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.
4/ This simulation assumes a well-mixed vehicle cab atmosphere (actually not a bad assumption in many vehicles). It does not account for closer contact, e.g., infected passenger sitting directly behind and speaking to driver, etc., or fomites as @CathNoakes points out.

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More from @CorsIAQ

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
3 Nov
1/ Source Reduction.

Ventilation & filtration are important, but so is source reduction.

"If there is a pile of manure in a space, do not try to remove the odor by ventilation. Remove the pile of manure." (Max von Pettenkofer, 1858)
2/ Humans who are infected are not manure, but we should do everything possible to reduce the emissions of infectors indoors (in addition to grater ventilation and improved filtration). So, how do we do that?
3/ First, anyone who has had contact w/ an infector should quarantine and not go to work, school, and other indoor environments other than their homes. They need to be removed from the playing field. Testing is also valuable for keeping positive cases in isolation & off field.
Read 7 tweets
1 Nov
1/ I have left my blog up on Inhaled Deposited Dose at corsiaq.com. IMO we should discuss this concept more & use it as a guide for how to effectively reduce dose, risk of infection, and infection outcomes.
2/ Without knowing what the actual dose-response relationship is we should assume that any level of inhaled deposited dose leads to some risk (precautionary principle). The higher the dose the higher the risk of infection.
3/ It is also likely that the higher the dose the worse the outcome (on average) from an infection. There is certainly individual variability (elderly, diabetics, etc.) wrt dose-response.
Read 5 tweets
31 Oct
1/ Previous analysis by my team of occupied-day average & peak CO2 concentrations in K-8 classrooms in Central Texas and Rio Grande Valley. Results shown as cumulative distribution plots. So, 35% of classrooms w/ CO2 less than 1,000 ppm & 65% greater (note ref on absenteeism).
2/ 20% of classrooms with average CO2 concentrations greater than 2,000 ppm and peak concentrations greater than 3,000 ppm! Sadly, conditions in the Rio Grande Valley were far worse than in Central Texas (an indoor socio-environmental justice issue). next ....
3/ Mean occupied day CO2 concentration in Central Texas = 1,300 ppm and in RGV = 1,800 ppm with similar disparity for peak values. Also compared portables versus traditional classrooms. more ...
Read 5 tweets

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