We use the Plantower PMS5003 sensor for PM2.5. This sensor has been extensively tested and is one of the most accurate low cost sensors.

All low cost sensors are using the laser scattering technique and thus do approximate the mass and not a direct measurement.

However tests show that PM2.5 is the most accurate and often PM10 in these sensors is not very good.

Thanks for the response!

Their website mentions the sensor they use directly on the kits page. It's a Plantower PMS5003 which does actually count particles: https://www.aqmd.gov/docs/default-source/aq-spec/resources-p...

While the spec sheet does say that, it's not actually true. The PMS5003 is a truncated nephelometer (https://amt.copernicus.org/articles/15/655/2022/) that measures the total scattered light from all particles with diameters less than ~1 µm. This single scalar value (proportional to the total scattered light, as collected across a wide viewing range) is then correlated to a reference measurement of PM2.5 and typically correlates quite well in most urban areas where PM2.5 and PM1 are highly correlated. For more info on the difference between particle counters and nephelometers in this context, see https://amt.copernicus.org/articles/13/6343/2020/.

TIL! Thank you for the detailed explanation and links to additional context.

Relevant disclaimer: I work for QuantAQ, another distributed Air Quality Monitoring company, my opinions are my own.

With proper calibration, the PMS5003 sensor AirGradient uses is a real and fairly good measurement of PM1 (<1 micron), which is often fairly correlated with (and makes up much of) PM2.5. However, the sensor cannot really see particles larger than 1 micron, which sometimes matters for PM2.5 (when the PM1:PM2.5 ratio changes, like wildfires), and very much matters for PM10. That's why QuantAQ uses a PMS5003 combined with a different sensing technology (an optical particle counter) to actually measure PM2.5 and PM10, not just extrapolate from a PM1 measurement.

We have a blog post here explaining more: https://blog.quant-aq.com/can-your-plantower-pms5003-based-a...

I love the work that AirGradient is doing making AQ sensing technology open and accessible, especially to hardware hackers. The BOM cost of the OPC sensor we use alongside the PMS5003 is more than the cost of the entire AirGradient kit, so it is valuable to have options in the market depending on application.

Thank you for sharing this. Are you using the AlphaSense OPC?

I'm just going to take a minute to be happy to see this friendly exchange of information in public between two people who are both knowledgeable about the subject and competitors.

Excellent overview; I think the space for air monitoring is only going to grow as time goes on, especially after COVID and with increased awareness of the downsides of airborne particulates and high CO2 exposure.

I've been setting up PM sensors in my home since installing a log-burning stove last winter; I've found a couple of interesting things thus far; Notably, despite the FUD, air quality _in_ my home isn't affected by it.

What does affect air quality in my home massively, are the people parking their vehicles surrounding my home morning and afternoon as they drop off and pick up their children from the nearby school. I see a 10x ambient measure at these times. I was starting to think about how I could use BLE monitoring to track this somehow (the other thing my home is surrounded with at these times is devices broadcasting Bluetooth "beacons"(?)); could be an interesting experiment.

The next step for me is really knowing what and how something can be done about the pollution (generally speaking); Monitoring is great, but what's the next step?

"Monitoring is great, but what's the next step?"

Short term: install air filters

Long term: banning ICE cars

Long term: move to a different home

Well, I did. But not everyone can. And long term it would be nice, if the cities would have breathable air again.

Also where there is good air, there ain't so many people.

Longer term: move to a different planet.

How much would it cost me to install a modulair-PM on my rooftop, assuming I did the work? I’m just an individual, i just want transparent information. I don’t want to “contact sales” as it says on the link from that blog post.

You could buy a Bosch BME680 or similar for $20 and add it to a Pi or Arduino.

A commercial model is around $200.

There are a lot of options so decide if you want to build it or buy it and plug it in!

Then you can list your data on a site like https://explore.openaq.org/

The BME 680 does temperature, humidity, barometric pressure, and VOC gas sensing. Maybe there's something reasonably-priced that does particulates, but this doesn't seem to be it. What's a good alternative?

That looks awesome, thanks! I already have some ESP32 devices acting as weather sensors that log to a Raspberry Pi over MQTT. I might have to add this too.

Very impressive. I looked up that Bosch device: https://www.bosch-sensortec.com/products/environmental-senso...

Then, I found a board from Adafruit. The chip is so tiny in the Adafruit photo!

https://www.adafruit.com/product/3660

Thanks for the interest! We have transparent pricing here: https://quant-aq.com/pricing

Short answer, $1500 + $300 annually (includes cellular, realtime data calibration in our cloud, and full API access).

Relevant to the topic above, we are building for a slightly different market than AirGradient, and want to make sure we're an appropriate solution for potential customers -- you might genuinely be better served by a different product! As such, we're currently not optimized for low touch single sales to individuals, but it's something we'd like to improve in the future.

If you do contact sales, and we end up being a good fit for what you're looking for, we'd love to help!

I’d be interested in a prosumer version of this that ditches the LTE and cloud system for wall power + WiFi or (ideally) PoE with a fully local backend via home assistant

I am curious, how do you do real-time calibration in the cloud?

I'm a big fan of QuantAQ. Speaking from a PM10 perspective, your monitors perform on-par with high-cost regulatory monitors in a much smaller package and far lower cost. I also love the open API. That said, I would love to see a locally-hosted variety for environments where LTE/cloud is not accessible/preferred.

Great response, I learned something new! Thanks