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Al Haddrell Profile picture
Al Haddrell
@ukhadds
Aerosol scientist/Aerobiologist, Canadian and #Canucks fan living in the UK. #eurovision enthusiast. I’m also at: https://t.co/Ut3mF6fa5w
5 subscribers
Aug 19 • 30 tweets • 8 min read
This article was published recently that reports the aerostability of SARS-CoV-2. I’ve been asked for my thoughts, and given that this is in my wheelhouse, I have a few.

First off, here’s the article:

nature.com/articles/s4429…
Aug 13 • 51 tweets • 15 min read
Straw Man Science and Covid Mitigation:

How poor experimental design coupled with media sensationalism undermines physical and engineering solutions to limit the spread of airborne diseases

A 🧵 Image Airborne disease transmission is a complex, and multidisciplinary process. As a result, understanding how various factors affects transmission rates is exceedingly difficult.

Consequently, designing effective physical mitigation strategies for this process remains a challenge. Image
Aug 9 • 18 tweets • 6 min read
CO2 monitors have become popular tools people can use to estimate their indoor air quality.

A new study was recently published that explores how we can use them to optimise occupancy thresholds and identify problem locations.

Actual practical science!!!

🧵 Image Here’s a link to the study. The lead author is Henry Oswin; he did his PhD with us, working with me on Covid. He’s now doing a postdoc with Lidia Morawska.

Both Lidia and Henry are excellent writers, so this is a particularly engaging and easy read.

sciencedirect.com/science/articl…
Jul 27 • 58 tweets • 18 min read
Recently, I posted a link to an article discussing how well masks work at limiting airborne disease transmission. Gillian read the link and asked the following question.

This gets to a critical issue I thought I’d discuss.

Alright, so the specific quote being highlighted is below. Now, this may seem alarming to many people.

To be clear, the author is saying that they estimate the number of infectious aerosol an infected person exhalesis extremely low. Image
Jul 24 • 18 tweets • 6 min read
I was at a restaurant in my hometown (Shaughnessy's Cove in Summerland, BC) and noticed the outdoor air conditioning system.

Whether they know it or not, they are using aerosol science to cool the air. I figured I’d put together a thread to explain how these work. Image So, what is actually happening?

By spraying a mist, the outdoor eating area is cooled. Now, the area isn’t cooled because water is being sprayed all over the surfaces, akin to spraying a hose of water everywhere. Something more interesting is happening. Image
Jun 30 • 6 tweets • 2 min read
There is no safe level of exposure to Asbestos. For this reason, it has been banned in >60 countries across the globe.

And yet, there is an effort in the US to bring it back. In this article, I discuss why this is happening, and what it all means.

theconversation.com/the-uss-asbest… This article is a byproduct of a previous thread I wrote about the dangers of asbestos. In it, I explain what to your body after you inhale it. In short, it doesn’t go anywhere, and causes harm for years.

Jun 21 • 19 tweets • 6 min read
Since there is talk about bringing back ASBESTOS (this is somehow true), I thought it would be useful to describe just some what happens to you when you breath this stuff into your lungs.

In short, it’s terrible.

A 🧵 Image What is asbestos?

Asbestos is a group of naturally occurring fibrous minerals. There are 6 types: Chrysotile, Amosite, Crocidolite, Tremolite, Actinolite and Anthophyllite.

They have some useful properties (including heat resistance, strength, durability and well insulating) Image
Jun 6 • 42 tweets • 11 min read
We just had an article published in ACS Central Science on the how the pH of exhaled aerosol evolves over time

As we’ve previously reported, respiratory aerosol pH (high pH!) is a driver of SARS-CoV-2 decay. Meaning, understanding the pH dynamics is important for estimating risk Image This paper is a step in the direction of improving our undertanding of exhaled aerosol pH.

Alright, so here’s a link to the article:

pubs.acs.org/doi/full/10.10…
May 26 • 21 tweets • 6 min read
Martha asked an interesting question, so I thought I’d try to answer it.

Essentially, the question is how long to wait before one is 95% certain that the room is Covid free, given a certain set of conditions. Disclaimer at the top: I am not a modeler, I am an experimentalist (that occasionally publishes simple models).

