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Jeff Gilchrist Profile picture
@jeffgilchrist
Feb 3, 2024 • 39 tweets • 11 min read • Read on X
Warning: Ultrasonic Humidifiers with Tap Water Generate lots of PM2.5 Pollution

Since we are in winter and humidity levels are much lower this time of year, I wanted to provide this warning after a recent experience of a colleague of mine.🧵1/ Graph of PM2.5 levels showing 3 large spikes between 150-200 ug/m3, three days in a row at night.
It is amazing what you can discover about your environment when you actually monitor it. My colleague recently purchased a particulate matter (PM) monitor for his home & after multiple days of nothing he saw massive spikes in PM2.5 levels every night for three nights in a row. 2/
The PM2.5 levels exceeded 150 ug/m3 the first night and over 200 ug/m3 the next two nights. While no level of PM2.5 is safe, the WHO warns of exposure to levels above 5 ug/m3 annually and 15 ug/m3 in a 24 hour period ( ). 3/ who.int/news-room/fact…
Graph of PM2.5 levels showing 3 large spikes between 150-200 ug/m3 from an ultrasonic humidifier that was using tap water instead of distilled water, three days in a row at night.
He was able to track down the source to an ultrasonic humidifier that had been filled with tap water to make humidity levels more comfortable in a bedroom. 4/
The PM monitor was actually in a different part of the house and he measured 3x higher levels in the room where the ultrasonic humidifier was operating. 5/
What happened? “Ultrasonic humidifiers generate humidity by breaking water into small droplets using a piezoelectric transducer, a device that vibrates very fast at the ultrasonic frequency." ( ). 6/ualberta.ca/science/news/2…
“These small water droplets are then sent into the air by a fan. That is the mist that we can see coming out of the humidifier." 7/
"Once released in the air, water evaporates quickly into the surrounding air, but the minerals and salts dissolved in tap water are left behind in the air as suspended PM.” 8/
The PM was not confined to the bedroom but spread all throughout his house where it was being breathed in by all family members. 9/
A study confirmed that using distilled water purchased from local grocery stores in ultrasonic humidifiers generated no PM pollution ( ). 10/onlinelibrary.wiley.com/doi/abs/10.111…
@threadreaderapp please unroll
It is important to note that PM generation happens with ultrasonic humidifiers but you can use tap water with evaporative, wick-based humidifiers which does not break up the water molecules in the same way. 11/
Thankfully he had a PM monitor and noticed there was something wrong so he was able to identify and correct the issue. 12/
Why bother using distilled water, what would be the impact if he just kept using the much cheaper tap water and breathing in high levels of PM every night? 13/
Berkeley calculated that exposure for every 22 ug/m3 of PM2.5 for 24 hours is equivalent to smoking 1 cigarette so if they kept using tap water for their humidifier it would be like smoking about 9 cigarettes every night for them ( ). 14/
I used a Model E PM monitor to measure how much outside PM pollution I was letting inside the house by opening a window and also how much frying an egg generates ( ). 15/co2.click
Cooking can also cause high levels of PM so please ensure good ventilation by turning on your range hood fan or opening a windows if possible and HEPA filtration/CR boxes help too ( ). 16/
You can read more about the importance of indoor air quality here ( ). 17/
Much of the PM we breathe in, even while indoors, comes from outdoor origin so it is also important to monitor outdoor PM air quality ( ). 18/
Many people have asked if carbon water filters help. People would need to measure & confirm their filter but most only remove some minerals/metal but not all so could potentially reduce PM levels but wouldn't eliminate ( ). 19/mytapscore.com/en-ca/blogs/ti…
Are the contents of water dangerous? Besides minerals there are metals commonly found in drinking water such as arsenic, copper, lead, iron, nickel, cadmium ( ) and ( ). 20/lakecountyil.gov/DocumentCenter…
mytapscore.com/en-ca/blogs/ti…
Since PM2.5 particles of any type are so small, "PM2.5 can pass through the lung–gas–blood barrier and the 'gut–microbial–brain' axis to cause systemic oxidative stress and inflammation, or directly enter brain tissue via the olfactory nerve" ( ). 21/ncbi.nlm.nih.gov/pmc/articles/P…
