In this article, you will find information about everything related to particulate matter. I will focus on PM2.5 as I believe it is the most universal indicator of air quality. Almost all scientific studies concentrate their attention to PM2.5 because there is a substantial availability of monitors/sensors. Some extracts were taken from my book See The Air – PROOF THAT AIR POLLUTION KILLS.

1) What is PM2.5?

Scientific explanation: PM2.5 is a mass concentration on basis of a separation curve, where the 50% value is at 2.5μm aerodynamic diameter. More precisely, the weighting function is much steeper (100% weighting <0.5μm, to 0% weighting> 3.5μm and 50% weighting at approximately 2.5μm). PM2.5 pollution can only be seen with an electron microscope.

Plain English explanation: PM2.5 referees to fine particles with a size of or less than 2.5μm (aka micron). By the way, soot, aerosols, dust, BC are other common terms to call particle pollution.

2) What is PM2.5 made of?

It is hard to determine a specific chemical composition, however, here is a list of all the chemicals that might be found in a single particle. Polycyclic aromatic hydrocarbons (naphthalene, acenaphthylene acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benzo(a)anthracene, chrysene, benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(a) pyrene, dibenzo(a,h)anthracene, benzo(g,h,i)perylene, and indene), metals (Al, Si, P, S, CI, K, Ti, Cr, Mn, Fe, Ni, Cu, Zn, Pb, Ca), others.

3) Which are the sources of PM2.5 indoors?

Fine particulate matter is produced from all types of combustion. Indoors, cooking is a major source of PM2.5 especially when gas or wood/coal cookstoves are used, but even if you cook on an electric stove, a huge amount of particles is released into the breathable air during frying. Other sources are vacuuming without proper filtration or sweeping. Candles, diffusers, humidifiers, burning of incense, burning sage, etc. Finally, pets and humans release some particles of biological origins.

4) Which are the sources of PM2.5 outdoors?

Outdoors, there are two type of sources of fine particulate matter. Anthropogenic and natural sources. Anthropogenic sources are internal combustion engines (cars, lorries, boats, planes, motorbikes, buses, etc), power plants, residential wood burning, agricultural burning, and some industrial processes which release toxic organic compounds and heavy metals. Natural sources are forest fires, desert dust, volcanic activities, and secondary organic aerosols formation from the release of VOCs in forests.

Also, plastic pollution contributes to particulate matter pollution. So, a plastic bottle may end up in the air you breathe as fine particulate matter or in the ocean were fish live and eat and will end up inside you as well. Everything is a circle.

5) How we quantify PM2.5 and what does mass concentration (μg/m³) mean?

We use two values to measure PM2.5. The first is a particle number concentration as most sensors are able to count or estimate the particles present in the sample of air that are reaching the heart of the sensor.

It is hard to wrap our heads around the particle number concentration as it tends to be really high when pollution is high, for this reason, we use the mass concentration (μg/m³). Mass concentration is not always the best way to reflect the level of pollution, especially for particles of smaller size, I will discuss that later.

In cleanrooms, particle number concentration is the adequate value to measure PM2.5 as we try to achieve as clean air as possible and we obtain very low numbers from the monitors.

6) How experts measure PM2.5?

Experts use various technologies and sophisticated types of equipment to measure PM2.5 among other particle sizes. For example, Beta attenuation monitoring (BAM) is one of the most common and widely used air monitoring techniques. Tapered element oscillating microbalance (TEOM) instruments are used for the real-time detection of particles. Laser scattering (aka Optical Particle Counters) is another common and economic technology to measure particles with good results. Here is a list of all the air quality monitors, focus on the B2B tab.

7) How building occupants measure PM2.5?

Building occupants use IoT air quality monitors which employ low-cost sensors similar to what experts use but sometimes of less accuracy. Homeowners and office occupants have different needs, so the monitors responsible for measuring air quality focus on features that will translate scientific information into more comprehensive for the average user with charts, visual elements, and text. Here is a list of all the air quality monitors, focus on the B2C tab.

8) Why we need to measure PM2.5 indoors and outdoors at the same time and in real-time?

There is a great relationship between both environments as we exchange air. We need to ventilate indoor air to dilute some chemicals and CO2 that may build up. A scientific study has demonstrated that without a filtration system in the air exchange system, buildings tend to have 50% of the pollutants present in the ambient air. For example, if outdoors the mass concentration of PM2.5 is 100μg/m3, indoors will be 50μg/m3, which is ten times above WHO air quality guidelines of 5μg/m3. If you want to learn more read a past article on mine here.

9) Where can you find information about local ambient air quality with PM2.5 data?

Almost all countries measure PM2.5 with National Air Quality Stations. Some places have many AQ stations and some other places have less or none. You can always google Air Quality and the name of your city. In the US, EPA has a mobile app and website called airnow.gov. Spain has a website called Indice Nacional de Calidad del Aire ica.miteco.es. In the UK, DEFRA has a site called the UK Emissions Interactive Map naei.beis.gov.uk and so on. You have to find out which website or app your government has developed. P.S. Sometimes it is not easy to find it. In that case, you have to use third-party apps and websites to check the air quality. A free app for your mobile phone is Local Haze which relies on a low-cost network of sensors, but it also supports official data from the government agencies. Breezometer, Windy, and Apple Weather apps are also good alternatives.

10) Are there other size ranges of particulate matter?

Yes!

Coarse PM10: 🫦👃😮‍💨 The definition given for the PM10 does not present a sharp distribution of emissions at an aerodynamic diameter of 10 micrometers (10μm); Rather, an attempt was made to simulate the deposition behavior of the upper respiratory tract: particles with an aerodynamic diameter of less than 1μm are fully included, with larger particles a certain percentage is evaluated, which decreases with increasing particle size and finally reaches 0% at approximately 15μm.

