This is a testing site only. See the live Public Lab site here »

Introduction to Particulate Matter

Particulate matter (PM) is airborne particles and droplets, that can be inhaled. Some PM is formed through physical motion, like pulverized dust getting wind swept, and other PM is formed through gaseous chemical reactions in the atmosphere. Particulate matter is [regulated](/wiki/pm-monitoring-regulations) because it has negative health consequences, especially when it is small enough to travel deep into the lungs, and be [respired.]( ####Pages in this research area: [Questions](/pm#Questions) [Understanding Particulate Matter]( [Collecting Data on Particulate Matter]( [Choosing a PM monitoring Method - Overview]( In depth: - [Visual monitoring](/wiki/visual-pm)- monitoring with your eyes - [Filter-based monitoring](/wiki/filter-pm) - monitoring with lab analysis - [Optical monitoring](/wiki/optical-pm) - monitoring with sensors - [Passive monitoring](/wiki/passive-pm) - monitoring with other sample collection tools - [Sticky Pad monitoring]( - using tape and other materials to monitor for particulates - [Public Lab PM monitoring tool development](/wiki/pm-dev) - [Passive Monitoring tool]( - [Silica Monitoring](/wiki/silica-monitoring) [Regulations on PM Monitoring]( _________________________________ ###Questions [questions:pm] ###Background Information Particulate Matter (PM) is airborne dust and particle pollution that settles onto surfaces and into lungs. As a [regulated pollutant PM](/wiki/pm-monitoring-regulations) is shorthand for inhalable and respirable particulate matter, or [particulate matter that can stick in the lungs.]( Based on size alone, small airborne particles can become lodged in the lungs or even enter the bloodstream. At this size, some non-toxic materials, such as [silica](/wiki/silica), can be carcinogenic. Historically, most dust was naturally occurring, but at present natural sources of particles such as wind erosion, volcanoes, pollen, and forest fires have been overtaken by human-generated particles from combustion, roads, agriculture, construction, and mining (citation:[EPA/600/R-95/115]( [Monitoring sources of particle pollution](/wiki/pm-monitoring) and [advocating for their reduction](/wiki/frac-sand-action-oriented-resources) can have positive public health impacts. [According to the CDC](, a 10% reduction in fine particles could prevent 13,000 deaths annually in the U.S. ###Airborne particles we can see [![visible-particles.png](//](// The smallest particles we can see with a naked eye are visible only because they diffract light to make a haze, usually with a reddish-purple tint. We cannot see haze particles directly, however, haze can be [monitored as a proxy for small particles](/wiki/visual-pm). Mold spores, lint, and household dust particles can be seen individually only when reflecting light, as in the rays coming through window into a dark room. Particles of fine sand and soil that are visible can get airborne for short periods of time. Fog are small raindrops falling slowly, and are just barely visible. Of visible particles, only haze-sized particles pose a significant health risk, [see Respirable Particles below]( ###Dust, droplets, & particle size Almost all airborne particles are either dust (solid particles broken from larger solids) or droplets (liquid particles which grow as they condense gases out of the air). A third category of nanometer-sized particles, ultrafines, are short-lived emissions from combustion. These three modes, ultrafines, droplets, and dust, are each clustered around a specific size range, such that the sizes of particles in the air are not evenly distributed. Ultrafines are short-lived, forming the center of droplets quickly. Large dust particles are also short lived, settling out. In the middle are mature droplets and fine dust that make up both the bulk of long-lived atmospheric particles and the most worrisome particles because of their [respirability]( [![CORRECTillustrative3-peak-ultradropdust.png](//](// ###Dust While some dust comes from biological sources (skin, bacteria, mold, pollen), most comes from dirt and rocks crushed small enough to get airborne. Only dust less than 10 μm can stay airborne for days, and dust less than 5 μm dust can travel for years. Larger dust settles out (called sedimentation), while smaller dust is removed by being washed away in rain or by running into objects (impaction). [![CORRECTillustrative3-peak-dust.png](//](// ###Droplets Droplets are formed as gases cool and condense. Atmospheric droplets condense from combustion gases, especially industrial and transportation emissions like sulfur dioxide and nitrogen dioxide, and also water. Atmospheric water dominates the droplet formation process. ####Droplet Formation [![droplet-formation.png](//](// Cooling gases quickly condense into droplets in what is called the ‘accumulation mode’ of droplets. Accumulating droplets are sometimes called ‘cloud scavenging’ for the way they grow by collecting gases and mixing with other droplets. Droplets gain and lose water as the humidity changes. Condensing water often brings multiple droplets together, and this ‘wetting’ and ‘drying’ of droplets can aid in droplet accumulation. [![CORRECTillustrative3-peak-droplet.png](//](// [![CORRECTillustrative3-peak-droplet-humidity.png](//](// ####Droplets’ Beginnings: Ultrafine nulceotoids While dust can only be ground to about 0.5 μm minimum, and most dust particles