This could impact your body differently than just drinking the water with the same content that is normally safe to drink. 22/
“These particles are so small that they can evade our filtration system in the upper airway and penetrate deep into our respiratory tract,” explained Lau. “Upon doing so, they also send chemical species associated with them into our bodies." ( ) 23/ualberta.ca/science/news/2…
People are also asking which PM monitors I use? I have been using air quality monitors by @IndianaTux, a Canadian company. The Model E, G, and X offer PM sensors in them. 24/co2.click
Their Model E and G are indoor monitors that measure PM and their X is an outdoor monitor for PM. The feature I like the best is that they can take measurements every minute and upload the data via WiFi so you can see what is going on in your space over time. 25/ Graph showing indoor particulate matter (PM) levels on the 2nd floor of a house as outdoor wildfire smoke PM levels increased and how indoor levels went down when switching the HVAC system to recirculate air through the HVAC filter and not bring in new outdoor air.
If you are interested in learning more, this thread shows some examples of how their Model X and E work and what their online portal looks like ( … ). Model G uses the same PM sensor as Model E-Lite but uses a non-colour display and is cheaper. 26/
As for more affordable options, I cannot vouch for how accurate they are or how well they work since I have never used them but IKEA sells couple of lower cost options ranging from $13 to $50 which do not have the data saved online ( ). 27/ikea.com/ca/en/cat/air-…
The $50 IKEA Vindstyrka Indoor Air Quality Monitor has been reviewed here ( ). 28/breathesafeair.com/ikea-vindstyrk…
The $13 IKEA Vindriktning Air Quality Monitor has been reviewed here ( ). 29/breathesafeair.com/ikea-vindriktn…
Some people have asked if boiling water will "purify" the water to remove minerals. Boiling water may kill bacteria but it will not remove the mineral content and may make it even more concentrated afterwards ( ). 30/mytapscore.com/en-ca/blogs/ti…
Does the PM from tap water in ultrasonic humidifiers impact people differently than outdoor PM pollution? This study takes a looks at what happens in the lungs of mice using different types of water ( ). 31/
@SaltyPeach51 Their Model E and G are indoor monitors that measure PM and their X is an outdoor monitor for PM. The feature I like the best is that they can take measurements every minute and upload the data via WiFi so you can see what is going on in the space over time. Graph showing indoor particulate matter (PM) levels on the 2nd floor of a house as outdoor wildfire smoke PM levels increased and how indoor levels went down when switching the HVAC system to recirculate air through the HVAC filter and not bring in new outdoor air.
@SaltyPeach51 If you are interested in learning more, this thread shows some examples of how their Model X and E work and what their online portal looks like ( ). Model G uses the same PM sensor as Model E-Lite but uses a non-colour display and is cheaper.
@SaltyPeach51 I cannot vouch for how accurate they are or how well they work since I have never used them but IKEA sells couple of lower cost options ranging from $13 to $50 which do not have the data saved online ( ).ikea.com/ca/en/cat/air-…
@SaltyPeach51 The $50 IKEA Vindstyrka Indoor Air Quality Monitor Review ( ).breathesafeair.com/ikea-vindstyrk…
@SaltyPeach51 The $13 IKEA Vindriktning Air Quality Monitor Review ( ).breathesafeair.com/ikea-vindriktn…
@spittykitty543 Since the particles are so small, "PM2.5 can pass through the lung–gas–blood barrier and the 'gut–microbial–brain' axis to cause systemic oxidative stress and inflammation, or directly enter brain tissue via the olfactory nerve" ( ). 2/ncbi.nlm.nih.gov/pmc/articles/P…
@spittykitty543 “These particles are so small that they can evade our filtration system in the upper airway and penetrate deep into our respiratory tract,” explained Lau. “Upon doing so, they also send chemical species associated with them into our bodies." ( ) 3/ualberta.ca/science/news/2…

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More from @jeffgilchrist

Jeff Gilchrist Profile picture
Oct 25
How does various mask fit compare to filter the air and protect you or others?