“Super” Fine PM1: 🫁 🫀 PM1 hasn’t been recognized as a pollutant by the US Environmental Protection Agency (EPA) or the European Environment Agency (EEA). For this reason, the most likely definition would be the mass concentration of ambient suspended particulate matter of an aerodynamic diameter of less than ≤1μm micrometer. The problem with that is that the mass of these very fine particles is no longer the most essential parameter, while their number/concentration undeniably is.

Ultra-Fine Particles: 🧠 Ultra-Fine Particles (UFPs) also known as ultrafine dust PM0.1 is defined as particles with a thermodynamic diameter of less than 0.1μm (100nm). The thermodynamic diameter describes a spherical particle with an identical diffusion behavior as the particle under consideration.

UFP is a term used in atmospheric sciences, while the term nanoparticles applies to material engineering, eventually, it is the same thing.

11) Should we measure PM10, PM1, and UFP apart from PM2.5?

Experts claim that PM1 is a better indicator for a roadside micro-environment than PM2.5 because compared with PM2.5 and PM10, it minimizes interference from natural sources.

In Shanghai, for example, about 85% of the mass concentration of the city’s PM2.5 is PM1. As a result, it would be more effective to conduct studies on PM1 than PM2.5.

Some scientists believe that a reduction in PM2.5 to improve air quality could aggravate the pollution of UPF as studies have shown that aromatic organic compounds from vehicle exhaust form these UFP. As a result, protecting public health needs a simultaneous reduction in PM2.5 and UFP. Automobile companies try to cheat once more by forcing the engines to produce more UFPs than PM2.5 in order to pass the emission tests that only pay attention to fine particles.

Recent research suggests these nanoparticles could be responsible for illness and death beyond our current understanding.

12) Why mass concentration is not adequate to measure PM1 and UFP?

Governmental authorities monitor PM2.5 by mass micrograms per cubic meter (μg/m3), consequently, million of nanoparticles may not even register in a single measurement by microgram. Some scientists worry that governmental reports under-represent the real danger. There aren’t any regulations for this size class of ambient air pollution particles, which are far smaller than the regulated PM10 and PM2.5 and are believed to have a more severe health impact than the PM2.5 and PM10.

In 2021 WHO in an effort to address and compensate the unregulated UFPs updated the Air Quality Guidelines (AQGs) with values for PM2.5 at 5 μg/m3.

On the table below we can see how mass concentration misrepresents the finer particulates. As you can see from the samples, 9530 particulates were detected in the 0.3 channel and only 209 particulates in the 2.5 channel. The estimated mass of the 2.5μm particulates in the 2.5 channel is more than 12 times as large. You may think that you are safe with a value of 0.24 μg/m3 but behind that number there are 9530 tiny particles capable of reaching deep inside the alveolar sacs.

Channel (μm)	Particle Count (#)	Mass Concentration (μg/m3)
0.1	31058	0.025
0.3	9530	0.24
0.5	7793	1.05
1	2261	2.13
2.5	209	2.95
5	12	2.34
10	9	14.04

13) How PM2.5 impact human health?

The smaller the particles the deeper they go inside our bodies. PM2.5 is around 2,500 nanometres (nm) in diameter. However, nanoparticles are 100nm or less. In comparison, they are 25 smaller, as a result, they can reach any organ in our bodies and there is no 2,500nm domestic filtration system to capture them efficiently.

14) What can you do to improve your indoor air quality and reduce PM2.5 concentrations?

My article/guide Spring Clean Your Indoor Air Quality is a good start, here is a summary.

• 1st Tip – Bed Linen
• 2nd Tip – Vacuum
• 3rd TIP – Dust
• 4th TIP – Ventilate
• 5th TIP – Monitor
• 6th TIP – Purify
• 7th TIP – Ditch Wood Stoves

15) What can you do to improve outdoor air quality?

When it comes to ambient air quality, a collective effort is needed from governments and companies that influence individual actions. A general ban of wood and biomass stove burning is needed especially in urban settings. A reduction of traffic across all roads in a city and not only from specific neighborhoods is also necessary for clean air. On my book, I present over 12 solutions and ideas on how to fix the air we breathe by promoting a sustainable future.

16) What are the Air Quality Standards for PM2.5?

Although there is no safe level of pollution exposure, governments and green building schemes have set some upper limits for PM2.5. In general, ambient AQ standards are brought into the indoor environments with the exception of cleanrooms which have to meet other regulations.

WHO	5 μg/m3 1-year (2021 AQGs)	15 μg/m3 24-hour
USA EPA	12 μg/m3 1-year	35 μg/m3 24-hour
EU	20 μg/m3 1-year (2020 revision)	N/A
UK	25 μg/m3 1-year (Scotland 10 μg/m3)	N/A
Australia	8 μg/m3 1-year	25 μg/m3 24-hour
India	40 μg/m3 1-year	60 μg/m3 24-hour
Mexico	15 μg/m3 1-year	N/A
Japan	15 μg/m3 1-year (Proposed in 2014)	N/A
Chile	20 μg/m3 1-year	N/A
Canada	10 μg/m3 1-year	N/A
Saudi Arabia	15 μg/m3 1-year (Proposed in 2014)	N/A
RESET	12 μg/m3 1-year	35 μg/m3 24-hour
LEED	15 μg/m3 1-year	N/A

Which one do you think is the best and more ambitious to protect people’s quality of life?