Cooper, Elizabeth Lydia; (2022) The use of portable air purifiers for the reduction of PM2.5 in residences: Effects on indoor pollutant concentrations, perceived air quality, and mortality. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Background: Time at home accounts for 65% of people’s time indoors, on average. It is, therefore, important to understand the quality of air in homes, how occupants perceive it, and how best to improve it to effectively manage the total exposure to airborne pollutants. Exposure to particulate matter, in particular, is associated with negative health outcomes that account for significant morbidity and mortality worldwide. Technologies are rapidly being developed and adopted to mitigate indoor air pollution. Portable home air purifiers (PAPs), especially those that employ HEPA filters, have the potential to effectively clean the surrounding air of harmful pollutants of both indoor and outdoor origin. / Aims: The three primary aims of the research presented here were to 1) test the field performance of commercially available air purifiers in bedrooms, 2) explore the primary drivers of occupants’ use of portable air purifiers, and 3) estimate the impact of the use of portable air purifiers on health outcomes associated with PM2.5 exposures at home in the UK. / Methods: The work presented here included air quality monitoring at 18 flats in three modern buildings at two sites in London from July through the end of December 2019. At the beginning and end of the monitoring period the participants were asked about several aspects of the environmental quality of their homes, as well as about their wellbeing and sleep whilst at home. Results from the monitoring and interviews were used, along with information from published literature, to parameterise health impact models to evaluate the potential for impact of PAP use on mortality and childhood asthma. / Results: Findings from the present study showed that PM2.5 concentrations in bedrooms were reduced by a mean of 45% over 90 minutes with PAP use. Participants’ subjective assessment of the indoor air when the PAP was on was positive. The predominant motivation and indicator of PAP use was thermal comfort, therefore if air purifiers are to be used for year-round removal of particulate matter it is important to consider other motivations of air purifier use, and/or other control solutions. The measured changes in indoor PM2.5 exposures in bedrooms from the monitored flats utilising PAPs in London were one metric used as a parameter in modelling the potential health impact of several PAP use scenarios across a wider UK population. Estimates of impacts on mortality outcomes (years of life gained and mean days gained) were calculated based upon life table modelling methods. The central scenario showed an increase in the number of years of life (YLG) in the UK of roughly 23 million over the modelled period. This YLG translates to an additional 138 and 120 days of life expectancy for males and females, respectively. Health impacts of reductions to exposure on childhood asthma were also estimated, and the number of QALYs saved by using appropriately sized and well-functioning air purifiers in the bedrooms of children during sleep was estimated to be 1,116 per 10,000 children annually. / Conclusions: In the work presented here, PAPs were effective at reducing PM2.5 levels in bedrooms. The associated reductions in exposure of the UK population whilst at home could, according to health impact models, add an average of more than 4 months to life expectancy. However, because occupants’ use of the PAPs was shown to be associated with thermal conditions and not PM2.5 concentrations, sensor-controlled devices may be necessary to ensure that the devices are operating as intended and to their full capacity. Further work is needed to verify the modelled connection between home air purifier use and improvements in health, as there is limited evidence found in the literature. Additionally, consideration should be given to the larger societal context in which recommendations for interventions are made. Indoor air quality may be especially poor in areas experiencing the greatest risk of economic deprivation. Therefore, although these devices may provide health benefits to those that have them, a reliance upon expensive devices to mitigate poor indoor air quality could exacerbate existing inequalities.

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