Indoor air quality

Indoor air quality (IAQ) is a term referring to the air quality within and around buildings and structures, especially as it relates to the health and comfort of building occupants.

IAQ can be affected by microbial contaminants (mold, bacteria), gases (including carbon monoxide, radon, volatile organic compounds), particulates, or any mass or energy stressor that can induce adverse health conditions. Indoor air is becoming an increasingly more concerning health hazard than outdoor air. Using ventilation to dilute contaminants, filtration, and source control are the primary methods for improving indoor air quality in most buildings.

Determination of IAQ involves the collection of air samples, monitoring human exposure to pollutants, collection of samples on building surfaces and computer modelling of air flow inside buildings.

Common pollutants

Radon

Main article: Radon

Radon is an invisible, radioactive atomic gas that results from the radioactive decay of radium, which may be found in rock formations beneath buildings or in certain building materials themselves. Radon is probably the most pervasive serious hazard for indoor air in the United States and Europe, probably responsible for tens of thousands of deaths from lung cancer each year.^[1] There are relatively simple tests for radon gas, but these tests are not commonly done, even in areas of known systematic hazards. Radon is a heavy gas and thus will tend to accumulate at the floor level. Building materials can actually be a significant source of radon, but little testing is done for stone, rock or tile products brought into building sites; radon accumulation is greatest for well insulated homes.^[2] The half life for radon is 3.8 days, indicating that once the source is removed, the hazard will be greatly reduced within a few weeks. However annually thousands of people go to radon contaminated mines for purposeful exposure to help with the symptoms of arthritis without any serious known health effects,^{[citation needed]} though lung cancer can take many years to develop. Radon mitigation methods include sealing concrete slab floors, basement foundations, water drainage systems, or by increasing ventilation.^[3] They are usually cost effective and can greatly reduce or even eliminate the contamination and the associated health risks.

Molds and other allergens

Main articles: Mold health issues and Mold growth, assessment, and remediation

These biological chemicals can arise from a host of means, but there are two common classes: (a) moisture induced growth of mold colonies and (b) natural substances released into the air such as animal dander and plant pollen. Moisture buildup inside buildings may arise from water penetrating compromised areas of the building envelope or skin, from plumbing leaks, from condensation due to improper ventilation, or from ground moisture penetrating a building part. In areas where cellulosic materials (paper and wood, including drywall) become moist and fail to dry within 48 hours, mold mildew can propagate and release allergenic spores into the air.

In many cases, if materials have failed to dry out several days after the suspected water event, mold growth is suspected within wall cavities even if it is not immediately visible. Through a mold investigation, which may include destructive inspection, one should be able to determine the presence or absence of mold. In a situation where there is visible mold and the indoor air quality may have been compromised, mold remediation may be needed. Mold testing and inspections should be done by an independent investigator to avoid any conflict of interest and to insure accurate results; free mold testing offered by remediation companies is not recommended.

There are some varieties of mold that contain toxic compounds (mycotoxins). However, exposure to hazardous levels of mycotoxin via inhalation is not possible in most cases, as toxins are produced by the fungal body and are not at significant levels in the released spores. The primary hazard of mold growth, as it relates to indoor air quality, comes from the allergenic properties of the spore cell wall. More serious than most allergenic properties is the ability of mold to trigger episodes in persons that already have asthma, a serious respiratory disease.

Mold is always associated with moisture,^[4] and its growth can be inhibited by keeping humidity levels below 50%. Moisture problems causing mold growth can be direct such as a water leaks and/or indirect such as condensation due to humidity levels.

Carbon monoxide

One of the most acutely toxic indoor air contaminants is carbon monoxide (CO), a colorless, odorless gas that is a byproduct of incomplete combustion of fossil fuels. Common sources of carbon monoxide are tobacco smoke, space heaters using fossil fuels, defective central heating furnaces and automobile exhaust. Improvements in indoor levels of CO are systematically improving from increasing numbers of smoke-free restaurants and other legislated non-smoking buildings. By depriving the brain of oxygen, high levels of carbon monoxide can lead to nausea, unconsciousness and death. According to the American Conference of Governmental Industrial Hygienists (ACGIH), the time-weighted average (TWA) limit for carbon monoxide (630-08-0) is 25 ppm^[vague].

