Seasonal variations in exposure to indoor air quality in existing UK social housing dwellings

Strategies for protecting the UK population against the health effects of indoor air pollution are constrained by the lack of empirical data on the impact of dwelling characteristics on exposure to air pollutants inside homes. Evidence is particularly limited over different seasons and by different housing typologies. This paper undertakes empirical measurements of indoor temperature, relative humidity (RH), carbon dioxide (CO2), particulate matter (PM)2.5, PM10 and volatile organic compounds (VOCs) (Isobutylene and EtOH) in the living rooms of 34 social housing dwellings located in Warwickshire (UK) during 2021-2022. Contextual data about the physical and household characteristics of the dwellings were gathered using in-person surveys. Results revealed that the effect of seasonality was apparent, with indoor air quality (IAQ) being particularly poor in winter. The seasonal discrepancy in ventilation practices was significant. Strong seasonal variations were observed in indoor temperature (ranging from 9°C to 37°C), with widespread overheating in summer and under heating prevalent in winter across the dwelling sample. The lowest mean wintertime indoor temperatures (17.7°C) and the highest mean summer indoor temperatures (25.7°C) were recorded in bungalows. RH levels remained stable across seasons and building typologies, averaging between 45% and 54%. Regardless of seasons or typologies, the concentrations of CO2 levels stayed above 900 ppm, indicating inadequate ventilation. CO2 concentrations were found to be particularly higher across bungalows inhabited continuously by elderly residents, while high PM concentrations of 100 µg/m3 and above were experienced in terraced dwellings, exceeding the WHO limits of 15 µg/m3 for PM2.5 and 45 µg/m3 for PM10. This was possibly due to residents’ indoor activities such as smoking and cooking, confounded by poor ventilation. About 12 out of 34 dwellings experienced mean VOCs levels higher than the sample means of 0.95 ppm (EtOH) and 0.11 ppm (Isobutylene). Given that these dwellings are likely to be energy retrofitted in the near future, it is vital that trends in IAQ are used to inform the retrofit measures, especially regarding adequate ventilation alongside insulation.