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

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

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

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

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

@GreenFrogg I was checking out your list of sensors on this page and didn't see the Purple Air. Have you worked with it? what are your thoughts on it in comparison to the ones you've been working with?

I don't have experience with the Purple Air. The page is an overview made by the Dutch institute of environmental health (RIVM). They coordinate. You can contact them directly about their knowledge about the Purple Air.

Hi @BrandonFeenstra ! I had a group asking me about the Dylos this morning, so I went to the AQMD website and found the report for it like the one you shared here (http://yourstory.aqmd.gov/aq-spec/evaluations/field <-- really useful link for anyone thinking about low cost PM monitoring!), but I was wondering if there's a report that does an overview of what was found on all of these?

Quick update - the sensor in the Purple Air seems to be this one or one very similar, a laser based sensor with a fan -- the PMS5003 --

$30 shipped on Amazon: https://www.amazon.com/Beaster-particle-Digital-Purifier-Precision/dp/B07F2X6RVF

Ah, yes, confirmed by @guolivar's post: https://publiclab.org/notes/guolivar/01-08-2018/thoughts-on-low-cost-air-quality-sensors

Just noting also a big round up of notes on humidity and fog with optical sensors here:

https://publiclab.org/questions/sarasage/08-10-2021/is-there-a-correlation-between-humidity-and-particulates-in-the-air#c29126

and at https://publiclab.org/tag/humidity

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