if you're interested, we made Dylos drivers for Open Pipe Kit for the Pi-- its a flexible platform for pushing data to Phant and any other database, based on command line scripting. http://openpipekit.github.io/

http://openpipekit.github.io/#configurator

awesome resources and case! hadn't seen this summary of low cost PM sensors: http://www.aqmd.gov/aq-spec/evaluations#&MainContent_C001_Col00=2

Thanks @mathew! Yeah @jeff showed those to me, the AQICN one was pretty straight up too and I just went with theirs because I read their tutorial first and I was pretty happy with the documentation.

@kevinvivergy great detailed post.

I'm not that familiar with the Dylos--haven't handled one--but looking at some photos maybe just cut out holes in the enclosure corresponding to the back of the instrument fan intake and exhaust vent. Hole saws are great for neatly cutting openings. Ideally that would expose the intake to the outside air and then the exhaust is plumbed out, yet you can still heat/cool the instrument enclosure without having to directly heat/cool the ambient air you're testing.

I do have concerns that the Dylos might not be made to operate 24/7, on constantly outside, even if kept from the elements--but try it!

For heating, a small silicone flexible heater makes sense. You can buy smaller versions than the one you have, but the cheaper ones also need thermostats. Watlow makes them but their online sales is virtually non-existent. McMaster sells similar Flexible Silicone-Rubber Heat Sheets which I'm not sure if these are Watlow or not. They require a thermostat wired in series, something like this. I haven't used these parts specifically, but have used the Watlow components to heat instruments. Alternatively, some pet supply stores my have little heaters made for lizards and other sm animal enclosures.

Like most on/off thermostats, the heat cycle is somewhat dependent on the distance between the heater and the thermostat so you might need to play around with the spacing to get it to work right--not over heat but not cycle constantly.

Ideally you'd have the heater PID controlled and record the enclosure temperature, etc. but that's not always practical or needed. Yet, some instruments are sensitive to temperature fluctuations and the heater cycling on/off can sometimes cause electrical line noise creating an artificial blip on your instrument reading, which the PID controller can help avoid that instant on/off electrical surge.

The low, low tech approach would be to really undersize the heater wattage then just plug it in without any thermostat and hope for the best, which I think is what your light bulb approach is doing. Inline fuses are always a good addition to a heating circuit to prevent a complete meltdown!

For summer you're probably going to want a cooling fan with filter. With these outdoor enclosures sometimes you just need to winterize them each fall (unplug fan, cover fan opening, plug in heater) and then summerize them each spring (unplug heater, remove fan cover, plug in fan).

Also, put a placard on it identifying it as a scientific instrument with your contact info just in case someone finds it unattended and calls the bomb squad.

@Davidmack all good thoughts, thanks for the detailed response.

-The big challenge with intake thing is that, if I understand your approach correctly, the intake cannot be exposed directly to outdoor air in the winter because it will not give accurate readings if incoming air is less than 40 degrees. So that is why it is currently on the opposite side of the container, on the other side of the heating. I do like the exhaust suggestion- cutting a separate hole just to handle exhaust correctly.

-Really like the heater ideas, I don't have any experience really with the electric wiring stuff, but the pet store idea is a good one for an easy way to try it out.

-The summer/winter version is definitely a good idea, that is why I did everything with Velcro, so it could all be moved or taken out. Cooling fan should be an easy add.

-You are very right about the placard! I was thinking, since I am planning on doing this at an elementary school, that I could let one of the kids paint the outside with whatever design they wanted. Would make it more approachable/attractive for kids instead of a black box.

I was thinking you could expose the intake to ambient temperature in winter and by heating the enclosure you'd be warming the instrument and air indirectly--but I'm not really sure if that would work or not. It's a little crude and you would probably still have issues in extreme cold and when there's a lot of fog. Below freezing the air is usually not wet enough to cause an issue unless you have snow or ice blowing in but you could prevent that with a baffle.

Does the Dyos have a temp requirement?

