Awesome!

On Tue, Nov 27, 2018, 11:45 PM \<notifications@publiclab.org wrote:

Public Lab contributor cfastie just posted a new research note entitled ' Nano particle monitoring':

Read and respond to the post here: https://publiclab.org/notes/cfastie/11-28-2018/nano-particle-monitoring

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PurpleAir air quality monitors send data about particles in the air to the web via WiFi. One version of the PurpleAir monitor saves the data to a microSD card. The number of particles in five size classes are reported in addition to three EPA PM standards (PM 10, PM 2.5, and PM 1.0). The devices cost $180 to $260. PurpleAir is not open source, but they provide a lot of information about the hardware. The $259 PA-II-SD seems to include the following components:

1. Plantower PMS5003 air particle sensor
2. BME280 temperature, humidity, and pressure sensor
3. ESP8266 microcontroller
4. microSD card module and card
5. Real-time clock

The PA-II and PA-II-SD monitors have "dual laser counters." I don't know what this means. Do they have two Plantower PMS5003 sensors? The ESP8266 is an Arduino-like microcontroller with integrated WiFi. All PurpleAir monitors use this microcontroller.

Figure 1. A Plantower PMS7003 particle sensor. This is a newer model than the PMS5003 and is half the size. It seems to operate the same as the PMS5003 and uses the same connections and code.

I bought the five components above on eBay for $32.00. As a test, I built a prototype monitor with a Nano Data Logger instead of the ESP8266. This poor man's version does not have WiFi capability but instead saves the data to microSD card like the PA-II_SD.

Figure 2. A Nano Data Logger with PMS7003 sensor and BME280 sensor. Data from both sensors are saved to the microSD card every minute. The Nano logging shield includes a real-time clock. Especially for outdoor monitoring, it is handy to have temperature and humidity data when interpreting the particle results.

The Nano Data Logger version of the particle monitor can be assembled without soldering. The Arduino Nano snaps into the logging shield which includes an SD card slot and real-time clock. The Nano is a 5 volt Arduino and the Plantower sensor requires 5 volts. The BME280 sensor requires 3 volts. The Nano has one 5v pin, one 3v pin, and two ground pins so seven DuPont wires can be slid on to make all the needed connections.

Figure 3. The PMS7003 particle sensor (blue, top) and a CCS-811 gas sensor (left, purple) installed in the case. The gas sensor and the BME280 are I2C sensors and connect the same way.

Figure 4. The Nano Data Logger (Arduino Nano plus logging shield) installed in the case. A USB cable plugs into the Nano to supply 5 volts of power from a phone charger.

Making connections to the PMS7003 sensor is a little confusing. It has a 10-pin connector which does not fit anything I have around the house. Mine came with a handy connector and cable with Molex 053261-0871 terminations. I didn't have anything to plug that connector into, but that is not required. The connector that plugs into the sensor also has regular 0.1 inch pins for the four important connections. In fact, only three of these are required to use the sensor (power, ground, TX). Adafruit has good instructions for making the connections.

Figure 5. The 10 pin connector on the PMS7003 sensor.

Figure 6. The connector and cable that came with the sensor. The cable is not needed. Three of the four pins broken out on the connector board are all that is needed to operate the sensor.

Figure 7. The connector plugged into the sensor and three DuPont wires connecting it to the Arduino.

I built three data loggers with PMS7003 sensors. Two also had CCS-811 gas sensors which report an estimate of volatile organic compounds (VOCs). These seemed more interesting that the BME280 temperature-humidity-pressure sensors in the PurpleAir monitors. The third monitor I built had an LCD which displayed PM 2.5 in real time.

Figure 8. The three monitors with PMS7003 sensors were on my mantle for several days. The woodstove directly below was burning 24/7 for those days.

The first test of the monitors was to operate three of them together to see if they sensed the same thing. The monitors were directly above my woodstove so I assumed I would record a pulse of particles and gas everytime I opened the stove door to add wood. The monitors collected data from the sensors every second and computed an average of 60 readings. So an average result was saved to SD card about once per minute.

Figure 9. Six days of PM 2.5 data from three PMS7003 particle sensors on my mantle. The letters in the middle panel: a. I cooked some bacon (I have no kitchen exhaust fan and the kitchen is 15 feet from the woodstove.) b. I tossed some wood ashes into the woodstove fan (which blows into the room). c. I was invited to Thanksgiving so I took Sensor #2 and ran it during dinner. The other two sensors stayed home alone. d. I tossed some more ashes into the fan (fun things should be done more than once). e. I vacuumed the room (some fun things make a mess). f. I accidentally spilled some wood ashes into the fan. g. I cooked pancakes (Wow). h. I don't know what this or the later peaks are because I got tired of writing everything down.

During the test the three PMS7003 sensors responded very similarly to indoor pollution events. This is very encouraging. Wood ashes must be too big to register strongly as PM 2.5 because there were a lot of ashes in the room and the sensor response was subtle. Cooking with oil in a hot pan and adding pancake batter produces a lot of PM 2.5 (also PM 1.0 and PM 10). It was 5°F outside so I didn't open a window, but I have to remember to do that next time. It took several hours to clear the air.

Figure 10. A closer look at the data from the two days after the pancake cloud dispersed. All three PM indexes are included from one of the three sensors.

I could not detect an association between opening the woodstove door and increased particulate matter. I have not yet looked closely at the gas sensor results for this period.

The files to print the small case for the Nano Data Logger and Plantower PMS7003 are at Thingiverse.

The sketch running on the Nano Data Logger (with PMS7003 and CCS-811) is here:NanoVOC7003v1.0.txt

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I'm going to be loling about Poorple all night! Amazing work, chris! And yes, I believe Purple has two of the same sensors to catch any low hanging fruit errors. This post is such a gem.

Thanks Nick. It's good to know about the duplicate sensors. That's an intriguing engineering decision.

Chris

@stevie awards a barnstar to cfastie for their awesome contribution!

I'm so excited to see this @cfastie. Love the play on words as always with the naming of the monitor. However, you may want to rename your research note because I thought you actually meant measuring nano-particles for air quality--that would be something! Would you be willing to lend one of your Poorple specials so I can test a fan/HEPA setup?

Leslie, I will lend you anything you need. Tell me about your HEPA setup. You must already have a 5V Arduino, so all you need is three DuPont wires to connect a Plantower sensor and display readings on the serial monitor. If you want to log data, I think you have an RTC and SD module so all you need is a Plantower. Until Trump pulls out of the UPU, it doesn't cost much more to order a Plantower on eBay than to pay USPS to get mine to you. Then you can test your HEPA fan till the dust settles.

Love this. I am definitely going to try building this at some point, but don't have the time right now. Perhaps after January term.

I am coming back now to work on this with a couple students. We have purchased the Arduino Nano boards since we are hoping to use these units remotely in the Amazon. We have also purchased the BME280 temp/pres boards, PMS7003 counters with interface boards and wires, and the real time clock with built in SD card slot. I have also purchased the WiFi units (ESP8266) for a later upgrade. Admittedly, this is all new to me, but it seems the sketch above is for the VOC chip rather than the BME280. Do you happen to have a sketch for the "Poor Man's" version you described above? Also, I don't see any mention of the indicator LED, I have a spot for it in my enclosure, but would love to know what pins to wire to. Thanks for the help!