Mitigating The Adverse Impact of
Particulates on Indoor Air
Views and Conclusions from the FINE Particles –
Technology, Environment and Health Technology Programme
Rauno Holopainen, Merja Hautamäki, Kaarle Hämeri, Esko Kukkonen,
Ilpo Kulmala, Jarek Kurnitski, Matti Lehtimäki, Tero Lähde, Jari Palonen,
Pertti Pasanen, Olli Seppänen, Jorma Säteri, Aimo Taipale, and Eija Vartiainen
Edited by Peter Herring
Mitigating The Adverse Impact of
Particulates on Indoor Air
Views and Conclusions from the FINE Particles
– Technology, Environment and Health Technology Programme
Part of a series of five reports that cover energy and industry, traffic and transport,
measurement technology, indoor air, and health and the environment.
Contact information:
• Helsinki University of Technology, Laboratory of Heating Ventilating and Air-Conditioning
(Rauno Holopainen, Jarek Kurnitski, Jari Palonen, and Olli Seppänen)
• Finnish Society of Indoor Air Quality and Climate (FiSIAQ) (Esko Kukkonen and Jorma Säteri)
• University of Helsinki, Department of Physical Sciences (Kaarle Hämeri, Tero Lähde, and Eija Vartiainen)
• University of Kuopio, Department of Environmental Sciences (Merja Hautamäki and Pertti Pasanen)
• VTT, Technical Research Centre of Finland (Ilpo Kulmala, Matti Lehtimäki, Aimo Taipale)
• Finnish Institute of Occupational Health (Merja Hautamäki, Kaarle Hämeri, Tero Lähde, and Eija Vartiainen)
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ISBN 952-457-247-8
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This publication includes material protected under copyright law, the copyright for which is held by Tekes or a third
party. Material contained here may not be used for commercial purposes. The contents are the opinion of the writers
concerned and do not represent the official Tekes position. Tekes bears no responsibility for any possible damage arising
from the use of this material. The original source must be mentioned when quoting from this publication.
Preface
T
he air we breathe exposes us to a growing number
of airborne contaminants, including particulate
matter invisible to the eye, as a result of ever-growing traffic volumes and ever-higher levels of energy generation, as well as other factors. Fine particulates are
known to have major health implications, and result in
the premature death of over 300,000 people in the EU
annually alone. Advances in technology are allowing us
to measure smaller and smaller sizes of particles and
gain a better understanding of how they impact health
and the environment, however.
The more we learn about the very real harm caused
by these types of emissions, the more the benefits of introducing tougher air quality standards become clearer.
Typical of the initiatives being introduced in this area is
the European Commission’s Clean Air for Europe (CAFE)
programme, the results of which will be used to enhance
European air quality from 2010 onwards.
Tekes launched a four-year programme in 2002 known
as the FINE Particles – Technology, Environment and
Health Technology Programme – together with the
Academy of Finland, the Ministry of Transport and
Communications, and the Ministry of the Environment – to address some of these challenges. In particular, to generate new research data, leverage the existing
broad range of Finnish expertise in fine particles and
develop it further, and catalyse business opportunities
in the field. The programme’s ultimate goal has been to
improve our understanding of the impact emissions of
this type have on health and the environment, identify
the potential for new technological innovations, and encourage their commercialisation.
The FINE programme involved over 50 individual
projects and close to 60 companies and 20 research institutions, and focused on emissions and technology in
five main areas: energy and industry, traffic and transport, measurement, indoor air, and health and the environment. A summary report has been produced on
each of these areas.
Drawing on the work of 11 projects – seven coordinated by universities and research institutes and four
by companies – this summary report focuses on the
particulate challenge in buildings and occupational environments. The FINE projects in this area covered a
range of areas linked to extending our knowledge of
the phenomena involved and reviewing the technological and business potential open to today’s and tomorrow’s technologies.
We would like to thank all the researchers and authors
that have contributed to the Fine Programme, and whose
work has made the publication of this report and the others in the series possible
3
Contents
Preface
4
3
1
Introduction
Sources and concentrations of indoor particulates
The regulatory environment
The focus of the FINE Programme
5
6
8
10
2
The indoor-outdoor particle connection
and particle dynamics indoors
Outdoor particle size distribution in urban areas
The indoor-outdoor connection
Indoor aerosol dynamics
Conclusions
13
13
13
14
15
3
The impact of ventilation on particle concentrations in indoor air
Natural and mechanical ventilation
Air distribution in ventilated rooms
Personal ventilation
Local exhaust ventilation
Room air cleaners
Pressure control
Problems with systems in residential buildings
Modelling tools
Conclusions
17
17
17
18
19
20
20
20
20
20
4
Filtration
Fibrous filters
Electrostatic precipitators
Decentralised air cleaning
Room air cleaners
Conclusions
21
21
24
25
26
27
5
Market potential
Market drivers in North America and Europe
29
29
6
Conclusions
33
References and literature
34
1
A
Introduction
number of epidemiological studies have shown
that ambient particulate pollution has an adverse
effect on human health. Observed effects include
increased respiratory symptoms, reduced lung function,
elevated respiratory morbidity, and elevated cardiopulmonary mortality (Pope et al. 1995). Figure 1 illustrates
the possible cardiovascular mechanisms resulting from
exposure to particulates.
The volume of hospitalisations is also higher (Linn
et al. 2000), with the elderly, young children, and people with chronic cardiopulmonary disease, influenza, or
asthma the most susceptible (Pope 2000).
Less attention, in contrast, has been paid to indoor
particles and their impact on health, despite the fact that
indoor air particle exposure may be even more harmful
than exposure to ambient particulate pollution. Indoor
particle concentrations are often lower compared to
outdoor levels due to supply air filtration, but they can
be much higher in the workplace, where particle composition can also be very different. Welding fumes, for
example, contain metals such as chromium, nickel, and
manganese that can impact health adversely, depending on their toxicity.
The role of particle size, mass, and number is still
unclear. It is suspected that ultrafine particles may be
more harmful than larger particles. As particle size decreases, surface area and particle number per unit mass
increases. Combustion processes, such as smoking tobacco, burning wood, and cooking produce largely ultrafine particles with a large surface area per unit mass
that can deposit deep in the respiratory track and access the pulmonary interstitium (Donaldson et al. 2001,
Oberdörster 2001).
Figure 1. Inflammation-induced cardiovascular effects after particle exposure (modified after Donaldson
and MacNee 2001).
5
Sources and concentrations of indoor particulates
perature than MS (Witschi et al. 1997). The concentration of some carcinogens, such as nitrosamines, is higher
in SS than in MS (Hoffman et al. 1987).
Smoking can increase indoor air particle concentrations significantly. Koistinen et al (2001) report a mean
PM2.5 concentration in smoking homes in Helsinki of
21 μg/m3 and 8.2 μg/m3 in non-smoking homes.
Kleeman et al. (1999) and Klepeis et al. (2003) identified particles with a mass median diameter (MMD) of
0.3–0.4 μm and 0.2 μm under chamber conditions. According to Nazaroff et al. (1993), nearly all the particulate matter in environmental tobacco smoke is smaller
than 2.5 μm.
The concentration of environmental tobacco smoke
particles in indoor environments varies temporally and
spatially. Temporal variation depends to a large extent
on smoking frequency, while spatial variability is influenced by airflow rates and building characteristics.
The typical particle mass emission rate for cigarettes is
0.7–0.9 mg/min, according to Klepeis et al. (2003). A
In homes and non-industrial environments, such as offices and schools, the concentration of particulate matter is usually 20–200 μg/m3. Extreme values can go as
high as 1000 μg/m3 (Mølhave et al. 2004). Indoor levels
show temporal and spatial variation reflecting outdoor
particulate concentrations and indoor sources.
Concentrations of indoor air particles depend on
human activities and the physical activity of occupants,
ventilation, air change rates, and building characteristics
(Abt et al. 2000a, Wallace et al. 2002). Temperature and
relative humidity contribute to microbial numbers.
Indoor chemical reactions generate secondary organic
aerosols, typically monitored as ultrafine particles (Weschler 2004, Weschler and Shields 1999). The presence
of these indoor sources may raise indoor air particle
concentrations above outdoor air concentrations. These
short-duration events indoors tend to generate high particle concentrations, sometimes several orders of magnitude higher than background particle levels.
OUTDOOR
AIR
INDOOR AIR
GENERATION
Smoking
Pets
Cooking
Heating
Candles
Microbes
Secondary particles
Ventilation, filtration,
penetration through
gaps
Resuspension
Deposition
(Vacuuming, dusting, movement of people)
Deposition
Figure 2. Indoor particle sources in a residential building.
The main sources of indoor air particulate matter are
tobacco smoke, cooking, resuspension of settled particles,
combustion, and outdoor air (Abt et al. 2000a, Wallace
et al. 2002, He et al. 2004). See Figure 2.
recently published study showed a PM2.5 and submicrometer particle emission rate of 0.99 mg/min resulting from smoking (He et al. 2004).
Cooking
Environmental tobacco smoke
Environmental tobacco smoke (ETS) is a major contributor to indoor air particle concentrations. Smoking
at home in Finland is quite uncommon today, however.
Only 10% of respondents in the EXPOLIS study, covering 434 subjects living in Helsinki, reported smoking
at home. These subjects were exposed to an average of
0.37 hours/day of ETS (Jantunen et al. 1999).
ETS is a mixture of gases and particles generated by
the combustion of tobacco products (Nasaroff and Klepeis 2004), and consists of 15% mainstream smoke (MS)
and 85% sidestream smoke (SS). These have a different
chemical composition, as SS is generated at a lower tem6
Cooking, such as frying, grilling, toasting and sautéing,
also generates particles, the size and number of which
depend on the methods and conditions employed and
the type of food cooked. Gas and electric stoves can
generate different particle profiles.
