Circadian Environments

Science · Core 7

Air

The air indoors is rarely the air outside.

Indoor air carries outdoor pollution plus everything produced inside: cooking, combustion, furnishings, cleaning, damp and the people in the room.

Why it matters

Air quality indoors depends on two things: what is released into the room, and how quickly it is removed. Common indoor sources include gas cooking, fine particles from cooking and outdoor traffic or smoke, volatile organic compounds (VOCs) from furnishings and products, moisture and mould, and carbon dioxide (CO2) from the people in the room. A review of measurements in homes identified a short list of priority hazards, including fine particles (PM2.5), nitrogen dioxide and formaldehyde 1.

What the research shows

Ventilation. A multidisciplinary review found that higher ventilation rates in offices were associated with fewer sick building symptoms, and that lower ventilation was linked with more inflammation, respiratory infections, asthma symptoms and short-term sick leave, although the data were limited 2.

Thinking and sleep. In a controlled study of 24 office workers, cognitive test scores were higher on days with lower VOC levels and more outdoor air, and both CO2 and VOCs were independently associated with scores 3. In bedrooms, improving ventilation lowered CO2 and improved measured sleep quality and next-day concentration 4.

Damp and mould. Meta-analyses found that dampness and mould in homes are associated with roughly 30 to 50 per cent increases in a range of respiratory and asthma outcomes 5.

Gas cooking. An Australian modelling study estimated that about 12 per cent of the childhood asthma burden was associated with gas stoves and about 8 per cent with damp housing, and that venting cooktops outdoors with an effective range hood would substantially reduce the gas-related share 6. Measurements in homes show gas cooking releases nitrogen oxides into indoor air, and without ventilation levels in small kitchens can exceed outdoor air standards within minutes 7.

Particles. The World Health Organization tightened its guideline for fine particles in 2021 to an annual average of 5 µg/m³ and a 24-hour level of 15 µg/m³ 8. Smoke and traffic pollution enter homes, and cooking adds its own.

Humidity. Very dry indoor air is associated with complaints of eye and airway irritation, while persistent moisture is a separate problem that supports mould growth 9.

What can be done

Start with the source: a ducted range hood that vents outside, used every time; electric or induction cooking where practical; fixing leaks and moisture. Then ventilation, from better use of windows to mechanical ventilation with heat recovery in airtight buildings. Then filtration, with portable or ducted filters sized to the room. CO2 monitoring is a simple, useful indicator of whether a room is getting enough fresh air.

How we assess it

We log CO2, fine particles, total VOCs, temperature and humidity over several days, and measure formaldehyde and nitrogen dioxide where relevant. We inspect for moisture and mould, and review ventilation, range hoods and filtration.

Evidence at a glance

  • Well supported

    Damp and mould are linked with respiratory and asthma symptoms. 5

  • Well supported

    Gas cooking adds nitrogen oxides to indoor air, and venting outdoors reduces exposure. 6,7

  • Reasonable

    Higher ventilation rates improve comfort, health and thinking. Consistent findings, though many studies are small or office-based. 2,3

  • Not supported

    Potted plants as a way to clean indoor air. Realistic numbers of plants remove far less than normal ventilation does. 10

General information only, not medical advice. How we grade evidence.

References

  1. Logue JM, McKone TE, Sherman MH, Singer BC. Hazard assessment of chemical air contaminants measured in residences. Indoor Air. 2011;21(2):92-109. doi.org/10.1111/j.1600-0668.2010.00683.x · PubMed 21392118
  2. Sundell J, Levin H, Nazaroff WW, et al. Ventilation rates and health: multidisciplinary review of the scientific literature. Indoor Air. 2011;21(3):191-204. doi.org/10.1111/j.1600-0668.2010.00703.x · PubMed 21204989
  3. Allen JG, MacNaughton P, Satish U, et al. Associations of cognitive function scores with carbon dioxide, ventilation, and volatile organic compound exposures in office workers: a controlled exposure study of green and conventional office environments. Environ Health Perspect. 2016;124(6):805-12. doi.org/10.1289/ehp.1510037 · PubMed 26502459
  4. Strøm-Tejsen P, Zukowska D, Wargocki P, Wyon DP. The effects of bedroom air quality on sleep and next-day performance. Indoor Air. 2016;26(5):679-86. doi.org/10.1111/ina.12254 · PubMed 26452168
  5. Fisk WJ, Lei-Gomez Q, Mendell MJ. Meta-analyses of the associations of respiratory health effects with dampness and mold in homes. Indoor Air. 2007;17(4):284-96. doi.org/10.1111/j.1600-0668.2007.00475.x · PubMed 17661925
  6. Knibbs LD, Woldeyohannes S, Marks GB, Cowie CT. Damp housing, gas stoves, and the burden of childhood asthma in Australia. Med J Aust. 2018;208(7):299-302. doi.org/10.5694/mja17.00469 · PubMed 29642816
  7. Lebel ED, Finnegan CJ, Ouyang Z, Jackson RB. Methane and NOx emissions from natural gas stoves, cooktops, and ovens in residential homes. Environ Sci Technol. 2022;56(4):2529-2539. doi.org/10.1021/acs.est.1c04707 · PubMed 35081712
  8. World Health Organization. WHO global air quality guidelines: particulate matter (PM2.5 and PM10), ozone, nitrogen dioxide, sulfur dioxide and carbon monoxide. Geneva: WHO; 2021. www.who.int/publications/i/item/9789240034228
  9. Wolkoff P. Indoor air humidity, air quality, and health: an overview. Int J Hyg Environ Health. 2018;221(3):376-390. doi.org/10.1016/j.ijheh.2018.01.015 · PubMed 29398406
  10. Cummings BE, Waring MS. Potted plants do not improve indoor air quality: a review and analysis of reported VOC removal efficiencies. J Expo Sci Environ Epidemiol. 2020;30(2):253-261. doi.org/10.1038/s41370-019-0175-9 · PubMed 31695112