What Causes Indoor Air Problems?
Indoor pollution sources that release gases or
particles into the air are the primary cause of indoor air quality problems in
homes. Inadequate ventilation can increase indoor pollutant levels by not
bringing in enough outdoor air to dilute emissions from indoor sources and by
not carrying indoor air pollutants out of the home. High temperature and
humidity levels can also increase concentrations of some pollutants.
Pollutant Sources
There are many sources of indoor air pollution
in any home. These include combustion sources such as oil,
gas, kerosene, coal, wood, and
tobacco products;
building materials and furnishings as diverse as deteriorated, asbestos-containing
insulation, wet or damp carpet, and cabinetry or furniture made of certain pressed
wood products; products for household cleaning and
maintenance, personal care, or hobbies; central heating and cooling
systems and humidification devices; and outdoor sources such as
radon,
pesticides, and outdoor air pollution.
The relative importance of any single source
depends on how much of a given pollutant it emits and how hazardous those
emissions are. In some cases, factors such as how old the source is and
whether it is properly maintained are significant. For example, an improperly
adjusted gas stove can emit significantly more carbon
monoxide than one that is properly adjusted.
Some sources, such as building materials,
furnishings, and household products like air fresheners, release pollutants
more or less continuously. Other sources, related to activities carried out in
the home, release pollutants intermittently. These include smoking, the use of
unvented or malfunctioning stoves, furnaces, or space heaters, the use of
solvents in cleaning and hobby activities, the use of paint strippers in
redecorating activities, and the use of cleaning products and pesticides in
house-keeping. High pollutant concentrations can remain in the air for long
periods after some of these activities.
Amount of Ventilation
If too little outdoor air enters a home,
pollutants can accumulate to levels that can pose health and comfort problems.
Unless they are built with special mechanical means of ventilation, homes that
are designed and constructed to minimize the amount of outdoor air that can
"leak" into and out of the home may have higher pollutant levels
than other homes. However, because some weather conditions can drastically
reduce the amount of outdoor air that enters a home, pollutants can build up
even in homes that are normally considered "leaky".
How Does
Outdoor Air Enter a House?
Outdoor air enters and leaves a house
by: infiltration, natural ventilation, and mechanical ventilation. In a
process known as infiltration, outdoor air flows into the house through
openings, joints, and cracks in walls, floors, and ceilings, and around
windows and doors. In natural ventilation, air moves through opened
windows and doors. Air movement associated with infiltration and natural
ventilation is caused by air temperature differences between indoors and
outdoors and by wind. Finally, there are a number of mechanical
ventilation devices, from outdoor-vented fans that intermittently remove
air from a single room, such as bathrooms and kitchen, to air handling
systems that use fans and duct work to continuously remove indoor air and
distribute filtered and conditioned outdoor air to strategic points
throughout the house. The rate at which outdoor air replaces indoor air is
described as the air exchange rate. When there is little infiltration,
natural ventilation, or mechanical ventilation, the air exchange rate is
low and pollutant levels can increase.
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Indoor Air Pollution and Health
Health effects from indoor air
pollutants may be experienced soon after exposure or, possibly, years later.
Immediate effects
Immediate effects may show up after a single
exposure or repeated exposures. These include irritation of the eyes, nose,
and throat, headaches, dizziness, and fatigue. Such immediate effects are
usually short-term and treatable. Sometimes the treatment is simply
eliminating the person's exposure to the source of the pollution, if it can be
identified. Symptoms of some diseases, including
asthma,
hypersensitivity pneumonitis, and humidifier fever,
may also show up soon after exposure to some indoor air pollutants.
The likelihood of immediate reactions to indoor
air pollutants depends on several factors. Age and preexisting medical
conditions are two important influences. In other cases, whether a person
reacts to a pollutant depends on individual sensitivity, which varies
tremendously from person to person. Some people can become sensitized to biological
pollutants after repeated exposures, and it appears that some people can
become sensitized to chemical pollutants as well.
Certain immediate effects are similar to those
from colds or other viral diseases, so it is often difficult to determine if
the symptoms are a result of exposure to indoor air pollution. For this
reason, it is important to pay attention to the time and place symptoms occur.
If the symptoms fade or go away when a person is away from home, for example,
an effort should be made to identify indoor air
sources that may be possible causes. Some effects may be made worse by an
inadequate supply of outdoor air or from the heating, cooling, or humidity
conditions prevalent in the home.
Long-term effects
Other health effects may show up either years
after exposure has occurred or only after long or repeated periods of
exposure. These effects, which include some respiratory diseases, heart
disease, and cancer, can be severely debilitating or fatal. It is prudent to
try to improve the indoor air quality in your home even if symptoms are not
noticeable.
While pollutants commonly found in indoor air
are responsible for many harmful effects, there is considerable uncertainty
about what concentrations or periods of exposure are necessary to produce
specific health problems. People also react very differently to exposure to
indoor air pollutants. Further research is needed to better understand which
health effects occur after exposure to the average pollutant concentrations
found in homes and which occurs from the higher concentrations that occur for
short periods of time.
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