Thread by @jeffgilchrist

Wildfire smoke - now extra toxic plumes from sun UV

Did you know just one of the many fires burning in Quebec is the size of an entire Canadian province (PEI), or large enough to stretch between the cities of Ottawa and Montreal or Toronto to Niagara Falls? 🧵1/

Read on to learn more about why the smoke now smells like plastic and the health impact. An unrolled one-page web view for this long thread that may be easier to read or share can be found here ( ). 2/

https://twitter.com/jeffgilchrist/status/1675166940078170114

You can see from this fire smoke map that tiny PM2.5 aerosols don't just drop 6 feet away but can travel all over the continent with the smoke from northern Quebec blanketing New York City and even producing hazy skies in Europe ( ). 3/ https://t.co/lBbNeaHVYPfiresmoke.ca/forecasts/curr…

Instead of the classic smell of burning wood in a fireplace or campfire, things are starting to smell more like burned plastic so what is going on? 4/

It turns out that when smoke stays in the air for prolonged periods of time, the UV radiation from the sun interacts with all the volatile organic compounds (VOCs) to form even more toxic gases. 5/

Now benzene and formaldehyde are being created in the atmosphere from the smoke + UV radiation which happen to smell like plastic but are toxic and can have very adverse effects on human/animal health ( ). H/T: @lisa_iannattone 6/ https://t.co/wYhh4UZJ48theweathernetwork.com/en/news/weathe…

You can learn more about formaldehyde here ( ) and benzene here ( https://t.co/9goF4bjn5n ). 7/epa.gov/indoor-air-qua…
emergency.cdc.gov/agent/benzene/…

Besides the PM2.5 particles in the smoke that can get into your lungs and bloodstream, wildfires smoke it also full of various toxic gases in the form VOCs and by-products like formaldehyde and benzene as we saw above. 8/

Well fitting respirators like N95 masks will do a great job at filtering out the PM2.5 particles from the air if you are outside, but they are not designed to filter out all the smoke related gases. 9/

You can learn more about how filtration material in N95s and HEPA filters actually filter out the tiny PM2.5 particles despite them being smaller than the holes in the material ( ). 10/

https://twitter.com/jeffgilchrist/status/1602994049815908353

While it is much better to wear a good mask outdoors during wildfire smoke events that filter the PM2.5 particles than nothing, you are still getting exposed to other toxic gases. 11/

There are elastomeric respirators with special cartridges that will filter out both the PM2.5 particles and also various gases which would provide better protection outside from smoke ( ). 12/cdc.gov/niosh/npptl/re…

If N95s can effectively filter out tiny smoke PM2.5 particles, why can you still smell things while wearing a good mask? While PM2.5 particles are 20x smaller than the width of a human hair, the gases you smell can be billions of times less atomic mass than PM2.5 particles. 13/

A dalton (Da) or unified atomic mass unit (u) is commonly used in physics and chemistry to express the mass of atomic-scale objects such as atoms, molecules, and elementary particles ( ). 14/en.wikipedia.org/wiki/Dalton_(u…

The mass of formaldehyde is 30 Da while benzene is 78 Da. Compare this size to a single virus particle (virion) at 6 billion Da or an aerosol droplet at 160 billion Da, both monstrous sizes in comparison ( ). 15/

https://twitter.com/jeffgilchrist/status/1602994130086682624

That is why molecules like oxygen (16 Da) can get in through respirators to you and exhaled carbon dioxide (44 Da) can get out so you don't suffocate. 16/

But it also means that toxic gases from wildfire smoke can get through N95 masks and why you can smell them so you may still want to limit your time outdoors during smoke events even while wearing a mask. 16/

Another thing I discovered is that Canada's Air Quality Health Index (AQHI) is not the best measure to use for wildfire smoke events. 17/

Ontario's AQHI readings actually weighs other pollutants much more than PM2.5 and was designed for urban car/factory pollution which builds slowly so they only look at 3 hour averages while wildfire smoke can jump quickly ( ). 18/thestar.com/news/canada/20…

Right now the Ontario AQHI level is rated at 4, the first level of moderate risk on a scale that only goes up to 10 ( ). 19/ https://t.co/3z3ucLmIazairqualityontario.com/aqhi/today.php…

USA has a PM2.5 air quality index (AQI) that goes up to 500. While the AQHI is showing 4 (yellow), the first level above low risk, the USA index is showing 158 (red) which they rate as unhealthy and the levels of concern increase much more rapidly ( ). 20/ https://t.co/gbu48iFOtPairnow.gov/aqi/aqi-basics/

For smoke, it is better to look at the actual raw PM2.5 levels to see what is going on so you don't have to worry about conversions. This time last year PM2.5 levels in Ottawa would typically range between 2-6 ug/m^3. 21/

Right now in Ottawa raw PM2.5 levels are 70 ug/m^3 which many air quality sites will provide PM2.5 such as PurpleAir here ( ) and even the Ontario air quality stations which is better than following their AQHI version ( https://t.co/0LGQ014KZE ). 22/ https://t.co/NvoFe3Bkyqmap.purpleair.com/1/m/i/mPM25/a1…
airqualityontario.com/history/pollut…

Since healthcare professionals are warning that there are no known safe levels of PM2.5 it would be prudent to limit exposure as much as possible. You can read more about the equivalent amount of cigarettes at various levels of PM2.5 here ( ). 23/

https://twitter.com/jeffgilchrist/status/1672979098778456066