I started down the air pollution measurement path with the “MQ” series of sensors and then after getting widely different results under the same conditions, I decided to switch to measuring particle counts. Like a few others I have read about, I excited about doing air pollution work because I suffered from respiratory attacks that were (finally) chased down to air pollution as the root cause.
However, the cheap PM sensors also showed variability and came with instructions of converting pulse durations or voltages into particle counts, but not into PM2.5 or PM10 measures. So I raised money ($4K) for a school project and purchased a PM2.5 sensor from Shinyei the AES-1 or PMS-1 – this was the least expensive one I could find – still cost me $1000! Shinyei says it is calibrated to the SHARP5030, an instrument that costs $15K, using the “Federal Equivalence Method”.
I hooked up the PPD42NS and the PPD60PV-T2 (courtesy Michael Heimbinder) to a Raspberry-Pi and the AES to the net and made measurements. While the correlation was not great, the T2 was much better than the 42. These plots are all taken from TempoDB, an excellent time-series cloud database that is super easy to write to and read from. All my data is stored there.
I got the idea of adding a fan from Tim Dye. After much trial and error I found that as airtight a seal between the sensor and the fan is needed to get better results. But when I did that successfully (more on this later), the results were much much better than relying on the heater in the sensor. Below is the plot of the T2 with the fan compare to the T2 without the fan above.
The vertical axis is the PCS count reported by either mapping the analog voltage or the low pulse occupancy from the Shinyei data sheets. A lot of the variability (called “noise”) in the T2 without the fan has gone away when the fan was added!
Now what remains is to compare the T2 with and without the fan to the AES1 PM2.5 sensor.
Next…..Calibrating the T2 with the fan with the Shinyei AES-1