Are we breathing dirtier air at home than outside?


by Dr Erika Ikeda 

Every day, a mix of smells – coming from traffic, cooking, cleaning and personal care products, and wood-burning – float out through vehicles, homes and businesses in the city of Bradford. Like many other cities, Bradford faces a combination of high levels of deprivation and ill health, with air pollution a key concern. 

Routinely monitored, outdoor nitrogen dioxide (NO2) and particulate matter (PM) in Bradford are above the World Health Organisation’s guidelines across the large part of the city, particularly around busy roads(1). It is estimated that a third of asthma cases in the city are attributable to air pollution(2). The poorest communities experience the most pollution-related disease and environmental risk factors including greater air pollution, more noise from traffic and less access to high-quality green spaces(3).

Our ARC’s Healthy Families theme has been studying links between air quality and health through its Born in Bradford (BiB) cohort studies involving over 50,000 Bradford families. Professor Rosie McEachan, Director of BiB, reported: “Our early BiB research found links between air pollution and low birth weight of babies in Bradford. We also found that exposure to air pollution during early life is related to high blood pressure and poorer cognitive development at the ages 4 to 5, and poor indoor air quality is related to childhood obesity at ages 6 to 11.”

Just like outdoor air, indoor air can be polluted – due to poor housing conditions (for example, lack of ventilation, damp or mould), heating sources (such as wood burners) and occupant behaviours (including cooking, cleaning and the use of personal care products)(4). In the UK, we spend about 90% of our time indoors with about two thirds of this in our homes(5). Surveys with the BiB cohort have shown that 23% of families report the presence of damp or mould in their homes, but there is currently limited information on what causes poor indoor air quality or how housing characteristics or occupant behaviours contribute to this.

To understand air pollution in homes, a research study called INGENIOUS ( will monitor indoor air quality in over 300 homes across Bradford from March 2023. With the agreement of households, we will place air quality monitors measuring a range of different air pollutants, as well as temperature and humidity, in kitchens, living spaces and bedrooms. To explore factors affecting air quality, they will assess housing characteristics and collect information on occupant behaviours (such as cooking and cleaning) and health-related symptoms over a two-week period. Nicola Carslaw, Professor in Indoor Air Chemistry at the University of York and the project lead, said: “We will use the findings to develop a range of policy and behaviour change approaches to improve indoor air quality in our homes.”

In Bradford, for example, reducing pollution from solid fuel burning in residential areas will be complemented by a low-emission energy plan for the district to include ground source heat pumps and solar sources in preference to biomass burning. 

For further information on the project, please visit BiB INGENIOUS webpage (, email us at or call us on 01274 274474.


  1. Department of Health and Social Care. Chief Medical Officer’s annual report 2022: Air pollution. (2022).
  2. Khreis, H. et al. Traffic-related air pollution and the local burden of childhood asthma in Bradford, UK. Int. J. Transp. Sci. Technol. 8, 116–128 (2019).
  3. Mueller, N. et al. Socioeconomic inequalities in urban and transport planning related exposures and mortality: A health impact assessment study for Bradford, UK. Environ. Int. 121, 931–941 (2018).
  4. National Institute for Health and Care Excellence. Indoor air quality at home: NICE Guideline NG149. (2020).
  5. Klepeis, N. E. et al. The National Human Activity Pattern Survey (NHAPS): A resource for assessing exposure to environmental pollutants. J. Expo. Anal. Environ. 

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