Particle Sensing
particle-sensing

**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. [![Screen_Shot_2014-04-16_at_11.49.08_PM.png](https://i.publiclab.org/system/images/photos/000/003/698/medium/Screen_Shot_2014-04-16_at_11.49.08_PM.png)](https://i.publiclab.org/system/images/photos/000/003/698/original/Screen_Shot_2014-04-16_at_11.49.08_PM.png) From [EPA/600/R-95/115](http://ofmpub.epa.gov/eims/eimscomm.getfile?p_download_id=4608) 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](publiclab.org/profile/DavidMack) [clarifies](http://publiclab.org/notes/Schroyer/06-26-2014/broadcast-dust-readings-from-a-smartphone#c94340) with summaries of the regulations for PM10 and PM2.5 via [EPA 40 CFR Part 50](http://www.ecfr.gov/cgi-bin/text-idx?tpl=/ecfrbrowse/Title40/40cfr50_main_02.tpl) as summarized in [Air Quality Criteria for Particulate Matter (Final Report, April 1996)](http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=2832): "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." [![pm.jpg](https://i.publiclab.org/system/images/photos/000/005/166/medium/pm.jpg)](https://i.publiclab.org/system/images/photos/000/005/166/original/pm.jpg) ### 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](http://ofmpub.epa.gov/eims/eimscomm.getfile?p_download_id=4608)]. **** ## 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](/wiki/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:* [![full-graphic.png](https://i.publiclab.org/system/images/photos/000/005/042/medium/full-graphic.png)](https://i.publiclab.org/system/images/photos/000/005/042/original/full-graphic.png) From [PowerMag/PM2.5: More Than Just Dust](http://www.powermag.com/blog/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](/air-sensors). There are several sensors available for particle sensing; see more in the questions below: [questions:air-sensors] **** ## Dust sampling [questions:dust-sampling] ### 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 ](http://www.sustainableaggregates.com/sourcesofaggregates/landbased/dust/dust_monitoring.htm) 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)](http://www.metone.com/particulate.php) or [tapered element oscillation method (TEOM)](http://www.thermoscientific.com/en/product/1405-teom-continuous-ambient-particulate-monitor.html). The complete list of approved instruments for NAAQS evaluating is provided on the EPA [Ambient Monitoring Technology Information Center (AMTIC) web site](http://www.epa.gov/ttn/amtic/criteria.html) ...


Author Comment Last activity Moderation
amirberAgain "What could be applicable here is a lens free holographic microscope. I've been wanting to build one for a long time, maybe this will be my excuse! ..." | Read more » almost 7 years ago
squattingdog "Thanks @warren and @richardbowman for replying, it's appreciated. I'm quite familiar with microscopes and macro photography. I have a Nikon Optipho..." | Read more » almost 7 years ago
warren "Indeed -- we're hoping the basic microscope kit will create an influx of folks who go on to make openFlexure microscopes! " | Read more » almost 7 years ago
richardbowman "Hi @squattingdog, just thought I'd pop up and say that the openflexure microscope is still very much under active development - I've improved my bu..." | Read more » almost 7 years ago
warren "Hi, @squattingdog - we've been working on an "introductory" microscope build that's an easier stepping stone to this one, which you can upgrade lat..." | Read more » almost 7 years ago
squattingdog "@mathew any progress on this build? I was interested in giving it a shot myself but wasn't sure where to start since I've seen very little activity..." | Read more » almost 7 years ago
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Tinashe "You don't state what happens with the 40 images taken. Are they stacked together for analysis or they are analysed individually. " | Read more » over 7 years ago
SimonPyle "@warren: The link above was the most recent version, though I just added a GNU GPLv3 license and created a github repository: https://github.com/si..." | Read more » almost 8 years ago
mathew "There is a large folder of sample image sets avaialble. I put a smaller set together here: https://publiclab.org/notes/mathew/10-07-2016/sizing-ima..." | Read more » almost 8 years ago
mathew "You can see more about the shape descriptors for each particle here: https://publiclab.org/notes/mathew/09-19-2015/using-imagej-to-process-passive-..." | Read more » almost 8 years ago
mathew "The image analysis creates: perimeter of each particle area of each particle circularity of each particle Circularity is the ratio between the..." | Read more » almost 8 years ago
warren "Is there any sample input/output sets from going through this process, manually or automatically? I was thinking that a good test/spec might inclu..." | Read more » almost 8 years ago
warren "Hi! Just re-reading, is it right that the image analysis produces (as it's complete output): perimeter of each particle area of each particle ..." | Read more » almost 8 years ago
warren "Hi! Is Simon's macro still at the URL listed above? Or is there a more up-to-date version, potentially open sourced? Thanks! " | Read more » almost 8 years ago
mathew "Followup on automating this process https://publiclab.org/notes/SimonPyle/05-13-2016/automating-imagej-for-particle-image-analysis " | Read more » over 8 years ago
mathew "Although we are hopeful that Simon's strategies listed here can get us to a particle count, If they aren't sufficient Rongjun Qin recommended we lo..." | Read more » over 8 years ago
mathew "You can get the analysis spreadsheet here: https://docs.google.com/spreadsheets/d/1xSVT9lxary0zZhhEqhrX3hsdIb4shbYhaOJx_RWhESg/edit#gid=0 " | Read more » over 8 years ago
mathew "That's a great writeup! thanks Simon. If anyone needs an image set to play with, please e-mail me, and I can share the files. They're too large t..." | Read more » over 8 years ago
tonyc "I'd like to do a screencap to show just how smooth this movement is. This is so cool to see in action. Exciting to see it built from plans to deplo..." | Read more » over 8 years ago
mathew "oh yes! please read our wiki on frac sand and PM, its getting pretty fleshed out: https://publiclab.org/wiki/frac-sand follow notes as they happen..." | Read more » over 8 years ago
sara "Super excited to read about this project, are their more recent notes on how your project's progressing? " | Read more » over 8 years ago
mathew "cool opportunity, @Philrosenberg! you may want to share it out with the Public Lab Air Quality list: http://publiclab.org/lists @Marlokeno: The q..." | Read more » over 8 years ago
philrosenberg "Just in case anyone on here is interested, I work for the Institute of Climate and Atmospheric Science at Leeds Uni. We actually have some of the D..." | Read more » over 8 years ago