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Indoor Air Quality

Factors Influencing Indoor Air Quality

Air quality inside of buildings is related to a diverse range of chemical, physical, and biological factors. In any situation, the importance of these many influences can vary greatly, depending on the emission rates of various chemicals, the frequency with which inside air is exchanged with ambient air, the efficiency of atmospheric circulation within the building, and numerous other factors.

In response to the need to conserve energy (and money), modern buildings are well insulated to retain their heat in winter and their coolness in summer. Such buildings receive almost all of their inputs of relatively clean, outside air through their carefully designed, ventilation system. Such systems have only a few, discrete intakes of ambient air, and outputs of "used" air back to the outside, as well as particular, internal-circulation characteristics. It is not possible, for example, to open any windows in many modern office buildings, because this would interfere with pressure gradients and upset the designed balance of the ventilation system. Of course, the ventilation characteristics of many recently constructed modern buildings have a substantial influence on the quality of the internal atmosphere of the structure.

When ventilation systems are operated with a view to saving energy, there are relatively few exchanges of indoor air with relatively clean, ambient air. Sometimes, too much attention to the efficiency of energy use in airtight buildings can lead to the build-up of excessive concentrations of indoor air pollutants, because of on-going emissions of chemicals within the building.

In addition, in some cases the intake pipes for ambient air to buildings are located too close to ducts that exhaust contaminated air from the same or a nearby building. This faulty design can lead to the intake of poor-quality outside air, impairing atmospheric quality within the building. Similarly, sinks and other water drains installed without proper systems to prevent the back-up of sewer gases can lead to incursions of noxious smells and chemicals into buildings. In other cases, the poor faulty design or operation of internal ventilation systems can lead to the development of local zones of restricted air circulation, which can develop into areas of degraded air quality within the building.

Clearly, the appropriate design and operation of airhandling systems in modern, air-tight buildings is a critical factor affecting indoor air quality.

Emission rates of chemicals and dusts within buildings are affected by many factors. The sorts of materials of which the building or its furnishings are constructed may be important in this regard. For example, minerals contained in cement or in stone may emit gaseous radon, or may slowly degenerate to release fine, inhalable dusts. The oxidation of materials in humidification systems and ventilation duct works can also generate large quantities of fine, metallic dusts, as can the wear of painted surfaces. Many composite wood products, such as plywood and particle boards, emit gaseous formaldehyde, as do many types of synthetic fabrics.

Chemicals may also be emitted to the internal air from laboratories that do not have adequate fume hoods to vent noxious vapors and gases to the atmosphere. Similarly, industrial processes involving chemicals may be an important source of emissions in some buildings. The use of some kinds of solvents, detergents, and other substances during cleaning and sanitation of the building may also be important.

Even the human occupants of buildings emit large quantities of gases and vapors that affect air quality, for example, carbon dioxide. Also, although the practice is increasingly being restricted, many people smoke tobacco inside of buildings, releasing diverse chemicals to the atmosphere. More than 2,000 chemicals have been identified in tobacco fumes, including various carcinogens such as benzo(a)pyrene and nickel carbonyl, as well as many other toxic chemicals.

These are just a few of the diverse sources of emissions of gases, vapors, and particulates inside of modern buildings. All of these sources of emissions contribute to the degradation of the quality of the indoor atmosphere.

Some buildings can develop indoor-air problems associated with fungi and other microbes that grow in damp places, and whose spores or other so-called bioaerosols become spread within the building through the ventilation system. This microbial problem can develop in systems designed to humidify the indoor air, in places where stagnant water accumulates within the aircirculation system, or in other damp places. Some people may be allergic to these spores, or in rare cases the microorganisms may be pathogens. The latter is the case of Legionnaires' disease, a rare condition involving pathogenic bacteria spread through the ventilation system of buildings.

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