Moisture is always a problem with light scattering devices and the cheap way to compensate for condensation is to heat the air to lower the relative humidity (RH). So ideally you would only heat the intake air when the air exceeds ~95% RH. But this would require a RH sensor with a heat controller. You could offset the intake with a pipe (anodized aluminum, non magnetic is best) and then wrap the flexible heater around the pipe, which a metal pipe would conduct the heat better than say PVC.

In general you want to "handle" the air sample as little as possible. When you heat the air you risk changing its composition: particle sizes can change; and carbon, particularly semi VOC can burn off. You want to warm the air when necessary but not over cook it or burn it. Plus anything in the enclosure is a potential PM emitter and source of contamination as you move it from site to site.

Also, not to be a kill joy, but you don't want to paint the enclosure. It would be another potential source of contamination.

Yeah I was thinking the same with the paint, introduces another source for pollutants.

When I called the Dylos folks, they said that the device will not break at temperatures below 32 Fahrenheit, but it will become increasingly inaccurate, so they recommended shooting for 40 degrees Fahrenheit to be safe.

I'm revisiting your note, just want to say again how cool this is! great to see you're still up and posting data.

Thanks @mathew! Has certainly been an adventure. Only consistent issue has been school internet security protocols- they treat the Raspberry Pi as an unknown device and block the posts. Fortunately we have been able to find a workaround at both schools.

I was planning on blogging about the results, but there has not been anything particularly concerning thus far! I am trying to figure out if the monitor is placed in the wrong place, or maybe the buses are just not putting out that much PM2.5. Trying to do the same thing with a NO2/CO sensor as well, but I am having a hard time finding one that is accurate and reasonably priced. Monitor currently located about 100 feet from bus dropoff/pickup.

hah! school networks are always a problem.

I posted a note recently on hotspot identification, the first stage of which involved a systematic survey with an optical monitor (like the dylos). I'm new to the idea, but wondering if these kind of 6-minute "snapshots" of different spots couldn't help pin down where the emissions are going. https://publiclab.org/notes/mathew/04-06-2016/mapping-dust-hotspots-with-low-cost-monitors

Wow that is super interesting. That would definitely cover the variation over space... but what about if the levels vary over time in each particular place? Even a couple 6 minute sample times would not be able to cover variation over the course of the day.

Unless that is part of the author's point, that variation over time is minimal compared to variation over space?

the authors did two levels of survey-- first the 6 minute 'snapshots' and then they used that to determine where to place passive monitors for long-term characterization. The second heat map is based multi-week monitoring at each site, using 7-day passive samples. So lower temporal resolution, but capturing the week-to-week average exposure hotspots.

Temporal variation is a big deal, but here they were just trying to demonstrate a means of characterizing spacial variability on the cheap using monitors that don't require power.

Ahhh I see. And it looks like both ways showed that there is a big plume of particulates coming out of the rock quarry that dissipated over the right side of town.

Great discussion and a lot of good ideas. The AQ-SPEC group (www.aqmd.gov/aq-spec) has published results on several PM sensors other than the Dylos. Particularly interesting is the performance of the "Purple Air" sensor ($150/unit) and the widely used Alphasense OPC-N2 monitor (which provides 3 size fractions and 16 size bins). I am personally more familiar w/ the hardware than the software (just stare using the RPi) and would be more than willing to collaborate with people that have good ideas on how to build a small sensor network. I have been looking into AWS IoT and products like Splunk for structuring, sorting, and plotting sensor data. Anyway...I am digressing. Great job w/ this Dylos project and keep up the good work :)

Thanks @drapoli! Yeah, when I built this thing I had not heard of Purple Air, I am really interested to learn more about it. The AQMD site has done a really good job of staying up to date and keeping up with new tech.

Hi @kevinvivergy, i have just tagged this note as an activity that others could try as well. I did this by adding the tag activity:open-air. If you could scroll up to the tag area on this note and click "click here" in the blue box to fill in the other details, it would help people find these instructions and try to build one themselves. Thanks and let me know any questions, i can support.

Can do @liz, any in particular you would recommend? Not familiar with the system!

Hey @kevinvivergy it's so great to hear from you!

Here's the blue tagging assistance box that you will see when you click on "click here":

...Within those questions, there are clickable links for finding out more about what each tag means.

Any more questions? Also, feel free to call me at +1 336-269-1539.