Volatile organic compounds

Volatile organic compounds (VOCs) are emitted as gases from certain solids or liquids. VOCs include a variety of chemicals, some of which may have short- and long-term adverse health effects. Concentrations of many VOCs are consistently higher indoors (up to ten times higher) than outdoors. VOCs are emitted by a wide array of products numbering in the thousands. Examples include: paints and lacquers, paint strippers, cleaning supplies, pesticides, building materials and furnishings, office equipment such as copiers and printers, correction fluids and carbonless copy paper, graphics and craft materials including glues and adhesives, permanent markers, and photographic solutions.^[5]

Organic chemicals are widely used as ingredients in household products. Paints, varnishes, and wax all contain organic solvents, as do many cleaning, disinfecting, cosmetic, degreasing, and hobby products. Fuels are made up of organic chemicals. All of these products can release organic compounds during usage, and, to some degree, when they are stored. Testing emissions from building materials used indoors has become increasingly common for floor coverings, paints, and many other important indoor building materials and finishes.^[6]

Several initiatives envisage to reduce indoor air contamination by limiting VOC emissions from products. There are regulations in France and in Germany, and numerous voluntary ecolabels and rating systems containing low VOC emissions criteria such as EMICODE^[7], M1^[8], Blue Angel^[9] and Indoor Air Comfort^[10] in Europe, as well as California Standard CDPH Section 01350^[11] and several others in the USA. These initiatives changed the marketplace where an increasing number of low-emitting products has become available during the last decades.

At least 18 Microbial VOCs (MVOCs) have been characterized^[12][13] including 1-octen-3-ol, 3-methyl furan, 2-pentanol, 2-hexanone, 2-heptanone, 3-octanone, 3-octanol, 2-octen-1-ol, 1-octene, 2-pentanone, 2-nonanone, Borneol, Geosmin, 1-butanol, 3-methyl-1-butanol, 3-methyl-2-butanol, and thujopsene. The first of these compounds is called mushroom alcohol. The last four are products of Stachybotrys chartarum, which has been linked with sick building syndrome.^[12]

Legionella

Legionellosis or Legionnaire's Disease is caused by a waterborne bacterium Legionella that grows best in slow-moving or still, warm water. The primary route of exposure is aerosolization, most commonly from evaporative cooling towers or showerheads. A common source of Legionella in commercial buildings is from poorly placed or maintained evaporative cooling towers, which often release aerosolized water that may enter nearby ventilation intakes. Outbreaks in medical facilities and nursing homes, where patients are immuno-suppressed and immuno-weak, are the most commonly reported cases of Legionellosis. More than one case has involved outdoor fountains in public attractions. The presence of Legionella in commercial building water supplies is highly under-reported, as healthy people require heavy exposure to acquire infection.

Legionella testing typically involves collecting water samples and surface swabs from evaporative cooling basins, shower heads, faucets, and other locations where warm water collects. The samples are then cultured and colony forming units (cfu) of Legionella are quantified as cfu/Liter.

Legionella is a parasite of protazoans such as amoeba, and thus requires conditions suitable for both organisms. The bacterium forms a biofilm which is resistant to chemical and antimicrobial treatments, including chlorine. Remediation for Legionella outbreaks in commercial buildings vary, but often include very hot water flushes (160 °F; 70 °C), sterilization of standing water in evaporative cooling basins, replacement of shower heads, and in some cases flushes of heavy metal salts. Preventative measures include adjusting normal hot water levels to allow for 120°F at the tap, evaluating facility design layout, removing faucet aerators, and periodic testing in suspect areas.

