Also, fangen wir mal hinten an, Ich werde jetzt nach und nach #Literatur zu den #Luftreinigern twittern, um die Diskussion zu substantivieren.

I'll do that mainly in English, at times in German.

Let's start. (AC-1) Nature News, October 2021.
1 Image
Of course, this is only a #News article in @Nature. The paper, at that time only a preprint, now appeared here:

AC-2 =
2 Image
In this work, authos state "Here we present
the first data providing evidence for the removal of SARS-CoV-2 and microbial bioaerosols from the air using portable air filters with UV sterilization on a COVID-19 ward."

I think this is true, in the paper actually particles...
were samples and analysed. Nucleic acids were isolated and PCR analysis performed. #SarsCov2 was identified by PCR, see SI and measured when the air cleaner was ON-OFF-ON. A reduction of #SarsCov2 was measured with air cleaner = ON.
Concl.: 'Portable air filtration devices may
mitigate the reduced availability of airborne infection isolation facilities when surges of COVID-19 patients overwhelm healthcare resources and improve safety of those at risk of exposure to respiratory pathogens such as SARS-CoV-2'
I'll continue this collection.
Also, allen einen Guten Morgen und einen sehr schönen Herbstsonntag. Weiter gehts.

Let's continue with collecting #aircleaner #literature.

Next is AC-3 = Rodriguez et al =
Well, first, they are asking the right question. 🎯
1 Image
Paper is of Sept. 1st 2021
Fm the abstract:
After the PAC usage, all samples except one were negative, displaying a 80% device effectiveness. Portable HEPA cleaners usage allowed the removal of SARS CoV-2 and, therefore, they could be recommended for places with inadequate ...
considering ventilation the limitations and functionality of the device.

The paper is not uncritical against portable #aircleaners or #PAC (at times) but concludes that they can be helpful for places with no good ventilation.
During the Jan 2021 pandemic, measurements of particles were performed in a number of households in Spain's Toledo province and particles samples according to usual provisions for particles and bioaerosol particles were taken.
There, in one household a #Covid19 positive person was quarantined. The particle samples were first taken with only the patient in the room and then with an aircleaner added.
All the particle samples were brought to the laboratory and analysed for viral #RNA by #RTPCR.
🇩🇪 Dieser Gedanke, dass #Luftreiniger eingesetzt werden sollten, wenn es keine gute #Ventilation (engl) oder, bei und, #RLT oder #Raumlufttechnik gibt, ist verständlich. Bei uns in Deutschland gibt es diese aber praktisch nirgends, siehe dazu viele Tweets von...
Fachleuten wie @KriegelMartin oder @leseerlaubnis
Ich würde hieraus also kein "Nein" für Deutschland ableiten mögen

The paper says #aircleaners can be useful in places with non-adequate ventilation. This is true in Germany for about all schools and most other buildings, really
and very different fm the #US. I would not count this as a general statement against #aircleaners
This kind of papers were the actual viral burden with in collected, previously air-suspended particles, is determined, is important bc it will show how viable the virus is and this is very important to know when calculating the demands on air cleaning. I will come back to that
but the available #SarsCov2 infection #risc #calculators need a virus load in the particles and, also, a critical number of virus copies being able to treigger an infection is used in these models. Therefore, we need these studies - urgently.
One more: Actually, there is a big number of papers where the effect of #aircleaners just on reducing #aerosol #particle #concentration. I'll cite some of these studies but they have certain points to be considered:
(a) They essentially aim to confirm what the #aircleaners
were constructed for. One could, say, they have a limited scientific scope but it seem useful to me that such studies have been undertaken and are documented. This is especially true in our current times when each and every finding is heavily questioned.
(b) Such studies can (and do) prove the effectiveness of #particle #removal but that does not prove that they really remove the virus copies or, the viral load. To this end, studies such as AC-2 and aC-3 are more advanced.
However, as, e.g., @leseerlaubnis states, it is very
reasonable to conclude that removal of the particles also removes the virus copies contained in them. I personally fully agree that this is reasonable and would suggest to widely apply #aircleaners already just bc of their proven removal of particulate matter #PM fm indoor air.
However, if you are very critical, you might question this logical path. Then, AC-1, AC-2 and more studies like this are for you.
As for #PM #removal and resulting improvements in air exchange rates, @dm_ms has recently collected a number of studies, see here:

