Thread by @HuffmanLabDU

1/ Interesting paper showing high efficacy of portable HEPA #filtration to reduce aerosol concentration in a high school classroom during use.

By very experienced German aerosol group Curtius et al.; via @ASTJournal.

With short🧵on room air filtration.
doi.org/10.1080/027868…

2/ "In times when classes were conducted with windows and door closed, the aerosol concentration was reduced by more than 90% within less than 30 min. when running the purifiers (air exchange rate 5.5 ACH). The reduction was homogeneous throughout the room ..."
[note log y-scale]

3/ Figure 3: Highly reproducible reduction in aerosol particle concentration [uCPC] in a closed classroom without air purifiers (blue line) and with 3 or 4 air purifiers operating at speed 3 or 4 (max).

4/ "The measurements are supplemented by a calculation estimating the maximum concentration levels of virus-containing aerosol from a highly contagious person speaking in a closed room with and without air purifiers."

5/ "Figure 8: #CO2 mixing ratio measured in class during a school day. Even after venting the room for several minutes w/ door & windows wide open, CO2 levels do not drop < 1000 ppm. ... levels quickly rise to mixing ratios of 2500 to 2800 ppm at the end of the lesson." #COVIDCO2

6/ Study conclusions: "Measurements and calculation demonstrate that [portable] air purifiers potentially represent a well-suited measure to reduce the risks of airborne transmission of SARS-CoV-2 substantially."

7/ "Staying for two hours in a closed room with a highly infective person, we estimate that the inhaled dose is reduced by a factor of six when using air purifiers with a total air exchange rate of 5.7 ACH"
#COVIDisAirborne

8/ "In summary, the operation of mobile air purifiers in classrooms seems feasible as a practical measure that can quickly be implemented during an epidemic."
#airpurifiers #aircleaners #HEPA #filtration
doi.org/10.1080/027868…

9/ "In order to reduce the risks of aerosol transmission for SARS-CoV-2 air purifiers can form an important additional measure of precaution, especially in cases where no fixed ventilation systems are installed and when windows cannot be opened properly." #aerosol

10/ The study conclusions are broadly consistent with lots of other experimental and modeling studies (i.e. portable filtration helps!). E.g. these are simple results I put together related to long-range aerosol risk modeling for classrooms on our campus:

https://twitter.com/HuffmanLabDU/status/1339650155033726976

11/ Practical follow-up to the study above.

Portable air filtration is an imp. component of layered reduction strategies against airborne viral infection. To learn more & est. right filtration for you, see tool by @ShellyMBoulder @j_g_allen @cedenolaurent
docs.google.com/spreadsheets/d…

12/ And to answer further questions about room air filtration, see answers in section 10 of this helpful #COVID #aerosol transmission FAQ guide. Avoid ionizers & other gimmicks for portable units, stay with proven filtration.
docs.google.com/document/d/1fB…

13/ Another potentially good option for ~$40 is a #DIY version using a box fan + furnace filter combo. E.g. see article by @JimRosenthal4. #boxfanfilter
wired.com/story/could-a-…

14/ This is a nice write-up on the DIY #boxfanfilter idea, via @JbcLiftec.
docs.google.com/document/d/1ja…

15/ A bonus of any good air filtration (central or portable) is that it can do a good job of removing all kinds of aerosol particles in a room, whether related to respiratory viruses, air pollution, or even wildfire smoke.

https://twitter.com/HuffmanLabDU/status/1303851720645079042