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Indoor air pollutants can originate from various sources, both inside and outside the building. These pollutants can be either anthropogenic (caused by human activities) or natural.
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== Combustion sources ==
Indoor air pollutants originate from a wide variety of sources located both inside and outside the building envelope<ref name="Bolan_2021" />. These contaminants can be either anthropogenic, meaning they are produced by human activities and everyday routines, or natural, arising from the surrounding geological environment<ref name="Bolan_2021" /><ref name="EDIAQI_D32" />. Because modern populations spend up to 90% of their time indoors, understanding where these pollutants come from is essential for maintaining a healthy indoor environment<ref name="Halios_2022" />.
Combustion processes, such as those from gas stoves, fireplaces, and smoking, release various pollutants into the air:


* '''Carbon monoxide (CO)'''
== Combustion Sources ==
* '''Nitrogen dioxide (NO2)'''
Combustion processes are among the most significant contributors to indoor air pollution<ref name="Bolan_2021" /><ref name="Sadrizadeh_2022" />. When fuels or organic materials are burned for heating, cooking, or other activities, they release a complex mixture of gases and fine particles directly into the living space<ref name="Halios_2022" /><ref name="Sadrizadeh_2022" />:
* '''Particulate matter (PM<sub>2.5</sub> and PM<sub>10</sub>)'''
 
* '''Volatile organic compounds (VOCs)'''
* '''Carbon Monoxide (CO):''' A colorless and odorless toxic gas produced by the incomplete combustion of carbonaceous fuels<ref name="WHO_2010" />. Major indoor sources include unvented or faulty gas stoves, poorly maintained heating appliances, fireplaces, and tobacco smoke<ref name="WHO_2010" /><ref name="Sadrizadeh_2022" />.
* '''Nitrogen Dioxide (NO2):''' An irritating combustion gas emitted by gas cookers, space heaters, and kerosene appliances, as well as by the infiltration of outdoor traffic exhaust<ref name="WHO_2010" /><ref name="Sadrizadeh_2022" />.
* '''Particulate Matter (PM2.5 and PM10):''' Fine and coarse microscopic particles generated by cooking activities, wood or pellet stoves, candles, incense, and tobacco smoke<ref name="Halios_2022" /><ref name="Sadrizadeh_2022" />.
* '''Polycyclic Aromatic Hydrocarbons (PAHs):''' Persistent toxic compounds bound to airborne particles, originating from indoor combustion sources such as wood burning, biomass heating, and smoking<ref name="Bolan_2021" /><ref name="Sadrizadeh_2022" />.


== Building Materials and Furnishings ==
== Building Materials and Furnishings ==
Many building materials and furnishings can emit VOCs, including:
The physical structure of a building and its interior finishes can continuously release chemical vapors into the air<ref name="Bolan_2021" /><ref name="Halios_2022" />:


* '''Paints and varnishes:''' These often contain solvents that release VOCs as they dry.
* '''Paints and Varnishes:''' Freshly applied paints, lacquers, and surface coatings contain organic solvents that release high levels of volatile organic compounds (VOCs) as they dry<ref name="Bolan_2021" /><ref name="Halios_2022" />.
* '''Adhesives and sealants:''' Used in construction and renovations, these can emit VOCs for extended periods.
* '''Adhesives and Sealants:''' Glues, caulks, and construction sealants used during renovations emit chemical vapors that can persist indoors for extended periods<ref name="Bolan_2021" /><ref name="Halios_2022" />.
* '''Carpets and flooring:''' Some carpets and flooring materials can release VOCs, especially when new.
* '''Carpets and Flooring:''' Synthetic carpets, flooring materials, and associated adhesives can off-gas VOCs, particularly when newly installed<ref name="Bolan_2021" /><ref name="Halios_2022" />.
* '''Furniture:''' Certain types of furniture, particularly those made with pressed wood products, can emit formaldehyde, a type of VOC.
* '''Furniture and Pressed Wood Products:''' Furniture manufactured from particleboard, plywood, and medium-density fiberboard frequently emits formaldehyde, a well-known VOC of health concern<ref name="Halios_2022" /><ref name="WHO_2010" />.


