The
following information is from the U.S. Environmental Protection Agency
(EPA)An Introduction to Indoor Air Quality (IAQ)
What Causes Indoor Air [Quality] 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. |
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. |
