Why is particulate matter smaller than 2.5µm not given much importance when discussing air quality? That being said, what are considered safe concentrations of PM0.3, PM0.5, and PM1.0?

We generally see the following sized particles discussed the most by air quality initiatives, and companies which make air quality monitors: 10µm, and 2.5µm.

Why is this the case, when the scientific material all talks about particulate matter SMALLER than 2.5µm being harmful for you?

My outdoor air quality sensor shows the following: https://imgur.com/a/jcwNXvr

As you can see, the the 0.3µm, 0.5µm, and 1.0µm readings are quite high, even though the main indicator is showing the air quality as being “clean,” on the basis of the PM2.5 readings.

Next, there’s a hidden (unlabelled) detail in the terms “PM10” and “PM2.5.” That is the “smaller than” piece. Each pollutant type is defined as that size and below. So PM10 is particles 10 microns and below. PM2.5 is 2.5 microns and below. (That means PM10 includes PM2.5.)

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I agree with your assessment of harmfulness … the smaller, the more capable of entering the bloodstream, and causing havoc.

My experience - if you smell firewood burning, it’s more than sufficient to register on the meter. In my case, if I smell it, my meter is never saying “clean” (defined as < 50 ).


Pm2.5 measures 2.5 and smaller. So it captures it all.

2.5 and below can get into red blood cells.

On fine particulate matter, PM2.5 and below, the WHO clearly states, there is no evidence of a safe level of exposure or a threshold below which no adverse health effects occur.
I disagree with the coloured scale used by AQIs; the wordings seem to be a cover-up. With PM2.5, fine particulate matter, readings in the red zone (between 101-150 and rising), one AQHI (federal) stated, “Ideal air quality for outdoor activities. Enjoy your usual outdoor activities.” My response was, make sure you breathe in deeply as if your life depended on it. It would directly affect the deepest recesses of lungs (alveoli), enter the bloodstream and go to the brain: (from personal experience) in short, increases breathing to compensate for a lack of oxygen, raises blood pressure- standby for a stroke (NBCW trained), and it was quick. My ongoing challenge on this issue is the indiscriminate use of open-fires in residential areas enabled by civic administration.
Thanks for your post, it was a reasonable question. PM2.5 is all encompassing, and the sensors are a great tool.

what about second hand cigarette smoke that passes through walls and or tiny cracks? what is the best tool for picking up those particles?

and also what about vaping? I am getting high tvoc readings but not increase in PM thanks