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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
6 subscribers
Oct 25 • 40 tweets • 11 min read
Over the past decade, various randomized control trials (RCT) have been published that attempt to measure the effectiveness of physical mitigation strategies of airborne disease transmission.

And for the most part, most of them are terrible.

Let me explain why.

A🧵 Image Airborne disease transmission is extraordinarily complicated, with many steps involved. Consequently, there are many different solutions that have been proposed to limit transmission. They largely involve the removal of exhaled aerosol from the air prior to inhalation. Image
Oct 20 • 34 tweets • 9 min read
If You Want Clean Indoor Air, Not One Thing Will Work!!

How Sadiq Khan is taking a page out of the Team GB Cycling Team’s playbook to clean up London’s air

A 🧵 Image People spend the majority of their time indoors. As a result, indoor air quality is incredibly important for public health. So then, how do we improve the quality of indoor air?

Well, there are countless ways. That said, they can be grouped into 3 broad areas. Image
Oct 14 • 19 tweets • 5 min read
Another article came out that is suggesting that ventilation doesn’t work in classrooms.

Does it actually showthat?

No.

Does it find out anything new?

Also, no.

Straw Man Science? Most definitely.

Let’s get into this 🧵 Image Here’s a link to the study:

jamanetwork.com/journals/jaman…
Sep 28 • 15 tweets • 5 min read
Violet Affleck made headlines this week with a powerful speech at the UN. In it, she discussed the importance of masking in limiting Covid transmission

Her speech also gave us insights into how the right-wing/Murdoch media engages with science in the age of Covid

Some thoughts Image Augmented Reality (AR): AR is a technology that takes “components of a digital world blend into a person's perception of the real world”. With AR, a person can make “reality” whatever they want it to be.

The Murdoch media empire behaves in a similar way.

en.wikipedia.org/wiki/Augmented…
Sep 8 • 9 tweets • 2 min read
Evidently this needs to be said:

Do not spray nitric acid into the air in the hopes of limiting viral transmission.

More pollution is not the solution. At all. This is in response to a paper that came out recently: nature.com/articles/s4200…
Sep 6 • 11 tweets • 4 min read
Got this question, and it reminded me of a story I heard back during my PhD days.

The question is essentially, is there a problem with breathing too clean of air?

I did my PhD in Simon Fraser University in Vancouver, Canada. As part of the project, I ended up working in St Paul’s hospital, specifically within the James Hogg iCapture Centre.

They have been rebranded, and remain a world leading research facility.

hli.ubc.ca/who-we-are/
Aug 31 • 18 tweets • 7 min read
One year ago today, I officially started a YouTube Channel.

I thought I’d take the opportunity to reflect on the year, and talk a little about what the channel is, what it isn’t, and what I’m hoping to accomplish with it. Image First off, here’s a link to the channel.

youtube.com/@AlHaddrell/fe…
Aug 28 • 7 tweets • 2 min read
When scientists say things like, "opening a window lowers the risk of transmission by 38%", where do they get these numbers? Well, they use airborne transmission models.

In my latest explainer video I walk through the history of these models, what they do, and what the don't. Image Here's a link to the video:
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