Frying meat produces 10–20 times higher levels of
particle concentrations than frying potatoes, regardless
of the type of stove used, according to Flückiger et al.
(2000). Dennekamp et al. (2001) noted that frying fatty
foods such as bacon generated significantly higher concentrations of ultrafine particles than frying vegetables,
again regardless of the stove used.
Candles
Candles can generate high indoor particle levels, especially
in the ultrafine size range. Afshari et al. (2005) measured
a maximum concentration of 241,500 particles/cm3 from
burning two pure wax candles. The estimated source
strength was 3.65 × 1,011 particles/min. Ultrafine particles predominated during burning, but the volume of
particles ranging from 0.3 to >1.0 μm increased rapidly
after the candles were extinguished.
Heating
Household fireplaces and stoves can increase indoor particle concentrations. The amount of supply air can also
have a strong impact on particle size distribution and
emissions of particle-bound polycyclic aromatic hydrocarbons (Hueglin et al. 1997). The count median diameter
of particles generated from wood burning with a flame
is 80 nm, and without a flame 55 nm (John 2001).
There are no substantial differences between heating
systems, according to Moriske et al. (1996), who looked
at homes heated by coal, a wood-burning fireplace, and
central heating. Total suspended particulate (TSP) measurements showed no significant differences, although
the amount of sedimented dust was higher during the
winter than in the summer in homes with coal- or woodburning appliances.
Secondary organic aerosols
Reactions between indoor air pollutants can increase the
size of particles or even form new particles. Secondary fine
aerosols are formed from gases in nucleation, condensation, and reaction processes. Products that have sufficient
low vapour pressure may form particles. The conversion
of sulphur dioxide (SO2), for example, produces sulphuric acid droplets (H2SO4) (Lippmann 2000).
Chemical reactions in indoor air generate secondary
organic aerosols (SOA). Terpenes and ozone are often
causative to these reactions. Ozone is usually transported
indoors from outside. Photocopiers, laser printers, electrostatic precipitators, and ozone generators are also
sources of ozone indoors. Terpenes are commonly used
in consumer products such as solvents, cleaners, odorants, and air fresheners. Unsealed wood products also
emit terpenes (Weschler 2004), and Weschler and Shields
(1999) have concluded that ozone/terpene reactions can
produce a significant increase in the mass and number
concentrations of submicrometer particles.
Office equipment
Photocopiers and printers are also sources of indoor particles in office environments. Dry process photocopiers
can produce respirable particle concentrations of 46–50
μg/m3 while operating (Brown 1999). Laser printers have
been found by Lee et al. (2001) to produce the highest
PM10 concentration (65 μg/m3), compared to ink-jet
printers (20–38 μg/m3) and all-in-one units (41 μg/m3).
In addition, secondary organic particles are produced
from ozone and VOC emissions emitted by printers and
photocopiers (Wolkoff 1999).
Ironing
Ironing also generates particles in indoor air. When looking at particulate emissions from ironing cotton sheets
with and without steam in a full-scale chamber, Afshari
et al. (2005) measured peak concentrations of 7,200 ultrafine particles/cm3 from steam ironing and 550 UFPs/
cm3 from non-steam ironing. A recent study in Finland
(2005) showed that steam-ironing towels produces mainly
ultrafine particles, with a maximum total concentration
of 3.6×104 particles/cm3 (unpublished data).
Bioaerosols
Bioaerosols consist of dust mites, moulds, pollen, bacteria, viruses, amoebae, fragments of plant materials, and
human and pet dander from both indoor and outdoor
sources. Outdoor sources include soil, plant surfaces,
water, sanitary vents, and building exhaust; while typical indoor sources include humans, pets, indoor plants,
showers, and heating and ventilation systems (Morawska and Salthammer 2004).
The size of viruses ranges from 0.02 to 0.3 μm, and that
of bacteria from 0.5 to 10 μm (Morawska and Salthammer 2004). The size of bacterial spores range from 0.5 to
3 μm (Reponen et al. 2001). Pollen particles are typically
10–100 μm, and dust mites about 10 μm (Morawska and
Salthammer 2004). The size of fungal spores varies between 1.5 and 30 μm (Reponen et al. 2001).
Dust mites and mite faeces are the most common allergens in indoor air. Mites live in carpets, sheets, mattresses, pillows, and upholstered furniture, and feed on
skin scale, fungi, and organic debris (Ledford 1994).
Spores are often resistant to environmental stresses
such as dryness, cold, heat, and ultraviolet radiation (Reponen et al. 2001); and live in soil, plant tissues, stored
organic material, and damp indoor environments, such
as basements, windowsills, showers, carpeting, air conditioning systems, and humidifiers.
In addition to fungal spores, fungal fragments are
released from surfaces contaminated with fungi. These
immunologically reactive particles are smaller than fungal spores and their amount can be much higher than
spore levels. Fungal fragments may comprise pieces of
spores or be formed through nucleation from secondary
metabolites (secondary organic compounds) of fungi.
The release rate depends on air velocity. Even gentle air
velocity (0.3 m/s) can aerosolise these fragments into the
indoor air (Górny et al. 2002, Górny et al. 2003).
Bacteria colonise in humidifiers and air-conditioning
equipment. Researchers have found that indoor concentrations of bacteria can be higher than concentrations
of fungi in dwellings with or without mould problems.
Toivola et al. (2004) found total bacteria levels of 60,600
7
cells/m3 in homes, 86,400 cells/m3 in personal samples,
and 145,000 cells/m3 at the workplace. The numbers
of viable bacteria were 338, 715, and 1,090 cfu/m3, respectively.
The size of airborne cat allergens – such as Fel d I –
ranges from 2.5 to 10 μm, and they are found in cat pelt,
saliva, basal squamous epithelial cells, and sebaceous
gland excretion. The major dog allergen – Can f I – is
detected mostly on the dog coat and in saliva (Ledford
1994). Allergens can be carried into homes without pets
on the clothing of visiting pet owners. Geometric mean
concentrations of Can f I and Fel d I in homes with a
cat or a dog have been measured at 69 and 200 μg/g, respectively. In homes without indoor pets, concentrations
have been measured above 1.0 μg/g (Arbes et al. 2004).
Man-made mineral fibres
Fibre dust particles have a length of >5 μm and a diameter of <3 μm. The length/diameter ratio for fibres is
typically 3:1. Man-made mineral fibres (MMMF), such
as glass wool, rock wool, and ceramic fibres are used
in acoustic and thermal insulation products. A study
by Skov et al. in Denmark (1987) identified airborne
MMMF levels in 14 town halls with a mean concentration of 5 fibres/m3 (range of variation 0−60 fibres/m3).
Schneider et al. (1990) measured dust in buildings with
MMMF ceiling boards, such as nurseries, kindergartens, schools, and office buildings. The average concentration ranged from 17 to 210 respirable MMMF/m3.
The lowest fibre levels were measured in mechanically
ventilated, clean rooms.
House dust
House dust is a mixture of biological material, such as
animal dander, hair, and fungal spores, and deposited
particulate matter, such as textile fibres, from indoor air
aerosols. It also includes soil particles brought indoors
by shoes. It consists of solid inorganic and organic materials from a variety of natural and synthetic origins
(Morawska and Salthammer 2004).
Particle size distribution and content varies between
sampling locations. Lewis et al. (1999) found the highest
mass (22.7%) in a particle size fraction of 53–106 μm in
residential house dust. Mølhave et al. (2000) measured
floor dust samples collected from offices and found the
following size distributions: 0–3 μm (<0.1%), 3–6 μm
(0.1%), 6–10 μm (0.4%), 10–25 μm (6.3%), 25–50 μm
(12%), 50–125 μm (41%), and >125 μm 40%.
House dust from kindergartens consists mostly of inorganic materials, such as sand and clay, while house dust
in residences of animal owners contains largely organic
material (Morawska and Salthammer 2004).
Resuspension
Human activity and cleaning can resuspend settled particles, thereby increasing PM concentrations in indoor
8
air. Dusting, vacuuming, making a bed, folding clothes
and blankets, and movement, such as walking through
a room, all cause resuspension. Resuspension rates are
higher for coarse particles than for fine and ultrafine particles, due to adhesion and detachment forces (Morawska and Salthammer 2004).
Several studies have reported increased particle concentrations from resuspension. Ferro et al. (2004) found
dusting and movement resulted in indoor PM2.5 concentrations of 32 μg/m3 and 15 μg/m3, respectively.
Resuspension rates also vary according to particle
size. As particle diameter gets larger, the resuspension
rate gets higher as well. Thatcher and Layton (1995)
observed that the resuspension rate is the highest for
particles larger than 5 μm, whereas particles smaller
than 1 μm showed almost no resuspension, even with
vigorous activity.
Wallace (2000) reported that a major source of coarse
particles in a townhouse is the physical movement of the
residents. Lioy et al. (1999) tested the performance of
11 vacuum cleaners in collecting fine particles and reported motor emission rates ranging from 0.028 to 176
μg/min. Vacuum cleaning resuspended coarse particles
effectively, but also released fine particles into indoor
air. The majority of the particles released were 0.3−0.5
μm in diameter. Vacuum cleaners equipped with highefficiency filters (HEPA) showed the lowest particle
emission rate.
In summary
Indoor particle sources have a significant impact on levels
of particulates in non-industrial buildings. This is particularly the case in homes, where ventilation systems
are often less effective than in public buildings. Indoor
particle generation is often short in duration, but can
increase particulate levels substantially for an extended
period. Properly fitted and maintained ventilation and
kitchen exhaust hoods are essential, therefore, to remove
particles indoors.
Table 1 provides a summary of the types of particulates found in indoor environments and the deposition
rates that have been measured for their incidence.