I have cited some before,
AC-5 = Curtius et al. =…
My Frankfurt colleague Joachim Curtius and his co-workers measured particle size distributions with scientific equipment in a Frankfurt school classroom. Not surprisingly, the #mobile #aircleaner worked - it was a Philipps 2887/10
7 Image
🇩🇪 Ich benutze diesen #Luftreiniger auch zuhause. Er hat einen Vorfilter, einen Aktivkohlefilter und einen #HEPAFilter.
Measurements were performed in one classroom with such #aircleaner and compared with measuements in a second calssroom without such a device. Particle concentrations were measured in the range 10 nm < Dp < 10 um toegther with PM10 und CO2.
Fm their Figure 2: Top: Small particles show a strong reduction in particle number density measured with two uCPCs Bottom: Very similar reductions also for coarse particles.
10 Image
'Measurements and calculation demonstrate that air purifiers potentially represent a wellsuited measure to reduce the risks of airborne transmission of SARS-CoV-2 substantially.'
Tbc for further studies reducing indoor #PM.
So, weiter zur Wirksamkeit mobiler Luftfilter: Meta-Studie zur Wirksamkeit von #HEPA-Filtern in Klassenräumen mit Fensterlüftung.

Report of the #NewZealand Ministry of Education, June 2022
1 Image
See here:…

These pages contain a lot great resources for all questions of #IAQ. German education ministries: Follow up !
This meta-study and review considers these single studies:
3 Image
As you can see, Curtius et al, AC-4, is included here. So you can check the other relevant studies as to mobile air cleaners work together with natural ventilation. These 7 papers were the ones with quantitative data out of a total of 142 studies which were checked.
Well, for those who try to assess the state-of-knowledge for mobile #aircleaners ( #S3 contributors ?), you can check here, how this is being done
What the result ? Here:
6 Image
So, there is the need for more studies..😀.. Then, the #aircleaners habe the potential to reduce risks of infection. Window natural ventilation is good and reduces infection risk but mobile aircleaners can add their respective benefits, e.g. leading to shorter window opening..
times in winter. So, I would count that as "ok to use mobile air cleaners" but, do also apply natural window ventilation plus #HEPA #mobile #cleaners. This makes sense:

'Summarily, these studies agree that combining opening doors and windows with HEPA air cleaners can lower
COVID-19 incidence in schools, and these are simple cost effective ways of improving ventilation.'
Habe noch ein Hinweis erhalten, die EN1822 gibt es in deutscher Sprache. Also, ja. Vielleicht ist das so gemeint, nicht nur von HEPA zu sprechen, sondern anzugeben H14, also die Filterklasse.
Von:… Image
Der gezeigte Phillips #Luftreiniger 2889 und ähnliche Modelle haben Filterklasse H13.
So, es soll weitergehen mit den Besprechungen von einzelnen Studien, aber auch Übersichten. Kleiner Nachtrag - die neuseeländische Metastudie, also dies hier =
möchte ich mit AC-6 (nach Curtius et al. = AC-5,
diese hatte ich leider einmal fälschlicher-
weise AC-4 genannt) bezeichnen.

Let's address the nice meta study fm Newzealand as AC-6.
Eine Reihe empirischer Studien unter Klassenraumbedingungen ist in der gestriegen Pressemitteilung (PM) von @_ProtectTheKids enthalten. Diese PM =
finde ich unbedingt unterstützenswert. Für alle, die das auch so sehen, große Empfehlung zum RT.
So, to continue treatment of #aircleaner studies. The German initiative @_ProtectTheKids yesterday issued a press-release to rebuttal some news articles questioning the proven effectiveness of mobile #aircleaners.
The thread by @_ProtectTheKids is here =

Let's collect the studies mentioned there in short:
Belgium-Study (500 schools and ongoing) =
Label that (AC-7)
Georgia-Studie (31 schools, via the @CDCgov ) =… (AC-8)

Italy study (preprint) =… (AC-9)

Review…, published in Otolaryngology–Head and Neck Surgery (AC-10)
Study fm the Netherlands = …… (AC-11).