are much bigger, smaller solid particles can be formed under intense heat and pressure, such as in a fire or engine. These ultrafine, or nanoparticles, are less than 0.1 μm and last only as long as their rapidly dissipating energy can keep them from bonding. With only a dozen to a few hundred molecules making up each ultrafine particle, the properties and behavior of ultrafines are poorly understood. Ultrafine material, especially elemental carbon nanoparticles from transportation and diesel, are a growing field of study. [![6.jpg](//](// As ultrafine particles lose energy, cooling gases condense around them, ‘nucleating’ (forming the center, or nucleus, of) a new droplet. Often the gases condensing onto ultrafines are in the same emissions stream from combustion, including sulfur dioxide, nitrogen oxides, and volatile organic compounds (VOCs). The droplets formed around ultrafines may also nucleate other droplets, especially ‘wet’ droplets of water. ###Respirable Particles The body removes objects from the lungs in two ways, by coughing (“expectorating”), or by absorption and removal by the blood stream. In order to enter the bloodstream, particles must pass the last branching passageways in the lungs: the terminal bronchioles. Particles above the terminal bronchioles are the “thoracic fraction” (thoracic means in the chest), and below the terminal bronchioles particles are considered respired particles. Respired particles may, however, still be removed by coughing. [![inhalable-respirable.png](//](// The most particles in the respiratory system average around 2.5 μm, while most in the thoracic fraction are are around 10 μm. The fate of short-lived ultrafine particles in the lungs is still being studied. [![CORRECTillustrative3-peak-respirable.png](//](// ###Regulation Particulate Matter is one of six ‘criteria pollutants’ determining National Ambient Air Quality Standards ([NAAQS](/wiki/frac-sand-legislation#National+Ambient+Air+Quality+Standards)). All of the EPA’s [technology-based particle regulations]( share features in common with the [PM10 standard](, and a deep look at the PM10 standard is illustrative. ####PM10 PM10 is the US EPA’s first attempt to capture a standardized indicator of respirable particles. “PM10” stands for Particulate Matter less than or equal to 10 μm in diameter. Established in 1987, PM10 is now a global benchmark. PM10 is a technology-based standard-- all PM10 tools and measurements are related back to the original reference [filter-based PM Monitors](/wiki/filter-pm) instrument. Similar measurement tools with a tight correlation with this original [Federal Reference Method (FRM)]( now share the FRM designation. Tools that use different processes and have a somewhat less tight correlation are designated [Federal Equivalent Methods (FEMs)](/wiki/pm-monitoring-regulations#Federal+Equivalent+Methods). You can read about the FRM PM10 monitor [in the Code of Federal Regulations]( [![er18jy97.022.png](//](// The goal of the FRM is to generate a 24 hour average of the concentration of respirable particles in the air. It does this by pumping a precise volume of air inside, selecting the particles smaller than 10 μm, and depositing them on a filter, and measuring their accumulated mass. Note that the FRM concentration is determine in "mass per volume" and not "number of particles per volume," and thus requires a gravimetric rather than a particle-counting technique. The particles are selected for size with a device called an impactor (o cyclone). The function of an FRM impactor is written into the regulation and legally defines what is and isn’t PM10. [![PM10-FRM.png](//](// An impactor sorts particles by momentum. As air is drawn into the instrument, an impactor plate interrupts the air’s linear flow. Light particles stay in the air stream and pass around the plate. Due to inertia, more massive particles can’t make the turn and hit the plate, thereby crashing out of the sample airstream: [![impactor.png](//](// The _cutoff_ size where particles either hit the plate or pass beyond it is not an absolute cutoff; there is a distribution of particle sizes that impact the plate or stay airborne. Different impactor designs are described by the 'sharpness' by which they select particles. [![cutpoint_vs_sharpness.png](//](// For a PM10 cutoff, 50% of particles that are 10 μm in diameter are passed by the impactor, and 50% crash. The distribution is not even, and the rate at which the impactor cuts off particles above 10 μm is the ‘sharpness’ of the cutoff. Other categories of regulation include PM2.5 and PM10-2.5, read more in [PM Monitoring Regulations](/wiki/pm-monitoring-regulations). [![CORRECTillustrative3-peak-pm10.png](//](// The PM2.5 FRM monitor is identical to the PM10 monitor, except for a second impactor for PM2.5 after the impactor for PM10. [![CORRECTillustrative3-peak-pm2.5.png](//](// [![CORRECTillustrative3-peak-pm10-25.png](//](// Note that neither category directly aligns with the size fraction that can travel into the bronchial region of the lungs, particles of approximately 5 μm. Also note that the FRMs collect particulate matter without determining the composition of that particulate matter, which can vary widely based on location and pollution sources. Inhaled silica is known to be especially damaging to human health, so **silica-specific exposure is [regulated in occupational settings, and in ambient settings in six states](/wiki/silica-monitoring).**...