== Household Products ==
== Household Products ==
A wide range of household products can contribute to indoor air pollution:
Everyday consumer goods used for home maintenance, hygiene, and convenience contribute significantly to the indoor chemical load<ref name="Bolan_2021" /><ref name="Halios_2022" />:


* '''Cleaning products'''
* '''Cleaning Agents:''' Surface cleaners, dishwashing detergents, polishes, and disinfectants release chemical vapors and can interact with other indoor gases to form secondary pollutants<ref name="Bolan_2021" /><ref name="Halios_2022" />.
* '''Personal care products'''
* '''Personal Care Products:''' Perfumes, deodorants, hair sprays, cosmetics, and nail polish removers introduce a variety of volatile organic compounds into indoor air<ref name="Halios_2022" /><ref name="SCHER_2008" />.
* '''Pesticides and insecticides'''
* '''Pesticides and Insecticides:''' Products used to control household pests release chemical residues that remain suspended in the air or settle into indoor dust.
* '''Air Fresheners:''' Scented candles, incense, plug-in air fresheners, and sprays emit numerous VOCs and fine particulate matter<ref name="Halios_2022" /><ref name="Sadrizadeh_2022" />.


== Biological Sources ==
== Biological Sources ==
Biological pollutants are living organisms or substances derived from them that can cause health problems.
Biological pollutants consist of living organisms or organic fragments suspended in the air that can trigger allergic reactions and respiratory illnesses<ref name="WHO_2009" />:


* '''Mold''': Mold spores can trigger allergies and respiratory problems. Mold growth is often associated with dampness and poor ventilation.
* '''Mold and Fungi:''' Spores and fragments grow on damp building materials, window frames, and unventilated surfaces, releasing mycotoxins and allergens linked to asthma exacerbation<ref name="WHO_2009" />.
* '''Bacteria and viruses:''' These can cause infections and illnesses.
* '''Bacteria and Viruses:''' Airborne pathogens can spread easily in crowded or poorly ventilated indoor spaces, increasing the risk of infections<ref name="EDIAQI_D32" />.
* '''Dust mites:''' Microscopic creatures that feed on dead skin cells and can trigger allergies and asthma.
* '''Dust Mites:''' Microscopic arachnids that thrive in warm, humid environments and feed on shed human skin cells, producing potent allergens found in house dust<ref name="WHO_2009" />.
* '''Pet dander:''' Tiny flakes of skin shed by pets that can cause allergies.
* '''Pet Dander:''' Tiny scales of animal skin, saliva, and protein secretions shed by pets can remain airborne and trigger allergic sensitization<ref name="WHO_2009" />.


== Indoor activities ==
== Indoor Activities ==
Various indoor activities can contribute to indoor air pollution:
Human routines and daily activities directly influence indoor air quality levels<ref name="Sadrizadeh_2022" />:


* '''Cooking:''' Cooking activities can release PM, VOCs, and other pollutants into the air.
* '''Cooking:''' Frying, boiling, and roasting food release cooking oil mists, fine particulate matter, and organic gases, especially when cooking ventilation hoods are not used<ref name="Halios_2022" /><ref name="Sadrizadeh_2022" />.
* '''Personal activities:''' Smoking, using hobby materials, and even breathing can contribute to indoor air pollution.
* '''Smoking and Vaping:''' Tobacco consumption and electronic cigarettes introduce thousands of hazardous chemicals, including nicotine, fine particles, and toxic gases, into the indoor environment<ref name="WHO_2010" /><ref name="Sadrizadeh_2022" />.
* '''Office Equipment:''' Laser printers, photocopiers, and scanners can emit ozone, ultrafine particles, and volatile organic compounds during operation<ref name="SCHER_2008" /><ref name="Halios_2022" />.


== Outdoor environment ==
== Outdoor Environment and Infiltration ==
Outdoor pollution sources can significantly impact indoor air quality through natural ventilation or infiltration<ref name="Bolan_2021" /><ref name="Sadrizadeh_2022" />:
 
* '''Outdoor Air Infiltration:''' Pollutants from nearby road traffic, industrial emissions, and urban smog enter buildings through open windows, doors, and structural cracks<ref name="Bolan_2021" /><ref name="Sadrizadeh_2022" />.
* '''Radon:''' A naturally occurring, radioactive gas formed by the decay of uranium in soil and rock. Radon can seep up through foundations, basement cracks, and building materials, accumulating in indoor spaces as a leading cause of lung cancer<ref name="WHO_2010" /><ref name="EDIAQI_D32" />.
 
