THREE MAJOR GROUPS OF INDOOR AIR CONTAMINANTS
• Dust Mite Allergen
• Animal Dander
• General Airborne Particles
• Carbon Dioxide
• Carbon Monoxide
Pollen from trees, weeds, and grasses can trigger allergic rhinitis symptoms. Pollen counts vary seasonally, depending on plant species; therefore, allergic rhinitis that is dependent upon pollen is sometimes called seasonal allergic rhinitis. Perennial allergic rhinitis is usually due to something to which you are exposed year round, such as dust mite allergen (see below), but symptoms can vary seasonally when the immune system is also reacting to pollen.
Plants that rely on wind for pollination produce huge quantities of pollen in order to reproduce. For example, ragweed plants may release up to one million pollen granules in a day. The massive amounts of pollen granules that some trees release can resemble clouds. Open windows are one way excessive pollen is introduced into the home.
Household dust mites are very small, about 0.3 mm! This is less than 1/64 of an inch long, invisible to the unaided eye. Dust mites produce some of the most allergenic substances found in house dust. It's not actually the mite itself that is allergenic, but a protein produced by the mite. Dust mites are thought to play a role in the rising prevalence of asthma. The first National Survey of allergens in 831 homes in the U.S. showed detectable levels of dust mite allergen in 84.2% of the homes. About one-half of the homes had a mite allergen level of at least 2.0 micrograms per gram of dust, the suggested threshold for allergic sensitization. Twenty-five percent of the homes had an allergen level of at least 10.0 micrograms per gram, the suggested threshold for triggering asthma. Independent predictors of dust mite allergen include high humidity, an older home, and musty or mildew odor.
Unlike pollen that varies seasonally, mold spores are present outdoors year round, unless there is snow cover. Mold can grow outdoors in damp humid soil, on decaying matter such as compost, hay, piles of leaves, and grass cuttings. It can also grow on field crops such as corn, wheat, and soybeans. Mold counts are usually higher than pollen counts and usually rise to peak levels during the summer months. The release of mold spores is controlled by a variety of factors, so mold spore counts can rise and drop dramatically, even within a 24 hour period.
Indoors, mold spores are everywhere, but usually only actively growing where there is moisture. Potted plants, bathrooms, basements and crawl spaces are all prime areas for mold growth. Mold can be growing in your air-conditioning cooling coils, and consequently, is likely to be distributed throughout your home by the air ducts. Mold is increasingly being observed and reported in indoor environments. Newer energy efficient homes are air tight, often leading to elevated humidity levels that support the growth of mold. Indoor humidity levels should be <50% in homes to prevent such occurrences.
Excessive concentrations of mold in the air may cause health problems. However, there are no rules, codes, laws, or regulations regarding indoor fungal bioaerosols or fungal loading levels. There are guidelines, however, for indoor spaces and fungal levels promulgated by several different organizations. They set the recommended guidelines for fungal bioaerosols at 200 colony forming units (CFU) / m3 (viable counts) and for nonviable counts at 1,000 spores / m3. For fungal loading of dust and debris, the guideline is 10,000 CFU / gram.
Family pets, especially dogs and cats, are frequently the source of allergy triggers. Many individuals mistakenly believe pet hair is the allergy trigger and that vacuuming up the pet hair removes the allergen. The allergy trigger is actually a protein present on the animal's dander (skin flakes) and in the saliva. The protein is easily transferred from person to person on clothing. Recent studies have demonstrated that even homes and schools with no history of cats or dogs often have cat and dog allergens present. The allergen can be deposited there from the clothing of pet owners or even picked up and transferred elsewhere by the clothing of nonpet owners.
This is a diverse category that contains such things as dust, skin cells, powder, cigarette smoke, fabric and building material breakdown particles. Dust is essentially tiny pieces of everything throughout your home! Airborne particles can also include those biological products listed above.
Some people are sensitive to chemicals in their environment, reporting allergy-like symptoms when exposed to them. This reaction to a chemical irritant may affect people with allergies more than others. Paints, carpeting, plastics, perfumes, household products, and cigarette smoke all contain chemicals to which many people are sensitive. These chemicals include benzene, methylene chloride, perchloroethylene, and formaldehyde. Formaldehyde is probably the most widely used and recognized product, used by industry to manufacture building materials and numerous household products. It is used in adhesives that contain urea-formaldehyde (UF) resins. These adhesives are frequently used in pressed wood products made for indoor use, including such products as: particleboard (used as sub flooring and in cabinets and other furniture); hardwood plywood paneling (used for decorative wall covering and used in cabinets and furniture); and medium density fiberboard (used for drawer fronts, cabinets, and furniture tops).
Since 1985, the Department of Housing and Urban Development (HUD) has permitted only the use of plywood and particleboard that conform to specific formaldehyde emissions limits in the construction of prefabricated and mobile homes. In the past, some of these homes had elevated levels of formaldehyde because of the large amount of high-emitting pressed wood products used in their construction.
(CO2) is a colorless, odorless, and tasteless gas that is a normal component of air. People exhale CO2 as a normal by-product of metabolism. Outdoor air ranges from 250 ppm to 600 ppm CO2. The legally permissible carbon dioxide concentration to which workers may be exposed for eight hours per day has been set by the Occupational Safety and Health Administration (OSHA) at 5,000 ppm. IAQ guidance documents have established a recommended limit of 1,000 ppm in indoor environments. The lower level has been recommended primarily because carbon dioxide buildup parallels that of other contaminants of greater concern (e.g. carbon monoxide, tobacco smoke, microorganisms, and organic vapors). If there is insufficient air exchange of the indoor air with the outdoor air, the carbon dioxide concentrations rise. Concentrations greater than 1,000 ppm are an indication that the ventilation is inadequate. The greater the level is above 1,000 ppm, the greater the frequency of indoor air complaints. In homes where ventilation is inadequate, carbon dioxide concentrations can increase to 2,000 ppm to 3,000 ppm or even greater! When this occurs, fresh air should be brought into the home either passively or by mechanical means using air cyclers or ventilators.
Carbon monoxide (CO) is a colorless, odorless, and tasteless gas produced by incomplete combustion of carbon fuels. Inhaled CO readily binds to the hemoglobin in red blood cells and decreases the amount of oxygen transported to the body's tissues. Symptoms become clinically apparent when the amount of CO bound to red blood cells reaches approximately 10%. A person at rest would have to inhale 80 ppm of CO for eight hours to reach this 10% carboxyhemoglobin level. OSHA has established the permissible exposure limit for CO at 50 ppm for an eight hour exposure. A malfunctioning gas stove, water heater, furnace, or boiler can give off CO and result in elevated levels in the home. In homes with adequate ventilation, CO concentrations will typically be 2 - 3 ppm.
The Environmental Protection Agency National Ambient Air Quality Standard for CO is 35 ppm for a one-hour exposure and 9 ppm for an eight-hour exposure. Based on this EPA standard, ASHRAE established an IAQ standard of 9 ppm of CO for an eight-hour exposure. Exposure to high concentrations may produce headaches, dizziness, fatigue, and nausea.