In industrial environments, the use of personal protective gloves and respirators, as well as local exhaust
ventilation, is appropriate, due to the higher impurity
levels encountered in these environments. In addition,
the particles generated in industrial workplaces are often more toxic.
The regulatory environment
Indoor air quality in industrial workplaces is often much
lower than in non-industrial buildings, and the concentration of impurities in workplace air is limited using
HTP values (HTP 2005). In respect of residential locations, a directive issued by the Finnish Ministry of Social Affairs and Health in 2003, and based on the Health
Source
Methods
Particle size
Emission or infiltration
rate/factor
Reference
Smoking
48 h condensation particle
counter measurements in
residences, time activity diary
PM2.5 and
submicrometer
particles
1.92×1011 particles/min
He et al. 2004
Smoking
Chamber tests, estimation
0.1–1.0 μm
(MMD 0.2 μm)
1.03–1.79 mg/min
Klepeis and
Nazaroff 2002
Smoking
Chamber tests
Respirable
particles
17 mg/cigarette
Leadeder and
Hammond 1991
Candles
Chamber tests
0.1–10 μm
11.8 mg/h
Fan and Zhang
2001
Afshari et al. 2005
Candles
Chamber tests
Ultrafine, fine
3.65×1011 particles/min
Cigarette
Chamber tests
Ultrafine, fine
3.76×1011 particles/min
Afshari et al. 2005
Cooking
48 h condensation particle
counter measurements in
residences, time activity diary
PM2.5 and
submicrometer
particles
Cooking: 0.11 mg/min
Frying: 2.68
Microwave: 0.03
Oven: 0.03
Stove: 0.24
Toasting: 0.11
He et al. 2004
Cooking
Hamburger and chicken
cooking tests with charbroiler,
emission rate measurement
PM2.5
Hamburger: 15 g/kg
McDonald et al.
Chicken (with skin): 7.2 g/kg 2003
Cooking
Particle concentration
measurements, time-activity
recordings, modelling
PM2.5, PM10
PM2.5: 1.7 mg/min
PM10: 4.1 mg/min
Wallace L 1996
Cooking
Chamber tests
Ultrafine, fine
Frying meat: 8.27×1011
particles/min
Electric stove: 6.8×1011
particles/min
Afshari et al. 2005
Ironing
Chamber tests
Ultrafine, fine
With steam: 0.06×1011
particles/min
Without steam: 0.007×1011
particles/min
Afshari et al. 2005
Deposition
Deposition rate measurements 0.014–10 μm
from cooking in 14 houses
PM2.5: 3.61 h-1
He et al. 2005
Resuspension
48 h condensation particle
counter measurements in
residences, time activity diary
Sweeping floor:
0.02×1011 particles/min
Vacuuming:
1.57×1011 particles/min
He et al. 2004
Resuspension, Aerosol number concentration 0.3 –> 25 μm
human activity and particle size measurement
in two-story residence
at summer, estimation of
resuspension rates (four
residents in the study house
performing normal light
activities)
0.3–0.5 μm: 9.9×10-7/h
0.5–1 μm: 4.4×10-7/h
1–5 μm: 1.8×10-5/h
5–10 μm: 8.3×10-5/h
10–25 μm: 3.8×10-4/h
>25 μm: 3.4×10-5/h
Thatcher and
Layton 1995
Resuspension, Modelling indoor and outdoor
cleaning
particle size distribution data
collected in four homes in
Boston
PM0.7–10
15.1 μm3/cm3/h
Abt et al. 2000b
Vacuum cleaner Chamber tests
with full bag
Ultrafine, fine
0.35×1011 particles/min
Afshari et al. 2005
Outdoor
PM2.5–PM10
Infiltration factors:
PM2.5: 0.74
PM10: 0.28
Long et al. 2001
Particle characterisation study
in Boston, continuous particle
measurement indoors and
outdoors
PM2.5 and
submicrometer
particles
Table 1. Particle emission and deposition rates for indoor particle sources.
9
Protection Act (763/94), covers regulations regarding
physical, chemical, and biological factors in housing and
other residential premises, and the methods for measuring these factors and interpreting the results.
The Finnish building code (ME 2003) provides regulations and guidelines for new ventilation systems. These
aim at ensuring healthy, safe, and comfortable indoor
air quality in new buildings. Ventilation systems must
be designed and installed so that they are clean before
commissioning and can be maintained without difficulty.
Outdoor air intakes should be located away from pollutant sources. The minimum distance depends on the
sources, and normally ranges between 0.9−8 m. Supply
air must be filtered using F7 and G4 (or better) filters in
urban areas and rural areas, respectively. Outdoor airflow
rates must be equal or higher than 6 dm3/s/person (0.35
dm3/s/m2), which corresponds to an air change rate of
0.5 times an hour in a room 2.5 metres high. The carbon dioxide concentration in an occupied room should
not exceed 1,200 ppm.
The Finnish FiSIAQ 2001 guideline was developed as
a tool for achieving healthy and comfortable indoor air
quality in new buildings, and introduces good design and
construction practices, as well as prudent material selection. The classification includes three categories for indoor
environments: S1, S2, and S3. The highest of these, S1, can
be achieved by using M1-classified building materials and
by following P1 instructions. Category S3 corresponds to
the official Finnish building code (ME 2003).
The focus of the FINE Programme
The FINE Programme involved 11 projects with a special focus on buildings and occupational environments,
seven coordinated by universities and research institutes
and four by companies. A total of 17 research groups
and 24 companies participated in the projects, which
accounted for about a quarter of the funding allocated
to the FINE Programme as a whole.
Projects focused both on office-type environments,
in which the outdoor-indoor connection is of central
significance and the main source of indoor air particles
is outdoor pollution, as well as traditional industrial
environments in the wood and metal industries, where
the main sources of aerosol particles are inside buildings and the focus is on preventing employee exposure
to fine and ultrafine particles.
Particle emissions from grinding operations in a plywood plant were studied in the FineWood project (Welling et al. 2005). Plywood grinding generated fine and ultrafine particles in the 200–400 nm and 20–40 nm size
ranges. Grinding medium-density fibreboard (MDF)
resulted in the highest particle emissions. Dust filtering
systems removed fine particles from the recirculation
air effectively. Filters collected 80% of particles in the
0.2–0.3 μm size range.
Fibre exhausts from sound attenuators used in
ventilation ducts were examined using laboratory
and field measurements as part of the ILMI project.
Laboratory tests included disturbance periods caused
by changes in airflow, brushing, and shaking. Fibre
concentrations varied between 0.01 and 3,000 fibres/
m3, depending on the test method and sound attenuator used. Based on the test results, researchers suggested new classification limits for the sound attenuators in the ventilation ducts. Field measurements were
conducted in office buildings. Fibre concentrations on
7000
dN/d log dp (cm-3)
6000
Outdoor air (measured)
Indoor air (measur e d)
Indoor air (model)
5000
4000
3000
2000
1000
0
0
6
12
18
24
30
36
42
48
Time (24 - 25 April, 2004)
Figure 3. Concentrations of particles with a geometric mean diameter of 0.103 μm in outdoor and indoor
air, together with data for modelled indoor concentrations (Holopainen et al. 2005).
10
Figure 4. A typical system installed to handle welding fumes.
surfaces and in the air were <0.1–14.9 and <0.01 fibres/
cm3, respectively.
In the HALVI project, a mathematical model was
constructed to simulate time-dependent particle concentrations in indoor air and evaluate the exposure of occupants (Holopainen et al. 2005). The model was validated
with laboratory (Björkroth et al. 2006) and field measurements (Holopainen et al. 2006) in the VALIDI project.
The model can be used to evaluate the indoor/outdoor
particle ratio and the exposure of occupants.
Figure 3 presents particle concentrations in the outdoor and indoor air on April 24–25, 2004, and modelled particle concentration in indoor air (Holopainen
et al. 2005).
The results show that particle concentrations in indoor
air can be roughly estimated from particle concentrations in outdoor air when the indoor air has only minor
particle sinks and sources, and particles transfer from
the outdoor to the indoor environment mainly via ventilation system. However, particle penetration through
cracks in the building envelope (leakage airflow) may
have a significant impact on the indoor/outdoor particle ratio, especially when supply air is filtered through a
high-efficiency filter (Holopainen et al. 2006).
The HIPHI Project focused on fine and ultrafine particles emissions formed during welding and cutting (see
Figure 4). Particulate emissions in the welding fume, as
well as their transformation in air, were studied, with
the aim of identifying the key operating parameters involved and reducing emissions of fine particles. Experi-
ments were conducted both in the laboratory and in the
field. The fine particles in the fume were measured using
cascade impactors (ELPI, DLPI) and a scanning mobility particle sizer (SMPS), and the number of particles
in different size classes, and their composition, shape,
reactivity, and other properties were determined. Both
personal welding helmets and fume extraction welding
guns were tested, in the laboratory and in industrial
workshops.
The main observation was that particle concentration is dominated by fine and ultrafine particles that
do not contribute significantly to the total mass. Both
size and concentration were functions of the operating
parameters, and emissions can be controlled by careful
selection of these parameters.
The BIOFINE Project focused on investigating the
fine particles that microbial damage to a building generates. The study was conducted by measuring fine particle
size distributions and characterising the microbial fraction of the airborne fine particulate matter qualitatively
and quantitatively using modern molecular biological
and chemical techniques. The investigations were carried
out in pairs of buildings, one of which had moisture and
microbial damage and where workers reported buildingrelated symptoms, while the other was an age- and building frame-matched control with no signs of moisture or
microbial damage or adverse health effects.
The results indicate that significantly higher fine particle concentrations were present in the indoor air of the
building with mould damage.
