indoor air quality#Volatile organic compounds

For health reasons it is crucial to breathe clean air, free from chemicals and toxicants as much as possible. It is estimated that humans spend approximately 90% of their lifetime indoors{{cite journal |last1=Klepeis |first1=Neil E |last2=Nelson |first2=William C |last3=Ott |first3=Wayne R |last4=Robinson |first4=John P |last5=Tsang |first5=Andy M |last6=Switzer |first6=Paul |last7=Behar |first7=Joseph V |last8=Hern |first8=Stephen C |last9=Engelmann |first9=William H |title=The National Human Activity Pattern Survey (NHAPS): a resource for assessing exposure to environmental pollutants |journal=Journal of Exposure Science & Environmental Epidemiology |date=July 2001 |volume=11 |issue=3 |pages=231–252 |doi=10.1038/sj.jea.7500165 |pmid=11477521 |bibcode=2001JESEE..11..231K |osti=785282 |s2cid=22445147 |url=https://digital.library.unt.edu/ark:/67531/metadc719357/ |access-date=March 30, 2024 |archive-date=March 28, 2023 |archive-url=https://web.archive.org/web/20230328171707/https://digital.library.unt.edu/ark:/67531/metadc719357/ |url-status=live }} and that indoor air pollution in some places can be much worse than that of the ambient air.U.S. Environmental Protection Agency. Office equipment: design, indoor air emissions, and pollution prevention opportunities. Air and Energy Engineering Research Laboratory, Research Triangle Park, 1995.U.S. Environmental Protection Agency. Unfinished business: a comparative assessment of environmental problems, EPA-230/2-87-025a-e (NTIS PB88-127030). Office of Policy, Planning and Evaluation, Washington, DC, 1987.

Various factors contribute to high concentrations of pollutants indoors, ranging from influx of pollutants from external sources, off-gassing by furniture, furnishings including carpets, indoor activities (cooking, cleaning, painting, smoking, etc. in homes to using office equipment in offices), thermal comfort parameters such as temperature, humidity, airflow and physio-chemical properties of the indoor air.{{Citation needed|date=March 2024}} Air pollutants can enter a building in many ways, including through open doors or windows. Poorly maintained air conditioners/ventilation systems can harbor mold, bacteria, and other contaminants, which are then circulated throughout indoor spaces, contributing to respiratory problems and allergies.

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.

File:Share of deaths from indoor air pollution, OWID.svg

IAQ is significant for human health as humans spend a large proportion of their time in indoor environments. Americans and Europeans on average spend approximately 90% of their time indoors.{{Cite journal |last1=Klepeis |first1=Neil E |last2=Nelson |first2=William C |last3=Ott |first3=Wayne R |last4=Robinson |first4=John P |last5=Tsang |first5=Andy M |last6=Switzer |first6=Paul |last7=Behar |first7=Joseph V |last8=Hern |first8=Stephen C |last9=Engelmann |first9=William H |date=July 1, 2001 |title=The National Human Activity Pattern Survey (NHAPS): a resource for assessing exposure to environmental pollutants |url=https://www.nature.com/articles/7500165 |journal=Journal of Exposure Science & Environmental Epidemiology |language=en |volume=11 |issue=3 |pages=231–252 |doi=10.1038/sj.jea.7500165 |pmid=11477521 |bibcode=2001JESEE..11..231K |osti=785282 |issn=1559-0631 |access-date=November 13, 2023 |archive-date=November 13, 2023 |archive-url=https://web.archive.org/web/20231113232225/https://www.nature.com/articles/7500165 |url-status=live }}{{Cite journal |last= |first= |date=2014 |title=Combined or multiple exposure to health stressors in indoor built environments: an evidence-based review prepared for the WHO training workshop "Multiple environmental exposures and risks": 16–18 October 2013, Bonn, Germany |url=https://iris.who.int/handle/10665/350495 |journal=World Health Organization. Regional Office for Europe |language=en |access-date=April 10, 2024 |archive-date=November 6, 2023 |archive-url=https://web.archive.org/web/20231106192839/https://iris.who.int/handle/10665/350495 |url-status=live }}

The World Health Organization (WHO) estimates that 3.2 million people die prematurely every year from illnesses attributed to indoor air pollution caused by indoor cooking, with over 237 thousand of these being children under 5. These include around an eighth of all global ischaemic heart disease, stroke, and lung cancer deaths. Overall the WHO estimated that poor indoor air quality resulted in the loss of 86 million healthy life years in 2019.{{Cite web |date=December 15, 2023 |title=Household air pollution |url=https://www.who.int/news-room/fact-sheets/detail/household-air-pollution-and-health |access-date=April 10, 2024 |website=World Health Organization |language=en |archive-date=November 12, 2021 |archive-url=https://web.archive.org/web/20211112161107/https://www.who.int/news-room/fact-sheets/detail/household-air-pollution-and-health |url-status=live }}

Studies in the UK and Europe show exposure to indoor air pollutants, chemicals and biological contamination can irritate the upper airway system, trigger or exacerbate asthma and other respiratory or cardiovascular conditions, and may even have carcinogenic effects.{{Cite journal |last1=Clark |first1=Sierra N. |last2=Lam |first2=Holly C. Y. |last3=Goode |first3=Emma-Jane |last4=Marczylo |first4=Emma L. |last5=Exley |first5=Karen S. |last6=Dimitroulopoulou |first6=Sani |date=2 August 2023 |title=The Burden of Respiratory Disease from Formaldehyde, Damp and Mould in English Housing |journal=Environments |language=en |volume=10 |issue=8 |pages=136 |doi=10.3390/environments10080136 |doi-access=free |bibcode=2023Envi...10..136C |issn=2076-3298}}{{Cite web |date=2023-11-16 |title=Chief Medical Officer (CMO): annual reports |url=https://www.gov.uk/government/collections/chief-medical-officer-annual-reports |access-date=2024-05-05 |website=GOV.UK |language=en}}{{Cite web |title=Project information {{!}} Indoor air quality at home {{!}} Quality standards {{!}} NICE |url=https://www.nice.org.uk/guidance/indevelopment/gid-qs10113 |access-date=2024-05-05 |website=www.nice.org.uk}}{{Cite web |title=The inside story: Health effects of indoor air quality on children and young people |url=https://www.rcpch.ac.uk/resources/inside-story-health-effects-indoor-air-quality-children-young-people |access-date=2024-05-05 |website=RCPCH |language=en}}{{Cite journal |last1=Halios |first1=Christos H. |last2=Landeg-Cox |first2=Charlotte |last3=Lowther |first3=Scott D. |last4=Middleton |first4=Alice |last5=Marczylo |first5=Tim |last6=Dimitroulopoulou |first6=Sani |date=15 September 2022 |title=Chemicals in European residences – Part I: A review of emissions, concentrations and health effects of volatile organic compounds (VOCs) |url=https://doi.org/10.1016/j.scitotenv.2022.156201 |journal=Science of the Total Environment |volume=839 |pages=156201 |doi=10.1016/j.scitotenv.2022.156201 |pmid=35623519 |bibcode=2022ScTEn.83956201H |issn=0048-9697|url-access=subscription }}{{Cite web |title=Literature review on chemical pollutants in indoor air in public settings for children and overview of their health effects with a focus on schools, kindergartens and day-care centres |url=https://www.who.int/europe/publications/i/item/9789289055642 |access-date=2024-05-05 |website=www.who.int |language=en}}

Poor indoor air quality can cause sick building syndrome. Symptoms include burning of the eyes, scratchy throat, blocked nose, and headaches.{{cite journal |last1=Burge |first1=P S |date=February 2004 |title=Sick building syndrome |journal=Occupational and Environmental Medicine |volume=61 |issue=2 |pages=185–190 |doi=10.1136/oem.2003.008813 |pmc=1740708 |pmid=14739390}}

{{Main|Household air pollution}}

{{Further|Energy poverty and cooking}}

File:Tortillera_en_Guatemala.jpg]]

Indoor combustion, such as for cooking or heating, is a major cause of indoor air pollution and causes significant health harms and premature deaths. Hydrocarbon fires cause air pollution. Pollution is caused by both biomass and fossil fuels of various types, but some forms of fuels are more harmful than others.

Indoor fire can produce black carbon particles, nitrogen oxides, sulfur oxides, and mercury compounds, among other emissions.{{cite journal |last1=Apte |first1=K |last2=Salvi |first2=S |title=Household air pollution and its effects on health. |journal=F1000Research |date=2016 |volume=5 |pages=2593 |doi=10.12688/f1000research.7552.1 |pmid=27853506 |pmc=5089137 |quote=Burning of natural gas not only produces a variety of gases such as sulfur oxides, mercury compounds, and particulate matter but also leads to the production of nitrogen oxides, primarily nitrogen dioxide...The burning of biomass fuel or any other fossil fuel increases the concentration of black carbon in the air |doi-access=free }} Around 3 billion people cook over open fires or on rudimentary cook stoves. Cooking fuels are coal, wood, animal dung, and crop residues.{{Cite web|date=February 7, 2020|title=Improved Clean Cookstoves|url=https://www.drawdown.org/solutions/improved-clean-cookstoves|access-date=December 5, 2020|website=Project Drawdown|language=en|archive-date=December 15, 2021|archive-url=https://web.archive.org/web/20211215040740/https://www.drawdown.org/solutions/improved-clean-cookstoves|url-status=live}} IAQ is a particular concern in low and middle-income countries where such practices are common.{{Cite book |title=WHO indoor air quality guidelines: household fuel combustion |publisher=World Health Organization |year=2014 |isbn=978-92-4-154888-5 |editor-last= |location=Geneva |editor-last2=}}

Cooking using natural gas (also called fossil gas, methane gas or simply gas) is associated with poorer indoor air quality. Combustion of gas produces nitrogen dioxide and carbon monoxide, and can lead to increased concentrations of nitrogen dioxide throughout the home environment which is linked to respiratory issues and diseases.{{Cite web |date=8 November 2023 |title=Clearing the Air: Gas Cooking and Pollution in European Homes |url=https://www.clasp.ngo/research/all/cooking-with-gas-findings-from-a-pan-european-indoor-air-quality-field-study/ |access-date=2024-05-05 |website=CLASP |language=en}}{{Cite web |last1=Seals |first1=Brady |last2=Krasner |first2=Andee |title=Gas Stoves: Health and Air Quality Impacts and Solutions |url=https://rmi.org/insight/gas-stoves-pollution-health/ |access-date=2024-05-05 |website=RMI |language=en-US}}

{{Main|Carbon monoxide poisoning}}

One of the most acutely toxic indoor air contaminants is carbon monoxide (CO), a colourless and odourless gas that is a by-product of incomplete combustion. Carbon monoxide may be emitted from tobacco smoke and generated from malfunctioning fuel burning stoves (wood, kerosene, natural gas, propane) and fuel burning heating systems (wood, oil, natural gas) and from blocked flues connected to these appliances.{{Cite book |last=Myers |first=Isabella |url=https://www.coresearchtrust.org/assets/uploads/images/CORT-Report-Medical-Examiners-Coroners-and-CO.pdf |title=The efficient operation of regulation and legislation: An holistic approach to understanding the effect of Carbon Monoxide on mortality |date=February 2022 |publisher=CO Research Trust}} In developed countries the main sources of indoor CO emission come from cooking and heating devices that burn fossil fuels and are faulty, incorrectly installed or poorly maintained.{{Citation |last1=Penney |first1=David |title=Carbon monoxide |date=2010 |work=WHO Guidelines for Indoor Air Quality: Selected Pollutants |url=https://www.ncbi.nlm.nih.gov/books/NBK138710/ |access-date=March 18, 2024 |archive-url=https://web.archive.org/web/20210308140149/https://www.ncbi.nlm.nih.gov/books/NBK138710/ |archive-date=March 8, 2021 |url-status=live |publisher=World Health Organization |language=en |isbn=978-92-890-0213-4 |oclc=696099951 |last2=Benignus |first2=Vernon |last3=Kephalopoulos |first3=Stylianos |last4=Kotzias |first4=Dimitrios |last5=Kleinman |first5=Michael |last6=Verrier |first6=Agnes}} Appliance malfunction may be due to faulty installation or lack of maintenance and proper use. In low- and middle-income countries the most common sources of CO in homes are burning biomass fuels and cigarette smoke.