<div class="mw-collapsible mw-collapsed" style="border: 1px solid #009688; padding: 12px; background-color: #f4fbf9; margin: 15px 0;">
'''[+] Click here to view technical details on pollutant behavior and emission dynamics'''
<div class="mw-collapsible-content">
Indoor pollutant concentrations are governed by complex dynamic processes, including indoor-outdoor air exchange rates, surface deposition, chemical reactions, and emission decay curves over time<ref name="Bolan_2021" /><ref name="Halios_2022" />. For instance, secondary organic aerosols can form indoors via reactions between ozone infiltrating from outdoors and unsaturated organic gases like terpenes emitted from cleaning products or air fresheners<ref name="Halios_2022" />. Furthermore, energy-efficient building retrofits that reduce air exchange rates without ensuring adequate mechanical ventilation can lead to the significant accumulation of indoor-generated VOCs and moisture<ref name="Sadrizadeh_2022" />.
</div>
</div>
 
== Related Project Pages ==
* [[What is IAQ?]]
* [[Main indoor air pollutants]]
* [[IAQ relationship to human health]]
* [[Controlling the pollution sources]]


=== Soil ===
* '''Radon:''' A naturally occurring radioactive gas that can seep into buildings from the ground and is a leading cause of lung cancer.
== References ==
== References ==
{{Reflist}}
<references>
<ref name="Bolan_2021">{{#lst:Reading List|Bolan_2021}}</ref>
<ref name="EDIAQI_D32">{{#lst:Reading List|EDIAQI_D32}}</ref>
<ref name="Settimo_2020">{{#lst:Reading List|Settimo_2020}}</ref>
<ref name="Halios_2022">{{#lst:Reading List|Halios_2022}}</ref>
<ref name="WHO_2010">{{#lst:Reading List|WHO_2010}}</ref>
<ref name="WHO_2009">{{#lst:Reading List|WHO_2009}}</ref>
<ref name="Sadrizadeh_2022">{{#lst:Reading List|Sadrizadeh_2022}}</ref>
<ref name="SCHER_2008">{{#lst:Reading List|SCHER_2008}}</ref>
</references>
 
[[Category:Indoor air pollutants]]

Revision as of 15:46, 16 September 2026


Indoor air pollutants originate from a wide variety of sources located both inside and outside the building envelope[1]. These contaminants can be either anthropogenic, meaning they are produced by human activities and everyday routines, or natural, arising from the surrounding geological environment[1][2]. Because modern populations spend up to 90% of their time indoors, understanding where these pollutants come from is essential for maintaining a healthy indoor environment[3].

Combustion Sources

Combustion processes are among the most significant contributors to indoor air pollution[1][4]. When fuels or organic materials are burned for heating, cooking, or other activities, they release a complex mixture of gases and fine particles directly into the living space[3][4]:

  • Carbon Monoxide (CO): A colorless and odorless toxic gas produced by the incomplete combustion of carbonaceous fuels[5]. Major indoor sources include unvented or faulty gas stoves, poorly maintained heating appliances, fireplaces, and tobacco smoke[5][4].
  • Nitrogen Dioxide (NO2): An irritating combustion gas emitted by gas cookers, space heaters, and kerosene appliances, as well as by the infiltration of outdoor traffic exhaust[5][4].
  • Particulate Matter (PM2.5 and PM10): Fine and coarse microscopic particles generated by cooking activities, wood or pellet stoves, candles, incense, and tobacco smoke[3][4].
  • Polycyclic Aromatic Hydrocarbons (PAHs): Persistent toxic compounds bound to airborne particles, originating from indoor combustion sources such as wood burning, biomass heating, and smoking[1][4].

Building Materials and Furnishings

The physical structure of a building and its interior finishes can continuously release chemical vapors into the air[1][3]:

  • Paints and Varnishes: Freshly applied paints, lacquers, and surface coatings contain organic solvents that release high levels of volatile organic compounds (VOCs) as they dry[1][3].
  • Adhesives and Sealants: Glues, caulks, and construction sealants used during renovations emit chemical vapors that can persist indoors for extended periods[1][3].
  • Carpets and Flooring: Synthetic carpets, flooring materials, and associated adhesives can off-gas VOCs, particularly when newly installed[1][3].
  • Furniture and Pressed Wood Products: Furniture manufactured from particleboard, plywood, and medium-density fiberboard frequently emits formaldehyde, a well-known VOC of health concern[3][5].

