# Question: How good is the PurpleAir sensor and what does it detect?

warren is asking a question about air-sensors:

warren asked on January 04, 2018 23:15
372 | 4 answers | shortlink

The website for PurpleAir (and the Wunderground page for it) speak very highly of it:

Using a new generation of laser particle counters to provide real time measurement of (amongst other data), PM1.0, PM2.5 and PM10. PurpleAir sensors are easy to install, requiring a power outlet and WiFi. They use WiFi to report in real time to the PurpleAir Map.

They seem to range from $179-$259 and detect:

PurpleAir sensors use a fan to draw air past a laser, causing reflections from any particles in the air. These reflections are used to count particles in six sizes between 0.3μm and 10μm diameter. Using one second particle counts, estimated total mass for PM1.0, PM2.5 and PM10 is averaged by the PurpleAir Internet of Things (IOT) control board.

https://www.purpleair.com/sensors

How well do these relate to health effects, or regulated air quality measurements? What are the pros/cons?

laser air-quality sensors dust particulate pm indoor-air air-sensors purpleair pm2.5 pm10 pm1.0

question:air-sensors question:indoor-air

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### 4 Answers

If you would like to learn more about Air Quality Sensors and their performance against regulatory instrumentation, I would recommend a visit to the South Coast Air Quality Management Districts's (SCAQMD) Air Quality Sensor Performance Evaluation Center (AQ-SPEC) web page. The purple air sensor has been evaluated in both the field and the laboratory. Program's website: http://www.aqmd.gov/aq-spec PA-II field report: http://www.aqmd.gov/docs/default-source/aq-spec/field-evaluations/purple-air-pa-ii---field-evaluation.pdf?sfvrsn=4 PA-II laboratory report: http://www.aqmd.gov/docs/default-source/aq-spec/laboratory-evaluations/purple-air-pa-ii---lab-evaluation.pdf?sfvrsn=4

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Wig Zamore also chimed in on the mailing list:

Hi Jeff - My guess is that if Weather Underground and EPA and CARB have been involved the product is probably pretty good. And Weather Underground is a great idea for a host network. They presented their initial ideas for this at an EPA community sensor conference in RTP NC several years ago. Dylos also makes some pretty well-regarded instruments that measure pretty small airborne particles. Ultimately it would be most helpful to have relatively inexpensive ultrafine particle (UFP) sensors that could count particles per cubic centimeter in the 5 nm to 100 nm size range.

Our bench instruments, used in the Boston area by Tufts and community partners like Somerville Transportation Equity Partnership (STEP) both in stationary boxes and in mobile labs, generally count between 10,000 and 50,000 UFP per cubic centimeter but sometimes more, depending on meteorology and proximity to sources, especially mobile sources like highways, rail and aviation. Or some indoor sources like candles and cooking. These monitors are both accurate and pretty expensive. There are some very inexpensive particle sensors, such as Shinyeis, but reports are that they are not always accurate.

Joshua Apte and co-authors have done very fine grained mobile lab street mapping using Google vehicles (http://apte.caee.utexas.edu/google-air-mapping/). Their particle metric is Black Carbon, a pretty good mobile indicator, and they look at Nitrogen Oxides also. Mueller and others have done similar projects (http://www.sciencedirect.com.ezproxy.library.tufts.edu/science/article/pii/S1352231015305409#bib10) in Zurich using multi-pollutant monitor boxes on top of light rail vehicles, a brilliant idea. They use DiscMINIs for the ultrafine particles.

As you know, I would also love to see a bicycle sensor network that could calibrate off of stationary monitors from time to time. Could be done with bike share. But so far cost is a real barrier for measuring ultrafine particles. Maybe the new nano labs will come up with something soon. - Cheers, Wig

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I tried to put a long answer here but it kept throwing errors so I wrote a note with my thoughts on this issue:

https://publiclab.org/notes/guolivar/01-08-2018/thoughts-on-low-cost-air-quality-sensors

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Hey folk, What kind of Framework (for Participatory PM2.5) can use for creating monitoring cities?

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