Health effects of CO poisoning may be acute or chronic and can occur unintentionally or intentionally (self-harm). By depriving the brain of oxygen, acute exposure to carbon monoxide may have effects on the neurological system (headache, nausea, dizziness, alteration in consciousness and subjective weakness), the cardiovascular and respiratory systems (myocardial infarction, shortness of breath, or rapid breathing, respiratory failure). Acute exposure can also lead to long-term neurological effects such as cognitive and behavioural changes. Severe CO poisoning may lead to unconsciousness, coma and death. Chronic exposure to low concentrations of carbon monoxide may lead to lethargy, headaches, nausea, flu-like symptoms and neuropsychological and cardiovascular issues.{{Cite web |date=24 May 2022 |title=Carbon monoxide: toxicological overview |url=https://www.gov.uk/government/publications/carbon-monoxide-properties-incident-management-and-toxicology/carbon-monoxide-toxicological-overview |access-date=2024-04-17 |website=UK Health Security Agency |language=en}}

The WHO recommended levels of indoor CO exposure in 24 hours is 4 mg/m³.{{cite book |url=https://iris.who.int/bitstream/handle/10665/345329/9789240034228-eng.pdf |title=WHO global air quality guidelines: particulate matter (PM2.5 and PM10), ozone, nitrogen dioxide, sulfur dioxide and carbon monoxide |date=2021 |publisher=World Health Organization |isbn=978-92-4-003422-8 |hdl=10665/345329 |hdl-access=free}}{{page needed|date=March 2024}} Acute exposure should not exceed 10 mg/m³ in 8 hours, 35 mg/m³ in one hour and 100 mg/m³ in 15 minutes.

{{Main|Passive smoking}}

Secondhand smoke is tobacco smoke which affects people other than the 'active' smoker. It is made up of the exhaled smoke (15%) and mostly of smoke coming from the burning end of the cigarette, known as sidestream smoke (85%).{{cite journal |last1=Soleimani |first1=Farshid |last2=Dobaradaran |first2=Sina |last3=De-la-Torre |first3=Gabriel E. |last4=Schmidt |first4=Torsten C. |last5=Saeedi |first5=Reza |date=March 2022 |title=Content of toxic components of cigarette, cigarette smoke vs cigarette butts: A comprehensive systematic review |journal=Science of the Total Environment |volume=813 |pages=152667 |bibcode=2022ScTEn.81352667S |doi=10.1016/j.scitotenv.2021.152667 |pmid=34963586}}

Secondhand smoke contains more than 7000 chemicals, of which hundreds are harmful to health. Secondhand tobacco smoke includes both a gaseous and a particulate materials which, with particular hazards arising from levels of carbon monoxide and very small particulates (fine particulate matter, especially PM2.5 and PM10) which get into the bronchioles and alveoles in the lung.{{Cite web |title=Considering smoking as an air pollution problem for environmental health | Environmental Performance Index |url=http://archive.epi.yale.edu/the-metric/considering-smoking-air-pollution-problem-environmental-health |url-status=dead |archive-url=https://web.archive.org/web/20180925172458/http://archive.epi.yale.edu/the-metric/considering-smoking-air-pollution-problem-environmental-health |archive-date=September 25, 2018 |access-date=March 21, 2018}} Inhaling secondhand smoke on multiple occasions can cause asthma, pneumonia, lung cancer, and sudden infant death syndrome, among other conditions.{{Cite journal |last1=Arfaeinia |first1=Hossein |last2=Ghaemi |first2=Maryam |last3=Jahantigh |first3=Anis |last4=Soleimani |first4=Farshid |last5=Hashemi |first5=Hassan |date=June 12, 2023 |title=Secondhand and thirdhand smoke: a review on chemical contents, exposure routes, and protective strategies |journal=Environmental Science and Pollution Research |volume=30 |issue=32 |pages=78017–78029 |bibcode=2023ESPR...3078017A |doi=10.1007/s11356-023-28128-1 |pmc=10258487 |pmid=37306877}}

Thirdhand smoke (THS) refers to chemicals that settle on objects and bodies indoors after smoking. Exposure to thirdhand smoke can happen even after the actual cigarette smoke is not present anymore and affect those entering the indoor environment much later. Toxic substances of THS can react with other chemicals in the air and produce new toxic chemicals that are otherwise not present in cigarettes.{{Cite journal |last1=Arfaeinia |first1=Hossein |last2=Ghaemi |first2=Maryam |last3=Jahantigh |first3=Anis |last4=Soleimani |first4=Farshid |last5=Hashemi |first5=Hassan |date=June 12, 2023 |title=Secondhand and thirdhand smoke: a review on chemical contents, exposure routes, and protective strategies |journal=Environmental Science and Pollution Research |language=en |volume=30 |issue=32 |pages=78017–78029 |bibcode=2023ESPR...3078017A |doi=10.1007/s11356-023-28128-1 |issn=1614-7499 |pmc=10258487 |pmid=37306877}}

The only certain method to improve indoor air quality as regards secondhand smoke is to eliminate smoking indoors.{{Cite web |last=Health |first=CDC's Office on Smoking and |date=May 9, 2018 |title=Smoking and Tobacco Use; Fact Sheet; Secondhand Smoke |url=https://www.cdc.gov/tobacco/data_statistics/fact_sheets/secondhand_smoke/general_facts/ |url-status=live |archive-url=https://web.archive.org/web/20211215040740/https://www.cdc.gov/tobacco/data_statistics/fact_sheets/secondhand_smoke/general_facts/ |archive-date=December 15, 2021 |access-date=January 14, 2019 |website=Smoking and Tobacco Use |language=en-us}} Indoor e-cigarette use also increases home particulate matter concentrations.{{cite journal |last1=Fernández |first1=E |last2=Ballbè |first2=M |last3=Sureda |first3=X |last4=Fu |first4=M |last5=Saltó |first5=E |last6=Martínez-Sánchez |first6=JM |date=December 2015 |title=Particulate Matter from Electronic Cigarettes and Conventional Cigarettes: a Systematic Review and Observational Study. |journal=Current Environmental Health Reports |volume=2 |issue=4 |pages=423–9 |doi=10.1007/s40572-015-0072-x |pmid=26452675 |doi-access=free|bibcode=2015CEHR....2..423F }}

Atmospheric particulate matter, also known as particulates, can be found indoors and can affect the health of occupants. Indoor particulate matter can come from different indoor sources or be created as secondary aerosols through indoor gas-to-particle reactions. They can also be outdoor particles that enter indoors. These indoor particles vary widely in size, ranging from nanomet (nanoparticles/ultrafine particles emitted from combustion sources) to micromet (resuspensed dust).{{Cite book |last1=Vu |first1=Tuan V. |title=Indoor Air Pollution |last2=Harrison |first2=Roy M. |date=8 May 2019 |publisher=The Royal Society of Chemistry |isbn=978-1-78801-803-6 |editor-last=Harrison |editor-first=R. M. |publication-date=2019 |chapter=Chemical and Physical Properties of Indoor Aerosols |editor-last2=Hester |editor-first2=R. E.}} Particulate matter can also be produced through cooking activities. Frying produces higher concentrations than boiling or grilling and cooking meat produces higher concentrations than cooking vegetables.{{Cite journal |last1=Abdullahi |first1=Karimatu L. |last2=Delgado-Saborit |first2=Juana Maria |last3=Harrison |first3=Roy M. |date=February 13, 2013 |title=Emissions and indoor concentrations of particulate matter and its specific chemical components from cooking: A review |url=https://linkinghub.elsevier.com/retrieve/pii/S1352231013000861 |url-status=live |journal=Atmospheric Environment |language=en |volume=71 |pages=260–294 |bibcode=2013AtmEn..71..260A |doi=10.1016/j.atmosenv.2013.01.061 |archive-url=https://web.archive.org/web/20230521205004/https://linkinghub.elsevier.com/retrieve/pii/S1352231013000861 |archive-date=May 21, 2023 |access-date=April 11, 2024}} Preparing a Thanksgiving dinner can produce very high concentrations of particulate matter, exceeding 300 μg/m³.{{Cite journal |last1=Patel |first1=Sameer |last2=Sankhyan |first2=Sumit |last3=Boedicker |first3=Erin K. |last4=DeCarlo |first4=Peter F. |last5=Farmer |first5=Delphine K. |last6=Goldstein |first6=Allen H. |last7=Katz |first7=Erin F. |last8=Nazaroff |first8=William W |last9=Tian |first9=Yilin |last10=Vanhanen |first10=Joonas |last11=Vance |first11=Marina E. |date=June 16, 2020 |title=Indoor Particulate Matter during HOMEChem: Concentrations, Size Distributions, and Exposures |url=https://pubs.acs.org/doi/10.1021/acs.est.0c00740 |url-status=live |journal=Environmental Science & Technology |language=en |volume=54 |issue=12 |pages=7107–7116 |bibcode=2020EnST...54.7107P |doi=10.1021/acs.est.0c00740 |issn=0013-936X |pmid=32391692 |archive-url=https://web.archive.org/web/20230428153441/https://pubs.acs.org/doi/10.1021/acs.est.0c00740 |archive-date=April 28, 2023 |access-date=April 11, 2024}}

Particulates can penetrate deep into the lungs and brain from blood streams, causing health problems such as heart disease, lung disease, cancer and preterm birth.{{Cite journal |last1=Thangavel |first1=Prakash |last2=Park |first2=Duckshin |last3=Lee |first3=Young-Chul |date=2022-06-19 |title=Recent Insights into Particulate Matter (PM2.5)-Mediated Toxicity in Humans: An Overview |journal=International Journal of Environmental Research and Public Health |language=en |volume=19 |issue=12 |pages=7511 |doi=10.3390/ijerph19127511 |doi-access=free |pmid=35742761 |pmc=9223652 |issn=1660-4601}}

