Indoor Air Quality (IAQ)

Indoor air quality (IAQ) describes the quality of the air found inside residential, commercial, institutional, and industrial buildings and other confined and indoor spaces. IAQ is primarily discussed in the context of human health, though usage of the term also extends to comfort considerations.

Multiple factors can impact IAQ, with major examples including ventilation, temperature, humidity, construction quality, and the materials used to build and finish interior-facing structures and building components. IAQ can also be affected by airborne contaminants such as dust and mold, and by chemical residues from sources including pesticides, cleaning products, aerosol sprays, and other synthetic materials.

Numerous health risks are associated with consistent exposure to low indoor air quality. The precise risks and their respective severity depend on the causes and extent of the indoor air contamination, but can range from mild discomfort to the development of chronic health conditions and serious diseases, including cancer.

Background

Estimates from the Environmental Protection Agency (EPA) suggest that the average U.S. resident spends approximately 90 percent of their time indoors. Indoor air quality therefore has a strong and direct impact on both short-term and long-term health. Researchers have linked IAQ deficiencies to symptoms including headaches, difficulty concentrating, lethargy, and irritations of the ear, nose, and throat (ENT) system. IAQ is also believed to impact the development and severity of asthmatic respiratory conditions, particularly in children. The World Health Organization (WHO) cites long-term and chronic exposure to poor household indoor air quality as a risk factor for serious diseases and medical conditions including chronic obstructive pulmonary disease (COPD), stroke, heart disease, and cancer. Certain contaminants, such as radon gas and asbestos, have asymptomatic effects but are also known to cause cancer.

The WHO estimates that approximately 2.4 billion people around the world cook using fuel sources such as wood, coal, charcoal, and organic waste material. Most live in low- and middle-income countries (LMICs), where large segments of the population have limited economic access to safer and more efficient cooking equipment. According to Our World in Data, a project affiliated with the University of Oxford, about 4.1 percent of all deaths globally are directly or indirectly caused by exposure to indoor air pollution. Our World in Data also reports that people in low-income countries die from causes related to air pollution at 1,000 times the rates seen in high-income countries.

In the United States, low indoor air quality affects people of all ages, races, and income levels, but the EPA reports that certain population groups are more likely to be affected by indoor air contaminants and pollutants including asbestos, toxic mold, secondhand smoke, and other ENT irritants. These groups include children and the elderly, low-income populations, members of racial minority groups, and tribal and Indigenous peoples. The EPA also notes that relative to outdoor air pollution, indoor environments can contain two to five times the concentration of contaminants, and that indoor environments with the poorest IAQ can have up to 100 times more pollutants than the air found in typical outdoor conditions.

In the United States and globally, residential settings remain the primary area of focus for researchers and advocates investigating low indoor air quality and its impacts. However, IAQ issues extend to practically all other indoor environments where people spend significant amounts of time. These include commercial and retail spaces, office buildings, educational institutions, places of worship, factories and other industrial workplaces, airplanes, public transportation stations and vehicles, and private automobiles, among others.

Global trends indicate that efforts to improve IAQ have seen significant progress in recent decades. According to Our World in Data, nearly every country in the world has posted meaningful declines since 1990 in the number of deaths associated with indoor air pollution. The percentage of global residents with regular access to cleaner cooking fuels has also steadily risen since that time, but was still limited to only 60 percent of the global population as of 2020, according to Our World in Data.

Overview

According to the EPA, the main sources of indoor air pollution in the United States include combustion appliances, tobacco smoke, personal care and household cleaning products, home heating and cooling systems, humidification systems, and contaminants originating from household insulation, flooring and floor treatments, and furnishings made from certain types of pressed wood. High moisture levels, which can facilitate the growth and spread of toxic mold, and external sources of pollution including pesticides, radon gas, and ambient contaminants such as fuel exhaust, can also contribute to IAQ losses in both residential and nonresidential settings. Such issues are also major contributing factors in many LMICs, but people living in lower-income countries are much more likely to suffer negative health impacts related to poor IAQ as a result of cooking with fuel sources that contaminate the air.

Other substances known to negatively affect indoor air quality include biological pollutants, lead, particulate matter, fireplaces and chimneys, and volatile organic compounds (VOCs). Biological pollutants include microbes and pathogens such as viruses and bacteria along with dust, mites, pollen, animal dander, and animal saliva. Lead-based paints have been banned for use in U.S. residences since 1978, but lead can still be introduced to indoor environments through the improper removal of old lead-based paint and other activities including soldering. Particulate matter describes a class of indoor air contaminants that include both liquid and solid particles, which originate from a variety of sources including cooking, combustion, and the smoke produced by wood-burning fireplaces. VOCs are found in many household and industrial products including paints, solvents, aerosols, disinfectants, cleaning products, pesticides, adhesives, photography chemicals, permanent markers, and supplies used in printing and photocopying, among other sources.

