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Particle Sensing

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Particle Sensing is the act of detecting dust in the air, and characterizing that dust and its potential health effects on those who may breathe it.

(Above photo: A man wearing a mask walks past the skyline of Singapore's business district Credit: Reuters/Edgar Su)

Why are we concerned about particles? because humans now make more dust than any natural process on earth.


From EPA/600/R-95/115

There are four major factors necessary to determining what particles are in the air and addressing the source, particle concentration, particle size, particle type, and particle source. Different particle sensing strategies are useful in determining these factors.

1. Particle Concentration

Particle concentration is the density of particles in the air. This is usually expressed as mass per volume, i.e. micrograms or milligrams per cubic meter, expressed μg/m3 or mg/m3.

2. Particle Size

Particles are measured in micrometers (millionths of a meter, or μm), but when talking about particle sizes, the literature speaks of idealized particles. Shorthand, such as 'PM10' meaning, particulate matter less than or equal to 10μm in diameter. but by diameter, the literature means "mass median aerodynamic diameter" which is a way of saying particles that fall through the air at the same rate as a perfect sphere of 10μm.

David Mack clarifies with summaries of the regulations for PM10 and PM2.5 via EPA 40 CFR Part 50 as summarized in Air Quality Criteria for Particulate Matter (Final Report, April 1996):

"The 50% cut point refers to the EFFICIENCY at which particles are removed by the selective inlet at the given size. So for PM10, the inlet removes 50% of particles at 10 microns but above 10 microns the removal efficiency increases and below 10 microns removal efficiency declines. Thus the resultant fraction is not a normal distribution (e.g. 50% above and 50% below) but a skewed distribution (see graph below). Also, the rate at which removal efficiency changes is referred to as the cut point SHARPNESS."


3. Particle Type

This can be conducted with a microscope for crystals, and using lab techniques for other types of particles. Mass spectrometry and x-ray spectrometry may also be used.

4. Particle Source

Usually directional and time-stamped data from multiple points are needed to extrapolate source, along with an understanding of particle type.

Researchers speak of two types of emissions that have a blurry line between them, 'process stream' emissions and 'fugitive emissions.' Process stream emissions are inherent to a process, like ash from a fire, and fugitive emissions are ancillary, like the dust kicked up bringing wood to a fire [EPA 3-2].

Particles of Concern

There are a lot of problematic dust particles. Generally speaking, particles smaller than 10μm get lodged in the lungs. But shape, material, and the sharpness of the particles matters. For instance, recently broken particles are sharper and more dangerous than dust that's been blowing around a while and been rounded out.

Silica is currently a Public Lab monitoring project. For silica, particles smaller than 5μm are considered the most dangerous.

The family of chemicals that make up Particulate Matter are subdivided into the different regulated pollutants:


From PowerMag/PM2.5: More Than Just Dust

Strategies and Sensors

Electronic sensors

Most electronic sensors are essentially a light that gets interrupted by a particle, with a camera or other optical sensor watching.

See more about air quality sensors on the Air Sensors page. There are several sensors available for particle sensing; see more in the questions below:

Title Author Updated Likes Comments
How to connect an anemometer to an air particulate monitor? @crispinpierce almost 3 years ago 0
What are your experiences using low-cost VOC sensors outdoors? And other questions about accuracy. @bhamster over 3 years ago 4
Have you used surveys to inform open hardware development? @kgradow1 about 4 years ago 1
Questions about Plantower sensors from the University of Wisconsin - Eau Claire @OrionAllgaier over 5 years ago 5
Should the Purple Air be co-located with a weather station? @stevie over 5 years ago 2
Why are the PM10 particles of the Purpleair monitor biased so high? @Cbarnes9 over 5 years ago 7
What type of aerosol was used for the calibration of the purpleair lasers? @Cbarnes9 over 5 years ago 5
Does particle composition that the purple air monitors measure greatly skew the data output? @Cbarnes9 over 5 years ago 4
How can we connect a PMS5003 dust sensor to an Arduino? @warren over 5 years ago 10
Looking for hands-on help with a datalogger! @Bronwen about 6 years ago 3
what data-logger will work with my portable HCHO meter? @nshapiro about 6 years ago 44
The difference between medical particle monitoring and your particle monitoring? @Ag8n over 6 years ago 4
3 particle type @Ag8n over 6 years ago 0
What different electronic particulate pollution sensors are available and at what cost? @warren over 6 years ago 4
How good is the PurpleAir sensor and what does it detect? @warren over 6 years ago 12
What are some ways to collect dust or particulate samples for analysis? @warren over 6 years ago 4
Is the dustduino (with Shinyei sensor) appropriate for use to study particulates at high altitude (100,00ft)? @rickwoodrickle over 9 years ago 1
Is it possible to log the data from a dustduino without a wifi network? @kp55 over 9 years ago 3

Dust sampling

Title Author Updated Likes Comments
What are some ways to collect dust or particulate samples for analysis? @warren over 6 years ago 4
What is the scenario under which you would use an optical vs. a passive monitor to measure dust? @kgradow1 over 6 years ago 1
How does the EPA measure things, especially the size of dust particles? @kgradow1 over 6 years ago 3
How big are silica particles, in microns? @warren almost 7 years ago 2
How big are smoke particles, in microns? @warren almost 7 years ago 4
Are there any methods to distinguish where particulate matter in the air comes from? @stevie about 7 years ago 4
Can PM4 be monitored with the MiniVol? @mathew over 7 years ago 1
Can a passive dust monitoring housing be made from a cheaper/easier material? @warren over 7 years ago 2
What kind/size of microdust does activated carbon give off & how much of a concern is it? @jfrankamp over 7 years ago 2

Sticky Pads

Essentially tape, sticky pads have the advantage of capturing a record of actual particles that can be analyzed later. They can be scanned and digitized for standardized readings. More can be found on the Sustainable Aggregates website.

EPA Test Methods

EPA approved instruments are designated as either a Federal Reference Method (FRM) or Federal Equivalent Methods (FEM). For PM testing, the FRM is typically a manual test method whereby PM is collected on a filter for 24-hours (daily). The mass is determined by gravimetric analysis (weighing the filter before and after sample collection) and the sample volume is calculated based on the air flow rate multiplied by the sample duration. Then the mass concentration (typically in microgram per cubic meter, ug/m3) is calculated as the mass collected divided by the sample volume.

The FEMs for PM utilize detectors capable of real time reporting. The air sample volume is usually determined by air flow rate and duration akin to the FRM. However, the mass may be measured by the beta ray attenuation method (BAM) or tapered element oscillation method (TEOM).

The complete list of approved instruments for NAAQS evaluating is provided on the EPA Ambient Monitoring Technology Information Center (AMTIC) web site