{{See also|Building materials|Red List building materials}}

Volatile organic compounds (VOCs) include a variety of chemicals, some of which may have short- and long-term adverse health effects. There are numerous sources of VOCs indoors, which means that their concentrations are consistently higher indoors (up to ten times higher) than outdoors.{{Cite journal |last1=You |first1=Bo |last2=Zhou |first2=Wei |last3=Li |first3=Junyao |last4=Li |first4=Zhijie |last5=Sun |first5=Yele |date=November 4, 2022 |title=A review of indoor Gaseous organic compounds and human chemical Exposure: Insights from Real-time measurements |journal=Environment International |language=en |volume=170 |pages=107611 |bibcode=2022EnInt.17007611Y |doi=10.1016/j.envint.2022.107611 |pmid=36335895 |doi-access=free}} Some VOCs are emitted directly indoors, and some are formed through the subsequent chemical reactions that can occur in the gas-phase, or on surfaces.{{Cite journal |last1=Weschler |first1=Charles J. |last2=Carslaw |first2=Nicola |date=March 6, 2018 |title=Indoor Chemistry |url=https://pubs.acs.org/doi/10.1021/acs.est.7b06387 |url-status=live |journal=Environmental Science & Technology |language=en |volume=52 |issue=5 |pages=2419–2428 |bibcode=2018EnST...52.2419W |doi=10.1021/acs.est.7b06387 |issn=0013-936X |pmid=29402076 |archive-url=https://web.archive.org/web/20231115234323/http://pubs.acs.org/doi/10.1021/acs.est.7b06387 |archive-date=November 15, 2023 |access-date=April 11, 2024|url-access=subscription }}{{Cite journal |last1=Carter |first1=Toby J. |last2=Poppendieck |first2=Dustin G. |last3=Shaw |first3=David |last4=Carslaw |first4=Nicola |date=January 16, 2023 |title=A Modelling Study of Indoor Air Chemistry: The Surface Interactions of Ozone and Hydrogen Peroxide |journal=Atmospheric Environment |language=en |volume=297 |pages=119598 |bibcode=2023AtmEn.29719598C |doi=10.1016/j.atmosenv.2023.119598 |doi-access=free }} VOCs presenting health hazards include benzene, formaldehyde, tetrachloroethylene and trichloroethylene.{{cite journal |last1=Tsai |first1=Wen-Tien |date=March 26, 2019 |title=An overview of health hazards of volatile organic compounds regulated as indoor air pollutants |journal=Reviews on Environmental Health |volume=34 |issue=1 |pages=81–89 |doi=10.1515/reveh-2018-0046 |pmid=30854833|bibcode=2019RvEH...34...81T }}

VOCs are emitted by thousands of indoor products. Examples include: paints, varnishes, waxes and lacquers, paint strippers, cleaning and personal care products, 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.{{cite web |date=August 5, 2010 |title=U.S. EPA IAQ – Organic chemicals |url=http://www.epa.gov/iaq/voc.html |url-status=live |archive-url=https://web.archive.org/web/20150909090046/http://www.epa.gov/iaq/voc.html |archive-date=September 9, 2015 |access-date=March 2, 2012 |publisher=Epa.gov}} Chlorinated drinking water releases chloroform when hot water is used in the home. Benzene is emitted from fuel stored in attached garages.

Human activities such as cooking and cleaning can also emit VOCs.{{Cite journal |last1=Davies |first1=Helen L. |last2=O'Leary |first2=Catherine |last3=Dillon |first3=Terry |last4=Shaw |first4=David R. |last5=Shaw |first5=Marvin |last6=Mehra |first6=Archit |last7=Phillips |first7=Gavin |last8=Carslaw |first8=Nicola |date=August 14, 2023 |title=A measurement and modelling investigation of the indoor air chemistry following cooking activities |journal=Environmental Science: Processes & Impacts |language=en |volume=25 |issue=9 |pages=1532–1548 |doi=10.1039/D3EM00167A |issn=2050-7887 |pmid=37609942|doi-access=free }}{{Cite journal |last1=Harding-Smith |first1=Ellen |last2=Shaw |first2=David R. |last3=Shaw |first3=Marvin |last4=Dillon |first4=Terry J. |last5=Carslaw |first5=Nicola |date=January 23, 2024 |title=Does green mean clean? Volatile organic emissions from regular versus green cleaning products |journal=Environmental Science: Processes & Impacts |language=en |volume=26 |issue=2 |pages=436–450 |doi=10.1039/D3EM00439B |issn=2050-7887 |pmid=38258874|doi-access=free }} Cooking can release long-chain aldehydes and alkanes when oil is heated and terpenes can be released when spices are prepared and/or cooked. Leaks of natural gas from cooking appliances have been linked to elevated levels of VOCs including benzene in homes in the USA.{{Cite journal |last1=Lebel |first1=Eric D. |last2=Michanowicz |first2=Drew R. |last3=Bilsback |first3=Kelsey R. |last4=Hill |first4=Lee Ann L. |last5=Goldman |first5=Jackson S. W. |last6=Domen |first6=Jeremy K. |last7=Jaeger |first7=Jessie M. |last8=Ruiz |first8=Angélica |last9=Shonkoff |first9=Seth B. C. |date=2022-11-15 |title=Composition, Emissions, and Air Quality Impacts of Hazardous Air Pollutants in Unburned Natural Gas from Residential Stoves in California |journal=Environmental Science & Technology |language=en |volume=56 |issue=22 |pages=15828–15838 |doi=10.1021/acs.est.2c02581 |issn=0013-936X |pmc=9671046 |pmid=36263944|bibcode=2022EnST...5615828L }} Cleaning products contain a range of VOCs, including monoterpenes, sesquiterpenes, alcohols and esters. Once released into the air, VOCs can undergo reactions with ozone and hydroxyl radicals to produce other VOCs, such as formaldehyde.

Health effects include eye, nose, and throat irritation; headaches, loss of coordination, nausea; and damage to the liver, kidney, and central nervous system.{{Cite web |last= |first= |date=2014-08-18 |title=Volatile Organic Compounds' Impact on Indoor Air Quality |url=https://www.epa.gov/indoor-air-quality-iaq/volatile-organic-compounds-impact-indoor-air-quality |access-date=2024-05-23 |website=United States Environmental Protection Agency |language=en}}

Testing emissions from building materials used indoors has become increasingly common for floor coverings, paints, and many other important indoor building materials and finishes.{{Cite web |date=January 21, 2013 |title=About VOCs |url=http://cal-iaq.org/separator/voc/about-vocs |archive-url=https://web.archive.org/web/20130121181543/http://cal-iaq.org/separator/voc/about-vocs |archive-date=January 21, 2013 |access-date=September 16, 2019}} Indoor materials such as gypsum boards or carpet act as VOC 'sinks', by trapping VOC vapors for extended periods of time, and releasing them by outgassing. The VOCs can also undergo transformation at the surface through interaction with ozone. In both cases, these delayed emissions can result in chronic and low-level exposures to VOCs.{{cite book |last1=Oanh |first1=Nguyen Thi Kim |title=Advanced Air and Noise Pollution Control |last2=Hung |first2=Yung-Tse |date=2005 |isbn=978-1-58829-359-6 |series=Handbook of Environmental Engineering |volume=2 |pages=237–272 |chapter=Indoor Air Pollution Control |doi=10.1007/978-1-59259-779-6_7}}

Several initiatives aim 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,{{cite web |title=Emicode |url=http://www.eurofins.com/emicode.aspx |url-status=dead |archive-url=https://web.archive.org/web/20150924003316/http://www.eurofins.com/emicode.aspx |archive-date=September 24, 2015 |access-date=March 2, 2012 |publisher=Eurofins.com}} M1,{{cite web |title=M1 |url=http://www.eurofins.com/m1.aspx |url-status=dead |archive-url=https://web.archive.org/web/20150924003357/http://www.eurofins.com/m1.aspx |archive-date=September 24, 2015 |access-date=March 2, 2012 |publisher=Eurofins.com}} Blue Angel{{cite web |title=Blue Angel |url=http://www.eurofins.com/blue-angel.aspx |url-status=dead |archive-url=https://web.archive.org/web/20150924003302/http://www.eurofins.com/blue-angel.aspx |archive-date=September 24, 2015 |access-date=March 2, 2012 |publisher=Eurofins.com}} and Indoor Air Comfort{{cite web |title=Indoor Air Comfort |url=http://www.indoor-air-comfort.com |url-status=dead |archive-url=https://web.archive.org/web/20110201124732/http://www.indoor-air-comfort.com |archive-date=February 1, 2011 |access-date=March 2, 2012 |publisher=Indoor Air Comfort}} in Europe, as well as California Standard CDPH Section 01350{{cite web |title=CDPH Section 01350 |url=http://www.eurofins.com/section-1350.aspx |url-status=dead |archive-url=https://web.archive.org/web/20150924003428/http://www.eurofins.com/section-1350.aspx |archive-date=September 24, 2015 |access-date=March 2, 2012 |publisher=Eurofins.com}} and several others in the US. Due to these initiatives an increasing number of low-emitting products became available to purchase.

At least 18 microbial VOCs (MVOCs) have been characterised{{cite web |title=Smelly Moldy Houses |url=http://www.bioidea.net/resources/smelly-musty-moldy-houses/ |url-status=live |archive-url=https://web.archive.org/web/20211215040749/https://www.bioidea.net/resources/smelly-musty-moldy-houses/ |archive-date=December 15, 2021 |access-date=August 2, 2014}}{{cite journal |last1=Meruva |first1=N. K. |last2=Penn |first2=J. M. |last3=Farthing |first3=D. E. |date=November 2004 |title=Rapid identification of microbial VOCs from tobacco molds using closed-loop stripping and gas chromatography/time-of-flight mass spectrometry |journal=J Ind Microbiol Biotechnol |volume=31 |issue=10 |pages=482–8 |doi=10.1007/s10295-004-0175-0 |pmid=15517467 |s2cid=32543591 |doi-access=free}} including 1-octen-3-ol (mushroom alcohol), 3-Methylfuran, 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 last four are products of Stachybotrys chartarum, which has been linked with sick building syndrome.

Many common building materials used before 1975 contain asbestos, such as some floor tiles, ceiling tiles, shingles, fireproofing, heating systems, pipe wrap, taping muds, 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. 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.

When asbestos-containing material is damaged or disintegrates, microscopic fibers are dispersed into the air. Inhalation of asbestos fibers over long exposure times is associated with increased incidence of lung cancer, mesothelioma, and asbestosis. The risk of lung cancer from inhaling asbestos fibers is significantly greater for smokers. The symptoms of disease do not usually appear until about 20 to 30 years after the first exposure to asbestos.

