been linked with exacerbation of asthma in sensitized individuals is mold. Hundreds of different
mold species can be found indoors, and the risk of
exposure can be difficult to diagnose as mold
colonies are not visible until fully grown. Mold
requires the right levels of moisture, oxygen, temperature, and nutrients to grow [61]. Excess moisture in furnishings and condensation on surfaces is
called dampness and is caused by high humidity
giving optimal conditions for growth of mold and
dust mites. Data shows associations between
doctor-diagnosed asthma cases and damp conditions, as well as asthma symptoms and dampness
[53]. Thus, there is evidence that dampness is a
cause and an exacerbating factor for asthma,
likely related to its promotion of mold and dust
mites [53].
Particulate matter has adverse health effects on
humans. The effects depend on the composition
and size of the PM, as this is directly linked to
deposition in the respiratory tract and the respiratory tree’s ability to remove the pollutants
[62]. Coarse PM tends to deposit in the nasal
and upper respiratory system, while fine PM and
UFP tend to deposit in the lower respiratory tract
and alveoli. Thus, fine particles and UFP penetrate
deeper into the human airways. UFP have large
surface areas per unit mass, which allows for the
particles to collect relatively large amounts of
toxic low-volatile compounds such as PAHs,
metals, and quinones [62]. These chemicals can
generate acute inflammation of the airways, and
sudden elevation of PM can trigger asthma flares.
These acute effects can be caused by exacerbation
of already existing airway inflammation and
hyper-reactivity. In addition, there is evidence
that air pollution including PM and NO x changes
the structure of biofilm making it thicker and more
porous, and thus a better substrate for infections.
There is increasing evidence that PM induces
sensitivity to common environmental allergens,
which means that long-term PM exposure may
lead to increases in asthma and allergy [63]. Pollutants can be removed by ventilation, and available data suggests that lower ventilation rates in
buildings are associated with increases in the frequency of asthma and allergy symptoms, due to
the accumulation of pollutants. Air exchange rates
above 0.5 h
À1 in Nordic homes are associated
with lower probabilities of both asthma and
allergy symptoms [64].
There are numerous negative health effects
associated with indoor air pollutants. These pollutants can come from products found in virtually
every household. In Table 6, some of the important indoor pollutants are listed as well as their
sources and effects on health.
Ensuring a healthy indoor environment is part
of UN Sustainable and Development Goal
3 concerning good health and well-being for people of all ages. This goal is to be accomplished by
2030 [69]. As humans spend the majority of their
time indoors, ensuring a healthy indoor environment and reducing building-related diseases is a
key component of the goal.
CO 2 as Measure for Indoor Air Quality
Historically, CO 2 has been used as a direct measure of overall indoor air quality. One example is
the limit of 1000 ppm CO 2 in the indoor environment set out in the ASHRAE-1989 standard [70],
which is still in use today. Several studies show
that CO 2 levels above 1000 ppm are linked to a
decrease in school attendance in students [71,
72]. It has been suggested that CO 2 in itself is
not the cause of absenteeism, but instead that an
increase in CO 2 levels is an indicator of insufficient ventilation (<7.5 l/s per person), which
leads to accumulation of other pollutants. Such
pollutants could be bioeffluents or the scents of
cleaning products, which along with their oxidation products cause discomfort [70]. Other pollutants could be any of the species implicated in sick
building syndrome, as described previously. CO 2
can thus be used as an indirect measure of ventilation rate and other odor pollutants, but only to a
certain extent [73]. CO 2 is also a pollutant in its
own right. A recent study shows that indoor CO 2
levels above 1000 ppm can cause drowsiness and
negatively affect focused activity [1]. Building
standards for ventilation should not be based on
indoor CO 2 levels alone, as this may not be the
most important indoor air pollutant [70]. A study
by Satish et al. finds that CO 2 levels of 1000 ppm
and 2500 ppm, relative to 600 ppm, caused a
statistically significant decrease in decision
Indoor Air Quality: Status and Standards
147
mold species can be found indoors, and the risk of
exposure can be difficult to diagnose as mold
colonies are not visible until fully grown. Mold
requires the right levels of moisture, oxygen, temperature, and nutrients to grow [61]. Excess moisture in furnishings and condensation on surfaces is
called dampness and is caused by high humidity
giving optimal conditions for growth of mold and
dust mites. Data shows associations between
doctor-diagnosed asthma cases and damp conditions, as well as asthma symptoms and dampness
[53]. Thus, there is evidence that dampness is a
cause and an exacerbating factor for asthma,
likely related to its promotion of mold and dust
mites [53].