So, all the studies reffered to by @_ProtectTheKids deal with rel-world classroom investigations and it therefore make sense to put them in one row with Curtius et al. (AC-5) and those reviewed in the Newzealand
meta-study (AC-6). For good reason, however, the press release of @_ProtectTheKids selects the studies AC-7 to AC-11 as they show the effects of mobile aircleaners of a larger number of classrooms thus providing a stronger evidence that mobiler aircleaners actually mitigate
#Covid19 #infection risks. All in all there is a big number of, let's call them '#aircleaner classroom studies' which clearly show that mobile aircleaners can reduce infection risk. Statements that this is not proven just show that people are not aware of the literature..
apparatus which must be considered here before conclude or even judge
Note, in addition to these classroom environment studies there are also studies investigating different kinds of rooms when characterizing mobile air cleaners such as Szabadi et al., work fm @achimdittler|s
In this paper of 02/2022, the authors measure particle size distributions ( i.e. how many particle exist in a defined particle size range over a wider particle size range) under varying conditions and apply a stirred tank model:
12 Image
The bottonline of this paper is, as written at the end of its abstract, that mobile aircleaners could be a component of mitigation but they should not be the sole means of cleaning indoor air.
There is another study where aircleaners have been characterized in a hospital by Dellweg et al. in #AAQR where the authors conclude that mobile aircleaner could help well to reduce concentrations of virus-containing particles (AC-12)
14 Image
Paper is here =…
Now, I would like to come back to something treated in AC-1 and AC-2, the #viralload.

Our current understanding is that particles carry the virus and, depending on size, each aerosol particle carries a number of virus copies, depending..
level of infection of the 'emitter' and particle size. For quite some time it was not clear how to actually measure these viral loads. Great care has to be taken to first collect the paricles but not to deactivate the viruses contained.
A very important paper in this context, and in my view, is this one:
18 Image
This early particle collection and viral load meausrment paper is here =…
I am going back a bit to the question whether #sarscov2 is really transmitted by aerosol particles bc, I think, this fact is also something which is not yet recognized as fully as needed. I hope we are on a good way that we can turn around the dogma from 'droplet infection'..
towards near-field and far-field aerosol-particle driven infection. That is a very important change in our understanding how pathogens spread and how infections are carried over and knowledege gathered here will also have implication for the spread
🇩🇪 Zum Schluß für jetzt, nochmal der Hinweis auf die Pressemitteilung von @_ProtectTheKids

finde ich unbedingt unterstützenswert. Für alle, die das auch so sehen, nochmals große Empfehlung zum RT.
🇩🇪 So, einen schönen Herbstsonntag allen und besonders den neuen Followern, Danke für Ihr Interesse !

Ich würde jetzt erstmal noch gerne einfügen, was es an Stellungnahmen zum Thema #SARSCoV2 gibt, da gibt es erstmal die Dinge, an denen ich selber beteiligt war, ..
im angehefteten Tweet, hier:

Dann gibt es noch weitere Stellungnahmen, von der @G_Ae_F und dem #Expertenkreis Aerosole in #BadenWürtemberg, diese sind in diesem Tweet verlinkt =
Dort ist auch verlinkt der Ausgangspunkt vieler Aktivitäten, nämlich der sog- "Aerosol-FAQ", den @jljcolorado ins Leben gerufen hat und wo er auch am meisten beigetragen hat, ich bin dort auch ein Beitragender. Hier nochmal in Deutsch = und..
Englisch =

So, now back to English, a very important wrap-up and overview paper according to the state of knowledge of autumn 2021 is the review by Wang et al where @kprather88, @jljcolorado and others are co-authors.
That review is here =…
This famous Figure is in this Wang et al (2021) review:
5 Image
Summary of review:
6 Image
Just as AC-1, AC-2 and the Sartapia et al. (2021) mentioned yesterday ( here = , should be AC-13), in August 2021 there were three more studies collecting #SarsCov2 loaden aerosol particles identified by PCR, refs 41, 42 & 43 in Wang et al. .
Sartapia et al. (AC-13) is 44 in Wang et al.

