Identification of sources of particulate contaminants in an indoor environment is important for implementation of appropriate air quality control strategies. Due to the difference in functions and structures of buildings, it is useful but very difficult to have a complete list of sources of particulate contaminants. Most of the airborne contaminants in residential buildings are also present in animal buildings. Additionally, more contaminants, usually in much higher concentrations, are found there. When considering typical airborne contaminants with sources found indoors, some deserve more detailed descriptions.
Asbestos is a generic term for a group of naturally occurring mineral silicates in various forms that have been used extensively for building materials including insulation, siding shingles, roofing materials, textured paints, and adhesives. Asbestos, like many other minerals, may be present in fibrous (asbestiform) or crystalline (nonasbestiform) forms.
There are thousands of commercial products because of its high tensile strength, flexibility, and resistance to temperature, acids, and alkali. Asbestos fibers have been widely used as a building material for fire prevention, thermal and acoustical insulation, and roofing; as a friction material in brake pads; and a reinforcing material for cement. Because of the widespread use of asbestos, its fibers are ubiquitous in indoor environments, but the danger is that asbestos materials may become damaged over time. The European Environment Agency (EPA) recommends the removal of badly damaged friable asbestos, leaving intact, well-maintained asbestos in place.
Formaldehyde, a colorless, pungent-smelling gas, is a major allergy agent in indoor environments. It can cause watery eyes, burning sensations in the eyes and throat, nausea, and difficulty breathing in some humans who are exposed at elevated levels (above 0.1 ppm). High concentrations may trigger attacks in people with asthma. There is evidence that some people can develop a sensitivity to formaldehyde. It has also been shown to cause cancer in animals and may cause cancer in humans. Formaldehyde is an important chemical used widely by industries to manufacture building materials and numerous household products. It is also a by-product of combustion and certain other natural processes. Thus, it may be present in substantial concentrations both indoors and outdoors. Sources of formaldehyde in homes include building materials, smoking, household products, and unvented, fuel-burning appliances such as gas stoves or kerosene space heaters. In the buildings, the most significant sources of formaldehyde are likely to be pressed wood products made using adhesives that contain urea-formaldehyde (UF) resins.
Molds are almost ubiquitous role in indoor environments and play an important part in life cycles:They are the primary forces in assisting with decomposition of organic materials. Some molds cause illness and some, such as penicillin, cure illness. Certain molds help to develop the flavor of wines and cheese, whereas others can cause them to spoil. There are thousands of types of molds and yeasts, the two groups of plants in the fungus family. Along with pollens from trees, grasses, and weeds, molds are an important cause of seasonal allergic rhinitis. Molds can live for years in dormant state. Molds can become airborne when their habitats are disturbed by shaking or sweeping. The airborne molds can travel with air current, land on surfaces, and settle into the tiniest cracks and crevices of carpets, furniture, draperies, insulation, rough textures, and smooth surfaces. Heating and cooling ducts, wet carpets, damp upholstery, and air filters on air conditioners and furnaces become common habituating places for molds. The mold allergic season often peaks from July to late summer. Many airborne molds in indoor environments are responsible for human respiratory allergies.