A typical North American spends more than 90 per cent of their time inside buildings. That makes the quality of the air in those spaces a big concern.

Although the concentrations of many pollutants are lower indoors, those levels can still be high enough to affect health. Meanwhile, concentrations of some pollutants are actually higher indoors than out.

Infiltration of outdoor pollution

Air pollutants make their way into homes and offices through open windows, doors and ventilation systems. They also infiltrate through cracks and leaks in the building envelope2. As a result, buildings located near busy roads and industrial areas can have dangerous elevated levels of nitrogen dioxide (NO2), volatile organic compounds (VOCs), particulates and more.

For example, schools located near petrochemical plants in Spain had higher levels of benzene in their classrooms3, while an Australian study found increased levels of NO2 and toluene in homes within 50 metres of major roads4.

This kind of industrial and traffic-related pollution can have serious consequences — increasing the risk of everything from low birth weight babies5 to asthma6, poor school performance7, cancer8 and dementia9.

Uniquely indoor dangers

However, outdoor sources are just one part of the problem. A number of dangerous pollutants actually originate indoors: from the operation of printers and photocopiers; off-gassing from new furniture and carpets; the use of paints, adhesives, cleaning chemicals and aerosol sprays; and activities such as cooking and smoking.

For example, research in the Chinese city of Hangzhou revealed VOC concentrations inside homes were higher than those recorded outside. The levels were highest in new buildings, due largely to solvents, paints and home decor10. According to the U.S. Environmental Protection Agency, health risks created by VOCs include headaches, nausea, fatigue, liver and kidney damage and cancer11.

Costly consequences

Because we spend so much time indoors, the health impacts can be serious — and even deadly. They hit children and the elderly particularly hard.

The latest statistics from the World Health Organization reveal 117,200 premature deaths in Europe were caused by indoor air pollution in 2012, while 3.9 million years were lost as a result of disease and premature death12. A recent French study estimated that healthcare expenses, loss of productivity and premature death from indoor air pollution cost the country €19 billion in 200413.

1Leech, J.A., Nelson, W.C., Burnett, R.T., Aaron, S., Raizenne, M.E. 2002. It’s about time: A comparison of Canadian and American time-activity patterns. J. Expo. Anal. Environ. Epidemiol. 12: 427–432. https://doi.org/10.1038/sj.jea.7500244

2Chen, C., Zhao, B. 2011. Review of relationship between indoor and outdoor particles: I/O ratio, infiltration factor and penetration factor. Atmos. Environ. 45(2): 275–288. https://doi.org/10.1016/j.atmosenv.2010.09.048

3Villanueva, F., Tapia, A., Lara, S., Amo-Salas, M. 2018. Indoor and outdoor air concentrations of volatile organic compounds and NO2 in schools of urban, industrial and rural areas in Central-Southern Spain. Sci. Total Environ. 622–623: 222–235. https://doi.org/10.1016/j.scitotenv.2017.11.274

4Lawson, S.J., Galbally, I.E., Powell, J.C., Keywood, M.D., Molloy, S.B., Cheng, M., Selleck, P.W. 2011. The effect of proximity to major roads on indoor air quality in typical Australian dwellings. Atmos. Environ. 45(13): 2252–2259. https://doi.org/10.1016/j.atmosenv.2011.01.024

5Gong, X., Lin, Y., Bell, M.L., Zhan, F.B. 2018. Associations between maternal residential proximity to air emissions from industrial facilities and low birth weight in Texas, USA. Environ. Int. 120: 181–198. https://doi.org/10.1016/j.envint.2018.07.045

6Bowatte, G., Erbas, B., Lodge, C.J., Knibbs, L.D., Gurrin, L.C., Marks, G.B., Thomas, P.S., Johns, D.P., Giles, G.G., Hui, J., Dennekamp, M., Perret, J.L., Abramson, M.J., Walters, E.H., Matheson, M.C., Dharmage, S.C. 2017. Traffic-related air pollution exposure over a 5-year period is associated with increased risk of asthma and poor lung function in middle age. European Respiratory Journal 50: 1602357. https://doi.org/10.1183/13993003.02357-2016; 
Gauderman, W.J., Avol, E., Lurmann, F., Kuenzli, N., Gilliland, F., Peters, J., McConnell, R. 2005. Childhood asthma and exposure to traffic and nitrogen dioxide. Epidemiology: 16(6): 737–743. https://doi.org/10.1097/01.ede.0000181308.51440.75

7Kweon, B-S., Mohai, P., Lee, S., Sametshaw, A.M. 2016. Proximity of public schools to major highways and industrial facilities, and students’ school performance and health hazards. Environ. Plan B Urban Anal. City Sci. 45(2): 312–329. https://doi.org/10.1177/0265813516673060

8Bidoli, E., Pappagallo, M., Birri, S., Frova, L., Zanier, L., Serraino, D. 2016. Residential proximity to major roadways and lung cancer mortality. Italy, 1990–2010: an observational study. Int. J. Environ. Res. Public Health 13(2): 191. https://doi.org/10.3390/ijerph13020191

9Chen, H., Kwong, J.C., Copes, R., Tu, K., Villeneuve, P.J., van Donkelaar, A., Hystad, P., Martin, R.V., Murray, B.J., Jessiman, B., Wilton, A.S., Kopp, A., Burnett, R.T. 2017. Living near major roads and the incidence of dementia, Parkinson’s disease, and multiple sclerosis: a population-based cohort study. Lancet: 389 (10070): 718–726. https://doi.org/10.1016/S0140-6736(16)32399-6

10Ohura, T., Amagai, T., Shen, X., Li, S., Zhang, P., Zhu, L. 2009. Comparative study on indoor air quality in Japan and China: Characteristics of residential indoor and outdoor VOCs. Atmos. Environ. 43(40): 6352–6359. https://doi.org/10.1016/j.atmosenv.2009.09.022



13Boulanger, G., Bayeux, T., Mandin, C., Kirchner, S., Vergriette, B., Pernelet-Joly, V., Kopp, P. 2017. Socio-economic costs of indoor air pollution: A tentative estimation for some pollutants of health interest in France.
Environment International 104: 14–24. http://dx.doi.org/10.1016/j.envint.2017.03.025