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.
Indoor Pollutant Sources
The many sources of indoor air pollution in any home include combustion sources such as
oil, gas, kerosene,
coal, wood, and
building materials and furnishings as diverse as deteriorated,
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
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 new homes are built with special mechanical means of ventilation,
homes that are designed and constructed in today's times to minimize the amount of
outdoor air that can "leak" into and out of the home,
resulting in higher
pollutant levels than often present in older 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
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
Indoor Air Pollution and Health
Health effects from indoor air pollutants may be
experienced soon after exposure or, possibly, years later.
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
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
biological pollutants after repeated exposures, and it appears
that some people can become sensitized to chemical pollutants as
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.
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
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.
Indoor Air Pollution / Indoor Air Quality Information Pages
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