Generated by indoor combustion 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. Around 3 billion people cook over open fires or on rudimentary cook stoves. Cooking fuels are coal, wood, animal dung, and crop residues. IAQ is a particular concern in
low and middle-income countries where such practices are common. 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.
Carbon monoxide 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. 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. Appliance malfunction may be due to faulty installation or lack of maintenance and proper use. Acute exposure should not exceed 10 mg/m3 in 8 hours, 35 mg/m3 in one hour and 100 mg/m3 in 15 minutes. Secondhand smoke contains more than 7000 chemicals, of which hundreds are harmful to health. Inhaling secondhand smoke on multiple occasions can cause
asthma,
pneumonia,
lung cancer, and
sudden infant death syndrome, among other conditions.
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. The only certain method to improve indoor air quality as regards secondhand smoke is to eliminate smoking indoors. Indoor
e-cigarette use also increases home
particulate matter concentrations.
Particulates 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). 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. Preparing a
Thanksgiving dinner can produce very high concentrations of particulate matter, exceeding 300 μg/m3. 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.
Generated from building materials, furnishing and consumer products Volatile organic compounds 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. 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. VOCs presenting health hazards include
benzene,
formaldehyde,
tetrachloroethylene and
trichloroethylene. 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. 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. Cooking can release long-chain
aldehydes and
alkanes when oil is heated and
terpenes can be released when spices are prepared and/or cooked. 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. Testing emissions from building materials used indoors has become increasingly common for floor coverings, paints, and many other important indoor building materials and finishes. 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. 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, M1,
Blue Angel and Indoor Air Comfort in Europe, as well as California Standard CDPH Section 01350 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 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. 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 remodeling. 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.
Microplastics Microplastic is a type of airborne
particulates and is found to prevail in air. 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). Airborne microplastic dust can be produced during
renovation, building, bridge and
road reconstruction projects and the use of
power tools.
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. 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. 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 Ventilation with outdoor air containing elevated ozone concentrations may complicate remediation attempts. 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.
Biological agents Mold and other allergens 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. While mold growth is associated with high moisture levels, 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. 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. 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%). 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. 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. Mold predominantly affects the airways and lungs. Known effects of mold on health include
asthma development and exacerbation, with children and elderly at greater risk of more severe health impacts. Infants in homes with mold have a much greater risk of developing
asthma and
allergic rhinitis. 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.
Virus 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. 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.
Carbon dioxide 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. 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. 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. Indoor carbon dioxide concentrations can be used to evaluate the quality of a room or a building's ventilation. 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. 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. The UK standards for schools say that carbon dioxide levels of 800 ppm or lower indicate that the room is well-ventilated. 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.
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. 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. 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. They are usually cost effective and can greatly reduce or even eliminate the contamination and the associated health risks. 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. 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. 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. Interactive maps of radon affected areas are available for various regions and countries of the world. == IAQ and climate change ==