Author Comment Last activity Moderation
stevie "From Mallory on the Purple Air team: "When a user registers their PurpleAir sensor, they select the location that they want the sensor icon to appe..." | Read more » over 3 years ago
eustatic "Thanks, Stevie. in the past, we've had surveyors for companies releasing PM trespass onto private property and reset the sensors. this was for imp..." | Read more » over 3 years ago
stevie " @stevie has marked @pat as a co-author. " | Read more » over 3 years ago
evandevnd12 "دوره آنلاین آموزش زبان انگلیسی یکی از جدیدترین و بهترین راه کارها برای یادگیری اصولی زبان انگلیسی است. امروزه یادگیری زبان انگلیسی یک مزیت که نه یک..." | Read more » over 3 years ago
subir "Wow thanks for organizing this and making all things accessible toward the end. " | Read more » over 3 years ago
stevie "Hi Yes! give me a day, and everything (chat links shared and such, as well as the call itself) will be shared on www/ " | Read more » over 3 years ago
subir "Hey all. It was a wonderful discussion, but after it ended the Zoom app thing closed down and i have no way to get back to all the chats that were ..." | Read more » over 3 years ago
stevie "Hi All! Reminder this OpenHour is today at 1pm ET (see your local timezone here,438)!! Here's a link to join..." | Read more » over 3 years ago
subir "Thanks @stevie . Looking forward to the discussion. " | Read more » over 3 years ago
Ag8n "Stevie, Sorry, I'm not available.  Thanks, Ag8n On February 13, 2020, at 3:14 PM, wrote:Hi! You were mentioned ..." | Read more » over 3 years ago
stevie "@guolivar Sorry about the timezone trouble. But no worries! All OpenHours are recorded. You can find them on this page:" | Read more » over 3 years ago
stevie "Hi! No worries. This link will get you directly into the call when it starts: Or you can call in from the US here: 1 6..." | Read more » over 3 years ago
subir "Hello @stevie. Yes i would love to be there. Thanks for organizing it. But i am not very sure how exactly could i 'join' in - little slow on modern..." | Read more » over 3 years ago
guolivar "I'm sorry but as usual the time difference kills me. I could potentially listen in but at that time I cannot join the discussions (I'm too busy get..." | Read more » over 3 years ago
stevie "Are you available to join on for OpenHour? @natevw @imvec @david_uwi @subir @tomp @charnes9 @OrionAllgaier @Ag8n @eustatic @bigmit37 @guolivar @ju..." | Read more » over 3 years ago
GBeast "If you are a music lover then visit at least once in life. Here " | Read more » over 3 years ago
Ag8n "My expertise is chemistry. But in working in a glp/gmp lab environmenment, I was trained in some of it. The major concern with HEPA filters was ..." | Read more » over 3 years ago
stevie "Hey @BostonFern thanks for posting. I don't have an answer for this question, but check out this page, it has some info on ultrafines on it. I thin..." | Read more » over 3 years ago
warren "OMG this is the best, Scott :-) Hey i'll be in NOLA next friday for a week!  -- ig: @unterbahn | he/him/his On Thu, Jan 30, 2020 at 5:10 PM \&l..." | Read more » over 3 years ago
eustatic "I did this with a Lighter and a Public Lab card, thanks to Stevie. Set the Public Lab card on a tiny fire, put it out, let it smoke up the sensor,..." | Read more » over 3 years ago
justcare "Thank you for sharing useful information. " | Read more » almost 4 years ago
AyushC "Nice is very useful by the way check out this website What To Watch On Netflix " | Read more » almost 4 years ago
piyasidayanmain "Breaking news for everyone Visit at and fix your dating with independent Chennai escorts girl with genuine price, in my opinion ..." | Read more » almost 4 years ago
subir "Wow, thanks once again. Its been many months searching for such information from 'experts' i know locally but none were so clear and responsive. Re..." | Read more » about 4 years ago