Household Products

Everyday consumer goods used for home maintenance, hygiene, and convenience contribute significantly to the indoor chemical load[1][3]:

  • Cleaning Agents: Surface cleaners, dishwashing detergents, polishes, and disinfectants release chemical vapors and can interact with other indoor gases to form secondary pollutants[1][3].
  • Personal Care Products: Perfumes, deodorants, hair sprays, cosmetics, and nail polish removers introduce a variety of volatile organic compounds into indoor air[3][6].
  • Pesticides and Insecticides: Products used to control household pests release chemical residues that remain suspended in the air or settle into indoor dust.
  • Air Fresheners: Scented candles, incense, plug-in air fresheners, and sprays emit numerous VOCs and fine particulate matter[3][4].

Biological Sources

Biological pollutants consist of living organisms or organic fragments suspended in the air that can trigger allergic reactions and respiratory illnesses[7]:

  • Mold and Fungi: Spores and fragments grow on damp building materials, window frames, and unventilated surfaces, releasing mycotoxins and allergens linked to asthma exacerbation[7].
  • Bacteria and Viruses: Airborne pathogens can spread easily in crowded or poorly ventilated indoor spaces, increasing the risk of infections[2].
  • Dust Mites: Microscopic arachnids that thrive in warm, humid environments and feed on shed human skin cells, producing potent allergens found in house dust[7].
  • Pet Dander: Tiny scales of animal skin, saliva, and protein secretions shed by pets can remain airborne and trigger allergic sensitization[7].

Indoor Activities

Human routines and daily activities directly influence indoor air quality levels[4]:

  • Cooking: Frying, boiling, and roasting food release cooking oil mists, fine particulate matter, and organic gases, especially when cooking ventilation hoods are not used[3][4].
  • Smoking and Vaping: Tobacco consumption and electronic cigarettes introduce thousands of hazardous chemicals, including nicotine, fine particles, and toxic gases, into the indoor environment[5][4].
  • Office Equipment: Laser printers, photocopiers, and scanners can emit ozone, ultrafine particles, and volatile organic compounds during operation[6][3].

Outdoor Environment and Infiltration

Outdoor pollution sources can significantly impact indoor air quality through natural ventilation or infiltration[1][4]:

  • Outdoor Air Infiltration: Pollutants from nearby road traffic, industrial emissions, and urban smog enter buildings through open windows, doors, and structural cracks[1][4].
  • Radon: A naturally occurring, radioactive gas formed by the decay of uranium in soil and rock. Radon can seep up through foundations, basement cracks, and building materials, accumulating in indoor spaces as a leading cause of lung cancer[5][2].

[+] Click here to view technical details on pollutant behavior and emission dynamics

Indoor pollutant concentrations are governed by complex dynamic processes, including indoor-outdoor air exchange rates, surface deposition, chemical reactions, and emission decay curves over time[1][3]. For instance, secondary organic aerosols can form indoors via reactions between ozone infiltrating from outdoors and unsaturated organic gases like terpenes emitted from cleaning products or air fresheners[3]. Furthermore, energy-efficient building retrofits that reduce air exchange rates without ensuring adequate mechanical ventilation can lead to the significant accumulation of indoor-generated VOCs and moisture[4].

Related Project Pages

References

  1. ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12
  2. ↑ 2.0 2.1 2.2
  3. ↑ 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 3.11 3.12 3.13 3.14 3.15
    Halios, C. H., Landeg-Cox, C., Lowther, S. D., Middleton, A., Marczylo, T., & Dimitroulopoulou, S. (2022). Chemicals in European residences–Part I: A review of emissions, concentrations and health effects of volatile organic compounds (VOCs). Science of the Total Environment, 839, 156201.
  4. ↑ 4.00 4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.10 4.11 4.12
    Sadrizadeh, S., Yao, R., Yuan, F., Awbi, H., Bahnfleth, W., Bi, Y., ... & Li, B. (2022). Indoor air quality and health in schools: A critical review for developing the roadmap for the future school environment. Journal of Building Engineering, 57, 104908.
  5. ↑ 5.0 5.1 5.2 5.3 5.4 5.5
  6. ↑ 6.0 6.1
    Scientific Committee on Health and Environmental Risks (SCHER). (2008). Opinion on risk assessment on indoor air quality. European Commission, Directorate-General for Health and Consumer Protection, Brussels.
  7. ↑ 7.0 7.1 7.2 7.3

Cite error: <ref> tag with name "Settimo_2020" defined in <references> is not used in prior text.

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