Community Monitoring after the Marshall Fire- Louisville/Superior CO

The PurpleAir sensor network is growing rapidly in Louisville and Superior Colorado, located in Boulder County. About 1000 homes were lost in this wildfire turned urban conflagration that occurred on 30 December 2021. Community members are understandably concerned about indoor and outdoor air quality in the wake of the fire. As cleanup of burned homes and lost progresses in the coming months, ash a debris will be disturbed and become airborne.

I installed my PurpleAir sensor in August 2020 and at that time, was one of only 2 sensors in the area. Today there are almost 40 sensors in the area. The city of Louisville has stated that they will be installing PurpleAir sensors on city buildings, and has arranged with interested homeowners for a group purchase of sensors.

In addition, I recently upgrade my sensor with the BME680 board to measure VOCs as well, and communicated this to the community. We now have over 14 VOC capable sensors in the network. I am anxious for this VOC data to get calibrated to a known scale, such as mg/m^3 or ppm. Right now the readings are just relative, but interesting nonetheless.

If you are interested in seeing our growing network, please check this map out


Thanks Bud for coordinating this effort across Louisville and Superior. VOCs still seem like something of a mystery to me and it’s interesting how they can change so quickly and vary so much with geographical distribution, unlike the particulates which seem more consistent across town. Would love to learn more about this and have the relative readings put in perspective with calibrated results!

I have noticed that the readings for VOC sensors seem to be subject to very local sources. This seems consistent with another post about community monitoring in PA that @Mark_from_Pittsburgh has going. So yeah, it is interesting. The relative nature is still valuable. Once we do get some sort of calibration to a scale we can always download the past data and look at trends over time which will be very interesting. Then perhaps we can compare local sensors in a more systematic fashion.

Then it will be time to fire up the #Rstats!

Have there been any updates on scaling the VOC readings? As far as I can see the numbers are reported in Bosch Static IAQ but then being applied to the normalized IAQ scale but I don’t know how to normalize the Static IAQ units.

I haven’t seen any udpates from PA on this yet. Some colleagues and I from CU Denver are working separately with our own low-cost AQ sensors which also use the BME680. We have co-located our sensors with some that are already calibrated against a mass spec, inside of a damaged home here in Louisville. Our data collection period for that part of the project ends Sunday, at which time we will move the sensors to a new location. So our team might have some better sense of the BME680 output for VOCs coming soon. But note that we are not using the BSEC package from Bosch- we are just using sensor output. PA is using the BSEC.

It sounds like you’re already familair with the BME680, @kshopenn ?

Just from good old internet research, trying to understand the values for the weekly effort to calm down people on the 80027 FB page.

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Yep I hear you. It’s really hard for people to look at numbers in a relative sense, especially those that are from tentative measurements. My wife (also a scientist) reminds me that “people just want colors” like green, yellow, red. So when they see dark red, they freak.

I requested a PA with the BME680, and recently installed it. It’s not in the burn area, but in Arvada so I figure it could at least be a relative comparison measurement. Looks like there is another VOC capable sensor in Boulder as well. I realize that VOC’s can be extremely localized, but a comparison could still be informative.

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Just an FYI - I had to have this PA replaced due to problems between Channels A and B, but the replacement sensor still has the BME680 so no loss in VOC data. The replacement sensor is put up in the same place. The old sensor data is still on the map and still available for download. The new sensor is now up and streaming data.

Hi @Bud_T ,
the BME680 is internal sensor and its life time is quite low outside. how did you deal with this problem?

What limits its useful lifetime outside? Exposure to moisture? Temperature extremes? I am unaware of any of these limitations.

As far as its use in the PA monitors, it is shielded from moisture. In our own low-cost AQ sensor packages, we use the BME680 primarily indoors, and in an enclosed case with an air inlet.

So that you all are aware, the next version of firmware that will be released for PurpleAir sensors will help better the BME680’s readings and work on its fundamentals. The firmware will use more memory to store variables that the BME680 will reference when reporting data. We will work on creating a post about the BME680 VOC sensor and this update soon.

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Hi - I’m a resident of Louisville and trying to decide what sensor to get. If I’m only getting one, is there an advantage to using an outdoor sensor vs indoor or vice versa? Seems like both locations would be important to have?

It appears the PA -II- FLEX has the BME680 with the VOC monitoring, however can this be added to any of the other units i.e the PA I if I only wanted an indoor unit?

Hi Cole. Welcome to the community. Depending on where you live in Louisville, you probably don’t need an outdoor sensor. Our sensor network is very dense now, and there may be sensors deployed very near you home. So if you are more concerned about your indoor air quality I would deploy a sensor inside your home.

I think PA support/sales may be able to offer you the best advice on which sensor to buy. I have the PA II (non-SD card version) that I added the BME680 to myself.

Hi Cole, I would recommend taking a look at this topic, which should give you a bit better idea of the differences between each PurpleAir sensor.

Also, all of the PA-II sensor models work both indoors and outdoors. This means that you can use the same sensor to test the air quality inside and outside by archiving and moving your sensor. You just wouldn’t be able to do both at the same time.

Hi @Cole, I asked PA if they can add the BME680 to the PA-II-SD that I ordered and they gladly did so. You can always ask them at

Thanks everyone for your help and input! @zulu isn’t adding the BME680 to the PA-II-SD essentially the same unit as the PA-II-FLEX? Is there a difference I don’t see (price?), or was the FLEX not available at the time? Thanks!

Hi @Cole the Flex wasn’t available when I ordered it. If it does have the BME680 it would be the same. It is missing the SD card, there’s a cool fancy LED indicating the AQI, and the mounting hardware looks updated. If you ask to add the BME680 to the PA-II-SD there’s about an $18 cost increase, so comes out to be about the same (minus the SD card). Might be worth the Flex for the fancy at-a-glance look of AQI?

Copy that, thank you!

Just putting this out here: All PA sensors support WS2812 LED’s. Up to 100 pixels! If you want to add LED’s to any PA-II or PA-II-SD, it is as simple as plugging them into the motherboard.

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