentrations inflammation of the lungs. Overload phenomena impair clearance processes because of overstrain of the pulmonary clearance mechanisms. These effects may only be significant at very high deposition doses, which can be scarcely found in the free atmosphere.

In addition to animal experiments and controlled inhalation experiments in humans epidemiological studies in industrial and rural environments can contribute to the question of health effects. The classical time series studies of smog episodes in Meuse Valley in 1930, Donora 1948, London 1952, 1956, 1962 showed increased mortality and morbidity rates of the affected population. However, the exposure situation cannot be defined very well retrospectively and in addition the monitoring equipment available at that time cannot compete with today's equipment. Generally, SO2 and acid components seem to be main factors affecting human health during these episodes. Recent epidemiological papers demonstrate remarkable associations between PM burden and morbidity and mortality in the general population, even at relatively low dust concentrations. The causal chain between PM burden and health effects is not clear, however, until today. Additional confounders like other air pollutants, climate, tobacco smoking, age, social status and harvesting effects (premature deaths) are not always considered correctly and are still a matter of discussion. Meta studies of all these projects show an increase of the relative mortality risk to between 1.03 and 1.17 for a PM increase of 100 µg/m3; the average risk comes to 1.10. The strongest associations could be found for the fine mode fraction especially if considering all the confounding factors. WHO too supports this concept in the new edition of the "Air quality guidelines for Europe". This risk increase may seem relatively low and sometimes is not even statistically significant but considering the high number of people affected the number of impaired persons is quite high.

The problems discussed above require intensive interdisciplinary approaches. The detailed investigation of chemical, physical, meteorologic, and geographical aspects have to be closely interwoven with health aspects of mortality and morbidity. The projects undertaken within this COST action are to be prepared and performed under these aspects. The Action pronounces the physico-chemical properties of the aerosol and the evolution of this aerosol in the atmosphere.

However, the COST Action is also aimed at developing links between the natural science and medical fields. Developing of such links will be an important task within the frame of this COST Action.

Relationship with other European programmes: Since many different studies on PM related problems are carried out throughout Europe and also world wide, a co-ordination and intensive exchange of experiences and results will be of great benefit to all participants. Due to the different approaches and structures of the projects going on, a bottom-up approach of co-ordination as it is the nature of COST would be very adequate. Other activities like projects within the European standardisation process (CEN) related to establishment of EU ambient air quality standards or research initiatives of the European Science Foundation have just been started and links will be established with them. Under the initiative of B. Brunekreef, University of Utrecht, a research network to combine epidemiologic activities in Europe is evolving (AIRNET). Close contacts to this group have shown that there is just enough overlapping between this initiative and the COST Action to establish a close and fruitful cooperation.

Since extended research activities on all PM related issues are conducted in the US (Supersite program, Particle Research Centers) also close links to American institutions should be maintained within the COST Action....

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