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 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."
Relative Humidity
Elevated relative humidity at a surface – 70 percent or higher
- can lead to problems with mold, corrosion, decay and other moisture related
deterioration. When relative humidity reaches 100 percent, condensation can
occur on surfaces leading to a whole host of additional problems. An elevated
relative humidity in carpet and within fabrics can lead to dust mite
infestation and mildew (mildew is mold growing on fabrics). Low relative
humidity can lead to discomfort, shrinkage of wood floors and wood furniture,
cracking of paint on wood trim and static electricity discharges. The key is
not to be too low and not to be too high. High enough to be comfortable, but
low enough to avoid moisture problems associated with mold, corrosion, decay,
and condensation.