Particulate matter has adverse health effects on
humans. The effects depend on the composition
and size of the PM, as this is directly linked to
deposition in the respiratory tract and the respiratory tree’s ability to remove the pollutants
[62]. Coarse PM tends to deposit in the nasal
and upper respiratory system, while fine PM and
UFP tend to deposit in the lower respiratory tract
and alveoli. Thus, fine particles and UFP penetrate
deeper into the human airways. UFP have large
surface areas per unit mass, which allows for the
particles to collect relatively large amounts of
toxic low-volatile compounds such as PAHs,
metals, and quinones [62]. These chemicals can
generate acute inflammation of the airways, and
sudden elevation of PM can trigger asthma flares.
These acute effects can be caused by exacerbation
of already existing airway inflammation and
hyper-reactivity. In addition, there is evidence
that air pollution including PM and NO x changes
the structure of biofilm making it thicker and more
porous, and thus a better substrate for infections.
There is increasing evidence that PM induces
sensitivity to common environmental allergens,
which means that long-term PM exposure may
lead to increases in asthma and allergy [63]. Pollutants can be removed by ventilation, and available data suggests that lower ventilation rates in
buildings are associated with increases in the frequency of asthma and allergy symptoms, due to
the accumulation of pollutants. Air exchange rates
above 0.5 h
À1 in Nordic homes are associated
with lower probabilities of both asthma and
allergy symptoms [64].
There are numerous negative health effects
associated with indoor air pollutants. These pollutants can come from products found in virtually
every household. In Table 6, some of the important indoor pollutants are listed as well as their
sources and effects on health.
Ensuring a healthy indoor environment is part
of UN Sustainable and Development Goal
3 concerning good health and well-being for people of all ages. This goal is to be accomplished by
2030 [69]. As humans spend the majority of their
time indoors, ensuring a healthy indoor environment and reducing building-related diseases is a
key component of the goal.
CO 2 as Measure for Indoor Air Quality
Historically, CO 2 has been used as a direct measure of overall indoor air quality. One example is
the limit of 1000 ppm CO 2 in the indoor environment set out in the ASHRAE-1989 standard [70],
which is still in use today. Several studies show
that CO 2 levels above 1000 ppm are linked to a
decrease in school attendance in students [71,
72]. It has been suggested that CO 2 in itself is
not the cause of absenteeism, but instead that an
increase in CO 2 levels is an indicator of insufficient ventilation (<7.5 l/s per person), which
leads to accumulation of other pollutants. Such
pollutants could be bioeffluents or the scents of
cleaning products, which along with their oxidation products cause discomfort [70]. Other pollutants could be any of the species implicated in sick
building syndrome, as described previously. CO 2
can thus be used as an indirect measure of ventilation rate and other odor pollutants, but only to a
certain extent [73]. CO 2 is also a pollutant in its
own right. A recent study shows that indoor CO 2
levels above 1000 ppm can cause drowsiness and
negatively affect focused activity [1]. Building
standards for ventilation should not be based on
indoor CO 2 levels alone, as this may not be the
most important indoor air pollutant [70]. A study
by Satish et al. finds that CO 2 levels of 1000 ppm
and 2500 ppm, relative to 600 ppm, caused a
statistically significant decrease in decision
Indoor Air Quality: Status and Standards
147