# 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? **URL:** \ **Category:** General\ **Created:** [January 29, 2023, 4:30pm UTC](https://community.purpleair.com/t/why-is-particulate-matter-smaller-than-2-5-m-not-given-much-importance-when-discussing-air-quality-that-being-said-what-are-considered-safe-concentrations-of-pm0-3-pm0-5-and-pm1-0/3438 "2023-01-29T16:30:36Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![Ammar\_Rai](https://sea2.discourse-cdn.com/flex020/user_avatar/community.purpleair.com/ammar_rai/32/1065_2.png) [@Ammar\_Rai](https://community.purpleair.com/u/Ammar_Rai)\ **Post date:** [January 29, 2023, 4:30pm UTC](https://community.purpleair.com/t/why-is-particulate-matter-smaller-than-2-5-m-not-given-much-importance-when-discussing-air-quality-that-being-said-what-are-considered-safe-concentrations-of-pm0-3-pm0-5-and-pm1-0/3438/1 "2023-01-29T16:30:36Z")
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. ---
**Author:** ![timh](https://avatars.discourse-cdn.com/v4/letter/t/ac91a4/32.png) [@timh](https://community.purpleair.com/u/timh)\ **Post date:** [January 30, 2023, 8:09pm UTC](https://community.purpleair.com/t/why-is-particulate-matter-smaller-than-2-5-m-not-given-much-importance-when-discussing-air-quality-that-being-said-what-are-considered-safe-concentrations-of-pm0-3-pm0-5-and-pm1-0/3438/2 "2023-01-30T20:09:22Z")
[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.)](https://smartairfilters.com/en/blog/pm10-pm2-5-difference-particle-air-pollution/) ---
**Author:** ![Robert](https://avatars.discourse-cdn.com/v4/letter/r/e95f7d/32.png) [@Robert](https://community.purpleair.com/u/Robert)\ **Post date:** [February 6, 2023, 11:50pm UTC](https://community.purpleair.com/t/why-is-particulate-matter-smaller-than-2-5-m-not-given-much-importance-when-discussing-air-quality-that-being-said-what-are-considered-safe-concentrations-of-pm0-3-pm0-5-and-pm1-0/3438/3 "2023-02-06T23:50:16Z")
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 ). Regards, Robert ---
**Author:** ![Eric](https://sea2.discourse-cdn.com/flex020/user_avatar/community.purpleair.com/eric/32/406_2.png) [@Eric](https://community.purpleair.com/u/Eric)\ **Post date:** [July 25, 2023, 1:18am UTC](https://community.purpleair.com/t/why-is-particulate-matter-smaller-than-2-5-m-not-given-much-importance-when-discussing-air-quality-that-being-said-what-are-considered-safe-concentrations-of-pm0-3-pm0-5-and-pm1-0/3438/4 "2023-07-25T01:18:13Z")
Pm2.5 measures 2.5 and smaller. So it captures it all. > **[Air pollution: The silent killer called PM2.5](https://www.mcgill.ca/newsroom/channels/news/air-pollution-silent-killer-called-pm25-329428)** > > Over half the world’s population lives without the protection of proper air quality standards. 2.5 and below can get into red blood cells. ---
**Author:** ![Serge](https://sea2.discourse-cdn.com/flex020/user_avatar/community.purpleair.com/serge/32/3355_2.png) [@Serge](https://community.purpleair.com/u/Serge)\ **Post date:** [September 29, 2023, 2:50pm UTC](https://community.purpleair.com/t/why-is-particulate-matter-smaller-than-2-5-m-not-given-much-importance-when-discussing-air-quality-that-being-said-what-are-considered-safe-concentrations-of-pm0-3-pm0-5-and-pm1-0/3438/5 "2023-09-29T14:50:58Z")
Hi, 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. ---
**Author:** ![qkcam](https://avatars.discourse-cdn.com/v4/letter/q/58f4c7/32.png) [@qkcam](https://community.purpleair.com/u/qkcam)\ **Post date:** [October 4, 2023, 11:12pm UTC](https://community.purpleair.com/t/why-is-particulate-matter-smaller-than-2-5-m-not-given-much-importance-when-discussing-air-quality-that-being-said-what-are-considered-safe-concentrations-of-pm0-3-pm0-5-and-pm1-0/3438/6 "2023-10-04T23:12:36Z")
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