Asbestos fibers

The U.S. Federal Government (www.osha.gov) and some States have set standards for acceptable levels of asbestos fibers in indoor air. Many common building materials used before 1975 contain asbestos, such as some floor tiles, ceiling tiles, taping muds, pipe wrap, mastics and other insulation materials. Normally significant releases of asbestos fiber do not occur unless the building materials are disturbed, such as by cutting, sanding, drilling or building remodelling. There are particularly stringent regulations applicable to schools.

Inhalation of asbestos fibers over long exposure times is associated with increased incidence of lung cancer.

Asbestos is found in older homes and buildings, but it is most dangerous in schools and industrial settings. It was once widely used in shingles, fireproofing, heating systems and floor and ceiling, tiles in older buildings. When asbestos-containing material is damaged or disintegrates, microscopic fibers are dispersed into the air. The risk of lung cancer from inhaling asbestos fibers is also greater to smokers. The symptoms of the disease do not usually appear until about 20 to 30 years after the first exposure to asbestos. Removal of asbestos-containing materials is not always optimal because the fibers can be spread into the air during the removal process. A management program for intact asbestos-containing materials is often recommended instead.

Carbon dioxide

Carbon dioxide (CO₂) is a surrogate for indoor pollutants emitted by humans and correlates with human metabolic activity. Carbon dioxide at levels that are unusually high indoors may cause occupants to grow drowsy, get headaches, or function at lower activity levels. Humans are the main indoor source of carbon dioxide. Indoor levels are an indicator of the adequacy of outdoor air ventilation relative to indoor occupant density and metabolic activity. To eliminate most Indoor Air Quality complaints, total indoor carbon dioxide should be reduced a difference of less than 600 ppm above outdoor levels. NIOSH considers that indoor air concentrations of carbon dioxide that exceed 1,000 ppm are a marker suggesting inadequate ventilation. ASHRAE recommends that carbon dioxide levels not exceed 700 ppm above outdoor ambient levels.^[14] The UK standards for schools say that carbon dioxide in all teaching and learning spaces, when measured at seated head height and averaged over the whole day should not exceed 1,500 ppm. The whole day refers to normal school hours (i.e. 9.00am to 3.30pm) and includes unoccupied periods such as lunch breaks. European standards limit carbon dioxide to 3500 ppm. OSHA limits carbon dioxide concentration in the workplace to 5,000 ppm for prolonged periods, and 35,000 ppm for 15 minutes.

Ozone

Ozone is produced by ultraviolet light from the Sun hitting the Earth's atmosphere (especially in the ozone layer), lightning, certain electric devices (such as air ionisers), and as a byproduct of other types of pollution.

Ozone exists in greater concentrations at altitudes commonly flown by passenger jets. Reactions between ozone and onboard substances, including skin oils and cosmetics, can produce toxic chemicals as byproducts. Ozone itself is also irritating to lung tissue and harmful to human health. Larger jets have ozone filters to reduce the cabin concentration to safer and more comfortable levels.^[15]

Outdoor air used for ventilation may have sufficient ozone to react with common indoor pollutants as well as skin oils and other common indoor air chemicals or surfaces. Particular concern is warranted when using "green" cleaning products based on citrus or terpene extracts as these chemicals react very quickly with ozone to form toxic and irritating chemicals as well as fine and ultrafine particles. Ventilation with outdoor air containing elevated ozone concentrations may complicate remediation attempts.^[16]

Developing countries

Main article: Indoor air pollution in developing nations

A major source of indoor air pollution in developing countries is the burning of biomass (e.g. wood, charcoal, dung, or crop residue) for heating and cooking.^[17] The resulting exposure to high levels of particulate matter resulted in between 1.5 million and 2 million deaths in 2000.^[18]

Effect of indoor plants

Main article: List of air-filtering plants

Houseplants together with the medium in which they are grown can reduce components of indoor air pollution, particularly volatile organic compounds (VOC) such as benzene, toluene, and xylene. Plants can also remove CO₂, which is correlated with lower work performance, from indoor areas.^[19] The effect was investigated in one study by NASA for use in space colonies.^[20] Plants also appear to reduce airborne microbes, molds, and increase humidity.^[21] However the presence of plants indoors has also been associated with higher humidity and airborne fungal concentrations.

