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# PurpleAir question:purpleair

The [PurpleAir](https://www.purpleair.com/) is one of many low cost devices that use laser optical particle counters to estimate particulate matter mass concentrations in air for PM2.5 and PM10. Other similar devices include the [Dustduino](https://publiclab.org/wiki/dustduino), [Speck](https://publiclab.org/notes/chrisbartley/04-15-2014/speck-particle-monitor), [Dylos](http://www.dylosproducts.com/?gclid=Cj0KCQjw5NnbBRDaARIsAJP-YR_IQiQC0876PaQmo6lWAuRPJ5FG3oh65dc7rsf95xSqDd0Wdqrs6OYaAsxtEALw_wcB) and more. The PurpleAir costs around $200 and provides real time air quality data that can be used to understand indoor or outdoor environments and conduct environmental investigations on air quality. **The intention of this page is to create a central location to discuss successful (and unsuccessful) use cases of the PurpleAir and problem solve together. Please contribute any experiences you've had with the PurpleAir. Perhaps consider visiting https://publiclab.org/simple-air-sensor to see the start of a barebones kit that is kicking off the development of a well-supported, open source air sensor similar to the PurpleAir.** ## Why use one? Every state in the US is mandated by the Environmental Protection Agency to create air quality sensor networks to monitor the six pollutants that the EPA defines as hazardous - Ground-level ozone, Carbon monoxide, Sulfur oxides, Nitrogen oxides, Lead and Particulate Matter. Read more about [particulate matter](https://publiclab.org/wiki/pm#Background+Information) here. However, due to the huge cost upwards of$25,000 associated with Federal Reference Method (FRM) and Federal equivalent method (FEM) sensors, most cities only have a handful of sensors, sometimes just one, measuring each category of pollutant. In addition, FRM sensors often have a lag of several months for quality control before the data is publicly accessible. Optical sensors provide a way to get near real-time data on the particulate matter in your home or community and to have autonomy over the locations being monitored. ##How it Works [This page](https://publiclab.org/wiki/optical-pm) does a great job of explaining how laser optical particle counters work in detail. But, the most important things to know when deciding to use an optical particle counter like the PurpleAir is that: 1. The data the PurpleAir (and other optical counters) produce is an _estimation_ of particulate mass concentration that relies on several assumptions for shape, diameter and density. The quality of your data will depend on those assumptions as well as environmental considerations such as humidity, light and temperature. 2. Because of the fact that optical counters rely on these assumptions, the data produced by them are _not_ FRM or FEM certified. That being said, there have been a number of academic studies that have quantified the performance and limitations of some of these optical sensors to help you choose which one to use depending on what you are trying to sense and what level of performance you are looking for. The EPA has an excellent summary of these studies in this table [here](https://www.epa.gov/air-sensor-toolbox/evaluation-emerging-air-pollution-sensor-performance). A higher R^2 value means better performance. [This page](https://publiclab.org/wiki/optical-pm) has some more links of studies to check out if you scroll a bit. [Here](http://www.aqmd.gov/docs/default-source/aq-spec/field-evaluations/purpleair---field-evaluation.pdf) is a study specific to PurpleAir. ## Use Cases - PurpleAir maintains a [map](https://www.purpleair.com/map?#0.27/0/-30) of every user's data from around the world. Check it out. - A use case in [Utah](https://www.good4utah.com/news/local-news/dirty-air-monitors-are-they-telling-us-the-whole-truth/382744964) - A use case in [California](https://cleantechnica.com/2018/07/09/my-new-favorite-gadget-a-purple-air-air-quality-monitor/) - [This facebook group](https://www.facebook.com/groups/purpleair/) includes people who own a PurpleAir and discuss their experiences - [This blog](https://www.wxforum.net/index.php?topic=33031.0) has some dialogue about various use issues Please add your experiences with PurpleAir too! ## Suggestions for conducting particulate matter investigations [This page](https://publiclab.org/wiki/general-environmental-monitoring-study-strategies) summarizes important considerations before starting an investigation. To add onto those, specifically in regards to air quality, here are some suggestions. Before ordering a sensor, check out the data that is freely available to you online. [Visit your state's department of environmental management website](https://www.epa.gov/home/health-and-environmental-agencies-us-states-and-territories) and their air quality section. With some poking around, you can find their ‘Air monitoring network plan’ which will show you the _exact locations_ of all of their different FEM/FRM sensors and what pollutant they are measuring. This can help to identify gaps in their monitoring network that you may be interested in. [AirNow](https://www.airnow.gov/index.cfm?action=airnow.main) has national daily data from FEM monitors. You can search for your zip code and see the live air quality forecast. This can be used to help inform your day to day movements especially if you are an asthmatic. You can also download data* from FRM monitors [here](https://www.epa.gov/outdoor-air-quality-data/download-daily-data). This is really cool because you can specify what data you want and it will generate an Excel file for you. You can then start making plots and figures to compare different time periods and locations. [Check out this post](https://publiclab.org/notes/jiteovien/08-01-2018/air-quality-data-visualization-no-coding-necessary) which used this online EPA data to create some visualization of the monitoring in Rhode Island. *NOTE: As mentioned earlier, the FRM data has a lag for quality assurance reasons. For example, the most current Rhode Island data is for May 2018. (It is August at the moment this is being written). Everyone, whether or not you own a Purple Air has free access to the Purple Air's database of global sensors. Read more about this in the activity [Download &amp; Analyze your Purple Air data](https://publiclab.org/notes/jiteovien/08-28-2018/download-analyze-your-purple-air-data?