Others mentioned there are:
Liu et al. (AC-14), doi: 10.1038/s41586-020-2271-3…
Guo et al . (AC-15), ), doi: 10.3201/eid2607.200885…

Chia et al. ( AC-16), doi: 10.1038/s41467-020-
The Wang et al. review and the refereed references there are a cornerstone in the current process of dogma change, i.e. how infectious deseases are spreading. That discussion is very far fm being finished.
Another specialised study is this one released by the @CDCgov in @CDCMMWR (Thank you @WolfmannotJack )

Interestingly, here a working meeting was simulated and the effect of both #masking and #aircleaners was studied trough measuring particle concentrations at the mouths of emitters (i.e. speakers) and recievers (i.e. partcipants).
12 Image
13 Image
That study really demonstrates how business meetings can be done in times of #Covid19 and #SARSCoV2. The use of an #HEPA #aircleaner is advantageous and reduced exposure much stronger than #masks alone do.
🇩🇪 Diese Studie ist wirklich interessant und wichtig, weil sich sicherlich viele Einrichtungen wie #Firmen, aber auch #Schulen #Universitäten fragen, was kann man tun, um einen #Präsenzbetrieb so sicher wie möglich zu machen. Antwort: #Masken plus mobile #Luftreiniger.
Man kann also etwas tun und sollte das auch. Die Folgen von #Infektionen und bes. #multipler #Infektionen sind so gravierend, dass man nicht auf #Schutzmaßnahmen verzichten sollte.

Thread wird fortgesetzt, tbc.
Es soll hier noch weiter gehen. Ich möchte verweisen auf Hinweise von Lesern. Zuerst hat @ChrHoegl auf zwei "typ. deutsche" Dokumente hingewiesen, in denen auch Luftreiniger behandelt werden, hier:……
Ich möchte auch noch feststellen, dass ich natürlich nicht der einzige bin, der auf Literatur hinweist. Getan hat das bis hierher auch @dm_ms, bes. mit seiner direkten Antwort zu den #Luftreiniger-Enthüllungen von Journalisten, also u.a. hier =
In dem genannten🧵bespricht @dm_ms etwa 15 Paper, einige davon kamen bei mir auch schon dran, aber ich muss die Besprechung der einzelnen Studien hier nicht wiederholen. Alles bestens, bitte in den o.a. 🧵schauen. Ich habe vor, eine umfassende Übersicht zu machen, dort
würde ich diese Paper dann auch aufnehmen.

Fm now on further in English, I would like to mention the papers which @dm_ds shortly for systematisation.

dm_ms_#1 =…
Belgium study
dm_ds_#2 = AC-18…

Ricolfi et al., with 3rd author
Lidia Morowska. Study fm the Italian Marche region
dm_ms_6 = AC-22…

I would like to mention, care has to be taken with MDPI publications. I treated this before.
The next one mentioned by @dm_ms is also and MDPI paper - careful, please.

dm_ms_7 = AC-23…
dm_ms_8 = AC-24
This is about the problems of virus spred in dentistry, a problem where @SourceControl21 is a very good reference and very active.…
Next, dm_ms_10 = AC-25 is a case study, Kim et al.
of a mitigation of an covid outbreak in a daycare center…
Kipen et al. as dm_ms_14 = AC-28