When CO2 concentrations are elevated indoors relative to outdoor concentrations, it is only an indicator that ventilation is inadequate to remove metabolic products associated with human occupancy. Plants require CO2 to grow and release oxygen when they consume CO2. A study published in the journal Environmental Science & Technology considered uptake rates of ketones and aldehydes by the peace lily (Spathiphyllum clevelandii) and golden pothos (Epipremnum aureum.) Akira Tani and C. Nicholas Hewitt found "Longer-term fumigation results revealed that the total uptake amounts were 30−100 times as much as the amounts dissolved in the leaf, suggesting that volatile organic carbons are metabolized in the leaf and/or translocated through the petiole." ^[22] It is worth noting the researchers sealed the plants in Teflon bags. "No VOC loss was detected from the bag when the plants were absent. However, when the plants were in the bag, the levels of aldehydes and ketones both decreased slowly but continuously, indicating removal by the plants" ^[23]

While results do indicate house plants may be effective at removing some VOCs from air supplies, many studies neglect to consider ventilation, reductions when faced with continuous emission rather than burst, and other real world factors. A review of studies between 1989 and 2006 on the performance of houseplants as air cleaners, presented at the Healthy Buildings 2009 conference in Syracuse, NY, concluded "...indoor plants have little, if any, benefit for removing indoor air of VOC in residential and commercial buildings." ^[24]

Since high humidity is associated with increased mold growth, allergic responses, and respiratory responses, the presence of additional moisture from houseplants may not be desirable in all indoor settings.^[25]

HVAC design

Environmentally Sustainable Design concepts also include aspects related to the commercial and residential heating, ventilation and air-conditioning (HVAC) industry. Among several considerations, one of the topics to attended to is the issue of indoor air quality throughout the design and construction stages of a building's life.

One technique to reduce energy consumption while maintaining adequate air quality, is demand controlled ventilation. Instead of setting throughput at a fixed air replacement rate, carbon dioxide sensors are used to control the rate dynamically, based on the emissions of actual building occupants.

For the past several years, there have been many debates among indoor air quality specialists about the proper definition of indoor air quality and specifically what constitutes "acceptable" indoor air quality.

One way of quantitatively ensuring the health of indoor air is by the frequency of effective turnover of interior air by replacement with outside air. In the UK, for example, classrooms are required to have 2.5 outdoor air changes per hour. In halls, gym, dining, and physiotherapy spaces, the ventilation should be sufficient to limit carbon dioxide to 1,500 ppm. In the USA, and according to ASHRAE Standards, ventilation in classrooms is based on the amount of outdoor air per occupant plus the amount of outdoor air per unit of floor area, not air changes per hour. Since carbon dioxide indoors comes from occupants and outdoor air, the adequacy of ventilation per occupant is indicated by the concentration indoors minus the concentration outdoors. The value of 615 ppm above the outdoor concentration indicates approximately 15 cubic feet per minute of outdoor air per adult occupant doing sedentary office work where outdoor air contains 385 ppm, the current global average atmospheric CO₂ concentration. In classrooms, the requirements in the ASHRAE standard 62.1, Ventilation for Acceptable Indoor Air Quality, would typically result in about 3 air changes per hour, depending on the occupant density. Of course the occupants aren't the only source of pollutants, so outdoor air ventilation may need to be higher when unusual or strong sources of pollution exist indoors. When outdoor air is polluted, then bringing in more outdoor air can actually worsen the overall quality of the indoor air and exacerbate some occupant symptoms related to outdoor air pollution.^[26] Generally, outdoor country air is better than indoor city air. Exhaust gas leakages can occur from furnace metal exhaust pipes that lead to the chimney when there are leaks in the pipe and the pipe gas flow area diameter has been reduced.

