1/ Complexity of Close Contact

Inhaled deposited dose of aerosol particles via close contact is difficult to model, even if two people stay facing each other at 4 - 6 feet apart, due to huge variations in emissions as well as dispersion of the plume between them.
2/ If the indoor space is a crowded event (e.g., wedding reception, bar, etc.) in which people move around, the complexity becomes even greater. How often does a person come in close contact with one or more infectors? What is the average contact time?
3/ I have been thinking back to my PhD dissertation (way back in the day) when I studied and applied surface renewal theory for gas transfer at interfaces where liquid-phase mass transfer dominates.
4/ "Packets" of liquid come to surface w/ frequency defined by mixing conditions, etc. Each packet stays at surface for a time period that can vary and be defined by a probability distribution. While at the surface chemicals can volatilize (transfer) from liquid to gas.
5/ Surface renewal theory is not unlike frequency of contact with infector, time spent in close contact, & transfer from infector to receptor resp systems.

My research dealt w/ volatilization of chemicals from raw sewage to overlying headspace in sewers. Someone had to do it!

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More from @CorsIAQ

13 Nov
1/ Heading to 200K/day this month & 300K/day in Dec. Increased death rates to follow. What got us here is obvious. Failed leadership. Ill preparedness. Stubbornness. Failed communication. Irresponsible behavior. Water under bridge now. Learn from it, but move on w/ urgency.
2/ Do we act now to save hundreds of thousands more from gasping for breath & dying without family around them, the heartache of losing loved ones, the struggles of those who survive, the horrific impacts on our economy? Acting now is responsible, empathetic, and patriotic.
3/ Please be a patriot. Act. Wear a mask in any indoor space other than your own home w/ immediate family present. Visit only essential indoor spaces where everyone wears a mask. Reduce time in those spaces. Distance. Ventilate. Filter. Sanitize hands. Help to educate others.
Read 5 tweets
11 Nov
1/ Gr8 that @cdc has discovered the dual (lower emissions & less inhalation dose) benefits of masks. A 5 min Sci Citation Index search leads to several past papers of relevance. Here is one by researchers @cdc's very own @NIOSH from 2010.

2/ This paper was cited in tweets by several researchers earlier in the pandemic & shows 40% to 60% removal efficiency (100% - penetration%) for 1 um particles at receptor end (& so even better for > 1 um) for some materials (much worse for others).
3/ More recent results reported by @linseymarr, @Smogdr, & their colleagues/teams significantly increase knowledge of different materials, layered materials, particle size effects, etc.

My previous tweet illustrating dual benefits. 40+40 = 64%, 50+40 = 70%, 60+60=84%, etc.
Read 4 tweets
7 Nov
1/ Yes! Right on, @CathNoakes. Infection via ride share (for both drivers and passengers) has indeed been a concern of mine for a long time given its increasing use.

Op-ed w/ Joe Allen here. And simulation below.

2/ Simulation I did for background aerosol particles in the cab of a typical-sized vehicle and realistic ventilation. The vertical axis is inhaled deposited dose in ride share normalized by that of those infected in Restaurant X in China with same infector emissions. Image
3/ That red bar with windows closed and no outdoor intake underscores high risk. Simulation is without masks, so bars lower if driver and passenger(s) wear masks. Opening windows (even a small amount) dramatically reduces dose. Avoiding busy commutes (shorter time) also helps.
Read 4 tweets
6 Nov
1/ Important move. Tamp it down before losing control.

"Oregon has recorded more coronavirus cases over the past week than at any point since the pandemic began"

"Active hospitalizations and the test positivity rate are also at record highs."
2/ But we could use more than limits (or recommendations) on social gatherings. Responsible businesses, gov agencies, school districts, etc., should require & enforce masks, employ strict physical distancing, increase outdoor air supply rates, & employ advanced filtration.
3/ If we are relentlessly committed to actions that dramatically reduce inhaled dose (whether from close contact or far field) of SARS-CoV-2 (it's wholly possible to reduce dose by 90 to 95% in most buildings), we can stop the frustrating cycle of starting & stopping in fits.
Read 4 tweets
5 Nov
1/ Pleased to be quoted in this chalkbeat article on portable air cleaners in NYC schools, which also links to the Harvard/CU Boulder calculator.

2/ “It is very important to understand that portable air cleaners, improved filtration in HVAC systems, and increased outdoor air supply can significantly reduce inhaled dose of aerosol particle concentrations in classrooms for those away from an infector”
3/ “They do not appreciably reduce the dose of aerosol particles for someone standing near an infector who is speaking or coughing. For this close contact case physical distancing and required mask wearing by everyone is critical.”
Read 4 tweets
5 Nov
1/ Just had a wonderful interview that took a tangent into terpenes and terpene alcohols associated with air "fresheners" (plug in, heated essential oils, etc.). They do NOT remove pollutants from indoor air. Period. Period. Period.
2/ They can be oxidized to form secondary organic aerosols and a wide range of oxygen-containing reaction products. Tox data on a large fraction of these reaction products do not exist (could be benign or not).
3/ Terpenes and terpene alcohols can mask (overwhelm) objectionable odors, but do not rid of the source of the odors. I suspect based on their popularity that many people also find these scenting agents to relieve stress.
Read 5 tweets

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