Effect of mobile aircleaners in appartments
So, a big Thank You again for the immediate reaction of @dm_ms of October 12th. Pls refer to that great thread for paper contents. Next, there is more papers which need to be summarized and collected and I reieived more mentions of materials, e.g. by @WolfmannotJack, your
hints and mentions will be included.
So, again, tbc.
So, soll noch weitergehen. Allen in #Sachsen einen schönen Feiertag heute.
A recent paper of August 2022, Ueki et al., in a medical journal. Here, chamber experiments were performed in a chamber in a biohazard S3 lab.…
The effekt of HEPA filters without and with an anti-viral coating (Cu+) were tested. A strong reduction of #viralload|s was found, not really influenced, however by the copper(I) coating.
Summary below. Paper AC-39
2 Image
Just yesterday, @WolfmannotJack mentioned a danish report, already of March 2021, here =…
It's interesting, but more like a project report, not an independently peer-reviewed scientific publication. We take it in as AC-40.
If there is more materials such as this one, pls contact
me for inclusion. In this project, aerosol particles were loaded with a bacteriphage and it was measured how the concentration of this was affected by the air cleaner. I understand the bacteriophage was used as a
virus proxy here. Note that this was an early study and meanwhile really coronaviruses or even 'the real' #SarsCov2 have been used in studies as we have already discussed.

Next is Coyle et al.,…, also by way of @WolfmannotJack. Again, a study in a MDPI
journal, one needs to be careful, at least to some extend. But its a very interesting & substantive study, AC-41.
Study is on the efficiency of #ventilation, mobile #HEPA #aircleaners, #masking & #distancing in a simulated meeting room
6 Image
Study layout
7 Image
Outcome: In support of all the mentioned interventions - supported by measured data under controlled conditions.
8 Image
I would like to go back to Wang et al., Science, here…
Up to here, we considered only evidence on viruses really being contained in aerosol particles, cf.
Here, #airflow, #ventilation and # filtration ore treated and there are references 145 & 148 on filtration.
10 Image
It good to see this as it is in a more medical journal and it discusses 'factors involved in aerosol transmission'
12 Image
13 Image
So, this one does not really address #aircleaners in its conclusions, it fousses on other equipment more specific for hospital such as negative pressure rooms and #PPE = personal protection equipment
What about the #148 in Wang et al. ? Its here, AC-43,…
Its a ventilation review to mitigate #SARSCoV2 airborne spread, very useful but not directly addressing mobile #aircleaners. If you want to learn about ventilation rates, ventilation concepts, directions and so forth, very good.
15 Image
So, with this I have addressed a lot of input which I gladly received by @WolfmannotJack and others.
We have now collected 43 papers. The newsealand meta-study traeted before contains a few more which should also be numbered in.
But, there is more and, hence, tbc.
So, gibt noch etliche Studien. AC-44 jetzt ist von den Kollegen vom IUTA Duisburg, Küpper et al.
Testing of an Indoor Air Cleaner for Particulate Pollutants under Realistic Conditions in an Office Room - Aerosol and Air Quality Research…
It about the efficiancy of a #mobile #aircleaner under #office conditions. It is of June 1, 2019 and hence pre-pandemic and once could say, the later Curtius study AC-5 complements this for classroom measurments.It studies als air exchange rates as a dependent of
filter age.
Another German study, AC-45 is this:… by Oberst et al. This paper of 2021 is fm medical doctors using a mobile aircleaner to lower aerosol particle load in a medical examination room. With success.
Next, AC-46, interestingly is a randomized crossover study by Huang et al. . Emphasis of this study is that the #aircleaners were run in 'auto mode'.
End of abstract says: "These findings suggest that using such PACs running in auto mode is a practical and effective way
4 Image
to reduce indoor PM2.5 levels.
#Aircleaners in #dentistry is treated in AC-46, here… by Ren et al.
Cf. @SourceControl21 This paper can be looked at together with AC-24. besides #mobile aircleaners it treats also ventilation.
6 Image
Next, AC-47, is on an intersting side effect. HEPA filters fm #mobile #aircleaners could be used for #sarscov2 surveillance. Paper by Fernandez de Mera et al. in #IndoorAir.…
AC-48, Paper of 2022 by Myers et al., also in #IndoorAir.…
Here, the important cas is treted to use #aircleaners to reduce aerosol particle viral loas when people quarantine at home. Often, this has resulted in infections of room sharers
and especially family members. Aircleaners are a means to reduce transmission in such cases.
9/9 Image