Ventilation has strong effects on indoor air quality: well-ventilated interior spaces tend to maintain higher levels of indoor air quality, while improperly or poorly ventilated indoor spaces can easily experience buildups of pollutants, contaminants, and particulates that can reach dangerous levels. Under certain conditions, exchanging indoor air for outdoor air can negatively affect IAQ. For example, residential buildings situated close to high-emission industrial facilities and major traffic routes such as freeways can introduce contaminated air through open windows and other air exchange media.

Numerous readily available devices can measure IAQ in both residential and nonresidential settings. These primarily include specialized monitoring devices that perform regular tests on air samples and report findings to building occupants through built-in displays or data relays to connected devices such as smartphones. Consumers can purchase equipment specifically designed to detect particulate matter, VOCs, and other particularly dangerous sources of indoor air pollution including radon and carbon monoxide. Inexpensive radon gas and carbon monoxide detectors are also widely available and highly recommended, given the potentially deadly effects of exposure to these odorless and invisible vapors.

The EPA cites three main strategies building occupants can use to improve indoor air quality, regardless of setting. These include ventilation, source control, and the use of products and systems that remove contaminants and pollutants from the air. Ventilation-based strategies mainly revolve around exchanging potentially polluted indoor air for cleaner outdoor air by opening windows and doors when weather allows, using fans to accelerate the rate of air exchange, activating vent-based fan systems in areas such as kitchens and bathrooms, and operating window-mounted air conditioning units with their vent controls open.

Source control aims to reduce or eliminate the introduction of contaminants that cause indoor air pollution. For instance, pollutants such as asbestos can be fully contained through specialized sealing, enclosing, removal, and disposal methods. In the United States, building materials containing asbestos have been phased out, but the substance may still be found in any structure that was built or renovated prior to the year 2000. Some other contaminant sources, such as combustion appliances, can be calibrated or configured to reduce the harmful emissions they produce, or replaced with newer models or alternative systems that were designed and manufactured to minimize or eliminate harmful emissions.

Air filtration and purification systems range in size and complexity from small appliances designed for use in a localized area to intricate air-exchange networks that serve an entire house or building. These systems and products vary widely in their ability to remove particulate matter and other contaminants from indoor air, with smaller appliances designed for localized use tending to deliver relatively limited benefits. The EPA also notes that most air filtration and purification systems, including whole-building air filtration networks, may not be able to eliminate gaseous contaminants such as carbon monoxide or radon.

Some people have advocated for the increased use of houseplants as a natural method for removing carbon-based pollutants and other contaminants from indoor air. Some scientific experiments, conducted in laboratory settings, appear to show that houseplants may be able to reduce the concentrations of some ambient pollutants, but their efficacy as a means of protecting or improving IAQ remains inconclusive. The EPA also notes that the excessive watering of houseplants can also cause IAQ declines, as moist soil can accelerate the growth rates and presence of microbes that can negatively affect people with allergies and other respiratory conditions.

Bibliography

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“Improving Indoor Air Quality.” Environmental Protection Agency, 6 July 2022, www.epa.gov/indoor-air-quality-iaq/improving-indoor-air-quality#Air‗Cleaners. Accessed 14 Mar. 2023.

“Indoor Air Quality.” National Institute of Environmental Health Sciences,29 Aug. 2022, www.niehs.nih.gov/health/topics/agents/indoor-air/index.cfm. Accessed 14 Mar. 2023.

“Indoor Air Quality.” Occupational Health and Safety Commission, www.osha.gov/indoor-air-quality. Accessed 14 Mar. 2023.

“Introduction to Indoor Air Quality.” Environmental Protection Agency,5 Dec. 2022, www.epa.gov/indoor-air-quality-iaq/introduction-indoor-air-quality#causes. Accessed 14 Mar. 2023.

Ritchie, Hannah and Max Roser. “Indoor Air Pollution.” Our World in Data, Jan. 2022, ourworldindata.org/indoor-air-pollution#only-60-of-the-world-has-access-to-clean-cooking-fuels. Accessed 14 Mar. 2023.

Taylor-Smith, Kerry. “How Is Air Quality Measured at Home?” Live Science,31 Aug. 2022, www.livescience.com/how-is-air-quality-measured-at-home. Accessed 14 Mar. 2023.

“The Inside Story: A Guide to Indoor Air Quality.” United States Consumer Product Safety Commission, www.cpsc.gov/Safety-Education/Safety-Guides/Home/The-Inside-Story-A-Guide-to-Indoor-Air-Quality. Accessed 14 Mar. 2023.