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or 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
housekeeping. 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 o 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.
WHAT IF YOU LIVE IN AN APARTMENT?
Apartments can have the same indoor air problems as single family
homes because many of the pollution sources, such as the interior
building materials, furnishings, and household products, are
similar. Indoor air problems similar to those in offices are
caused by such sources as contaminated ventilation systems,
improperly placed outdoor air intakes, or maintenance activities.
Solutions to air quality problems in apartments, a
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