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Al Haddrell Profile picture
@ukhadds
Jun 22, 2023 • 3 tweets • 1 min read • Read on X
I’m proud to have our latest research published on how long #SARSCoV2 remains infectious while airborne! We studied the fundamental processes that drive the loss of viral infectivity in the aerosol phase. #COVIDisAirborne

Here’s a thread going over some of the findings. Image
@ParentMishmash Interesting question btw. Actually, all of your questions have been. Thanks!
@J__Doh Here are the specific values. So, about 10 to 20 times faster decay in sunlight (depending on the season). Image

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More from @ukhadds

Al Haddrell Profile picture
Mar 21
Aerosols are very small, have a high surface to volume ratio and can readily reach super saturation. This combination makes them a unique environment for chemical reactions. We had a paper published in JACS that looked into the rate of chemical reactions within and on aerosols. Image
This work has implications from material fabrication through to understanding disease transmission.

The project was headed by Bryan Bzdek (University of Bristol, whose office is 3 doors down from mine).

Here’s a link to the article:

pubs.acs.org/doi/10.1021/ja…
Context: The chemistry at the air-liquid interface of a sample will be different than in the bulk. There are many reasons for this, such as the molecular orientation, higher solute concentration (due to evaporation of the solvent at the surface) and unusual acidity/basicity. Image
Read 16 tweets
Al Haddrell Profile picture
Mar 15
A preprint came out that measured how acidic vapour affects influenza aerostability.

How the pH of exhaled aerosol evolves over time will dictate both how long microbes remain viable in the air, but also how effective different mitigation strategies will work.

Let’s discuss. Image
Here’s a link to the preprint:

researchsquare.com/article/rs-902…
Context: Our team has studied how long numerous microbes remain viable in the air. In these studies, we found that the alkalinity of exhaled aerosol drove the decay of SARS-CoV-2. Consequently, elevated levels of CO2 results in SC2 remaining viable in the air for a longer period. Image
Read 30 tweets
Al Haddrell Profile picture
Mar 1
An article came out recently that looked at the effect of CO2 on influenza decay in sessile saliva droplets.

The study confirms what we have been saying since 2022: respiratory fluids become highly alkaline when they leave the body, and this in turn affects microbe viability Image
Given that this is a research area where our team has made a lot of waves, I thought I should share my thoughts.

Here’s a link to the article:

pubs.acs.org/doi/10.1021/ac…
Context: Prior to 2020, the assumption in the literature around respiratory aerosol pH was that was acidic. There were a few reasons for this, but it largely came down to the fact that almost all environmental aerosol is acidic, so it was assumed respiratory would be the same Image
Read 18 tweets
Al Haddrell Profile picture
Feb 23
I got this question over on BlueSky that I thought some might find interesting.

In short, why does the CO2 levels in a hockey arena trend upwards even though it has an upgraded HVAC? Image
When HVAC systems are installed, certain assumptions are made, largely because they need to be. One is that the air within the space is evenly mixed.

The problem is that it rarely is. Image
In a perfectly designed space, for every litre of fresh air brought into a space, 1 litre of air would be removed. For this to occur, a room would have be essentially a pipe. Image
Read 9 tweets
Al Haddrell Profile picture
Feb 7
The risk of the airborne transmission of disease correlates with the amount of infectious exhaled aerosol. Since people exhale CO2 with aerosol, its conc has been used as proxy for exhaled aerosol

In this article, researchers propose a new way to estimate risk of transmission Image
Here’s a link to the article (the first author is Henry Oswin, a former PhD student from our group who is currently working with Lidia Morawska):

sciencedirect.com/science/articl…
For a variety of reasons, CO2 may not be a good proxy for exhaled aerosol. eg, it will underestimate the risk when people are talking, or overestimate when filtration is used.

I walked through some of this in my explainer video (excerpt shown below):

Read 10 tweets
Al Haddrell Profile picture
Jan 22
Not so fun fact: Tear gas isn’t a “gas”

If it’s not a gas, then what is it?

Answer: it’s an aerosol. And this distinction matters.

Let’s discuss 🧵 Image
The burning sensation of tear gas is caused by the compound 2-chlorobenzalmalononitrile.

Rather than discussing how this chemical affects the body biologically, let’s go over how this chemical is dispersed physically, and why that matters (aerosol science!). Image
Tear gas is delivered a couple different ways.

1) Pyrotechnic canister where the device produces a cloud of hot smoke.

2) Aerosol spray devices where the chemical is dissolved in a solvent and then sprayed. Image
Read 18 tweets

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