Although all asbestos is hazardous, products that are friable, e.g. sprayed coatings and insulation, pose a significantly higher hazard as they are more likely to release fibers to the air.{{cite journal |date=2016 |title=Atmospheric carbon dioxide passes 400 ppm everywhere |journal=Physics Today |issue=6 |page=8170 |doi=10.1063/pt.5.029904|bibcode=2016PhT..2016f8170. }}

{{Main|Microplastics}}

{{seealso|Renovation|Particulates}}

{{expand section|1=E.g., [https://www.mdpi.com/2673-4079/5/2/11]|date=October 2024}}

Microplastic is a type of airborne particulates and is found to prevail in air.{{cite journal |vauthors=Xie Y, Li Y, Feng Y, Cheng W, Wang Y |title=Inhalable microplastics prevails in air: Exploring the size detection limit |journal=Environ Int |volume=162 |issue= |pages=107151 |date=April 2022 |pmid=35228011 |doi=10.1016/j.envint.2022.107151 |bibcode=2022EnInt.16207151X |url=|doi-access=free }}{{cite journal |vauthors=Liu C, Li J, Zhang Y, Wang L, Deng J, Gao Y, Yu L, Zhang J, Sun H |title=Widespread distribution of PET and PC microplastics in dust in urban China and their estimated human exposure |journal=Environ Int |volume=128 |issue= |pages=116–124 |date=July 2019 |pmid=31039519 |doi=10.1016/j.envint.2019.04.024 |bibcode=2019EnInt.128..116L |url=|doi-access=free }}{{cite journal | last1=Yuk | first1=Hyeonseong | last2=Jo | first2=Ho Hyeon | last3=Nam | first3=Jihee | last4=Kim | first4=Young Uk | last5=Kim | first5=Sumin | title=Microplastic: A particulate matter(PM) generated by deterioration of building materials | journal=Journal of Hazardous Materials | publisher=Elsevier BV | volume=437 | year=2022 | issn=0304-3894 | doi=10.1016/j.jhazmat.2022.129290 | page=129290| pmid=35753297 | bibcode=2022JHzM..43729290Y }}{{cite journal | last1=Eberhard | first1=Tiffany | last2=Casillas | first2=Gaston | last3=Zarus | first3=Gregory M. | last4=Barr | first4=Dana Boyd | title=Systematic review of microplastics and nanoplastics in indoor and outdoor air: identifying a framework and data needs for quantifying human inhalation exposures | journal=Journal of Exposure Science & Environmental Epidemiology | publisher=Springer Science and Business Media LLC | volume=34 | issue=2 | quote=MPs have been found in water and soil, and recent research is exposing the vast amount of them in ambient and indoor air. | date=6 Jan 2024 | issn=1559-0631 | doi=10.1038/s41370-023-00634-x | doi-access=free | pages=185–196 | pmid=38184724 | pmc=11142917 | bibcode=2024JESEE..34..185E | url=https://www.nature.com/articles/s41370-023-00634-x.pdf | access-date=19 Dec 2024}} A 2017 study found indoor airborne microfiber concentrations between 1.0 and 60.0 microfibers per cubic meter (33% of which were found to be microplastics).{{cite journal |last1=Gasperi |first1=Johnny |last2=Wright |first2=Stephanie L. |last3=Dris |first3=Rachid |last4=Collard |first4=France |last5=Mandin |first5=Corinne |last6=Guerrouache |first6=Mohamed |last7=Langlois |first7=Valérie |last8=Kelly |first8=Frank J. |last9=Tassin |first9=Bruno |year=2018 |title=Microplastics in air: Are we breathing it in? |url=https://hal-enpc.archives-ouvertes.fr/hal-01665768/file/Gasperi_Chapter_CurrentOpinion_VF.pdf |journal=Current Opinion in Environmental Science & Health |volume=1 |pages=1–5 |doi=10.1016/j.coesh.2017.10.002 |bibcode=2018COESH...1....1G |s2cid=133750509 |access-date=11 July 2019 |archive-date=6 March 2020 |archive-url=https://web.archive.org/web/20200306202059/https://hal-enpc.archives-ouvertes.fr/hal-01665768/file/Gasperi_Chapter_CurrentOpinion_VF.pdf |url-status=live}} Airborne microplastic dust can be produced during renovation, building, bridge and road reconstruction projects{{cite journal | last1=Prasittisopin | first1=Lapyote | last2=Ferdous | first2=Wahid | last3=Kamchoom | first3=Viroon | title=Microplastics in construction and built environment | journal=Developments in the Built Environment | publisher=Elsevier BV | volume=15 | year=2023 | issn=2666-1659 | doi=10.1016/j.dibe.2023.100188 | doi-access=free}} and the use of power tools.{{cite web | last=Galloway | first=Nanette LoBiondo | title=Ventnor introduces ordinance to control microplastics contamination | website=DownBeach | date=13 Sep 2024 | url=https://downbeach.com/news/2024/sep/13/ventnor-introduces-ordinance-to-control-microplastics-contamination/ | access-date=2 Oct 2024}}

{{See also|Ground-level ozone}}

Indoors ozone (O₃) is produced by certain high-voltage electric devices (such as air ionizers), and as a by-product of other types of pollution. It appears in lower concentrations indoors than outdoors, usually at 0.2-0.7 of the outdoor concentration.{{Cite journal |last=Weschler |first=Charles J. |date=December 2000 |title=Ozone in Indoor Environments: Concentration and Chemistry: Ozone in Indoor Environments |url=http://doi.wiley.com/10.1034/j.1600-0668.2000.010004269.x |url-status=live |journal=Indoor Air |language=en |volume=10 |issue=4 |pages=269–288 |doi=10.1034/j.1600-0668.2000.010004269.x |pmid=11089331 |archive-url=https://web.archive.org/web/20240415110851/https://onlinelibrary.wiley.com/doi/full/10.1034/j.1600-0668.2000.010004269.x |archive-date=April 15, 2024 |access-date=April 11, 2024|url-access=subscription }} Typically, most ozone is lost to surface reactions indoors, rather than to reactions in air, due to the large surface to volume ratios found indoors.{{Cite journal |last1=Weschler |first1=Charles J. |last2=Nazaroff |first2=William W |date=February 22, 2023 |title=Human skin oil: a major ozone reactant indoors |journal=Environmental Science: Atmospheres |language=en |volume=3 |issue=4 |pages=640–661 |doi=10.1039/D3EA00008G |issn=2634-3606 |doi-access=free|bibcode=2023ESAt....3..640W }}

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, because these chemicals react very quickly with ozone to form toxic and irritating chemicals as well as fine and ultrafine particles.{{Cite journal |last1=Kumar |first1=Prashant |last2=Kalaiarasan |first2=Gopinath |last3=Porter |first3=Alexandra E. |last4=Pinna |first4=Alessandra |last5=Kłosowski |first5=Michał M. |last6=Demokritou |first6=Philip |last7=Chung |first7=Kian Fan |last8=Pain |first8=Christopher |last9=Arvind |first9=D. K. |last10=Arcucci |first10=Rossella |last11=Adcock |first11=Ian M. |last12=Dilliway |first12=Claire |date=February 20, 2021 |title=An overview of methods of fine and ultrafine particle collection for physicochemical characterisation and toxicity assessments |journal=Science of the Total Environment |volume=756 |pages=143553 |bibcode=2021ScTEn.75643553K |doi=10.1016/j.scitotenv.2020.143553 |pmid=33239200 |s2cid=227176222 |doi-access=free |hdl-access=free |hdl=10044/1/84518}} Ventilation with outdoor air containing elevated ozone concentrations may complicate remediation attempts.{{cite journal |last1=Apte |first1=M. G. |last2=Buchanan |first2=I. S. H. |last3=Mendell |first3=M. J. |date=April 2008 |title=Outdoor ozone and building-related symptoms in the BASE study |journal=Indoor Air |volume=18 |issue=2 |pages=156–170 |bibcode=2008InAir..18..156A |doi=10.1111/j.1600-0668.2008.00521.x |pmid=18333994 |doi-access=free}}

The WHO standard for ozone concentration is 60 μg/m³ for long-term exposure and 100 μg/m³ as the maximum average over an 8-hour period. The EPA standard for ozone concentration is 0.07 ppm average over an 8-hour period.{{Cite web |title=Eight-hour Average Ozone Concentrations {{!}} Ground-level Ozone {{!}} New England {{!}} US EPA |url=https://www3.epa.gov/region1/airquality/avg8hr.html |url-status=live |archive-url=https://web.archive.org/web/20211215040747/https://www3.epa.gov/region1/airquality/avg8hr.html |archive-date=December 15, 2021 |access-date=September 16, 2019 |website=United States Environmental Protection Agency |language=en}}

{{Main|Indoor mold|Mold health issues}}

Occupants in buildings can be exposed to fungal spores, cell fragments, or mycotoxins which can arise from a host of means, but there are two common classes: (a) excess moisture induced growth of mold colonies and (b) natural substances released into the air such as animal dander and plant pollen.{{cite journal |last1=Park |first1=J. H. |last2=Cox-Ganser |first2=J. M. |year=2011 |title=Meta-Mold exposure and respiratory health in damp indoor environments |journal=Frontiers in Bioscience |volume=3 |issue=2 |pages=757–771 |doi=10.2741/e284 |pmid=21196349 |doi-access=free}}

While mold growth is associated with high moisture levels,{{Cite web |date=December 4, 2018 |title=CDC – Mold – General Information – Facts About Mold and Dampness |url=https://www.cdc.gov/mold/dampness_facts.htm |url-status=live |archive-url=https://web.archive.org/web/20191216124251/https://www.cdc.gov/mold/dampness_facts.htm |archive-date=December 16, 2019 |access-date=June 23, 2017}} it is likely to grow when a combination of favorable conditions arises. As well as high moisture levels, these conditions include suitable temperatures, pH and nutrient sources.{{Cite book |url=https://www.taylorfrancis.com/books/9781135824624 |title=Building Mycology |publisher=Taylor & Francis |year=1994 |isbn=978-1-135-82462-4 |editor-last=Singh |editor-first=Dr Jagjit |edition=1 |language=en |doi=10.4324/9780203974735 |editor-last2=Singh |editor-first2=Jagjit}} Mold grows primarily on surfaces, and it reproduces by releasing spores, which can travel and settle in different locations. When these spores experience appropriate conditions, they can germinate and lead to mycelium growth.{{Cite journal |last1=Clarke |first1=J.A |last2=Johnstone |first2=C.M |last3=Kelly |first3=N.J |last4=McLean |first4=R.C |last5=anderson |first5=J.A |last6=Rowan |first6=N.J |last7=Smith |first7=J.E |date=January 20, 1999 |title=A technique for the prediction of the conditions leading to mould growth in buildings |url=https://linkinghub.elsevier.com/retrieve/pii/S0360132398000237 |url-status=live |journal=Building and Environment |language=en |volume=34 |issue=4 |pages=515–521 |bibcode=1999BuEnv..34..515C |doi=10.1016/S0360-1323(98)00023-7 |archive-url=https://web.archive.org/web/20221026052956/https://linkinghub.elsevier.com/retrieve/pii/S0360132398000237 |archive-date=October 26, 2022 |access-date=April 10, 2024|url-access=subscription }} Different mold species favor different environmental conditions to germinate and grow, some being more hydrophilic (growing at higher levels of relative humidity) and other more xerophilic (growing at levels of relative humidity as low as 75–80%).{{Cite journal |last1=Vereecken |first1=Evy |last2=Roels |first2=Staf |date=November 15, 2011 |title=Review of mould prediction models and their influence on mould risk evaluation |url=https://linkinghub.elsevier.com/retrieve/pii/S0360132311003830 |url-status=live |journal=Building and Environment |language=en |volume=51 |pages=296–310 |doi=10.1016/j.buildenv.2011.11.003 |archive-url=https://web.archive.org/web/20240302035904/https://linkinghub.elsevier.com/retrieve/pii/S0360132311003830 |archive-date=March 2, 2024 |access-date=April 11, 2024|url-access=subscription }}

Mold growth can be inhibited by keeping surfaces at conditions that are further from condensation, with relative humidity levels below 75%. This usually translates to a relative humidity of indoor air below 60%, in agreement with the guidelines for thermal comfort that recommend a relative humidity between 40 and 60 %. Moisture buildup in buildings may arise from water penetrating areas of the building envelope or fabric, from plumbing leaks, rainwater or groundwater penetration, or from condensation due to improper ventilation, insufficient heating or poor thermal quality of the building envelope.{{Cite book |title=BS 5250:2021 - Management of moisture in buildings. Code of practice |date=October 31, 2021 |publisher=British Standards Institution (BSI) |isbn=978-0-539-18975-9}} Even something as simple as drying clothes indoors on radiators can increase the risk of mold growth, if the humidity produced is not able to escape the building via ventilation.{{Cite journal |last1=Madgwick |first1=Della |last2=Wood |first2=Hannah |date=August 8, 2016 |title=The problem of clothes drying in new homes in the UK |url=https://www.emerald.com/insight/content/doi/10.1108/SS-10-2015-0048/full/html |url-status=live |journal=Structural Survey |language=en |volume=34 |issue=4/5 |pages=320–330 |doi=10.1108/SS-10-2015-0048 |issn=0263-080X |archive-url=https://web.archive.org/web/20210507231216/https://www.emerald.com/insight/content/doi/10.1108/SS-10-2015-0048/full/html |archive-date=May 7, 2021 |access-date=April 11, 2024}}