The use of air filters can trap some of the air pollutants. The Department of Energy's Energy Efficiency and Renewable Energy section wrote "[Air] Filtration should have a Minimum Efficiency Reporting Value (MERV) of 13 as determined by ASHRAE 52.2-1999."^[27] Air filters are used to reduce the amount of dust that reaches the wet coils. Dust can serve as food to grow molds on the wet coils and ducts and can reduce the efficiency of the coils.

Moisture management and humidity control requires operating HVAC systems as designed. Moisture management and humidity control may conflict with efforts to try to optimize the operation to conserve energy. For example, Moisture management and humidity control requires systems to be set to supply Make Up Air at lower temperatures (design levels), instead of the higher temperatures sometimes used to conserve energy in cooling-dominated climate conditions. However, for most of the US and many parts of Europe and Japan, during the majority of hours of the year, outdoor air temperatures are cool enough that the air does not need further cooling to provide thermal comfort indoors. However, high humidity outdoors creates the need for careful attention to humidity levels indoors. High humidities give rise to mold growth and moisture indoors is associated with a higher prevalence of occupant respiratory problems.

The "dew point temperature" is an absolute measure of the moisture in air. Some facilities are being designed with the design dew points in the lower 50's °F, and some in the upper and lower 40's °F. Some facilities are being designed using desiccant wheels with gas fired heater to dry out the wheel enough to get the required dew points. On those systems, after the moisture is removed from the make up air, a cooling coil is used to lower the temperature to the desired level.

Commercial buildings, and sometimes residential, are often kept under slightly-positive air pressure relative to the outdoors to reduce infiltration. Limiting infiltration helps with moisture management and humidity control.

Dilution of indoor pollutants with outdoor air is effective to the extent that outdoor air is free of harmful pollutants. Ozone in outdoor air occurs indoors at reduced concentrations because ozone is highly reactive with many chemicals found indoors. The products of the reactions between ozone and many common indoor pollutants include organic compounds that may be more odorous, irritating, or toxic than those from which they are formed. These products of ozone chemistry include formaldehyde, higher molecular weight aldehydes, acidic aerosols, and fine and ultrafine particles, among others. The higher the outdoor ventilation rate, the higher the indoor ozone concentration and the more likely the reactions will occur, but even at low levels, the reactions will take place. This suggests that ozone should be removed from ventilation air, especially in areas where outdoor ozone levels are frequently high. Recent research has shown that mortality and morbidity increase in the general population during periods of higher outdoor ozone and that the threshold for this effect is around 20 parts per billion (ppb).

Building ecology

It is common to assume that buildings are simply inanimate physical entities, relatively stable over time. This implies that there is little interaction between the triad of the building, what’s in it (occupants and contents), and what’s around it( the larger environment). We commonly see the overwhelming majority of the mass of material in a building as relatively unchanged physical material over time. In fact, the true nature of buildings can be viewed as the result of a complex set of dynamic interactions among their physical, chemical, and biological dimensions. Buildings can be described and understood as complex systems. Research applying the approaches ecologists use to the understanding of ecosystems can help increase our understanding. “Building ecology “ is proposed here as the application of those approaches to the built environment considering the dynamic system of buildings, their occupants, and the larger environment.

Buildings constantly evolve as a result of the changes in the environment around them as well as the occupants, materials, and activities within them. The various surfaces and the air inside a building are constantly interacting, and this interaction results in changes in each. For example, we may see a window as changing slightly over time as it becomes dirty, then is cleaned, accumulates dirt again, is cleaned again, and so on through its life. In fact, the “dirt” we see may be evolving as a result of the interactions among the moisture, chemicals, and biological materials found there.

