What Causes Indoor Air Problems?
How Does Outdoor Air Enter a
What if You Live in an Apartment?
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.
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 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."
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.
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
Solutions to air quality problems in apartments, as in homes and offices,
involve such actions as: eliminating or controlling the sources of pollution,
increasing ventilation, and installing air cleaning devices. Often a resident
can take the appropriate action to improve the indoor air quality by removing
a source, altering an activity, unblocking an air supply vent, or opening a
window to temporarily increase the ventilation; in other cases, however, only
the building owner or manager is in a position to remedy the problem. (See "The
Inside Story: A Guide to Indoor Air Quality"). You can encourage building
management to follow guidance in EPA and NIOSH's "Building Air Quality: A
Guide for Building Owners and Facility Managers" (http://www.epa.gov/iaq/largebldgs/index.html).