Mold predominantly affects the airways and lungs. Known effects of mold on health include asthma development and exacerbation,{{Cite web |last1=May |first1=Neil |last2=McGilligan |first2=Charles |last3=Ucci |first3=Marcella |date=2017 |title=Health and Moisture in Buildings |url=https://ukcmb.org/wp-content/uploads/2019/10/health-and-moisture-in-buildings-report-1.pdf |url-status=live |archive-url=https://web.archive.org/web/20240411070746/https://ukcmb.org/wp-content/uploads/2019/10/health-and-moisture-in-buildings-report-1.pdf |archive-date=April 11, 2024 |access-date=April 11, 2024 |website=UK Centre for Moisture in Buildings}} with children and elderly at greater risk of more severe health impacts.{{Cite web |date=September 7, 2023 |title=Understanding and addressing the health risks of damp and mould in the home |url=https://www.gov.uk/government/publications/damp-and-mould-understanding-and-addressing-the-health-risks-for-rented-housing-providers/understanding-and-addressing-the-health-risks-of-damp-and-mould-in-the-home--2 |url-status=live |archive-url=https://web.archive.org/web/20240410023335/https://www.gov.uk/government/publications/damp-and-mould-understanding-and-addressing-the-health-risks-for-rented-housing-providers/understanding-and-addressing-the-health-risks-of-damp-and-mould-in-the-home--2 |archive-date=April 10, 2024 |access-date=April 11, 2024 |website=GOV.UK |language=en}} Infants in homes with mold have a much greater risk of developing asthma and allergic rhinitis.{{Cite journal |last1=Clark |first1=Sierra N. |last2=Lam |first2=Holly C. Y. |last3=Goode |first3=Emma-Jane |last4=Marczylo |first4=Emma L. |last5=Exley |first5=Karen S. |last6=Dimitroulopoulou |first6=Sani |date=2023-08-02 |title=The Burden of Respiratory Disease from Formaldehyde, Damp and Mould in English Housing |journal=Environments |language=en |volume=10 |issue=8 |pages=136 |doi=10.3390/environments10080136 |doi-access=free |bibcode=2023Envi...10..136C |issn=2076-3298}} More than half of adult workers in moldy or humid buildings suffer from nasal or sinus symptoms due to mold exposure. Some varieties of mold 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.

{{unreferenced section|date=September 2024}}

Legionnaires' disease is caused by a waterborne bacterium Legionella that grows best in slow-moving or still, warm water. The primary route of exposure is through the creation of an aerosol effect, 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 water in an aerosol which 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 at 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/taps, 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 protozoans 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 ({{convert|160|F|C}}), sterilisation of standing water in evaporative cooling basins, replacement of shower heads, and, in some cases, flushes of heavy metal salts. Preventive measures include adjusting normal hot water levels to allow for {{Convert|120|F|C}} at the tap, evaluating facility design layout, removing faucet aerators, and periodic testing in suspect areas.

File:Bacteria (26 2 27) Airborne microbes.jpg

There are many bacteria of health significance found in indoor air and on indoor surfaces. The role of microbes in the indoor environment is increasingly studied using modern gene-based analysis of environmental samples. Currently, efforts are under way to link microbial ecologists and indoor air scientists to forge new methods for analysis and to better interpret the results.[http://www.microbe.net/ Microbiology of the Indoor Environment] {{Webarchive|url=https://web.archive.org/web/20110723210118/http://www.microbe.net/ |date=July 23, 2011 }}, microbe.net

A large fraction of the bacteria found in indoor air and dust are shed from humans. Among the most important bacteria known to occur in indoor air are Mycobacterium tuberculosis, Staphylococcus aureus, Streptococcus pneumoniae.{{citation needed|date=September 2024}}

File:Hotel Metropole 9th floor layout SARS 2003.svg

Viruses can also be a concern for indoor air quality. During the 2002–2004 SARS outbreak, virus-laden aerosols were found to have seeped into bathrooms from the bathroom floor drains, exacerbated by the draw of bathroom exhaust fans, resulting in the rapid spread of SARS in Amoy Gardens in Hong Kong.http://www.info.gov.hk/info/sars/pdf/amoy_e.pdf {{Bare URL PDF|date=May 2025}}https://www.info.gov.hk/info/sars/graphics/amoyannex.jpg {{Bare URL image|date=May 2025}} Elsewhere in Hong Kong, SARS CoV RNA was found on the carpet and in the air intake vents of the Metropole Hotel, which showed that secondary environmental contamination could generate infectious aerosols and resulted in superspreading events.{{cite web|url=https://wwwnc.cdc.gov/eid/article/19/6/13-0192_article|quote=environmental contamination with SARS CoV RNA was identified on the carpet in front of the index case-patient's room and 3 nearby rooms (and on their door frames but not inside the rooms) and in the air intake vents near the centrally located elevators ... secondary infections occurred not in guest rooms but in the common areas of the ninth floor, such as the corridor or elevator hall. These areas could have been contaminated through body fluids (e.g., vomitus, expectorated sputum), respiratory droplets, or suspended small-particle aerosols generated by the index case-patient; other guests were then infected by fomites or aerosols while passing through these same areas. Efficient spread of SARS CoV through small-particle aerosols was observed in several superspreading events in health care settings, during an airplane flight, and in an apartment complex (12–14,16–19). This process of environmental contamination that generated infectious aerosols likely best explains the pattern of disease transmission at the Hotel Metropole.|title=Progress in Global Surveillance and Response Capacity 10 Years after Severe Acute Respiratory Syndrome}}

Humans are the main indoor source of carbon dioxide (CO₂) in most buildings. Indoor CO₂ levels are an indicator of the adequacy of outdoor air ventilation relative to indoor occupant density and metabolic activity.

Indoor CO₂ levels above 500 ppm can lead to higher blood pressure and heart rate, and increased peripheral blood circulation.{{cite journal |last1=Azuma |first1=Kenichi |last2=Kagi |first2=Naoki |last3=Yanagi |first3=U. |last4=Osawa |first4=Haruki |title=Effects of low-level inhalation exposure to carbon dioxide in indoor environments: A short review on human health and psychomotor performance |journal=Environment International |date=December 2018 |volume=121 |issue=Pt 1 |pages=51–56 |doi=10.1016/j.envint.2018.08.059 |pmid=30172928 |bibcode=2018EnInt.121...51A |doi-access=free }} With CO₂ concentrations above 1000 ppm cognitive performance might be affected, especially when doing complex tasks, making decision making and problem solving slower but not less accurate.{{cite journal |last1=Du |first1=Bowen |last2=Tandoc |first2=Michael |date=June 19, 2020 |title=Indoor CO2 concentrations and cognitive function: A critical review |journal=International Journal of Indoor Environment and Health |volume=30 |issue=6 |pages=1067–1082 |bibcode=2020InAir..30.1067D |doi=10.1111/ina.12706 |pmid=32557862 |s2cid=219915861 |doi-access=free}}{{Cite journal |last1=Fan |first1=Yuejie |last2=Cao |first2=Xiaodong |last3=Zhang |first3=Jie |last4=Lai |first4=Dayi |last5=Pang |first5=Liping |date=June 1, 2023 |title=Short-term exposure to indoor carbon dioxide and cognitive task performance: A systematic review and meta-analysis |journal=Building and Environment |language=en |volume=237 |pages=110331 |bibcode=2023BuEnv.23710331F |doi=10.1016/j.buildenv.2023.110331 |doi-access=free}} However, evidence on the health effects of CO₂ at lower concentrations is conflicting and it is difficult to link CO₂ to health impacts at exposures below 5000 ppm – reported health outcomes may be due to the presence of human bioeffluents, and other indoor air pollutants related to inadequate ventilation.{{Cite journal |last1=Lowther |first1=Scott D. |last2=Dimitroulopoulou |first2=Sani |last3=Foxall |first3=Kerry |last4=Shrubsole |first4=Clive |last5=Cheek |first5=Emily |last6=Gadeberg |first6=Britta |last7=Sepai |first7=Ovnair |date=16 November 2021 |title=Low Level Carbon Dioxide Indoors—A Pollution Indicator or a Pollutant? A Health-Based Perspective |journal=Environments |language=en |volume=8 |issue=11 |pages=125 |doi=10.3390/environments8110125 |doi-access=free |bibcode=2021Envi....8..125L |issn=2076-3298}}

Indoor carbon dioxide concentrations can be used to evaluate the quality of a room or a building's ventilation.{{cite journal |last1=Persily |first1=Andrew |title=Development and application of an indoor carbon dioxide metric |journal=Indoor Air |date=July 2022 |volume=32 |issue=7 |pages=e13059 |doi=10.1111/ina.13059 |doi-access=free |pmid=35904382 |bibcode=2022InAir..3213059P }} To eliminate most complaints caused by CO₂, the total indoor CO₂ level should be reduced to a difference of no greater than 700 ppm above outdoor levels.{{Cite web |date=February 25, 2022 |title=Indoor Environmental Quality: HVAC Management {{!}} NIOSH {{!}} CDC |url=https://www.cdc.gov/niosh/topics/indoorenv/hvac.html |access-date=April 1, 2022 |website=www.cdc.gov |language=en-us |archive-date=April 1, 2022 |archive-url=https://web.archive.org/web/20220401185820/https://www.cdc.gov/niosh/topics/indoorenv/hvac.html |url-status=live }} The National Institute for Occupational Safety and Health (NIOSH) considers that indoor air concentrations of carbon dioxide that exceed 1000 ppm are a marker suggesting inadequate ventilation.[https://www.cdc.gov/niosh/topics/indoorenv/BuildingVentilation.html Indoor Environmental Quality: Building Ventilation] {{Webarchive|url=https://web.archive.org/web/20220120160414/http://www.cdc.gov/niosh/topics/indoorenv/buildingventilation.html |date=January 20, 2022 }}. National Institute for Occupational Safety and Health. Accessed October 8, 2008. The UK standards for schools say that carbon dioxide levels of 800 ppm or lower indicate that the room is well-ventilated.{{Cite web |title=SAMHE - Schools' Air quality Monitoring for Health and Education |url=https://samhe.org.uk/resources/samhe.org.uk |access-date=March 18, 2024 |website=samhe.org.uk |language=en |archive-date=March 18, 2024 |archive-url=https://web.archive.org/web/20240318200228/https://samhe.org.uk/resources/samhe.org.uk |url-status=live }} Regulations and standards from around the world show that CO₂ levels below 1000 ppm represent good IAQ, between 1000 and 1500 ppm represent moderate IAQ and greater than 1500 ppm represent poor IAQ.

