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Part 2 of 3
What is the relationship between indoor and outdoor air quality (pollution)?
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No building is perfectly sealed and so the air inside ultimately originates outside. Air pollution present in the outdoor environment will therefore enter into the building as well. Generally, pollutants present in the outdoor environment are present at a somewhat lower concentration than outside (probably 10 to 90% in most cases).
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There are several reasons for this. Some pollutants are absorbed by materials in the building. Others deteriorate or react chemically and so disappear. Still others may be filtered out by the ventilation system. Also as it takes some time for the outdoor air to enter in quantities, there may be a delay from the time a contaminant appears outdoors, to when it becomes a problem indoors. Smog from outdoors reaches its peak indoors some time after the outdoor peak.
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Outdoor contaminants may be present indoors at a sufficient concentration to affect the occupants. Examples are pollen and mold spores from outdoors causing hay fever and allergies indoors; and high smog levels affecting occupants inside a building. Incidentally, there is no such thing as a good smog day close to a major highway (expressway/freeway).
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How common are IAQ problems?
According to the World Health Organization, approximately 30% of all commercial buildings have significant IAQ problems. Similar estimates have been made by others.
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