Buildings are designed or intended to respond actively to some of these changes in and around them with heating, cooling, ventilating, air cleaning or illuminating systems. We clean, sanitize, and maintain surfaces to enhance their appearance, performance, or longevity. In other cases, such changes subtly or even dramatically alter buildings in ways that may be important to their own integrity or their impact on building occupants through the evolution of the physical, chemical, and biological processes that define them at any time. We may find it useful to combine the tools of the physical sciences with those of the biological sciences and, especially, some of the approaches used by scientists studying ecosystems, in order to gain an enhanced understanding of the environments in which we spend the majority of our time, our buildings.

Building ecology was first described by Hal Levin in an article in the April 1981 issue of Progressive Architecture magazine. A longer discussion of Building ecology can be found at ^[28] and extensive resources can be found on the Building Ecology web site ^[29] Building ecology.com.

Institutional programs

The topic of IAQ has become popular due to the greater awareness of health problems caused by mold and triggers to asthma and allergies. Awareness has also been increased by the involvement of the United States Environmental Protection Agency. They have developed an "IAQ Tools for Schools" program to help improve the indoor environmental conditions in educational institutions (see external link below).

The National Institute for Occupational Safety and Health conducts Health Hazard Evaluations (HHEs) in workplaces at the request of employees, authorized representative of employees, or employers, to determine whether any substance normally found in the place of employment has potentially toxic effects, including indoor air quality.^[30]

A variety of scientists work in the field of indoor air quality including chemists, physicists, mechanical engineers, biologists, bacteriologists and computer scientists. Some of these professionals are certified by organizations such as the American Industrial Hygiene Association, the American Indoor Air Quality Council and the Indoor Environmental Air Quality Council.

On the international level, the International Society of Indoor Air Quality and Climate (ISIAQ), formed in 1991, organizes two major conferences, the Indoor Air and the Healthy Buildings series.^[31] ISIAQ's journal Indoor Air is published 6 times a year and contains peer-reviewed scientific papers with an emphasis on interdisciplinary studies including exposure measurements, modeling, and health outcomes.^[32]

See also

• Air Quality Index
• Air Pollution Index
• Council-certified Indoor Environmental Consultant
• Council-certified Indoor Air Quality Manager
• Environmental management
• Green Cleaning
• GREENGUARD Environmental Institute
• Guatemala Stove Project
• HVAC
• Home performance
• Indoor bioaerosol
• International Association of Certified Indoor Air Consultants (IAC2)
• List of air-filtering plants
• Mold health issues
• Mold growth, assessment, and remediation
• Olfactory fatigue
• Phase I Environmental Site Assessment
• Radon
• Radon mitigation
• Room air distribution
• Sick Building Syndrome
• Thermal comfort
• UVGI