11
12
2
The indoor-outdoor particle connection
and particle dynamics indoors
I
ndoor aerosol particle concentrations and size distribution depend on particle transport from outdoors
to indoors, indoor emission sources, and aerosol dynamics indoors. Transport indoors depends on several
factors: the type of ventilation and air exchange rate,
filtration, leaks in the building structure, etc. The main
aerosol dynamical processes are deposition (particle
attachment to surfaces), condensation (particle growth
from vapours) and nucleation (particle formation from
vapours), evaporation, and occasionally agglomeration
(particle collision and attachment). All of these processes depend on particle size distribution, and detailed
studies on indoor aerosols require information on size
distribution.
The origin of indoor particulate matter depends to a
large extent on ventilation methods and indoor activities.
The main source of indoor particulate matter is typically
outdoor particulates, particularly in buildings with no
strong emission sources, such as offices.
Outdoor particle size distribution in urban areas
Urban outdoor particle number size distribution is typically trimodal. Size distribution consists of a strong nucleation mode with a geometric mean diameter (GMD)
of <30 nm, an Aitken mode with a GMD of between
20−100 nm, and a weak accumulation mode with a
GMD of >90 nm (Hussein et al. 2004b).
Number size distribution in nucleation and Aitkenmode GMDs, as well as in accumulation-mode particle concentrations, has been shown to be dependent on
the distance between the measurement location and the
main source, traffic. Close to the centre of Helsinki, nucleation-mode GMD was 11.7 nm, Aitken mode GMD
was 37.3 nm, and accumulation GMD was 150.5 nm,
GMDs measured 3 km out of the centre and 200 metres from a major highway were bit higher, at 13.8 nm,
42.5 nm, and 151.8 nm respectively.
The long-term mean number concentrations in central
Helsinki were 7,000 cm-3 for nucleation mode, 6,000 cm-3
for Aitken mode, and 1,000 cm-3; and number concentrations 3 kilometres from the centre were 5,500 cm-3,
4,000 cm-3, and 1,000 cm-3, respectively. Particle total
number concentrations may exceed 100,000 cm-3 during the rush hour, however.
Measured nucleation-mode GMD is approximately
the same as in other parts of Europe, but both Aitken
and accumulation-mode GMDs are a little larger in
Europe than in Helsinki (Hussein et al. 2004b, Birmili
et al. 2001).
Temporal variation was also seen in distribution
GMDs and total particle concentration on a seasonal,
weekly, and daily basis. Nucleation and Aitken-mode
GMDs and concentrations have been shown to vary
both at the daily and weekly level, depending on traffic densities and global radiation. No such dependence
has been shown for accumulation mode. The sources
for accumulation-mode particles in the Helsinki area
have been identified as regional combustion processes
or long-range transport (Pakkanen et al. 2003, Hussein
et al. 2004b). Particulate mass size distribution has been
shown to be trimodal in the Helsinki area, with the most
dominant, traffic-originated mode in the 0.15–0.24 μm
size class (Pakkanen et al. 2003).
The indoor-outdoor connection
Outdoor particle matter is transported indoors through
ventilation ducts, windows, doors, and cracks in the
building envelope (Thatcher et al. 2001).
Buildings can be divided into two main categories on
the basis of the type of ventilation mechanism employed:
mechanical supply and exhaust ventilation with supply
air filters, and exhaust (natural or fan-driven) ventilation
with envelope infiltration. The ratio of indoor particle
concentration to outdoor particle concentration (I/O)
differs between these two categories.
Mechanical supply and exhaust ventilation
Indoor air in mechanically ventilated buildings is mainly
exchanged through fans. The supply air is typically also
filtered, and exhaust air is often re-circulated when temperatures outside are low.
The main route for particulate transport indoors is
through filter assemblies. The particle size-segregated I/O
distribution curves follow roughly the known filter penetration efficiency curves. Typically, the I/O ratio falls sharply
as particle size drops below 100 nm (Zhu et al. 2005, Koponen et al. 2001, Hussein et al. 2004a and 2005).
The I/O ratios measured by Koponen et al. (2001)
and Hussein et al. (2005) are both below the ideal penetration efficiencies of the filters used in the measured
buildings. Particulate deposition on ventilation duct and
indoor surfaces enhance particulate losses both in the
ultrafine and in coarse size ranges (Lai 2004).
Koponen et al. (2001) have also found that I/O ratios
in the 8 nm to 25 nm particle size range decreased when
ventilation systems were switched on. Modelling shows
that air exchange rates increase the I/O ratio in this size
range (Hussein et al. 2005).
13
Exhaust ventilation
Indoor aerosol dynamics
Particulates move indoors primarily through the building shell in structures without a mechanical air supply.
(Thatcher et al. 2001). Small cracks in the building envelope may raise the penetration factor to nearly unity
(Liu and Nazaroff 2003).
I/O ratios have been shown to be a little higher in
buildings without a mechanical air supply throughout
the measured size range. Building age also plays a major role in I/O ratios or penetration factors, as the shells
of older buildings are less enclosed and the penetration
factor may be close to unity (Thatcher et al. 2003).
In buildings without a mechanical air supply, I/O ratios vary strongly in line with outdoor pollution levels,
and increase as outdoor concentrations increase (Franck
et al. 2003, Zhu et al. 2005). No clear outdoor particulate concentration dependency is seen for buildings with
a filtered supply air.
The difference in small particle fraction (diameter <10
nm) I/O ratios, measured in buildings with and without
mechanical air supply, has at least three explanations. It
could be a measurement artefact deriving from the statistical inaccuracy of measurement devices; a loss of volatile materials from particles during infiltration; or there
could be an unidentified indoor source in indoor space
(Zhu et al. 2005). The volatility of ultrafine particles is
smaller indoors than outdoors (Kuhn et al. 2005).
The indoor particulate population is modified by all the
typical aerosol processes, such as deposition, condensation, nucleation, evaporation, and coagulation. The
dominant process influencing population size distribution is particle deposition.
Deposition
Deposition lowers indoor particle concentrations, and is
a strongly size-dependent aerosol process. Small particles
(diameter below 100 nm) are deposited due to Brownian
or turbulent diffusion, electrical forces, or thermophorecy; and large particles (diameter above 1000 nm) as a result of gravitational forces or ‘turbophorecy’ (Lai 2004).
Overall deposition depends to a large extent on room
airflows and room furniture (Thatcher et al. 2002).
Deposition is considered to be the only process that
lowers particulate concentration indoors in buildings
without a mechanical air supply. Deposition also affects
particle concentrations in buildings with a mechanical
supply and exhaust, but exhaust airflows also reduce
particle concentrations. Deposition rates increase with
higher air exchange rates (He et al. 2005).
Condensation and nucleation
The condensational growth of particles depends on
condensing vapour concentrations to a large extent. In-
I/O size distribution Vs. distance from freeway
1,2
1
I/O
0,8
0,6
0,4
0,2
Zhu 35 m
Zhu 60 m
Zhu 37 m
Zhu 35 m eas t
0
1
10
diameter [nm]
100
1000
Figure 5. I/O ratios calculated from the results measured at different distances from the road under
different ventilation conditions. All measurements except Zhu 35 m east were taken on the west side of
the road. (Data adapted from Zhu et al. 2005).
14
door condensation and nucleation have been connected
to ozone-terpene reactions recently. Terpenes are found
in cleaning agents and air fresheners, and particles are
formed through the ozone-terpene reaction in indoor air
(Fan et al. 2005). Terpene-based condensation nucleation
has been found to be strongest in indoor spaces with a
low air exchange rate (Weschler 2003).
Evaporation
Traffic-originated particle volatility changes when particles migrate indoors. Indoor particles are less volatile
than outdoor particles. Large particles (with a diameter from 50 nm to 100 nm) are more volatile than small
ones (diameter≈ 30 nm), and particles are more volatile
in indoor spaces near traffic than those further away
from traffic sources (Kuhn et al. 2005). Outdoor-originated particulate chemical composition changes due to
evaporation indoors (Lunden et al. 2003).
Some interesting changes in I/O ratios linked to the
distance of an indoor space from a major road have
been measured by Zhu et al. (2005), and are illustrated
in Figure 5. The authors have speculated that the high
indoor concentrations of fractions below 10 nm might
be residues of partially volatilised particles. The I/O ratio of the size range is higher near the road.
Agglomeration
Agglomeration rate depends on the second power of
total particle concentration, and the agglomeration
process typically occurs where there are strong particle sources, such as cigarette smoke, present in indoor
spaces. Agglomeration has not been considered to have
a strong influence on indoor particle size distribution
(Nazaroff 2004).
Conclusions
Although indoor particulate dynamics and the indooroutdoor connection are attracting a lot of attention
in the scientific world today, they are quite poorly understood phenomena. Simultaneous aerosol processes
such as deposition and filtration, and unidentified indoor sources, as well as the diversity of indoor spaces
and measurement methods, together with the strong
size dependency of the phenomena involved, make it
hard to generalise.
Assuming that there are no indoor sources, one could
suggest that particulate concentrations will be lower in
mechanically ventilated indoor spaces than outdoors.
The I/O ratio is typically lower in indoor spaces with a
mechanical supply of filtered air, and is strongly sizedependent in both ventilation cases.
15
16
3
The impact of ventilation on particle
concentrations in indoor air
V
entilation plays an important role in maintaining
indoor air quality. Ventilation supplies clean, fresh
air to buildings and extracts contaminants. Although
the ventilation of industrial premises focuses on controlling airborne contaminants, and that of non-industrial
premises on controlling room temperature, humidity,
and odour, the same kind of equipment is used in both
types of applications. Industrial systems require some
unique and specific design features, however.
