Air Quality Measurements
Singapore is facing a severe haze crisis. Besides the subjective " this is bad", I got curious how the official air quality gets reported. Singapore's National Environment Agency uses the US devised Pollution Standard Index, but reports that onlt only as 24h, but also 3 h average for different places in the republic. Besides that they report the 2.5µ particle (PM2.5) count that isn't part of the PSI ( PM stands for particulate matter).
So far it feels like the information is genuine. Nevertheless knowing how an abstract number is formed is the first step to independent verification. With a little digging NEA provides the detailed instructions how the value is computed. The substances measured are: Sulphur dioxide (µg/m³). Particles with 10µ or more size (µg/m³), Carbon Monoxide (mg/m³), Ozone (µg/m³) and Nitrogene dioxide (µg/m³) which NEA publishes separately including a haze map:
Source: NEA
A quick check on Google reveals, that air quality measurement is quite a popular application both with Arduino as well as the Raspberry PI (there are more). It seems the Arduino has an edge when it comes to coupling the sensors, while the Raspberry PI shines in aggregation and web accessibility. Probably a combination of both would be a winner. Something like the Pinoccio meshed with a Raspberry Pi powered CouchDB for aggregation.
The real challenge however are the sensors (and their calibration later on). The PSI measurements are in weight per volume, while most of the data sheets for the sensors I found state sensitivity in particles per million (PPM) or particles per billion (PPB). Luckily LennTech provides an online calculator to transcribe the values for us:
The PM concentration can't be converted from weight/volume into ppm using a static formula, since particles can be anything with different weight. It needs to be measured.
So the hunt for suitable sensors starts. SO2 seems to be the biggest item on the list. I've looked so far at the following providers:
So far it feels like the information is genuine. Nevertheless knowing how an abstract number is formed is the first step to independent verification. With a little digging NEA provides the detailed instructions how the value is computed. The substances measured are: Sulphur dioxide (µg/m³). Particles with 10µ or more size (µg/m³), Carbon Monoxide (mg/m³), Ozone (µg/m³) and Nitrogene dioxide (µg/m³) which NEA publishes separately including a haze map:
Source: NEA
A quick check on Google reveals, that air quality measurement is quite a popular application both with Arduino as well as the Raspberry PI (there are more). It seems the Arduino has an edge when it comes to coupling the sensors, while the Raspberry PI shines in aggregation and web accessibility. Probably a combination of both would be a winner. Something like the Pinoccio meshed with a Raspberry Pi powered CouchDB for aggregation.
The real challenge however are the sensors (and their calibration later on). The PSI measurements are in weight per volume, while most of the data sheets for the sensors I found state sensitivity in particles per million (PPM) or particles per billion (PPB). Luckily LennTech provides an online calculator to transcribe the values for us:
| Substance | range (weight/volume) | Parts per million | Parts per billion |
|---|---|---|---|
| Sulphur dioxide | 80-2620 µg/m³ | 0.0284 - 0.9289 | 28.4 - 928.9 |
| Carbon monoxide | 5-57.5 mg/m³ | 4.05 -46.6 | 4050 - 46600 |
| Ozone | 118-1180 µg/m³ | 0.0558 - 0.558 | 55.8 - 558 |
| Nitrogen dioxide | 1130 - 3750 µg/m³ | 0.558 - 1.85 | 558 - 1850 |
So the hunt for suitable sensors starts. SO2 seems to be the biggest item on the list. I've looked so far at the following providers:
- Futurlec (no luck with SO2 here)
- Alphasense
- Aliexpress (most of the stuff is made in China anyway) - with an impressive 75 different gas sensors rom just one company
- Sparkfun (of course) - no luck on SO2,
- Parallax
- The Sensor Portal
Posted by Stephan H Wissel on 23 June 2013 | Comments (1) | categories: After hours Singapore