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More from @H_Herrmann24

Oct 29, 2022
Also, hier Stellungnahmen von KollegInnen aus #Atmosphären- und #Gesundheitsforschung zum Vorschlag der @EU_Commission vom 26.10. für neue Grenzwerte bei wichtigen Spurengasen und #Feinstaub (#PM), aber auch einigen Einzelsubstanzen in Gas-
& Partikelphase - dies von @smc_germany

Interessant ist Art 13:
Es wird jetzt 'limit values', also Grenzwerte geben für
Schwefeldioxid (SO2)
Stickstoffdioxid ( NO2)
Feinstaub als PM10 & PM2.5
Kohlenstoffmonoxid (CO)
und einen "target value" = Zielwert für Ozon
( O3) in der Gasphase.
Entsprechend wird es 'limit values' , also Grenzwerte geben für folgende Substanzen in der Partikelphase:
Damit werden die regulierten Einzelsubstanzen ausgeweitet, bisher war hier nur Benzo(A)Pyren reguliert, und zwar
Read 13 tweets
Sep 3, 2022
Ich stimme @SourceControl21 hier zu, habe mir das Update der Stellungnahme angesehen. Viele Kollegen und ich teilen diese Einschätzung zu mobilen Luftreiniger nicht, vgl. zunächst einmal die umfangreichen Aktivitäten in den USA dazu. (1/n)
Mobile Luftreiniger können schwer die alleinigen Problemlöser sein, aber einen wertvollen Beitrag zur Reduktion der Viruslast leisten. Dieses ist durch viele Publikationen belegt. Dass "keine epidemiologische Evidenz" vorliegt, gilt auch für viele andere sinnvolle ... (2/n)
Maßnahmen. Dieses ist eine sehr zu stark durch die Medizin geprägte Sichtweise, die nun sinnvolles Handel verhindern soll - Warum ? Landesregierungen mit Ihren zuständigen Ministerien sind dieser Stellungnahme gefolgt - #Sachsen und ... (3/n)
Read 9 tweets
Jul 13, 2022
Das sehe ich grundsätzlich auch so. #Luftreiniger senken die Aerosolpartikellast. Allerdings kann diese im Raum so hoch werden, z.B. duch mehrere atmende Infizierte, dass die Reinigung allein die Infektion nicht mehr verhindern kann. Dann wird mit Außenluft verdünnt... (1/2)
werden müssen, am besten durch eine moderne raumlufttechnische Installation mit #Wärmerückgewinnung. Bei einer solchen Virenlast ist dann auch die #Maske angezeigt, (2/n)
Read 4 tweets
May 1, 2022
Kurzer 🧵 von @twpiggott, mit leider zutreffender Einleitung von @Kaddand67376085
Habe noch ein paar Sachen dazu geschrieben zum Stand bei #Covid19, vielleicht ein #Rant
#Nichtmedizinische #Interventionen müssten bald einmal angegangen werden, sieht leider nicht so aus, (1/n)
und zwar aufgrund politscher Entscheidungen, das wird uns wieder einholen.

Die Konsequenz, "Das wurde nun politisch entschieden, damit sind wir fertig", finde ich nicht richtig, denn die Entscheidungen sind ja nicht hinreichend wissenschaftlich basiert. Daher müssen (2/n)
#Wissenschaft & Co die richtigen Maßnahmen weiter vertreten, auch wenn es nervenzehrend ist
#Covid19 Eindämmung und Bekämpfung wird nur durch Kombination medizinischer und nichtmedizinischer Maßnahmen gelingen = #Käsescheibenmodell. Bei den #NMI sind wir ganz am Anfang (3/n)
Read 8 tweets
Feb 21, 2022
#Wegfall der #Maskenpflicht am #Sitzplatz an #Schulen via @ChanasitJonas

Grundfalsch ! Das Virus wird über Aerosolpartilkel übertragen, zu MV:

Aerosol FAQ
AAF Stellungnahme

#Covidisairborne (1/n) Image
Die Grafik kommt von Rechnungen von @KriegelMartin , aufbereitet vom ZDF = (2/n)
Mehr "Aerosol" Stellungnahmen
@G_Ae_F : (3/n)
Read 8 tweets

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