Thread by @ARISense_AQ

#AAAR2022 Absolute Respiratory Particle Number and Mass Exhalation Rates and Size Distributions during Breathing and Vocalizing. JONATHAN P. REID et al., University of Bristol

begin - team is huge / lots of help / team effort -

150 human participant

What we're trying to do.. breathing, speaking, coughing - there's multimode aerosol size distributions that get emitted. Number of mode - aerosols from lower respir, middle-bits of your lungs, and then from speech. 99% of total number are sub 10 microns.

# concentration are extremely small. You really have to sample for 10s of minutes to get enough signal.

Comes from the PREFORM study - looking at singers, instrument-blowers, professional athletes, kids, etc.

Begin: Concentration are extremely low - that means we have to measure this stuff in a very very very clean background (zero PM in the room).

Again, the whole story is bkg aerosol, if you don't get rid of all the bkg aerosols

Using APSs to measure flow (this is a 70K USD object). Combined with gas exchange rates, CO2, etc.

Example of the minute ventilation rate and how it scales with adult and kids doing all sorts of activities.

Water sensitive paper - to collect particles up to mm size to back out droplet sizes.. neat.

exhaled aerosols when people breathe. Looking at this as number of particles vs particle diameter. broad distribution at breathing, no difference between kids and adults - wide range of concentrations. 150 ppl no real correlations with BMI * age.

There are some really large emitters. The dependence on the loudness of speaking and singing. Steady increase in exhaled concentration with the loudness. you should sing quietly...shhhhhhhhhh less aerosols.

exhaled number rate per second - comparing breathing, speaking, singing - when I show this to a lot of audiences - get it: IT'S EXTREMELY SMALL NUMBER CONCENTRATIONS FOLKS

You can do some interesting calculations - we are talking about tiny tiny numbers of aerosol particles. Gauge risk. Work out mass exhalation rates to quantify risk...

mass exhalation rates comparing vigorous vs less vigorous exercise and speaking at normal volumes.

For larger droplets, using the water sensitive paper - be careful. spit paper. Identify the droplet and measure the number exhalation rates in droplets larger than 20 um in diameter across diff activities.

Gravitational settling! It is a thing. If you're big enough.

Vocal activities are pretty consistent. "Happy Birthday" droplets.

We can also measure the exhaled CO2 concentrations and relate the particles and CO2 breathing vs exercises. Clear correlation between mass emission rate - Vocalization increases particles regardless of CO2. Beware of the CO2 as metric to exhaled virus!!! Oh.. Interesting.

Again - we're making measurements in a 0 bkg PM space. Range of exercises. Across a range of activities - breathing to speaking to tongue trills (what?) measuring aerosols in front of the face mask. Dropping concentrations by order of magnitude when measuring behind mask.

Mass emission rate under vocalizations adds to the aerosol mass emission rate in a way that does not scale with CO2. That's a neat conclusion. You get more aerosol bang for your CO2 buck under these vocalization activities.

Q&A: Did you measure on the side of the mask?

We did that too.. just not presented here.

Q&A (Jose): Enrichment of virus compared to bulk? Potential scaling of viral load and siliva - simple calculation used here.. Validated these numbers for ballistic droplets vs inhaled aerosol (Ans. No not yet).

Q&A: Fraction of aerosols above and below 1 um.

APS does measure down to 0.5 um.. so we have some data.

Q&A: Capture efficiency of the funnel thingie?

5 APS systems pulling through the same funnel. Jeeeze.. 5 APSs. That's like... ~ $350,000 of size resolved aerosol measurements..

That's a lot of MOD-PMs...