Fine dust – Particulate Matter

Introduction

The atmosphere around us is filled with tiny microscopic particles known to us as aerosols. While reading this first sentence, you are likely to breath in anything from 10,000 to 100,000 of these tiny particles!

Aerosol particles are any solid or liquid (or a combination of both) suspended (or floating) in the atmosphere. They exist in a multitude of forms and and sizes, but generally go unnoticed in everyday life.

A particle is defined as small discrete mass of solid or liquid matter.

Presence in the atmosphere

Airborne solid and liquid particles (e.g. in the form of dust, smoke, mist and fog) have always been a component of the atmosphere. Together they are referred to as aerosol. Natural sources that contribute to the release of primary particles into the air include oceans, deserts, plants, volcanic eruptions, erosion and fire.

In addition, atmospheric photochemistry involving biogenic volatile organic compounds (known as precursor gases, such as isoprene and monoterpenes) leads to the generation of secondary particles.

Urban pollution

Since the industrial revolution, in particular, primary or secondary anthropogenic particles have been making up a growing proportion of the atmospheric particle spectrum.

Large amounts of carbon dioxide, carbon monoxide, nitrogen oxides, sulfur dioxide, organic and elementary carbon, plus other gaseous and particulate substances, reach the troposphere via industrial processes and the combustion of fossil oil products, black coal, brown coal and biomass.

According to the World Health Organisation (WHO), particular sources of high concentrations of anthropogenic airborne particles include combustion processes and photochemical reactions from anthropogenic precursor gases.

Abrasion and re-entrainment processes (e.g. those involving bulk freight, industry, agriculture, the construction industry) can also contribute to fine dust pollution, especially with the coarse mode fraction.

The interaction between natural and anthropogenic aerosols from local, regional and remote sources results in ambient aerosol, in which composition undergoes pronounced spatial and temporal fluctuations. In towns, ambient aerosol is often referred to as urban aerosol.

Ambient aerosol is made up of various particle sizes, i.e. ultrafine, fine and coarse particles. The chemical composition can vary greatly, depending on the source and transport conditions. Elevated concentrations are measured in the vicinity of industrial facilities. Particles with a diameter less than 50 nm are essentially composed of low-volatility organic compounds.

Airborne particles are thus a cluster of various pollutant species with high variation in shape, size, chemical composition and physical properties

Indoor pollution

Fine dust concentrations indoors can originate from continuous (e.g. ambient air, heating) and from intermittent (e.g. cooking, smoking, burning candles, printers) sources. As a result of these different source locations and dynamics, the size distribution and composition of indoor particles vary markedly. The processes mentioned below are of special importance. All processes together induce and determine the dynamics of the indoor particle spectrum.

What are the sources of fine dust?

The indoor sources of particulate matter are diverse. If the premises are in use, the indoor aerosol is often affected by indoor sources, which may be located either in the investigated room itself or in adjacent rooms.

Typical sources found in different types of premises and which should be taken into consideration are listed below.

a) The typical sources in living rooms include:

1) cooking, heating, smoking, candles, fireplaces and fragrant oil burners;

2) body care and cleaning materials (e.g. sprays);

3) electric appliances (e.g. refrigerators, vacuum cleaners);

4) people and domestic animals;

5) abrasion of textiles and textile floor coverings.

b) The typical sources in an office include:

1) office machines (e.g. printers, copiers, computers);

2) air-conditioning units;

3) people;

4) external inputs (e.g. smoking, adjoining manufacturing premises);

5) abrasion of textiles and textile floor coverings.

c) The typical sources in kindergartens and schools include:

1) human and external inputs brought in with clothing (e.g. animal hairs);

2) activities (e.g. cooking, art, crafts);

3) electric appliances (e.g. printers, copiers, computers);

4) soft furnishings;

5) air-conditioning units where relevant.

Indoor airborne particles cover a large size range from a few nanometres up to 100 μm. Particle size is deeply influenced by origin, but also by chemical or physical reaction following generation. A non-exhaustive list of typical sources of indoor airborne particles with their typical size ranges is presented in the following figure.

How do PM get into the air?

  • Infiltration of outdoor aerosol through windows, doors and the building
    envelope. In the case of high levels of air exchange, the likelihood of particles from the ambient air entering the building is very high; it drops with decreasing air exchange. The presence of an air-conditioner and related air-filtration system has a huge impact. The fraction of the ambient aerosol found indoors (even with closed windows) depends on particle size, and is highest for particles around 0,3 μm.
  • Combustion processes, such as smoking, burning candles, open fires, fireplaces and incense sticks.
  • Activities, such as cooking, cleaning, hobbies, DIY activities, textile abrasion, and using household and office appliances.
  • Humans and domestic animals (skin flakes and hair particles), microorganisms (moulds, bacteria, cell fragments, etc.), pollen and other allergens.
  • Particle reformation through physico-chemical reactions of volatile organic compounds (VOC), e.g. ozone-terpene reaction.
  • Resuspension of deposited particles. Various activities may cause the re-suspension of particles from room surfaces

What are the health effects of PM?

Epidemiological studies show that high concentrations of fine dust in the ambient air are associated with health consequences, such as damage to the cardiovascular system and the respiratory tract, and with increased morbidity and mortality. A summarising analysis of European time-series and panel studies on the effects of particles from the ambient air, carried out in 2004 for WHO, demonstrated

  • statistically significant elevated risk associated with total mortality
  • mortality caused by respiratory tract and
  • cardiovascular diseases

in all age groups and hospital admissions of elderly patients. Accordingly, limits have been developed for ambient air concentration of fine dust. Compared with the number of studies that describe the effect of ambient air aerosols on human health, so far there exist few studies dealing with indoor air.

Evaluation, guideline and limit values

The Directive 2008/50/EC envisages limits for the daily and annual means of PM10 in ambient air. For the PM2.5 fraction, the amendment of this Directive specifies an annual mean of 25 μg/m³ as a limit from 2015, and which from 2020 is to be lowered to 20 μg/m³. The PM10 limits remain unchanged in the 2008 revision of this Directive (24 h mean: 50 µg/m³, which may be exceeded 35 times per year; annual mean: 40 μg/m³). The limit set by the EU Air Quality Directive for PM10 represents, in terms of type, level and measurement strategy, a convention for limiting the health risks caused by fine dust in the ambient air.

In principle, the global interim and target values proposed by WHO in 2006 for fine dust in ambient air can also be used for indoor situations. However, this WHO proposal relates primarily to particles emitted by combustion sources; these are mostly particles belonging to the PM2.5 fraction.

WHO Guidelines:

PM2.5:

10 μg/m³ annual mean

25 μg/m³ 24-hour mean

PM10:

20 μg/m³ annual mean

50 μg/m³ 24-hour mean

How can PM be reduced?

There is no general solution to reduce PM in your house. Each house has different sources and sinks, dominating domestic air pollution. Is outdoor air pollution the main source, air filters on the windows or in the airco/ventilation system can deliver a reduction. If possible, quit reduce smoking, limit the use of burning candles, adding a good filter to the vacuum cleaner, change the kitchen stove from gas to induction, etc. When sources are determined during a measurement, a possible solution can be given.

How do we measure PM?

At Aristoteles Consulting, we measure PM with continuously registering measuring devices. This devices are equipped with an optical particle counter (OPC). The measured data are saved by a data logger, which can be read out after the measurement to get information about either the particle number of different sizes or the concentration of fractions PM2.5 and PM10; and to create data tables and graphs showing time dependent variations.

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