Natural and mechanical ventilation
Natural ventilation depends on wind and buoyancy forces due to density differences or a combination of both
forces. Mechanical ventilation uses fans to supply and
remove air from a space. Natural ventilation and mechanical exhaust ventilation have been popular in apart-
(a)
(b)
(c)
(d)
ment buildings in Finland in recent decades. Due to the
requirements of the current building code (ME 2003),
mechanical supply and exhaust ventilation has become
the dominant solution in new apartment buildings. In
office buildings, mechanical supply and exhaust ventilation with supply air filter has been the most popular
system since the 1960s.
Air distribution in ventilated rooms
The ventilation principle is based on the airflow pattern
in a room. The two main principles are mixing and thermally controlled ventilation. In addition, piston flow
and short circuit flow are possible. Figure 6 shows the
principle of airflow patterns and contaminants distribution in a room.
Figure 6. Principle of room airflow patterns: (a) piston flow, (b) displacement ventilation, (c) complete
mixed ventilation, and (d) short circuit flow.
17
Piston flow
Mixing ventilation
The aim of piston flow is to provide a unidirectional airflow field over a room by supply air. Piston flow has the
shortest possible air change time. In one configuration
sometimes referred to as vertical laminar flow rooms,
cleaned air enters the room through the floor and exits
through ceiling grilles or through continuous outlets in
the walls at ceiling level.
The aim of mixing ventilation is to provide uniform conditions throughout a ventilated room. Airflow pattern
in the room is typically controlled by high momentum
supply airflow. Contaminant removal efficiency in complete mixing ventilation is equal to one. However, if part
of the supply airflow fails to ventilate the occupied zone
(short circuit flow), efficiency may be below one.
Displacement ventilation
Short circuit flow
The aim of displacement ventilation is to provide a similar temperature and contaminant distribution throughout a room. Room airflow pattern is created by replacing
the airflow leaving the room with supply air. Room airflow patterns are controlled mainly by buoyancy, i.e. the
natural convection flows are the engine of displacement
ventilation (DV 2001). Air quality in the occupied zone
is generally better than with mixing ventilation.
Contaminant distribution in a displacement-ventilated room depends on the position of the contamination
sources and heat sources, if they are also contaminant
sources. Thermal flow around a person may provide
them with cleaner air to inhale in the case of displacement ventilation (Mundt et al. 2004). This local modification of concentration distribution may affect personal exposure when the vertical temperature gradient
of room air is available (Mundt et al. 2004). See Figure
7 (a). Poor system performance is found in the case of
a passive contaminant released in the lower part of the
room close to the occupants. Figure 7 (b) shows an example of contaminant removal effectiveness as a function of supply airflow rate (Mathisen 1984).
Short circuit flow takes place when supply air goes from
inlet to outlet without passing the occupied zone. Direct
loss of supply air occurs when the air discharged from
the supply travels only a short distance before it reaches
the extraction device.
Personal ventilation
Personal ventilation systems have been developed to improve the temperature and quality of air for people in
open-plan offices (Melikov 2004, 2006). Personalised supply air systems include individual control of airflow rate,
and provide air directly to occupants’ breathing zones.
Systems have the potential to improve the quality of inhaled air and ventilation efficiency compared to conventional mixing ventilation systems, but their performance
depends on the supply air terminal device.
Figure 8 presents the principle of personalised supply
air systems and their efficiency, depending on the position of personalised air terminals (Melikov 2006).
The exposure of exhaled air is low and independent
of the room air distribution when a high-efficiency personalised air terminal is used. It is possible to provide
high heat load
low heat load
40
1.1 m above floor
1.7 m above floor
20
<¡c>
10
5
2.5
1.25
0.6
4
(a)
(b)
6
8
10
12
14
16
q (m3/hm2)
Figure 7. (a) Thermal flow around a human may give cleaner inhaled air using displacement ventilation
(Mundt et al. 2004). (b) An example of contaminant removal effectiveness as a function of supply airflow
rate and heat load (Mathisen 1984).
18
1.6
Personal exposure index
Local ventilation efficiency
1.49
1.4
1.34
1.24
<¡c>
1.2
1.0
1.12
1.02
1.03
0.8
0.6
0.4
(a)
(b)
Displacement diffuser
Top desk grill
Under desk grill
Figure 8. (a) Principle of personalised supply air systems. (b) A comparison of the personal exposure index
and efficiency for three types of personalised ventilation system (Melikov 2006).
100% clean air to the breathing zone when the supply
air device is located close to the face. Properly managed
personal ventilation has a greater potential to prevent
the transmission of contagious contaminants between
occupants than total volume ventilation (Melikov 2004).
Early results suggest that combining mixing ventilation
with personal ventilation will protect occupants from
the airborne transmission of infectious agents and will
be superior to mixing ventilation alone. Personal ventilation promotes the mixing of exhaled air in rooms
with displacement ventilation. The air change rate of
a room needs to sufficiently high, even where personal
ventilation is used.
Local exhaust ventilation
Tobacco smoke and cooking odour from other flats are
the most commonly occurring indoor-related odour
problems in apartment buildings (Palonen 1998). Local ventilation, such as kitchen exhaust hoods, is an efficient method for reducing the exposure of occupants.
Capture efficiency should be the prime criterion when
designing local ventilation systems of this type. Figure
9 illustrates the principles involved and some typical
design parameters.
The smaller the living space, the more important
it is to reach high capture effectiveness at the lowest exhaust airflow, due to the problems in ensuring
qle
_
_
y
z
ms
ms
D
(a)
(b)
Figure 9. (a) Principle of the kitchen hood. (b) Typical design criteria for receptor hoods (ACGIH 1992).
19
that outdoor air compensates for the exhaust airflow
rate. When a kitchen hood is located in the middle of
a kitchen allowing free movement around the unit, it
is difficult to reach high capture efficiency. The shape
and dimension of the hood do not have an effect on
capture efficiency, according to Heinonen and Seppänen (1994).
Room air cleaners
Several studies have tried to prove the benefits of room
air clearers in terms of health. There is limited exposure
data available for those tests, however. Fisk et al. (2002)
carried out comprehensive quantitative experiments to
assess the capabilities of several air-cleaning devices to
create a particle-free microenvironment as a therapy for
sleeping people affected by allergic rhinitis and asthma.
Six devices were evaluated, of which five were portable
and intended to provide general air cleaning for bedroom-sized spaces. The sixth was intended for installation in front of the headboard of a bed and was designed
to provide clean air in the immediate space occupied by
the sleeper. It was found that the latter was clearly superior to all the other air-cleaning devices (Hacker and
Sparrow 2005).
Portable room air cleaners can be used to reduce exposure to outdoor fine particles in existing residential
buildings and houses fitted with mechanical exhaust air
systems. Effective airflow rate must be sufficiently high,
however, and noise levels low, especially in bedrooms.
Residents living in family houses are very sensitive to
ventilation noise in their bedrooms (Kurnitski et al.
2005), and noise is the main reason cited for reducing
ventilation fan speed.
Small ventilation units are often placed in the middle of a flat, which requires quite long ducts between
the outdoor air intake and the ventilation unit. Dust
from outdoor air can accumulate in this section and
cause potential odour problems. The quality of outdoor air filtration is low in existing flats or houses with
mechanical exhaust system. Some outdoor air filters
for outdoor air vents are available, but their filtration
classes are G3 or less.
It appears that the quality of the filtration of outdoor
air in existing apartment buildings is not likely to improve in the immediate future. Budgets for modernising
social housing are often unable to stretch to installing
mechanical supply and exhaust ventilation systems and
better energy economy. Privately owned buildings face
large economical problems in meeting all their maintenance needs. Existing building codes (ME 2003) do not
allow residents to make personal improvements to ventilation system in apartment buildings, and air cannot be
discharged from small wall-mounted ventilation units.
Modelling tools
The motion of particles in indoor air can be evaluated
using computational fluid dynamics (CFD) simulation
and multizone models. To date, CFD simulation is the
current method of choice for evaluating indoor air conditions in research (Etheridge and Sandberg 1996).
A multizone model was developed as part of the
HALVI Project, including well-mixed zones with sinks
and sources, as well as particle interaction resulting from
the coagulation process. Particle transportation between
the zones is described using zone-to-zone airflows (Holopainen et al. 2005).
Pressure control
Conclusions
Temporal pressurisation is used successfully in houses
with fireplaces to prevent smoke penetration, by temporarily reducing the exhaust airflow rate while keeping the
supply airflow constant. The same technology can also
be used to prevent tobacco smoke penetration through
cracks in the walls between two apartments.
Ventilation systems are shut down in Finland during emergency situations, such as major fires and cases
of radioactive fallout to reduce harmful exposure from
outdoor pollutants. A survival room (bathroom) can be
built in a family house, and the room pressurised with a
separate supply air fan fitted with HEPA and gas filters
(Siren and Paalanen 1994).
Ventilation and air filtering play a major role in contributing to good indoor air quality. Particle concentrations can be reduced by mechanical ventilation systems
and filtering supply air. The efficient filtration of supply air, in particular, reduces the transport of particles
from outside significantly. The air distribution method
affects personal particle exposure. Personal ventilation
systems are the most promising air delivery systems for
cutting the exposure of occupants. They are not yet
widely applied in office environments, however, due to
the problems of connecting supply air to terminal devices at workstations.
Problems with systems in residential buildings
Small supply and exhaust air ventilation units incorporating heat recovery have been quite popular in apartment
buildings since the early 1990s. In many cases, outdoor
air intakes are placed near balconies. This solution has
caused a lot of complaints among neighbours, however,
with tobacco smoke penetration into other flats.
20
4
Filtration
Figure 10. Fibrous filter materials.
E
fficient filtration of supply air is one of the major tools for improving indoor air quality. In the
past, air filters were primarily used for protecting
ventilation systems against particulate contamination.