The data used to make these estimates are from experimental studies. The absolute values will not be exact, but the general trends and scales will be accurate.
May 25 • 32 tweets • 9 min read
The article claiming that SARS-CoV-2 remains infectious in the air for 16 hours has been making the rounds on social media again.

I thought I would take this opportunity to discuss it, what it shows, what it doesn’t, and why I think it shouldn’t be taken seriously.

A 🧵 First off, here’s the article:

wwwnc.cdc.gov/eid/article/26…
May 19 • 20 tweets • 5 min read
We just had an important paper published that compares different technologies used to measure aerosolised microbes.

This resulted from a collaboration between multiple research teams in the USA and the UK. Image Here’s a link to the article:

tandfonline.com/doi/full/10.10…
Apr 23 • 15 tweets • 5 min read
Climate change is a massive problem.

Geoengineering, even if possible, is not going to be a good solution for a variety of ethical (and technical) reasons.

Some thoughts. 🧵 First off, here's a link to The Guardian article that got me thinking about this:
theguardian.com/environment/20…
Mar 22 • 16 tweets • 5 min read
I received this question over on B-Sky, and thought maybe other might have it as well. I thought the easiest way to answer would be to put together a short thread. Image When it comes to short distance transmission, the proximity one has to the exhalation plume is important. But what dictates the size of the plume (ie how far does the exhaled aerosol initially travel)? And what factors matter? Image
Mar 18 • 8 tweets • 3 min read
A new study came out showing that smoking cannabis leads to “myocardial infarction and cardiovascular risks”. If you understand what happens when inhale a tremendous amount of particulate matter, these findings are not at all surprising.

Some thoughts.

Exposure to elevated levels of particulate air pollution begins a cascade of biological responses.
Mar 6 • 20 tweets • 6 min read
A study has come out the discusses how “new inactivation data significantly influences infection risk predictions”.

Since that “new inactivation data” was from our team’s research, I have some thoughts. Image Here’s a link to the study:

link.springer.com/article/10.100…
Mar 1 • 17 tweets • 4 min read
I was asked this question, and thought since it will take a bit of an explanation, I figured I’d make a thread. Essentially, the question is about the degree to which exhaled water vapour from evaporating aerosol would affect the humidity in a room.
Feb 26 • 16 tweets • 4 min read
A paper was published that presented a new model to predict airborne disease transmission. There were many features included in this model that make it interesting.
I have some thoughts. First off, here's the paper.

royalsocietypublishing.org/doi/10.1098/rs…
Feb 11 • 17 tweets • 5 min read
AI (eh-eye, not AL) has rapidly become a common tool people use to answer complex science questions.

But is it reliable?

Storytime. 🧵 Recently, I made a two-part series on my YouTube channel where I discussed the effect of humidity on the transmission of Covid-19.

Feb 2 • 28 tweets • 9 min read
This study made some waves on social media yesterday. It purports to show that CO2 concentration doesn’t correlate with covid transmission.

Let’s talk about this, I have some thoughts.

sciencedirect.com/science/articl… Context: Why do people think knowing the CO2 concentration is important when it comes to Covid transmission?

There are 3 unique reasons.
Jan 19 • 4 tweets • 2 min read
You have no idea. Ironically, I found out about this letter when I was on my way to a dinner to celebrate the end of a 5 year covid project I was on. This project resulted in 14 papers in high impact journals where we explored how SARS-CoV-2 is aerosolised through talking/singing Needless to say, to find out right then that the government had produced this letter was bizarre and upsetting. Like, why are we doing all of this research if they are just going to ignore it?

When I shared the letter with others on the team, it got a little awkward....
Dec 29, 2024 • 4 tweets • 2 min read
If you got a CO2 monitor for Christmas and are wondering what exactly the device is used for, I’ve put together a video to walk you through some ways you can use it improve your indoor air quality, and to lower your risk of catching airborne viruses (C19)
With New Years coming up, you may be having friends over. You can use a CO2 monitor to see how best to ventilate your home, to make sure that your friends and family start the year off healthy! I walk you through how to measure your home's ventilation here