Methodology of an air cleaner cluster RCT in classrooms comparing control, HEPA and ionizers just published.
The trial happened in 2023-2025 but was only registered in March 2026. Original conception was to study covid but will measure particulates and microbes in the air 🧵1/n
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Firstly it is a bit odd to publish the trial and methodology after the trial has completed, as this could allow researchers to change measured metrics. Initially the idea of the study was in the context of COVID-19, but it would seem little SARS-CoV-2 was detected in the air 2/n
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An initial study was done winter 2023/24 and then expanded to further schools in winter 24/25. A total of 180 classrooms participated 3/n
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As with other similar studies, some PAC units not considered due to negative feedback from users with regards to practicality (size and noise). This can limit the amount of CADR possible 5/n
Aug 27, 2026 · 10:32 AM UTC
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The study did baseline sampling for 3 weeks, followed by 3x 3 week intervention period and a 2 week post intervention (the paper mentions that some baseline data was collected after the intervention and not before - not ideal) 6/n
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Low cost sensors used to measure air quality indicators, PMs, VOC, CO2. Static sheets to collect dust were used for microbial air sampling, although a select few classrooms had active air sampling. Not sure how good these sheets are at collecting microbes from air 7/n
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Microbial targets include streptococcus species, RSV, flu...but it seems that collected amounts were low because it says microbials will only be analyzed where quantitative measurements permit..we will see when results are published 8/n
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The researchers note that successful implementation depends on user acceptance, noise and that any reduction in airborne exposure must be interpreted in context of device size, costs etc 9/n
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Researchers suggest that data from this trial may inform predictive models of airborne transmission or identify contexts where PACs are most warranted such as in suboptimal air quality or periods of heightened respiratory risk 10/n
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What might we expect from the results of this study? My guess is little microbial data and probably no statistical differences between control and PACs. Probably a reduction in particulates because filters are good at filtering. We shall see... 11/n
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Evaluating air cleaner effectiveness in schools: a
comprehensive review and protocol of a cluster-randomized controlled trial of physicochemical and microbial markers is available \end frontiersin.org/journals/pub…
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