The growing awareness of the adverse health effects of
airborne particles has shifted the role of air filtration towards protecting people, and F7 and F8 class fine filters
have become more and more common in public buildings.
The threat of terrorism, in the shape of possible attacks
using biological and chemical weapons, will probably encourage the demand for high-efficiency filtration.
Glass fibre filters installed in a central unit are the
most widely used air cleaning technique today. The role
of traditional electrostatic precipitators has diminished
in recent years, while the use of electrically charged air
filters has increased. New techniques based on air cleaning in the terminal devices of the supply air system have
also become available. Room air cleaners continue to be
used to reduce the concentration of airborne particles.
Fibrous filters
A fibrous air filter works by collecting particles from
the air stream on to the surfaces of a set of filter fibres.
The process by which an aerosol particle is attached can
be affected by several mechanisms, which makes the
detailed modelling of the operation of a fibrous filter
quite complicated. The basic filtration processes can be
illustrated with reasonable accuracy using rather simple
mathematical models, however.
The removal efficiency of a fibrous filter medium is
affected by many factors. The most important material
properties are packing density and fibre diameter. The
thickness of the filter material also has a major influence on efficiency.
Charged air filter media are widely used today, which
means that the fibre charge must be taken into account
when discussing material parameters. Other parameters
that influence the removal process are air velocity in the
filter medium, particle size, particle density, the electrical
charge of the particles, and their dielectric properties.
Packing densities can vary rather widely (from 0.01
to 0.3) depending on the filter type. Fibre diameter can
also vary widely (typically from below 1 μm to 40 μm)
depending on the type and application of the filter. See
Figure 10.
The structure of a fibrous filter is open, and the fibres
form a very large collection area. The surface area can
be very high. In a filter medium with a packing density
of 0.01, a fibre diameter of 1 μm, and a material thickness of 5 mm, the fibre surface area is 200 times higher
than the face area of the filter. Thus, a typical bag filter with 10 m2 of face area contains 2,000 m2 of fibre
surface area.
21
The performance of an air filter is linked to two parameters: efficiency and pressure drop. Efficiency is normally illustrated by removal efficiency, which provides
information about the fraction of particles collected by
the filter. However, the collected particles are not of great
importance compared to the particles that penetrate the
filter in most cases. As a result, filter penetration should
be favoured over efficiency.
In the case of a conventional fibrous filter, overall
single fibre efficiency is governed by three major mechanical removal mechanisms:
• interception
• impaction, and
• diffusion.
In the case of a charged filter medium, particle removal is due to the combined effect of mechanical and
electrical mechanisms.
The pressure drop across the filter medium is directly
proportional to the air velocity and the thickness of the
filter layer, and inversely proportional to the square of
the fibre diameter. The flow resistance of a filter material is often illustrated by permeability.
The features of a good filter include low penetration
(high removal efficiency) and low pressure drop. A practical measure of these properties is filter quality factor.
Basic mechanical removal mechanisms
Interception is probably the most straightforward removal
mechanism, as the particles that follow the streamlines
close to the surface of the fibre may become attached.
This takes place at low velocity, and it is reasonable to
assume that whenever a particle touches the fibre it becomes captured due to adhesion forces. Interception is
not affected by air velocity, however, only by the properties of the filter and particle size.
Impaction is another basic mechanism that affects
removal particles from the air stream. Impaction is due
to particle inertia, when particles cannot follow the
streamline and impact on the surface of the fibre. They
do not always attach, however, as they may have enough
energy to bounce off.
Impaction is characterised using a dimensionless parameter, known as the Stokes number, which depends
on several factors, including particle velocity, particle
density, the slip correction factor, and the viscosity of
the air. Although the basic theoretical model is only a
rough approximation, it provides a good estimate of
the effects of various filtration parameters, such as the
fact that the importance of impaction increases with
air velocity.
Interception and impaction are important mechanisms
for large particles. The removal of very fine particles is
governed by the third basic removal mechanism: diffusion. Small particles do not follow the streamlines completely, because of random motion or diffusion, and can
find their way to the surface of the filter fibre.
The efficiency of a filter depends on the overall effect
of these three basic removal mechanisms. Each mechanism is particle size-dependent, which means that penetration is a complicated function of particle size. Dif-
100
Diffusion
Interception
80
Penetration (%)
Impaction
TOTAL
60
40
20
0
0.01
0.1
1
Particle size (μm)
Figure 11. Fractional efficiency of a fibrous filter.
22
10
(a)
(b)
Figure 12. Bag filters manufactured from glass fibre (a) and polymer (b).
(a)
(b)
(c)
Figure 13. Rigid cell air filters (a) and (b), and a pleated air filter (c).
23
fusion is an effective mechanism for very fine particles,
while interception and impaction remove large particles
effectively. In the intermittent region, none of the mechanisms is highly effective, which means that maximum
penetration can be found at this particle size range.
The combined effect of the basic mechanical removal
mechanisms is illustrated in Figure 11. The penetration
maximum of the fibrous air filter can be found in the
0.1 to 0.5 μm size range.
Particle removal due to electrostatic force plays a
very important role in the case of charged filter mediums. Charged air filters normally contain a layer of
fibres that have been electrically charged or polarised
during the manufacturing process. These fibres create
local electric fields that can enhance collection efficiency considerably.
therefore uses less energy than methods where separation
energy must be applied primarily to the gas flow.
High voltage electrode ( ion source)
Neutral
particle
Gas ions
Charged particle
Gas velocity
Electric field
Drift velocity
Collection electrode ( ground potential)
Figure 14. Principle of electrostatic precipitation,
showing the single-stage process.
Filter design
As air filters are normally constructed to provide an adequate amount of filter material in a reasonable volume,
their geometry differs significantly from ideal plane filter geometry.
The most commonly type of filter structure used in
general ventilation systems is the bag filter, containing
several filter bags installed side by side to form a compact
filter with a large filter surface. Bag filters are manufactured from glass fibre and polymer fibre (Figure 12).
In addition to bag filters, general ventilation systems can be equipped with rigid cell filters, as shown in
Figure 13. The filter media used here is similar to that
used in bag filters, but the structure of the filter is more
compact. The depth of the rigid cell filter is typically
300 mm. Rigid cell filters are relatively common in the
US, but quite rare in Finland.
The structure of a rigid cell filter somewhat resembles that of a pleated air filter made of thin filter material (or filter paper). The depth of a pleated air filter
is normally 20−100 mm, which is much smaller than
that of a rigid cell filter. Pleated filters are widely used
in applications where the available space is small, such
as in vehicles and small-scale air cleaning applications.
Pleated air filters are made from a variety of materials,
including cellulose, glass fibre, and polymer.
Pleated filter structures are also used in general ventilation filters, in V-shaped structures that reduce the face
air velocity to a suitable level.
Electrostatic precipitators
Electrostatic precipitation is one of the fundamental
means of separating solid or liquid particles from gas
streams, and has been utilised in numerous applications,
including industrial gas cleaning systems, air cleaning
in general ventilation systems, and household room air
cleaners. See Figure 14.
This method is based on an electrostatic force applied
directly to the particles rather than the entire gas flow, and
24
The operation of an electrostatic precipitator is based
on three major factors:
• particle charging
• electrostatic collection of charged particles, and
• removal of collected particles.
Particle charging takes place with a continuous flow
of gas ions across the space between two electrodes. One
of the electrodes is connected to a high-voltage power
supply, while the other is connected to ground. Particles
become charged when passing through this region. The
electric field between the electrodes produces an electrostatic force on the charged particles, leading to particle
drift towards the grounded collection electrode.
Particle charging and collection can take place in different sections, as illustrated in Figure 15. In this twostage system, particle collection takes place in a region
without gas ions.
High voltage electrode
( ion source)
Neutral
particle
High voltage electrode
Gas ions
Electric field
Charged particle
Gas velocity
Electric field
Drift velocity
Collection electrodes (ground potential)
Figure 15. Principle of electrostatic precipitation
utilising separate charging and collection sections.
The electrostatic force is directly proportional to the
net charge of an aerosol particle. Effective charging of
the particles is, therefore, of great importance. Airborne
particles are normally charged either due to their birth
processes or due to charge transfer from gas ions to
particles. The natural charging of particles is normally
so weak that it has no practical importance for electrostatic air cleaning.
Particle charging in electrostatic precipitators is
caused by gas ions generated by a high-voltage corona
discharge, which is utilised to create regions with a high
concentration of unipolar gas ions. Electrostatic force
is proportional to the particle charge and the electric
field. A strong electric field is important for good performance.
The principles of single-stage and two-stage electrostatic precipitators are shown in Figure 16. Single-stage
units are rarely used in ventilation applications. There
are exceptions to this, however, as in the case of the air
cleaning techniques used in systems developed by Ion
Blast and Genano.
A two-stage electrostatic precipitator consists of
separate sections for particle charging and collection.
In practice, however, the two sections are integrated to
form a compact unit.
In principle, the major advantages of the electrostatic
precipitator are its low flow resistance and the possibility to wash the contaminated collector regularly. This
makes electrostatic precipitators ideal for fulfilling two
important requirements for air cleaning: low operating
cost and cleanliness of the filtration system. These properties are not widely used in conventional ventilation
applications, however, probably because of two major
drawbacks: the high initial cost of electrostatic precipi-
Single-stage ESP
Charging & collection
section
Corona discharge
tator-based air cleaning systems and, in some cases, the
poor reliability of the filtration they offer.
Decentralised air cleaning
Purifying air in buildings is normally carried out on a
centralised basis, with air filters in a general ventilation
system. This approach has many good features, such as
ease of maintenance. One of its drawbacks, however, is
inflexibility, as different levels of air treatment cannot be
provided easily in different parts of a building.