Carbon dioxide concentrations in closed or confined rooms can increase to 1,000 ppm within 45 minutes of enclosure. For example, in a {{convert|3.5|x|4|m|adj=on}} sized office, atmospheric carbon dioxide increased from 500 ppm to over 1,000 ppm within 45 minutes of ventilation cessation and closure of windows and doors.{{Cite web |title=Document Display {{!}} NEPIS {{!}} US EPA |url=https://nepis.epa.gov/Exe/ZyNET.exe/00000AOV.TXT?ZyActionD=ZyDocument&Client=EPA&Index=1991+Thru+1994&Docs=&Query=&Time=&EndTime=&SearchMethod=1&TocRestrict=n&Toc=&TocEntry=&QField=&QFieldYear=&QFieldMonth=&QFieldDay=&IntQFieldOp=0&ExtQFieldOp=0&XmlQuery=&File=D:%5Czyfiles%5CIndex%20Data%5C91thru94%5CTxt%5C00000009%5C00000AOV.txt&User=ANONYMOUS&Password=anonymous&SortMethod=h%7C-&MaximumDocuments=1&FuzzyDegree=0&ImageQuality=r75g8/r75g8/x150y150g16/i425&Display=hpfr&DefSeekPage=x&SearchBack=ZyActionL&Back=ZyActionS&BackDesc=Results%20page&MaximumPages=1&ZyEntry=1&SeekPage=x&ZyPURL |access-date=October 19, 2023 |website=nepis.epa.gov |language=en |archive-date=November 16, 2023 |archive-url=https://web.archive.org/web/20231116064926/https://nepis.epa.gov/Exe/ZyNET.exe/00000AOV.TXT?ZyActionD=ZyDocument&Client=EPA&Index=1991+Thru+1994&Docs=&Query=&Time=&EndTime=&SearchMethod=1&TocRestrict=n&Toc=&TocEntry=&QField=&QFieldYear=&QFieldMonth=&QFieldDay=&IntQFieldOp=0&ExtQFieldOp=0&XmlQuery=&File=D%3A%5Czyfiles%5CIndex%20Data%5C91thru94%5CTxt%5C00000009%5C00000AOV.txt&User=ANONYMOUS&Password=anonymous&SortMethod=h%7C-&MaximumDocuments=1&FuzzyDegree=0&ImageQuality=r75g8%2Fr75g8%2Fx150y150g16%2Fi425&Display=hpfr&DefSeekPage=x&SearchBack=ZyActionL&Back=ZyActionS&BackDesc=Results%20page&MaximumPages=1&ZyEntry=1&SeekPage=x&ZyPURL |url-status=live }}

{{Main|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. It is a major cause of lung cancer, responsible for 3–14% of cases in countries, leading to tens of thousands of deaths.{{sfn|Zeeb|Shannoun|2009|p=3}}

Radon gas enters buildings as a soil gas. As it is a heavy gas it will tend to accumulate at the lowest level. Radon may also be introduced into a building through drinking water particularly from bathroom showers. Building materials can be a rare source of radon, but little testing is carried out for stone, rock or tile products brought into building sites; radon accumulation is greatest for well insulated homes.C.Michael Hogan and Sjaak Slanina. 2010, [http://www.eoearth.org/ Air pollution. Encyclopedia of Earth] {{Webarchive|url=https://web.archive.org/web/20061012144354/http://www.eoearth.org/|date=October 12, 2006}}. eds. Sidney Draggan and Cutler Cleveland. National Council for Science and the Environment. Washington DC There are simple do-it-yourself kits for radon gas testing, but a licensed professional can also check homes.

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. Radon mitigation methods include sealing concrete slab floors, basement foundations, water drainage systems, or by increasing ventilation.{{cite web |title=Radon Mitigation Methods |url=http://radon-solution.com/pg_mitigation_methods.php |url-status=dead |archive-url=https://web.archive.org/web/20081215190050/http://radon-solution.com/pg_mitigation_methods.php |archive-date=December 15, 2008 |access-date=December 2, 2008 |publisher=Radon Solution—Raising Radon Awareness}} They are usually cost effective and can greatly reduce or even eliminate the contamination and the associated health risks.{{citation needed|date=March 2024}}

Radon is measured in picocuries per liter of air (pCi/L) or becquerel per cubic meter (Bq m^-3). Both are measurements of radioactivity. The World Health Organization (WHO) sets the ideal indoor radon levels at 100 Bq/m-³.{{sfn|Zeeb|Shannoun|2009|p={{page needed|date=March 2024}}}} In the United States, it is recommend to fix homes with radon levels at or above 4 pCi/L. At the same time it is also recommends that people think about fixing their homes for radon levels between 2 pCi/L and 4 pCi/L.{{cite web |title=Basic radon facts |url=https://www.wvdhhr.org/rtia/pdf/Radon%20Facts.pdf |url-status=live |archive-url=https://web.archive.org/web/20220113132625/https://www.wvdhhr.org/RTIA/pdf/Radon%20Facts.pdf |archive-date=January 13, 2022 |access-date=September 18, 2018 |publisher=US Environmental Protection Agency |language=en}} {{PD-notice}} In the United Kingdom the ideal is presence of radon indoors is 100 Bq/m-³. Action needs to be taken in homes with 200 Bq/m⁻³ or more.{{Cite web |title=Radon Action Level and Target Level |url=https://www.ukradon.org/information/level |url-status=live |archive-url=https://web.archive.org/web/20240318160250/https://www.ukradon.org/information/level |archive-date=March 18, 2024 |access-date=March 18, 2024 |website=UKradon}}

Interactive maps of radon affected areas are available for various regions and countries of the world.{{Cite web |title=Radon Zone Map (with State Information) |url=https://gispub.epa.gov/radon/ |url-status=live |archive-url=https://web.archive.org/web/20230401042017/https://gispub.epa.gov/radon/ |archive-date=April 1, 2023 |access-date=April 10, 2024 |website=U.S. Environmental Protection Agency}}{{Cite web |title=UK maps of radon |url=https://www.ukradon.org/information/ukmaps |url-status=live |archive-url=https://web.archive.org/web/20240307083700/https://www.ukradon.org/information/ukmaps |archive-date=March 7, 2024 |access-date=April 10, 2024 |website=UKradon}}{{Cite web |title=Radon map of Australia |url=https://www.arpansa.gov.au/understanding-radiation/radiation-sources/more-radiation-sources/radon-map |url-status=live |archive-url=https://web.archive.org/web/20240320110315/https://www.arpansa.gov.au/understanding-radiation/radiation-sources/more-radiation-sources/radon-map |archive-date=March 20, 2024 |access-date=April 10, 2024 |website=Australian Radiation Protection and Nuclear Safety Agency (ARPANSA)}}

{{See also|Effects of climate change on human health}}

Indoor air quality is linked inextricably to outdoor air quality. The Intergovernmental Panel on Climate Change (IPCC) has varying scenarios that predict how the climate will change in the future.{{Cite web |title=Climate Change 2021: The Physical Science Basis |url=https://www.ipcc.ch/report/ar6/wg1/ |access-date=April 15, 2024 |website=Intergovernmental Panel on Climate Change |language=en |archive-date=May 26, 2023 |archive-url=https://web.archive.org/web/20230526182346/https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Chapter09.pdf |url-status=live }} Climate change can affect indoor air quality by increasing the level of outdoor air pollutants such as ozone and particulate matter, for example through emissions from wildfires caused by extreme heat and drought.{{Cite journal |last1=Chen |first1=Guochao |last2=Qiu |first2=Minghao |last3=Wang |first3=Peng |last4=Zhang |first4=Yuqiang |last5=Shindell |first5=Drew |last6=Zhang |first6=Hongliang |date=19 July 2024 |title=Continuous wildfires threaten public and ecosystem health under climate change across continents |journal=Frontiers of Environmental Science & Engineering |language=en |volume=18 |issue=10 |page=130 |doi=10.1007/s11783-024-1890-6 |issn=2095-2201|doi-access=free |bibcode=2024FrESE..18..130C }}{{Cite journal |last1=Gherasim |first1=Alina |last2=Lee |first2=Alison G. |last3=Bernstein |first3=Jonathan A. |date=November 14, 2023 |title=Impact of Climate Change on Indoor Air Quality |url=https://linkinghub.elsevier.com/retrieve/pii/S0889856123000851 |journal=Immunology and Allergy Clinics of North America |language=en |volume=44 |issue=1 |pages=55–73 |doi=10.1016/j.iac.2023.09.001 |pmid=37973260 |access-date=April 15, 2024 |archive-date=November 15, 2023 |archive-url=https://web.archive.org/web/20231115075718/https://linkinghub.elsevier.com/retrieve/pii/S0889856123000851 |url-status=live |url-access=subscription }} Numerous predictions for how indoor air pollutants will change have been made,{{Cite journal |last1=Lacressonnière |first1=Gwendoline |last2=Watson |first2=Laura |last3=Gauss |first3=Michael |last4=Engardt |first4=Magnuz |last5=Andersson |first5=Camilla |last6=Beekmann |first6=Matthias |last7=Colette |first7=Augustin |last8=Foret |first8=Gilles |last9=Josse |first9=Béatrice |last10=Marécal |first10=Virginie |last11=Nyiri |first11=Agnes |last12=Siour |first12=Guillaume |last13=Sobolowski |first13=Stefan |last14=Vautard |first14=Robert |date=February 1, 2017 |title=Particulate matter air pollution in Europe in a +2 °C warming world |url=https://linkinghub.elsevier.com/retrieve/pii/S1352231017300456 |journal=Atmospheric Environment |language=en |volume=154 |pages=129–140 |doi=10.1016/j.atmosenv.2017.01.037 |bibcode=2017AtmEn.154..129L |access-date=April 15, 2024 |archive-date=November 17, 2023 |archive-url=https://web.archive.org/web/20231117225734/https://linkinghub.elsevier.com/retrieve/pii/S1352231017300456 |url-status=live |url-access=subscription }}{{Cite journal |last1=Lee |first1=J |last2=Lewis |first2=A |last3=Monks |first3=P |last4=Jacob |first4=M |last5=Hamilton |first5=J |last6=Hopkins |first6=J |last7=Watson |first7=N |last8=Saxton |first8=J |last9=Ennis |first9=C |last10=Carpenter |first10=L |date=September 26, 2006 |title=Ozone photochemistry and elevated isoprene during the UK heatwave of august 2003 |url=https://linkinghub.elsevier.com/retrieve/pii/S1352231006007254 |journal=Atmospheric Environment |language=en |volume=40 |issue=39 |pages=7598–7613 |doi=10.1016/j.atmosenv.2006.06.057 |bibcode=2006AtmEn..40.7598L |access-date=April 15, 2024 |archive-date=October 26, 2022 |archive-url=https://web.archive.org/web/20221026103502/https://linkinghub.elsevier.com/retrieve/pii/S1352231006007254 |url-status=live |url-access=subscription }}{{Cite journal |last1=Salthammer |first1=Tunga |last2=Schieweck |first2=Alexandra |last3=Gu |first3=Jianwei |last4=Ameri |first4=Shaghayegh |last5=Uhde |first5=Erik |date=August 7, 2018 |title=Future trends in ambient air pollution and climate in Germany – Implications for the indoor environment |journal=Building and Environment |language=en |volume=143 |pages=661–670 |doi=10.1016/j.buildenv.2018.07.050 |bibcode=2018BuEnv.143..661S |doi-access=free }}{{Cite journal |last1=Zhong |first1=L. |last2=Lee |first2=C.-S. |last3=Haghighat |first3=F. |date=December 1, 2016 |title=Indoor ozone and climate change |url=https://linkinghub.elsevier.com/retrieve/pii/S2210670716302748 |journal=Sustainable Cities and Society |language=en |volume=28 |pages=466–472 |doi=10.1016/j.scs.2016.08.020 |access-date=April 15, 2024 |archive-date=November 28, 2022 |archive-url=https://web.archive.org/web/20221128061645/https://linkinghub.elsevier.com/retrieve/pii/S2210670716302748 |url-status=live |url-access=subscription }} and models have attempted to predict how the forecasted IPCC scenarios will vary indoor air quality and indoor comfort parameters such as humidity and temperature.{{Cite journal |last1=Zhao |first1=Jiangyue |last2=Uhde |first2=Erik |last3=Salthammer |first3=Tunga |last4=Antretter |first4=Florian |last5=Shaw |first5=David |last6=Carslaw |first6=Nicola |last7=Schieweck |first7=Alexandra |date=December 9, 2023 |title=Long-term prediction of the effects of climate change on indoor climate and air quality |journal=Environmental Research |language=en |volume=243 |pages=117804 |doi=10.1016/j.envres.2023.117804 |pmid=38042519 |doi-access=free }}

