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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 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
Al Haddrell Profile picture
Dec 30, 2025
In 2025, I’ve put together many threads discussing various aspects of science, science communication, aerosol science, or airborne disease transmission

With it being the end of the year, and social media being largely fleeting, I thought I’d highlight a few worth revisiting Image
A few of the threads discussed the fundamental challenges around measuring the effectiveness of mitigation strategies.

In this thread I discuss some of the challenges around designing RCT studies.

In this thread, I discussed how poor experimental design leads to incorrect conclusions about the effectiveness of ventilation/filtration, etc. on disease mitigation.

Read 11 tweets
Al Haddrell Profile picture
Dec 20, 2025
One of the reasons why I go so hard on science misinformation/disinformation, is that as a working scientist it is frustrating to see your research misreported to push an agenda.

For example, consider this piece of right-wing propaganda from The Telegraph that was just published Image
Here’s a link to the article (free to access on Yahoo).

Spoiler alert: it’s rubbish.

yahoo.com/news/articles/…
The article is an opinion piece masquerading as journalism. While this is typical of these sorts of trashy publications, what concerned me was that they highlighted my research specifically to push their message.

Consequently, I feel like I ought to respond. Image
Read 13 tweets

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