An assessment of air quality in buildings and homes is based on physical and chemical monitoring of contaminants, physiological measurements, or psychosocial perceptions. Indoor air quality measures can also refer to the air inside types of transportation such as airplanes, trains, buses, and passenger cars. Factors contributing to the quality of indoor air include lighting, ergonomics, thermal comfort, tobacco smoke, noise, ventilation, and psychosocial or work-organizational factors such as employee stress and satisfaction. Sick building syndrome (SBS) and building-related illness (BRI) are responses to indoor air pollution commonly described by office workers. Most symptoms are nonspecific; they progressively worsen during the week, occur more frequently in the afternoon, and disappear on the weekend.
Gases leak indoors from the polluted outdoor environment, but more often the serious pollutants arise from processes that take place indoors. There has been particular concern with indoor air quality regarding the generation of nitrogen oxides by sources such as gas stoves. Similarly formaldehyde (CH2O) from insulating foams causes illnesses and adds to concerns about human exposure to a substance that may induce cancer over a period of time. In the early twenty-first century, it became clear that radon (Rn) leaks from the ground can expose some members of the public to high levels of this radioactive gas within their own homes. Cancers may also result from the emanation of solvents from consumer products, glues, paints, and mineral fibers (asbestos). More generally, these compounds and a range of biological materials, animal hair, skin and pollen spores, and dusts can cause allergic reactions in some people. At one end of the spectrum, these simply cause annoyance, but in extreme cases, such as found with the bacterium Legionella, a large number of deaths can occur.
There are also important issues surrounding the effects of indoor air pollutants on materials. Many industries, especially the electronics industry, must take great care over the purity of indoor air where a speck of dust can destroy a microchip or low concentrations of air pollutants change the composition of surface films in component design. Museums must care for delicate, priceless objects over long periods of time, so precautions must be taken to protect delicate dyes from the effects of photochemical smog, paper and books from sulfur dioxide, and metals from sulfide gases.
The prominence of IAQ issues has risen in part due to well-publicized incidents involving outbreaks of Legionnaires' disease, Pontiac fever, SBS, multiple chemical sensitivity, and asbestos mitigation in public buildings such as schools. Legionnaire's disease, for example, caused 29 deaths in 1976 in a Philadelphia, Pennsylvania, hotel due to infestation of the building's air conditioning system by bacteria now called Legionella pneumophila. This microbe affects the gastrointestinal tract, kidneys, and central nervous system. It also causes the nonfatal Pontiac fever.
IAQ is important to the general public for several reasons. First, individuals typically spend the vast majority (80% to 90%) of their time indoors. Second, an emphasis on energy conservation measures, such as reducing air exchange rates in ventilation systems and using more energy efficient but synthetic materials, has increased levels of air contaminants in offices and homes. Newer buildings are often airtight and have fewer cracks and openings so minimal fresh air enters these buildings. Low ventilation and exchange rates can result in increased indoor levels of carbon monoxide (CO), nitrogen oxides (NOx), ozone (O3), volatile organic compounds, bioaerosols, pesticides, and high levels of second-hand tobacco smoke. Thus, many contaminants are found indoors at levels that greatly exceed outdoor levels. Third, an increasing number of synthetic chemicals—found in building materials, furnishing, cleaning and hygiene products—are used indoors. Fourth, studies show that exposure to indoor contaminants such as radon (Rn), asbestos, and tobacco smoke pose significant health risks. Fifth, poor IAQ is thought to adversely affect child development and lower productivity in the adult population. Demands for IAQ investigations of problem buildings increased through the 1990s and early 2000s, and many buildings have been identified as having IAQ problems.
Indoor air contains many contaminants at varying but generally low concentration levels. These cause indoor air pollution and can also produce various symptoms.
