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 Particles are very small solid or liquid substances that are light enough to float suspended in air (e.g., mists, dust, mold spores or pollen). They are composed of diverse materials including inorganic and organic compounds and dormant and living organisms. Of primary concern from a health standpoint are: 1) small, invisible respirable-size particles, with a higher probability of penetrating deep into the lungs, where they may stay a long time and may cause acute or chronic effects, and 2) larger particles, such as some molds, pollen, animal dander, and house dust allergens, which do not penetrate as deeply, but may cause an allergic response.
Respirable-size particles include, but are not limited to, those from cigarette smoke; unvented combustion appliances such as gas stoves and kerosene heaters; viruses, bacteria, and some molds; and fragments of materials which, when whole, would be considered larger than respirable size particles. Health effects from exposure to respirable-size particles in the air depend on the types and concentrations of particles present, the frequency and duration of exposure, and individual sensitivity. Health effects can range from irritation of the eyes and/or respiratory tissues to more serious effects, such as cancer and decreased lung function. Biological particles, such as animal and insect allergens, viruses, bacteria, and molds, can cause allergic reactions, infectious diseases, and/or can produce toxic products which may be released into the air.
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