The net-zero challenge requires significant changes in the performance of both new and retrofitted buildings. However, increased energy efficient housing will trap pollutants inside, whether produced indoors or outdoors, and lead to an increase in human exposure.{{Cite journal |last=Niculita-Hirzel |first=Hélène |date=March 16, 2022 |title=Latest Trends in Pollutant Accumulations at Threatening Levels in Energy-Efficient Residential Buildings with and without Mechanical Ventilation: A Review |journal=International Journal of Environmental Research and Public Health |language=en |volume=19 |issue=6 |pages=3538 |doi=10.3390/ijerph19063538 |issn=1660-4601 |pmc=8951331 |pmid=35329223 |doi-access=free}}{{Cite book |last=UK Health Security Agency |url=https://www.gov.uk/government/publications/climate-change-health-effects-in-the-uk |title=Health Effects of Climate Change (HECC) in the UK: 2023 report |year=2024 |publication-date=15 January 2024 |chapter=Chapter 5: Impact of climate change policies on indoor environmental quality and health in UK housing |orig-date=1 September 2012}}

For occupational exposure, there are standards, which cover a wide range of chemicals, and applied to healthy adults who are exposed over time at workplaces (usually industrial environments).These are published by organisations such as Occupational Safety and Health Administration (OSHA), the National Institute for Occupational Safety and Health (NIOSH), the UK Health and Safety Executive (HSE).

There is no consensus globally about indoor air quality standards, or health-based guidelines. However, there are regulations from some individual countries and from health organisations. For example, the World Health Organization (WHO) has published health-based global air quality guidelines for the general population that are applicable both to outdoor and indoor air, as well as the WHO IAQ guidelines for selected compounds,{{Cite book |url=https://www.worldcat.org/title/696099951 |title=Who guidelines for indoor air quality: selected pollutants |date=2010 |publisher=WHO |isbn=978-92-890-0213-4 |editor-last=World Health Organization |location=Copenhagen |oclc=696099951}} whereas the UK Health Security Agency published IAQ guidelines for selected VOCs.{{Cite web |date=13 September 2019 |title=Air quality: UK guidelines for volatile organic compounds in indoor spaces |url=https://www.gov.uk/government/publications/air-quality-uk-guidelines-for-volatile-organic-compounds-in-indoor-spaces |access-date=2024-04-17 |website=Public Health England |language=en}} The Scientific and Technical Committee (STC34) of the International Society of Indoor Air Quality and Climate (ISIAQ) created an open database that collects indoor environmental quality guidelines worldwide.{{Cite web |title=Home - IEQ Guidelines |url=https://ieqguidelines.org/ |access-date=2024-04-17 |website=ieqguidelines.org}} The database is focused on indoor air quality (IAQ), but is currently extended to include standards, regulations, and guidelines related to ventilation, comfort, acoustics, and lighting.{{Cite journal |last1=Toyinbo |first1=Oluyemi |last2=Hägerhed |first2=Linda |last3=Dimitroulopoulou |first3=Sani |last4=Dudzinska |first4=Marzenna |last5=Emmerich |first5=Steven |last6=Hemming |first6=David |last7=Park |first7=Ju-Hyeong |last8=Haverinen-Shaughnessy |first8=Ulla |last9=the Scientific Technical Committee 34 of the International Society of Indoor Air Quality, Climate |date=19 April 2022 |title=Open database for international and national indoor environmental quality guidelines |journal=Indoor Air |language=en |volume=32 |issue=4 |pages=e13028 |doi=10.1111/ina.13028 |pmid=35481936 |pmc=11099937 |bibcode=2022InAir..3213028T |issn=0905-6947}}{{Cite journal |last1=Dimitroulopoulou |first1=Sani |last2=Dudzińska |first2=Marzenna R. |last3=Gunnarsen |first3=Lars |last4=Hägerhed |first4=Linda |last5=Maula |first5=Henna |last6=Singh |first6=Raja |last7=Toyinbo |first7=Oluyemi |last8=Haverinen-Shaughnessy |first8=Ulla |date=4 August 2023 |title=Indoor air quality guidelines from across the world: An appraisal considering energy saving, health, productivity, and comfort |url=https://linkinghub.elsevier.com/retrieve/pii/S0160412023004002 |journal=Environment International |language=en |volume=178 |pages=108127 |doi=10.1016/j.envint.2023.108127|pmid=37544267 |bibcode=2023EnInt.17808127D }}

Since indoor air pollutants can adversely affect human health, it is important to have real-time indoor air quality assessment/monitoring system that can help not only in the improvement of indoor air quality but also help in detection of leaks, spills in a work environment and boost energy efficiency of buildings by providing real-time feedback to the heating, ventilation, and air conditioning (HVAC) system(s).{{cite journal |last1=Pitarma |first1=Rui |last2=Marques |first2=Gonçalo |last3=Ferreira |first3=Bárbara Roque |title=Monitoring Indoor Air Quality for Enhanced Occupational Health |journal=Journal of Medical Systems |date=February 2017 |volume=41 |issue=2 |page=23 |doi=10.1007/s10916-016-0667-2 |pmid=28000117 |s2cid=7372403 }} Additionally, there have been enough studies that highlight the correlation between poor indoor air quality and loss of performance and productivity of workers in an office setting.{{cite journal |last1=Wyon |first1=D. P. |title=The effects of indoor air quality on performance and productivity: The effects of IAQ on performance and productivity |journal=Indoor Air |date=August 2004 |volume=14 |pages=92–101 |doi=10.1111/j.1600-0668.2004.00278.x |pmid=15330777 }}  

Combining the Internet of Things (IoT) technology with real-time IAQ monitoring systems has  tremendously gained momentum and popularity as interventions can be done based on the real-time sensor data and thus help in the IAQ improvement.{{cite journal |last1=Son |first1=Young Joo |last2=Pope |first2=Zachary C. |last3=Pantelic |first3=Jovan |title=Perceived air quality and satisfaction during implementation of an automated indoor air quality monitoring and control system |journal=Building and Environment |date=September 2023 |volume=243 |pages=110713 |doi=10.1016/j.buildenv.2023.110713 |doi-access=free |bibcode=2023BuEnv.24310713S }}   

{{Expand section|small=no|date=November 2023}}

{{See also|Air purifier|Air conditioner|Air filter|Cleanroom|Particulates#Controlling technologies and measures|Pollution control|Ventilation (architecture)}}

{{Further|Fan (machine)|Dehumidifier|Heater}}Indoor air quality can be addressed, achieved or maintained during the design of new buildings or as mitigating measures in existing buildings. A hierarchy of measures has been proposed by the Institute of Air Quality Management. It emphasises removing pollutant sources, reducing emissions from any remaining sources, disrupting pathways between sources and the people exposed, protecting people from exposure to pollutants, and removing people from areas with poor air quality.{{Cite book |last=IAQM |url=https://iaqm.co.uk/wp-content/uploads/2013/02/iaqm_indoorairquality_v4_consultation_draft.pdf |title=Indoor Air Quality Guidance: Assessment, Monitoring, Modelling and Mitigation |publisher=Institute of Air Quality Management |year=2021 |edition=Version 0.1 |location=London}}

A report assisted by the Institute for Occupational Safety and Health of the German Social Accident Insurance can support in the systematic investigation of individual health problems arising at indoor workplaces, and in the identification of practical solutions.{{Cite web |last=Institute for Occupational Safety and Health of the German Social Accident Insurance |title=Indoor workplaces – Recommended procedure for the investigation of working environment |url=https://www.dguv.de/ifa/praxishilfen/innenraumarbeitsplaetze/index-2.jsp |url-status=live |archive-url=https://web.archive.org/web/20211103172404/https://www.dguv.de/ifa/praxishilfen/innenraumarbeitsplaetze/index-2.jsp |archive-date=November 3, 2021 |access-date=June 10, 2020}}

{{empty section|date=September 2024}}

{{Main|HVAC|Air handler|Ventilation (architecture)}}

{{more citations needed section|date=November 2019}}

Environmentally sustainable design concepts include aspects of commercial and residential heating, ventilation and air-conditioning (HVAC) technologies. Among several considerations, one of the topics attended to is the issue of indoor air quality throughout the design and construction stages of a building's life.{{citation needed|date=September 2024}}

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.{{citation needed|date=September 2024}}

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 US, 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 over 400 ppm{{Cite web |date=2024-04-09 |title=Climate Change: Atmospheric Carbon Dioxide {{!}} NOAA Climate.gov |url=http://www.climate.gov/news-features/understanding-climate/climate-change-atmospheric-carbon-dioxide |access-date=2024-05-06 |website=www.climate.gov |language=en}} (global average as of 2023). 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. As the occupants are not the only source of pollutants, outdoor air ventilation may need to be higher when unusual or strong sources of pollution exist indoors.

When outdoor air is polluted, 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. Generally, outdoor country air is better than indoor city air.{{citation needed|date=September 2024}}

The use of air filters can trap some of the air pollutants. Portable room air cleaners with HEPA filters can be used if ventilation is poor or outside air has high level of PM 2.5. Air filters are used to reduce the amount of dust that reaches the wet coils.{{citation needed|date=September 2024}} Dust can serve as food to grow molds on the wet coils and ducts and can reduce the efficiency of the coils.{{citation needed|date=September 2024}}

The use of trickle vents on windows is also valuable to maintain constant ventilation. They can help prevent mold and allergen build up in the home or workplace. They can also reduce the spread of some respiratory infections.{{Cite web |date=August 2, 2022 |title=Ventilation to reduce the spread of respiratory infections, including COVID-19 |url=https://www.gov.uk/guidance/ventilation-to-reduce-the-spread-of-respiratory-infections-including-covid-19 |access-date=April 15, 2024 |website=GOV.UK |language=en |archive-date=January 18, 2024 |archive-url=https://web.archive.org/web/20240118112231/https://www.gov.uk/guidance/ventilation-to-reduce-the-spread-of-respiratory-infections-including-covid-19 |url-status=live }}

Moisture management and humidity control requires operating HVAC systems as designed. Moisture management and humidity control may conflict with efforts 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.{{citation needed|date=September 2024}} However, high humidity outdoors creates the need for careful attention to humidity levels indoors. High humidity give rise to mold growth and moisture indoors is associated with a higher prevalence of occupant respiratory problems.{{citation needed|date=September 2024}}

The "dew point temperature" is an absolute measure of the moisture in air. Some facilities are being designed with dew points in the lower 50s °F, and some in the upper and lower 40s °F.{{citation needed|date=September 2024}} Some facilities are being designed using desiccant wheels with gas-fired heaters to dry out the wheel enough to get the required dew points.{{citation needed|date=September 2024}} 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.{{citation needed|date=September 2024}}

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.