The flow of outdoor particles to indoor air can be
reduced by improving the removal efficiency of air filters and minimising uncontrolled leakages in the building envelope. Increasing the filtration efficiency of existing HVAC systems is a straightforward approach for
improving air quality.
Greater flexibility can be achieved by utilising decentralised air filtration, using air filtration in terminal
devices or room air cleaners. See Figure 17.
An air filter can be installed in an air duct to serve
several rooms or a single room. In principle, air filters
can be integrated with terminal supply air devices.
All these alternatives require that the pressure drop
of the filter is low, to prevent any significant changes in
airflows occurring. The space available for a terminal air
filter may be small, however, making the use of conventional air filtration techniques unfeasible. However, terminal air filtration has been successfully accomplished
with the aid of a sophisticated air cleaning technique
that combines effective electrostatic particle filtration
with chemical filtration based on activated carbon.
Two-stage ESP
Charging
section
Collection
section
Corona discharge
Figure 16. Principles of single-stage and two-stage electrostatic precipitators.
25
General ventilation
air filter
Room air
cleaner
In-duct
air filter
Terminal
device
air filter
Figure 17. Decentralised air filtration.
Room air cleaners
Air recirculation and filtration of room air is another
alternative for reducing the concentration of impurities in indoor air. Recirculation can be implemented
using compact devices known as room air cleaners, as
shown in Figure 18. These units contain filters and
a recirculation fan and are widely used in homes, offices, and restaurants. One of the advantages of room
air cleaners is that they can be used in buildings without mechanical supply air ventilation and centralized
air filtration systems.
When evaluating the suitability and efficiency of a
room air cleaner, the following aspects have to be carefully considered:
• the volume of the space where the air cleaner will
be used
• the ventilation rate, and
• the types and concentrations of impurities to be
removed.
The capacity of a room air cleaner must be dimensioned correctly to ensure a significant reduction in im26
purity concentration. This requires that the effective flow
rate or clean air delivery rate (efficiency x flow rate) is
significantly higher than the airflow rate due to ventilation or infiltration. In addition, the effective flow rate
must be high enough to cause a reduction in concentration that clearly exceeds the speed of the natural decay
of the impurity.
The filters used in room air cleaners are selective,
which means that their efficiency can be virtually 100%
for one impurity, but almost zero for another. In the
case of aerosol particles, filtration efficiency is usually
dependent on particle size.
Unfortunately, some air cleaners have only a marginal
effect on particle concentrations in room air. Some with
a reasonably high effective flow rate, however, offer true
air cleaning potential. High flow rate is usually associated with a high level of noise, however. Combining good
efficiency with low noise appears to be extremely difficult. In this respect, the low flow resistance and high efficiency of an electrostatic precipitator provides a good
basis for effective room air cleaning.
Figure 18. One of the advantages of room air cleaners like this is that they can be used in buildings without mechanical supply air ventilation and centralised air filtration systems. Courtesy Genano Ltd.
Conclusions
Air cleaning based on general ventilation systems will
probably remain the primary technique for combating
outdoor air impurities. The rising awareness of the harmful health effects of fine particles, and the risk of terrorist attacks with chemical and microbiological weapons,
will increase the need for higher efficiency filtration and
removing harmful gaseous impurities. Lower operating
costs will also become a growing priority.
Meeting these requirements means that new filtration systems will have to be developed, leveraging areas such as charged air filter media. Improving chemical filtration will call for new smart filtration media for
specific compounds.
In addition to fibrous filtration, the potential of
electrostatic precipitators, a long-established technology, should not be overlooked. Utilising new materials
and combining electrostatic precipitation with fibrous
filtration techniques open up the potential for creating
reliable and cost-effective systems. One of the key is-
sues here will be to reduce the initial high cost of electrostatic precipitators.
Decentralised air filtration has a lot to offer in terms
of efficiency and flexibility over and above centralised
systems. Some terminal devices provide an ideal location
for air filters. Air cleaning can also be integrated with
supply air duct systems to serve one room or a group of
rooms. These applications require filters with high efficiency and capacity, and low pressure drop.
Room air cleaners remain a potential tool for improving air quality in limited areas of a building. Achieving
a significant improvement in air quality requires that
the flow rates of air cleaners can be increased without
generating excessive noise. In addition, the cost of air
cleaners needs to be reduced if the technique is to gain
wider acceptance.
27
28
5
T
Market potential
he demand for solutions to improve indoor air
quality is growing due to the increased awareness
of consumers and active marketing by manufacturers. Building users and owners are also paying more
attention to health and productivity. New information
on the adverse health effects of fine particles, and measures introduced to reduce exposure to them, will create
new market potential for filters in ventilation systems
and air terminal devices, room air cleaners, and supply
and exhaust ventilation systems. The key questions are
how fast this development will be, and can something
be done to speed it up.
Demand varies between building types. The clearest
situation can be found in industries where production
processes are highly dependent on the quality of indoor
air. Examples of such premises include the clean rooms
needed for DNA and nanotechnology work and some
hospital environments. The technological challenge is to
achieve high cleaning efficiency and reliability. Cost is not
such an issue, compared to the value of the space.
High-end commercial and office buildings are approaching these types of production facilities in terms
of the premium they now put on good indoor air quality.
Employers are beginning to understand the importance
of a healthy and comfortable work environment on employee productivity. High-quality premises are also an
important factor in creating corporate image.
The spearhead of this development has been temperature control in the form of mechanical cooling. The
trend is towards more individual control of the indoor
environment, which could also mean the possibility to
clean the air around individual workstations. The cost
of creating a positive individual indoor environment is
insignificant compared to the salaries of the personnel
concerned, but the link between clean air and productivity
has to be verified by building owners and employers.
Many current public and office buildings have low
targets for their indoor environment. The majority of
these buildings in Finland, for example, have mechanical supply and/or extraction ventilation systems, typically fitted with low-performance filters. Reducing people’s exposure to fine particles can usually be achieved
by relatively simple technological solutions, using conventional supply air filters. This group of buildings has
a large market potential for high-volume products. The
cost of filtering solutions is a major factor here, and the
emphasis should be on increasing people’s awareness of
the importance of clean indoor air.
An extremely wide market potential could open up
if air cleaning and supply air filtering solutions were to
penetrate the residential sector. The majority of these
buildings have no mechanical ventilation system, which
makes it a difficult market for supply air filters. Northern European countries have a strong tradition of mechanical ventilation, so there are more possibilities here
for filtering supply/inlet air.
Another problem in the residential sector is the small
influence that many residents, particularly in large buildings, have on the technical solutions in their home. People living in detached houses, in contrast, are somewhat
differently placed. Local and governmental authorities
will be key players in improving the situation.
Some of the tools developed under the FINE Programme will give valuable input for this. A good example is the validated mathematical model that has been
developed for simulating time-dependent particle concentrations in indoor air and evaluating the exposure
of occupants. Using this model, it is possible to demonstrate the effects of various control techniques to residents and decision-makers.
Market drivers in North America and Europe
There are no clear regulatory drivers for indoor clean air
technologies in North America. However, non-regulatory
drivers are leading to increased demand for high-technology solutions, particularly in commercial buildings and
R&D applications. The market potential in residential
and industrial buildings is more limited.
The key non-regulatory market drivers for commercial buildings are building vulnerability, sustainable design, and traditional IAQ issues.
Building vulnerability relates to the potential of a
structure to be impacted by materials such as chemical,
biological, or radioactive agents introduced through an
act of bioterrorism or through a HVAC system. Bioterrorism is perceived as a growing risk in North America, and building designers and owners are conducting
growing numbers of building security evaluations including Threat and Risk Analysis (TARA) as part of
the designs for new buildings and on-going operations
for existing buildings. This type of evaluation is not currently required in the US, but many commercial building-owners are aware of the importance of this proactive approach.
The US Green Building Council (USGBC) has developed a certification known as Leadership in Energy
and Environmental Design (LEED), which has become
a nationally recognised standard for developing highperformance, sustainable buildings. Credits related to
indoor air can be obtained directly from the indoor environmental quality section or indirectly through the
energy and atmosphere section. Many new buildings
29
and major modernisation projects for the public sector
are seeking certification through the LEED programme.
Three states are currently considering LEED adoption
for state projects, and five states have proposed or passed
bills to establish a green building tax credit based on the
LEED rating system.
In Europe, the overall market volume for IAQ-related ventilation products is valued at around €20 billion,
of which Finland accounts for some €500 million. The
market volume for air filters is in the order of €100-150
million for Europe as a whole. These figures reflect the large
available potential in Europe, where the level of filtering
is generally lower than in Finland and Scandinavia.
The technology for controlling fine particles in indoor
air (supply air filtering and air cleaning) is well developed in Finland, and this high level of technology will
give Finnish companies a competitive edge.
In addition to the market potential in buildings, there
are other potential market areas as well, in the shape of
cars, buses, aircraft, and metros – all places responsible
for a significant proportion of human exposure to fine
particulates. This has not yet been widely acknowledged,
but public awareness is steadily rising, and we can expect
to see the demand for vehicle solutions increase.
Measurement instruments represent another market
opportunity. Instruments demonstrating current exposure and the effects of mitigation technology are needed
by building owners and HVAC manufacturers. There is
still much room for development here, to make measurements easier to take and more precise.
Another interesting new technology is detecting mould
damage using particle monitors. There is a large market
worldwide for these types of services, but the reliability
of the methods behind them needs to be scientifically
demonstrated before this potential can be realised. The
service dimension offers the most opportunities here,
rather than the hardware.
Air filters
Improved filtering of supply air will bring improved business opportunities in Finland, Europe, and worldwide.
Competition in this area is tough, and success will depend on finding technologically superior products and/
or product lines.