Common contaminants include radon and radon progeny from the entry of soil gas and groundwater; from concrete and other mineral-based building materials; tobacco smoke from cigarette and pipe smoking; formaldehyde from polyurethane foam insulation and building materials; volatile organic compounds (VOCs) emitted from binders and resins in carpets, furniture, or building materials, as well as VOCs used in dry cleaning processes and as propellants and constituents of personal use and cleaning products, such as hair sprays and polishes; pesticides and insecticides; carbon monoxide, nitrogen oxides, and other combustion productions from gas stoves, appliances, and vehicles; asbestos from high temperature insulation; and biological contaminants, including viruses, bacteria, molds, pollen, dust mites, and indoor and outdoor biota. Many or most of these contaminants are present at low levels in all indoor environments. High humidity and temperatures can result in increased concentration of some pollutants.
The quality of indoor air can change rapidly over time and from room to room. Many diverse sources emit various physical and chemical forms of contaminants. Some releases are slow and continuous, such as out-gassing associated with building and furniture materials, whereas others are nearly instantaneous, like in the use of cleaners and aerosols. Many building surfaces demonstrate significant interactions with contaminants in the form of sorption-desorption processes. Building-specific variation in air exchange rates, mixing, filtration, building and furniture surfaces, and other factors alter dispersion mechanisms and contaminant lifetimes. Most buildings employ filters that can remove particles and aerosols. Filtration systems do not effectively remove very small particles and have no effect on gases, vapors, and odors.
The diagnosis of medical problems associated with indoor air pollution is difficult to differentiate from other common causes of respiratory illnesses. A diagnosis of respiratory problems caused by indoor air pollutants is based partially on the presence of common symptoms such as respiratory irritation, shortness of breath, coughing and wheezing, nausea, and headaches. It is also based on the environment within the indoor setting, such as the cleanliness of the volume, the introduction of new furniture, carpet, draperies, or other materials, and other such factors that can cause indoor air pollution.
Signs that indoor air pollution could be present include:
Sources of poor indoor air quality originate from numerous sources. Some of them include:
The treatment of illnesses caused by air pollution depends on the specific illness present. However, generally, anyone with chronic lung or heart disease caused by indoor air pollution should get an annual influenza (flu) shot. People with cardiopulmonary disease related to indoor air pollution should seek medical treatment that parallels those treatments for asthma, chronic obstructive pulmonary disease (COPD), congestive heart failure, and coronary artery disease.
Indoor air quality can be improved with regular and aggressive cleaning methods, which helps remove the source of as many allergens as possible, including those from carpets, drapes and other window dressings, nonencased mattresses and pillows, materialstuffed furniture, pets, and stuffed toys.
The Asthma and Allergy Foundation of America has identified the following ways for improving indoor air quality:
Outdoor air enters indoor spaces via three different methods termed infiltration, natural ventilation, and mechanical ventilation. In infiltration, air enters through cracks and openings around windows, flooring, doors, and walls. Natural ventilation is achieved by opening windows and doors. Mechanical ventilation can be accomplished through the use of outdoorvented fans or air handling systems that use fans and ducts to remove air from inside and to introduce outdoor air inside. By removing indoor air and replacing it with outdoor air, it is possible to remove contaminants or pollutants that have built up inside. Ventilation and air exchange units designed in the heating and cooling systems of buildings are designed to diminish levels of these contaminants by dilution. In most buildings, however, ventilation systems are turned off at night after working hours, leading to an increase in contaminants through the night. Though operation and maintenance issues are estimated to cause the bulk of IAQ problems, deficiencies in the design of the heating, ventilating, and air conditioning (HVAC) system can cause problems as well. For example, locating a building's fresh air intake near a truck loading dock will bring diesel fumes and other noxious contaminants into the building.
See also Air pollution ; Asbestos ; Asthma ; Chemical sensitivity ; Legionnaire's disease ; Ozone ; Sick building syndrome ; Smog ; Smoking ; Viruses .
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Agency for Toxic Substances and Disease Registry, 4770 Buford Hwy. NE, Atlanta, GA, 30341, (800) 232-4636, http://www.atsdr.cdc.gov .
American Lung Association, 1301 Pennsylvania Ave. NW, Ste. 800, Washington, DC, 20004, (202) 785-3355, firstname.lastname@example.org, http://www.lungusa.org .
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