Most masks, even baggy blue procedure masks use filtering material that can filter 95%+ of particles that pass through it, but the key is "pass through it". 🧵1/ Bar chart titled “Equivalent Exposure Time to Unmasked Person.” The chart compares how long different masks/respirators extend the equivalent exposure time relative to being unmasked. The x-axis shows unmasked infection times of 1, 5, and 10 minutes. The y-axis shows equivalent masked exposure time, ranging up to 5000 minutes. Seven mask types are represented by colored bars: - Procedure mask (loose fit, FF=2) - Ear loop mask (tight fit, FF=6) - Vertical bifold headband mask (FF=30) - N95 headband masks with fit factors of 100, 200, and 500 Key pattern: higher fit factor masks dramatically ...
Protection mostly depends on how well that mask fits your specific face and one that does not fit well, much of the air you breathe will go around the filter material and filter 0% of those particles. 2/
There has been a chart going around recently that talks about "Time it takes to transmit an infectious dose of COVID-19" which is misleading if you don't understand all of the details of how that table was made and what each component means. 3/
Read 25 tweets
Jeff Gilchrist Profile picture
Oct 19
** Ontario Variant Update (to Oct. 3, 2025) **

The XFG.* "Stratus" family is accounting for 83% while the next closest variant family NB.1.8.1.* "Nimbus" is 12.8% of sequenced genomes from COVID tests. 🧵1/ Line graph showing COVID-19 variant family frequencies in Ontario, Canada, from June to October 2025, based on 3,722 sequenced genomes.
Looking at specific variants, XFG.3 has dropped considerably and its descendent XFG.3.15 now takes first place at 6.2%, followed by XFG.3 at 5.2% and XFG.2 at 4.5%. 2/ Line graph showing specific COVID-19 variant frequencies in Ontario, Canada, from June to October 2025, based on 3,722 sequenced genomes.
It looks like PY.1.1.1 was trying to make a run for the top in mid-September but has decreased significantly. PY.1.1.1 is a descendant of LF.7 while the XFG variant is a recombination of LF.7 and LP.8.1.2 so they would share some mutations in common. 3/
Read 10 tweets
Jeff Gilchrist Profile picture
Sep 9
*** Ontario Variant Update (to: Aug. 16, 2025) ***

Ontario COVID sequence updates have been more frequent over the past month with the XFG.* "Stratus" family of variants now at 74% of sequences, NB.1.8.1.* "Nimbus" at 22% and LP.8.1.* down to 3%. #Variants #XFG #Stratus 🧵1/ Line graph showing COVID-19 variant frequencies in Ontario, Canada, from May to mid August 2025, based on 1,772 sequenced genomes. The XFG.* Stratus variant rises sharply to dominate over 70% by August. Other variants, including FLiRT and LP.8.1.*, decline over the same period, while NB.1.8.1.* Nimbus remains steady around 20% and several minor variants remain at low levels.
Looking at specific variants as of mid August, XFG.5.1 is most prevalent at 13%, NB.1.8.1 in second at 10%, XFG.2 in third at 8.6% and XFG.3 in fourth at 7.4%. 2/ Line graph showing COVID-19 variant frequencies in Ontario from 5 July to 16 August 2025, based on 750 sequenced genomes. Seven variants are tracked: NB.1.8.1, XFG.2, XFG.3, XFG.3.4.1, XFG.3.1, XFG.4.1, and XFG.5.1. Frequencies range from 0% to about 14%, with some variants rising, others falling, and some fluctuating over time. A bar chart below shows the number of samples collected on each date.
LP.8.1 is what this fall's Japan Novavax vaccine and the mRNA vaccines are designed for which is now almost gone and typical of how these things work with vaccine manufacturing timing while Novavax is providing the previous year's JN.1 vaccine formula for the USA again. 3/
Read 18 tweets
Jeff Gilchrist Profile picture
Jun 9
Understanding Canadian Air Quality Health Index (AQHI) & Wildfire Smoke