References

1. ^ U.S. EPA Indoor Environment Division, Radon
2. ^ C.Michael Hogan and Sjaak Slanina. 2010, Air pollution. Encyclopedia of Earth. eds. Sidney Draggan and Cutler Cleveland]. National Council for Science and the Environment. Washington DC
3. ^ "Radon Mitigation Methods". Radon Solution—Raising Radon Awareness. http://radon-solution.com/pg_mitigation_methods.php. Retrieved 2008-12-02. 
4. ^ of WHO guidelines for indoor air quality: dampness and mould. Report on a working group meeting, 17-18 October 2007”
5. ^ U.S. EPA IAQ - Organic chemicals
6. ^ California IAQ Information: Volatile Organic Compounds
7. ^ EMICODE
8. ^ M1
9. ^ Blue Angel
10. ^ Indoor Air Comfort
11. ^ CDPH Section 01350
12. ^ ^{a b} "Smelly Moldy Houses". http://www.bioidea.net/resources/smelly_houses/. 
13. ^ Meruva NK, Penn JM, Farthing DE (2004 Nov). "Rapid identification of microbial VOCs from tobacco molds using closed-loop stripping and gas chromatography/time-of-flight mass spectrometry". J Ind Microbiol Biotechnol. 31 (10): 482–8. PMID 15517467. 
14. ^ Indoor Environmental Quality: Building Ventilation. National Institute for Occupational Safety and Health. Accessed 2008-10-08.
15. ^ Study: Bad In-Flight Air Exacerbated by Passengers Talk of the Nation, National Public Radio. September 21, 2007.
16. ^ Outdoor ozone and building related symptoms in the BASE study
17. ^ Duflo E, Greenstone M, Hanna R (2008). "Indoor air pollution, health and economic well-being". S.A.P.I.EN.S. 1 (1). http://sapiens.revues.org/index130.html. 
18. ^ Ezzati M, Kammen DM (November 2002). "The health impacts of exposure to indoor air pollution from solid fuels in developing countries: knowledge, gaps, and data needs". Environ Health Perspect. 110 (11): 1057–68. doi:10.1289/ehp.021101057. PMC 1241060. PMID 12417475. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1241060. 
19. ^ Tarran et al. (2007). USE OF LIVING POT-PLANTS TO CLEANSE INDOOR AIR–RESEARCH REVIEW.
20. ^ Wolverton BC, Johnson A, Bounds K. (1989). Interior Landscape Plants for Indoor Pollution Abatement. NASA.
21. ^ BC Wolverton, JD Wolverton. (1996). Interior plants: their influence on airborne microbes inside energy-efficient buildings. Journal of the Mississippi Academy of Sciences.
22. ^ Akira Tani and C. Nicholas Hewitt "Uptake of Aldehydes and Ketones at Typical Indoor Concentrations by Houseplants" Enivronmental Science & Technology, American Chemical Society, October 6, 2009 [1]
23. ^ S Down. Spectroscopynow.com (2009) "Houseplants as air fresheners"
24. ^ JR Girman, T Phillips, H Levin. "Critical Review: How Well Do House Plants Perform as Indoor Air Cleaners?". Healthy Buildings 2009, Syracuse, NY. [2]
25. ^ Institute of Medicine, National Academy of Sciences, 2004. "Damp Indoor Spaces and Health" Damp Indoor Spaces and Health. National Academy Press
26. ^ "Major Study Shows: Outdoor Air Quality Matters: Ozone, Filters, and SBS"
27. ^ DOE EERE Indoor Air Quality - MERV 13 Air Filters
28. ^ [3]
29. ^ [4]
30. ^ NIOSH Topic Area - Indoor Environmental Quality
31. ^ Isiaq.Org
32. ^ Indoor Air: International Journal of Indoor Environment and Health - Journal Information

• Salthammer, T., ed (1999). Organic Indoor Air Pollutants — Occurrence, Measurement, Evaluation. Wiley-VCH. ISBN 3527296220. 
• Spengler, J.D., Samet, J.M. (1991). Indoor air pollution: A health perspective. Baltimore: Johns Hopkins University Press. ISBN 0801841259. 
• Spengler, J.D., Samet, J.M. & McCarthy, J.F. (2001). Indoor Air Quality Handbook. NY: McGraw–Hill. ISBN 0-07-445549-4. 
• Tichenor, B. (1996). Characterizing Sources of Indoor Air Pollution and Related Sink Effects. ASTM STP 1287. West Conshohocken, PA: ASTM. ISBN 0-8031-2030-3. 
• http://www.epa.gov/ebtpages/airindoorairpollution.html - Website of the United States Environmental Protection Agency (US EPA)
• Study: Bad In-Flight Air Exacerbated by Passengers Talk of the Nation, National Public Radio. September 21, 2007.
• Outdoor ozone and building related symptoms in the BASE study

External links

• US Environmental Protection Agency info on IAQ
• Government of Hong Kong Occupational Safety and Health Council, Air Contaminants in the Workplace
• American Chemistry Council on IAQ
• Indoor Air Quality at Health Canada