Supply and exhaust ventilation systems are common
in Finland and Scandinavia, due to the region’s tough
building codes. The requirements for supply air filtering in new construction have recently been tightened in
Finland, and this trend is expected to continue in other
EU countries. Many companies consider the pace to be
too slow, however. The focus of regulations has been on
coarser particles or TSP, but will gradually move to ultrafine particles. Companies expect traction from voluntary IAQ classification systems, such as the Finnish
Indoor Climate Classification 2000 (FiSIAQ 2001).
Regulations usually only guide new construction, which
is in the order of 1% of the entire building stock, which
30
means that the market potential resulting from the regulatory framework is limited compared to that of existing
buildings. In the case of the latter, it will be important to
pay attention to non-regulatory drivers. Increased public
awareness about fine particles and the indoor environment
as a whole will be the key to these markets. Further research is needed to educate the public about the harmful
effects of fine particles, and emphasis should also be laid
on disseminating existing knowledge, over and above what
has already been achieved. See Figure 19.
In addition to marketing new products, it is important
to stress the importance of maintaining existing systems
appropriately. Meeting consumers’ expectations in terms
of better indoor air requires HVAC systems to function
faultlessly and for filters to be serviced regularly. This is
likely to see higher demand for maintenance services and
for tools for continuously measuring air quality.
Room air cleaners
In theory, room air cleaners could be used in every
building and room, and can be installed independently
of ventilation solutions. In practise, the market potential here is limited by the technological challenges involved.
To clean indoor air effectively, the airflow through
a cleaner must be higher than the ventilation airflow
through a room. Creating such airflow without disturbing noise and draught is still a challenge for current solutions. New technologies and materials with low pressure
drop can be expected to gradually close the gap, however. Another possibility is to deliver clean air directly
to the breathing zone, which reduces the volume of air
to be processed significantly and current technology can
offer good results here. One emerging technology is to
integrate room air cleaners into furniture.
See Figure 20 for an example of how personalised air
supply can be integrated into desks and space dividers
in an office environment.
The key market driver is consumers’ requirement for
clean air. Regulations are unlikely to drive the market,
although by setting the pace in new construction they
could provide the foundation for developments in existing buildings. Increased public awareness of fine particles
and the indoor environment as whole will again be key
to these markets. Reliability and ease of maintenance
will be required from consumer applications, and there
will be demand for maintenance services.
Environments with special indoor air quality requirements are an important application area for room air
cleaners. These environments include industrial clean
rooms, hospitals, or areas intended for people with allergies or respiratory illnesses. The recent SARS epidemic
was a good example, pinpointing the need for clean air
technologies. The ongoing risk of avian flu will keep
demand active in hospitals and patient transport vehicles. In the industrial sector, the rapid development and
application of DNA technology and nanotechnologies
Figure 19. Air filters are particularly useful in improving air quality for people with allergies, such as
children. Courtesy LIFA Air Ltd.
31
will increase the demand for customised clean room
applications.
Air cleaners also have significant market potential
in vehicles. Solutions are particularly needed to protect
employees spending all their working day in a vehicle.
Meeting this demand will require new technological solutions. High outdoor concentrations of particles and
gases, together with the small space available for equipment, pose a particular challenge.
As the technological performance of different air
cleaners do not differ significantly, the competition between products and manufacturers can be expected to
remain tough.
Filters in air terminal devices
One possibility for introducing supply air filtering in buildings is to install filters in supply terminals or inlet devices.
This is a more flexible solution than locating filters in central units, as it enables filters to be installed in only part of
a building or even individual rooms. This could open up
new markets in existing office buildings, as filtering solutions could be sold to the users of specific spaces rather
than the overall owner of a building. These solutions usually require re-balancing of a ventilation system, however,
which may make the situation more complicated. Filters
with a low pressure drop are required to avoid problems
with the ‘background’ ventilation system.
Supply air inlets can also be equipped with filters in
buildings with natural or mechanical exhaust ventilation.
With natural (passive stack) ventilation, the available
pressure difference, however, limits filtering capacity.
In these distributed filter solutions, the number of
service points increases significantly. Extra emphasis
must be placed on ease of maintenance and the cost
of filters. As of now, there are only a few solutions that
are technically and economically feasible, and further
development is clearly needed.
Supply and exhaust ventilation systems
The increased demand for clean supply air will also increase the need for supply and exhaust ventilation systems. These are the best solution for new construction,
as they also include heating and cooling, as well as heat
recovery. As the requirements for filtering become tougher, the market for supply and exhaust ventilation systems
will increase, which means that the regulatory environment will play an important role in this sector.
It will be important, however, to convince decisionmakers, such as building owners, construction clients,
and architects, about the importance of a good indoor
environment.
New markets, such as those in residential buildings
in particular, will bring new challenges. Customers will
expect turnkey delivery and that systems meet the IAQ
and energy requirements they have set. Quality issues
and life cycle costs will be emphasised.
As filtering in a central unit can be handled using
several different technologies, this will give manufacturers the possibility to optimise their solutions. Pressure
drop will be one of the key factors in selecting the most
appropriate filter solution, because of the increased requirement to reduce electricity costs.
Figure 20. Personalised supply air systems offer individual control of airflow rates, and provide air directly
to occupants’ breathing zones. Courtesy Martela Oyj.
32
6
T
Conclusions
he impact of particulates on health has been widely investigated in recent years, and many studies
have shown that these particles increase the incidence of respiratory and cardiovascular diseases. Mild
inflammation and airway obstruction are also observed.
Exposure to ultrafine particles may be more harmful
than that to larger particles because ultrafine particles
deposit deeper in the respiratory track. There is a lack
of detailed data, however, on particle numbers and mass
concentrations in different size classes emitted from indoor sources, which is essential to assess the health impact of particle exposure. The evidence currently available is inadequate, and more information will be needed
to demonstrate the health impact of particles according
to their source, size, and mass.
Future research will also need to focus on the nanoparticles that are being used in increasing quantities in
many fields of industry. The number of people exposed
to these new nanomaterials, such as fullerenes, carbon
nanotubes, and titan dioxide nanoparticles (TiO2), is
growing, and they pose significant exposure potential,
because they can be deposited in the lungs or on the skin
and translocate within the body.
Particle concentration and size distribution in indoor
air are influenced significantly by outdoor air quality, as
particles transfer into the indoor environment through
leaks in the building envelope and ventilation systems.
Events that generate particles indoors are often of short
duration, but may increase particle concentration in the
air considerably. If the aim is to reduce the exposure of
occupants, actions to reduce fine particle concentration
should be focused on the breathing zone.
Ventilation and air filtering play a major role in creating good indoor air quality. Ventilation systems need
to be designed, installed, and maintained appropriately to create a healthy, safe, and comfortable indoor environment. Particular attention has to be paid to the
ventilation of rooms intended for special purposes,
such as people with allergies. To date, personal ventilation systems are the most promising air distribution
method for reducing exposure, but these systems have
encountered many practical problems due to the difficulty of supplying fresh air directly to workstations in
office environments.
The threat of terrorism and attacks using biological
and chemical weapons will probably fuel demand for
higher-efficiency filtration in buildings. A major challenge in the future will be how to achieve high filtration
efficiency, as well as a low pressure drop, as filtration systems need to be effective against gaseous impurities.
New information about the adverse health effects of
fine particles, and the need to mitigate them by reducing
exposure, will create new market potential for filters in
ventilation systems and air terminal devices, room air
cleaners, as well as increase the popularity of supply
and exhaust ventilation systems. These technologies are
already widely used in office buildings throughout the
developed world, but there is increasing market potential for high-end solutions.
Extremely extensive market potential will open up
when these types of technologies begin to penetrate the
residential sector and public buildings. To reach these
markets, it will be necessary to highlight the importance
of indoor environment exposure to consumers, local and
governmental authorities, and other decision-makers.
33
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Tekes – Your contact for Finnish technology
Tekes, the Finnish Funding Agency for Technology and
Innovation is the main publicly funded organisation for financing
applied and industrial R&D in Finland.
Tekes’ primary objective is to promote the competitiveness
of industry and the service sector in Finland by enhancing
the country’s technological potential – through such areas as
diversifying production structures, increasing production and
exports, and creating a more solid foundation for prosperity
today and into the future.
Tekes’ technology programmes are a key part of the Finnish
innovation system, and have proved a highly efficient means
of encouraging and stimulating cooperation and networking
between companies, universities, and research institutes for
developing innovative products, processes, and services.
Programmes focus on specific sectors of technology or industry,
and are designed to give business access to the latest research
results. Together with the Tekes network in Finland and overseas,
they also provide an excellent framework for international R&D
cooperation.
As a result of ever-growing traffic volumes and ever-higher
levels of energy generation, the air we breathe exposes us to
a growing number of airborne contaminants, including minute
particulate matter. These particulates are known to have major
health implications, and result in the premature death of over 300,000
people in the EU annually alone. Advances in technology are allowing
us to measure smaller and smaller sizes of particles and gain a better
understanding of how they impact our health and the environment, however.
Tekes launched a four-year technology programme in 2002, known as
FINE, together with the Academy of Finland, the Ministry of Transport
and Communications, and the Ministry of the Environment, to focus on
particulate emissions. This concentrated on five main areas: energy and
industry, traffic and transport, measurement technology, indoor air, and
health and the environment. All in all, the FINE Programme involved over 50
projects and close to 60 companies and more than 20 research institutions.
A summary report has been produced on each of these areas. This report
concentrates on the particulate challenge in buildings and occupational
environments. The FINE projects in this area covered a range of challenges
linked to extending our knowledge of the phenomena involved and
reviewing the technological and business potential open to today’s and
tomorrow’s technologies.
Tekes, the Finnish Funding Agency for Technology and Innovation is the
main publicly funded organisation for financing applied and industrial R&D
in Finland. For more information, see www.tekes.fi
ISBN 952-457-247-8