Wildfire smoke consists of toxic gases and particulate matter (PM) when breathed in gets into our lungs, bloodstream, and even our brain. 🧵1/
#iaq #wildfire #smoke #AQI #AQHI #Canada Bar chart of Canadian Air Quality Health Index (AQHI) - Equivalent # Cigarettes after Exposure ranging from 0.5 cigarettes after 8 hours exposure at AQHI level 3 to 0.9 cigarettes at level 6 and 1.5 at level 10.
Graph of Particulate Matter (PM) Levels in Ottawa from June 6, 2025 to June 8, 2025 from a VisiblAir Model X air quality sensor ( https://visiblair.com/ ).
The web version of this article with nice table of contents and easy to share with others can be found here ( tinyurl.com/AQHIwildfire ) and ( docs.google.com/document/d/1s9… ). 2/ Table of Contents: * Introduction * Air Quality Health Index (AQHI) * Health impact of Wildfire Smoke * Protect Yourself
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 ( ). 3/theweathernetwork.com/en/news/weathe…
Read 41 tweets
Jeff Gilchrist Profile picture
Jun 6
Pollution levels in Ottawa are very high from wildfire smoke. The particulate matter (PM)2.5 levels surpassed 140 ug/m^3 Thursday evening and are still above 130 on my VisiblAir Model X outdoor sensor ( ). 🧵1/ #iaq #wildfire #smoke visiblair.comLine graph showing PM2.5 levels in Ottawa increasing above 140 ug/m^3 and still above 130 now
Readings from a VisiblAir Model X outdoor air quality monitor showing levels in Ottawa above 130 ug/m^3 for PM2.5 wildfire smoke pollution
The EPA maps fine particulate pollution to their Air Quality Index where anything above 125.5 PM is Very Unhealthy which is a "Health alert: The risk of health effects is increased for everyone" ( ). 2/airnow.gov/aqi/aqi-basics/
EPA Categories:
* Unhealthy for Sensitive Groups (Orange) = 35.5-55.4 PM ug/m^3
* Unhealthy for everyone (Red) = 55.5 to 125.4 PM ug/m^3
* Very Unhealthy (Purple) = 125.5 to 225.4 PM ug/m^3
* Hazardous (Brown) = 225.5+ PM ug/m^3

3/
Read 13 tweets
Jeff Gilchrist Profile picture
Feb 10
#Ottawa, #Ontario, #Canada Virus Update:

You can see in the graph, COVID makes up the majority of new hospitalizations due to #Flu, #RSV or #COVID throughout the year, and even stays ahead during winter respiratory virus season. 🧵1/ A line graph displaying the percentage of patients hospitalized due to COVID-19, Influenza, or RSV over time, from September 1, 2023, to January 26, 2025. The x-axis represents weeks within this period, and the y-axis shows percentages from 0% to 100%. The graph has three colored lines: blue for COVID-19, purple for Influenza, and teal for RSV. The graph shows fluctuations in the percentage of hospitalizations due to each cause over time, with COVID-19 consistently having the highest percentage, followed by Influenza and RSV.
New hospitalizations are increasing again. This last update was the first time Flu hospitalizations (42) were significantly higher than COVID (34) in the same week with RSV at 14 people. 2/ The bar chart shows the number of new hospitalizations per week in Ottawa from August 27, 2023, to January 26, 2025. The y-axis represents the number of patients, ranging from 0 to 100. The x-axis represents the weeks. The bars are color-coded: blue for COVID-19, purple for Influenza, and teal for RSV. The chart shows fluctuations in hospitalizations over time, with notable peaks around December 2023 and January 2025.
In Ottawa, test positivity for Flu A (bright green) has really increased, COVID is still in second place, but seasonal human coronavirus is almost the same level, followed by Entero/Rhinovirus, and then RSV for the top 5. 3/ A stacked area chart displaying the percentage of positive tests for various viruses over time, from October 1, 2022, to January 26, 2025. The x-axis represents weeks within this period, while the y-axis represents the percentage, cumulatively stacked to 100%. The chart features the following viruses, each depicted in a distinct color: COVID-19 (red), Entero/Rhinovirus (yellow), Seasonal human coronavirus (purple), RSV (green), Parainfluenza (all types) (blue), Influenza B (dark purple), Influenza A (light green), Human metapneumovirus (pink), and Adenovirus (dark blue). The data shows fluc...
Read 6 tweets

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