_=1535473842). ## Questions Questions can be either frequently asked questions, or "next step" challenges we're looking to solve. [questions:purpleair] ## Activities Activities show how to use this project, step by step. [activities:purpleair] ## Other things to know about using your Purple Air The PurpleAir sensor has two 'channels' that measure data. Channel A and Channel B. Each channel has a 'primary' and 'secondary' data set. The data that Channel A measures is described below: PrimaryData - field1: PM1.0 (CF=ATM) ug/m3 - field2: PM2.5 (CF=ATM) ug/m3 - field3: PM10.0 (CF=ATM) ug/m3 - field4: Uptime (Minutes) - field5: RSSI (WiFi Signal Strength) - field6: Temperature (F) - field7: Humidity (%) - field8: PM2.5 (CF=1) ug/m3 This is the field to use for PM2.5 SecondaryData - field1: 0.3um particles/deciliter - field2: 0.5um particles/deciliter - field3: 1.0um particles/deciliter - field4: 2.5um particles/deciliter - field5: 5.0um particles/deciliter - field6: 10.0um particles/deciliter - field7: PM1.0 (CF=1) ug/m3 This is the field to use for PM1.0 - field8: PM10 (CF=1) ug/m3 This is the field to use for PM10 particles/deciliter is a particle count per volume measurement. ug/m3 is the particle mass concentration - the popular method of measuring particulate matter. Channel B measures the exact same primary and secondary data. This is likely just done for robustness just in case one of the channel fails or has an error. These setup instructions are included with the Simple Air sensors and can be reprinted Purple_Air_Instructions.pdf ...

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 2 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 2 years ago
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joyofsoy "Yes. In my opinion. They’ll catch the particles. The speed will depend on the degree of mixing , ventilation and the size of the restroom. You may ..." | Read more » almost 3 years ago
joyofsoy "We shared this on Twitter and got this response: my students have easily detected vaping signals on similar low-cost pm sensors. that being said, ..." | Read more » almost 3 years ago
Bronwen "I don't know if this is helpful at all, but it shows a comparison of PM associated with e-cigarette vapors: https://www.ncbi.nlm.nih.gov/pmc/articl..." | Read more » almost 3 years ago
Bronwen "This is a really interesting question! I know that the plantower sensors are affected by vapor, humidity, aerosols, though how comparable those res..." | Read more » almost 3 years ago
warren "OK, update - since the B sensor was covered yesterday, it's now showed as "downgraded" just as the A was yesterday: My question now, is apart fr..." | Read more » over 3 years ago
warren "OK! After now blocking the B sensor instead, it's accepting A data once more, and hasn't yet flagged the B sensor. Interesting! " | Read more » over 3 years ago
warren "Aha! One day later, my sensor A has been "downgraded"! I'll move the tape to the other sensor and see what happens. " | Read more » over 3 years ago
warren "i'll post more soon, but one is now totally blocked and it shows on the graph, but it's not rejecting the data. I'll let this run for a day. Then ..." | Read more » over 3 years ago
warren "OK, i covered it more thoroughly and will wait a while to report back on what happens. " | Read more » over 3 years ago
warren " OK testing this out now. Here's our sensor, on Cromwell St at our office: https://www.purpleair.com/map?582419|582421#13/41.81161/-71.41883 Note ..." | Read more » over 3 years ago
warren "This is great, thanks @kkoerner -- and interesting to see that they'll flag sensors. I wonder how much two would have to not correlate before it go..." | Read more » over 3 years ago
kkoerner "So from my experience they're used primarily as a sanity check. I'm not sure of the math behind it, and since PA removed the R2 values that used to..." | Read more » over 3 years ago
warren " @julieta @nanocastro have either of you used 2 sensors in your DIY #plantower -based devices? #maca etc? " | Read more » over 3 years ago
warren "And just linking to here, where the wiki page documents the 2 channels, which i would guess are from the 2 sensors? https://publiclab.org/wiki/purp..." | Read more » over 3 years ago
warren "@CBarnes9 @samr @Tomp @OrionAllgaier @wu_ming2 @guolivar @BrandonFeenstra @kkoerner, any thoughts or info to share on exactly what the #purpleair d..." | Read more » over 3 years ago
samr "We are connecting the pms5003 to an arduino mega 2650 micro controller along with some other sensors such as a BME280 temp, pressure, humidity sens..." | Read more » over 3 years ago
samr " Thank you so much for the very clear and helpful information! " | Read more » over 3 years ago
warren " Here's a good overview from EPA Region 1, New England: https://www3.epa.gov/region1/airquality/pm-aq-standards.html Although it's a bit jargony. " | Read more » over 3 years ago
guolivar " The particle size distribution (mass, volume or number) is very variable and even though "on average" it's fairly stable, the day-to-day variabili..." | Read more » over 3 years ago