Image:Spider Plant Blades.JPG) absorb some airborne contaminants.]]

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 remove CO₂ and release oxygen and water, although the quantitative impact for house plants is small. The interest in using potted plants for removing VOCs was sparked by a 1989 NASA study conducted in sealed chambers designed to replicate the environment on space stations. However, these results suffered from poor replication{{cite journal |last1=Dela Cruz |first1=Majbrit |last2=Christensen |first2=Jan H. |last3=Thomsen |first3=Jane Dyrhauge |last4=Müller |first4=Renate |date=December 2014 |title=Can ornamental potted plants remove volatile organic compounds from indoor air? — a review |journal=Environmental Science and Pollution Research |volume=21 |issue=24 |pages=13909–13928 |bibcode=2014ESPR...2113909D |doi=10.1007/s11356-014-3240-x |pmid=25056742 |s2cid=207272189}} and are not applicable to typical buildings, where outdoor-to-indoor air exchange already removes VOCs at a rate that could only be matched by the placement of 10–1000 plants/m² of a building's floor space.{{cite journal |last1=Cummings |first1=Bryan E. |last2=Waring |first2=Michael S. |date=March 2020 |title=Potted plants do not improve indoor air quality: a review and analysis of reported VOC removal efficiencies |journal=Journal of Exposure Science & Environmental Epidemiology |volume=30 |issue=2 |pages=253–261 |doi=10.1038/s41370-019-0175-9 |pmid=31695112 |bibcode=2020JESEE..30..253C |s2cid=207911697}}

Plants also appear to reduce airborne microbes and molds, and to increase humidity.{{cite journal |last1=Wolverton |first1=B. C. |last2=Wolverton |first2=J. D. |date=1996 |title=Interior plants: their influence on airborne microbes inside energy-efficient buildings |journal=Journal of the Mississippi Academy of Sciences |volume=41 |issue=2 |pages=100–105}} However, the increased humidity can itself lead to increased levels of mold and even VOCs.{{Cite web |last=US EPA |first=OAR |date=July 16, 2013 |title=Mold |url=https://www.epa.gov/mold |url-status=live |archive-url=https://web.archive.org/web/20200518223635/https://www.epa.gov/mold |archive-date=May 18, 2020 |access-date=September 16, 2019 |website=US EPA |language=en}}

Since extremely 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 if watering is done inappropriately.{{cite book |author1=Institute of Medicine (US) Committee on Damp Indoor Spaces and Health |url=https://www.ncbi.nlm.nih.gov/books/NBK215643/ |title=Damp Indoor Spaces and Health |date=2004 |publisher=National Academies Press |isbn=978-0-309-09193-0 |pmid=25009878 |access-date=March 30, 2024 |archive-url=https://web.archive.org/web/20230119023355/https://www.ncbi.nlm.nih.gov/books/NBK215643/ |archive-date=January 19, 2023 |url-status=live}}{{page needed|date=March 2024}}

File:ELIMINATE TRIGGERS (14305286383).jpg

The topic of IAQ has become popular due to the greater awareness of health problems caused by mold and triggers to asthma and allergies.

In the US, the Environmental Protection Agency (EPA) has developed an "IAQ Tools for Schools" program to help improve the indoor environmental conditions in educational institutions. 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.{{cite web |url=https://www.cdc.gov/niosh/topics/indoorenv/ |title=Indoor Environmental Quality |publisher=US National Institute for Occupational Safety and Health |location=Washington, DC |access-date=May 17, 2013 |archive-date=December 3, 2013 |archive-url=https://web.archive.org/web/20131203030020/http://www.cdc.gov/niosh/topics/indoorenv/ |url-status=live }}

A variety of scientists work in the field of indoor air quality, including chemists, physicists, mechanical engineers, biologists, bacteriologists, epidemiologists, 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.

In the UK, under the Department for Environment Food and Rural Affairs, the Air Quality Expert Group considers current knowledge on indoor air quality and provides advice to government and devolved administration ministers.{{Cite report |url=https://uk-air.defra.gov.uk/assets/documents/reports/cat09/2211011000_15062022_Indoor_Air_Quality_Report_Final.pdf |title=Indoor Air Quality |last1=Lewis |first1=Alastair C |last2=Allan |first2=James |date=2022 |publisher=Air Quality Expert Group |doi=10.5281/zenodo.6523605 |language=en |last3=Carslaw |first3=David |last4=Carruthers |first4=David |last5=Fuller |first5=Gary |last6=Harrison |first6=Roy |last7=Heal |first7=Mathew |last8=Nemitz |first8=Eiko |last9=Reeves |first9=Claire |access-date=April 15, 2024 |archive-date=June 5, 2023 |archive-url=https://web.archive.org/web/20230605190450/https://uk-air.defra.gov.uk/assets/documents/reports/cat09/2211011000_15062022_Indoor_Air_Quality_Report_Final.pdf |url-status=live }}

At 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.{{cite web |url=http://isiaq.org/ |title=Isiaq.Org |publisher=International Society of Indoor Air Quality and Climate |access-date=March 2, 2012 |archive-date=January 21, 2022 |archive-url=https://web.archive.org/web/20220121171412/https://www.isiaq.org/ |url-status=live }}

• Environmental management
• Healthy building
• Indoor bioaerosol
• Microbiomes of the built environment
• Olfactory fatigue

{{Reflist}}

; Monographs

{{Refbegin}}

• {{cite book |last1=May |first1=Jeffrey C. |title=The mold survival guide for your home and for your health |url=https://archive.org/details/moldsurvivalguid00jeff |url-access=registration |year=2004 |publisher=Johns Hopkins University Press |location=Baltimore |isbn=978-0-8018-7938-8 |author3=Ouellette, John J. |author2=Connie L. May |author4=Reed, Charles E. }}
• {{cite book |last=May |first=Jeffrey C. |title = My house is killing me! : the home guide for families with allergies and asthma |year=2001 |publisher=The Johns Hopkins University Press |location=Baltimore |isbn=978-0-8018-6730-9 }}
• {{cite book |last = May |first = Jeffrey C. |title = My office is killing me! : the sick building survival guide |year = 2006 |publisher = The Johns Hopkins University Press |location = Baltimore |isbn = 978-0-8018-8342-2 |url-access = registration |url = https://archive.org/details/myofficeiskillin0000mayj }}
• {{cite book |editor=Salthammer, T. |title=Organic Indoor Air Pollutants — Occurrence, Measurement, Evaluation |publisher=Wiley-VCH |year=1999 |isbn=978-3-527-29622-4 |url-access=registration |url=https://archive.org/details/organicindoorair0000unse }}
• {{cite book |author1=Spengler, J.D. |author2=Samet, J.M. |title=Indoor air pollution: A health perspective |publisher=Johns Hopkins University Press |location=Baltimore |year=1991 |isbn=978-0-8018-4125-5 |url-access=registration |url=https://archive.org/details/indoorairpolluti0000unse_m9a3 }}
• {{cite book |author1=Samet, J.M. |author2=McCarthy, J.F. |title = Indoor Air Quality Handbook |publisher=McGraw–Hill |location=NY |year=2001 |isbn=978-0-07-445549-4 }}
• {{cite book |author=Tichenor, B. |title = Characterizing Sources of Indoor Air Pollution and Related Sink Effects |publisher=ASTM |location = West Conshohocken, PA |year=1996 |isbn=978-0-8031-2030-3 |series = ASTM STP 1287 }}
• {{cite book |editor-last=Zeeb |editor-first=Hajo |editor-last2=Shannoun |editor-first2=Ferid |title=WHO Handbook on Indoor Radon: A Public Health Perspective |date=2009 |publisher=World Health Organization |isbn=978-92-4-154767-3 |id={{NCBIBook2|NBK143216}} |pmid=23762967 |url=https://www.who.int/publications/i/item/9789241547673 |access-date=March 30, 2024 |archive-date=March 30, 2024 |archive-url=https://web.archive.org/web/20240330134105/https://www.who.int/publications/i/item/9789241547673 |url-status=live }}

{{Refend}}

; Articles, radio segments, web pages

{{Refbegin}}

• {{cite journal |last1=Apte |first1=M. G. |last2=Buchanan |first2=I. S. H. |last3=Mendell |first3=M. J. |title=Outdoor ozone and building-related symptoms in the BASE study |journal=Indoor Air |date=April 2008 |volume=18 |issue=2 |pages=156–170 |doi=10.1111/j.1600-0668.2008.00521.x |pmid=18333994 |bibcode=2008InAir..18..156A |doi-access=free }}
• [https://www.npr.org/templates/story/story.php?storyId=14594337 Bad In-Flight Air Exacerbated by Passengers] {{Webarchive|url=https://web.archive.org/web/20211215041942/https://www.npr.org/templates/story/story.php?storyId=14594337 |date=December 15, 2021 }}, Talk of the Nation, National Public Radio, September 21, 2007.
• [https://web.archive.org/web/20020601212819/http://www.epa.gov/ebtpages/airindoorairpollution.html Indoor Air Pollution index page], United States Environmental Protection Agency.
• {{cite journal |doi=10.1016/j.buildenv.2016.11.009 |title = Ten questions concerning air fresheners and indoor built environments |journal = Building and Environment |volume=111 |pages=279–284 |year=2017 |last1 = Steinemann |first1 = Anne |doi-access=free |bibcode = 2017BuEnv.111..279S |hdl=11343/121890 |hdl-access=free }}

{{Refend}}

• {{cite journal | title=A Review of Recent Advances in Research on PM2.5 in China| year=2018| pmc=5876983| last1=Lin| first1=Y.| last2=Zou| first2=J.| last3=Yang| first3=W.| last4=Li| first4=C. Q.| journal=International Journal of Environmental Research and Public Health| volume=15| issue=3| page=438| doi=10.3390/ijerph15030438| pmid=29498704| doi-access=free}}
• {{cite journal |last1=Abdel Hameed |first1=A. A. |last2=Yasser |first2=I. H. |last3=Khoder |first3=I. M. |title=Indoor air quality during renovation actions: a case study |journal=Journal of Environmental Monitoring |date=2004 |volume=6 |issue=9 |pages=740–744 |doi=10.1039/b402995j |pmid=15346177 }}

• [http://www.epa.gov/iaq/ US Environmental Protection Agency info on IAQ]
• [https://www.epa.gov/indoor-air-quality-iaq/best-practices-indoor-air-quality-when-remodeling-your-home Best Practices for Indoor Air Quality when Remodeling Your Home, US EPA]
• [https://www.epa.gov/indoor-air-quality-iaq/addressing-indoor-environmental-concerns-during-remodeling Addressing Indoor Environmental Concerns During Remodeling, US EPA]
• [https://www.epa.gov/iaq-schools/renovation-and-repair-part-indoor-air-quality-design-tools-schools Renovation and Repair, Part of Indoor Air Quality Design Tools for Schools, US EPA]
• [https://9foundations.forhealth.org/ The 9 Foundations of a Healthy Building], Harvard T.H. Chan School of Public Health

{{Pollution}}

{{Natural resources}}

{{Occupational safety and health}}

{{HVAC}}

{{Authority control}}

Category:Building biology

Category:Indoor air pollution

Category:Industrial hygiene

Category:Heating, ventilation, and air conditioning

Category:Occupational safety and health