1/12 As the efficacy, eye and skin safety of Far-UVC have largely been proven, the debate has now moved onto air quality. Superficially this paper suggests problems, but...
In this thread I will show that the real issue is poor ventilation, not Far-UVC.
pubs.acs.org/doi/10.1021/ac…
In this thread I will show that the real issue is poor ventilation, not Far-UVC.
pubs.acs.org/doi/10.1021/ac…
2/12 Firstly, the paper is a model. My background is in computational chemistry (albeit not in atmospheric chemistry) with published papers on improving mathematical models for simulating complex chemical systems.
pubs.rsc.org/en/content/art…
pubs.rsc.org/en/content/art…
3/12 Models can often provide insight, but can also be wildly incorrect, and are secondary to real world observation. They are only as good as the assumptions applied and the quality of the input data.
4/12 My main observation on this paper relates to the simulated conditions. The paper chooses to highlight a classroom simulation with 0.5 ACH as the central scenario. There is a paucity of real world data measuring classroom ventilation rates. Published work in general finds...
5/12 ....average rates of 2 – 3 ACH when this is physically measured, but with some cases, in some seasons, of rates as low as 0.5 ACH. The authors chose to present this abnormally low ACH rate as their main scenario.
This matters.
This matters.
6/12 The model shows that in poorly ventilated classrooms (0.5 ACH) there is a small increase in secondary pollutants from Far-UVC at irradiance levels below the UVC exposure threshold. At levels *above* the safety threshold, this became a more significant health hazard. 
7/12 However, at 2 ACH and Far-UVC irradiance below the safety threshold (simulation 13) the total production of surface derived oxidative products (pollutants) is negligible. For some (eg formaldehyde, NO3) peak levels with Far-UVC are below the 0.5 ACH baseline levels (no UVC).
8/12 Furthermore, tucked away in the supplementary data (Fig S5) are the data from the 2 ACH simulations – far closer to ‘normal’ real world conditions, but still way below the Building Regulations standard of 6 ACH.
The picture changes dramatically.
The picture changes dramatically.
9/12 At 2 ACH, with Far-UVC below the irradiance threshold (dark blue line 13) pollutant levels are almost indistinguishable from the baseline (purple line). The results are, in fact, *excellent* news for the deployment of Far-UVC.
The issue here is ventilation rates *not* UVC.
The issue here is ventilation rates *not* UVC.
10/12 Sometimes you need to see the big picture.
As a PhD student I was once told that too many scientific papers are published without proper contextualisation. The real issue here is inadequate ventilation of classrooms, not Far-UVC. The authors say as much in the conclusions.
As a PhD student I was once told that too many scientific papers are published without proper contextualisation. The real issue here is inadequate ventilation of classrooms, not Far-UVC. The authors say as much in the conclusions.
11/12 Upcoming papers on real world Far-UVC and aerosol chemistry appear very encouraging and I'll report on these in due course.
This isn’t an either/or, ventilation vs UVC. But every day we stall the deployment of UVC/Far-UVC is another day that we are harming children.
This isn’t an either/or, ventilation vs UVC. But every day we stall the deployment of UVC/Far-UVC is another day that we are harming children.
12/12 Poorly ventilated classrooms are harming children from infections *and* pollutants. Far-UVC is one of the best solutions for part of that problem, ventilation is the other. No child should be forced to learn in classes with 0.5 ACH ventilation rates, irrespective of Far-UVC
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