Air pollution contributed to 6.5 million premature deaths worldwide in 2015 – similar to deaths from smoking . Burning of carbon based fuels in industry, homes and vehicle engines, pollutes the air, especially when the fuels are impure or are burnt in a poorly controlled manner. In European cities like London, road transport is one of the main sources of air pollution - by the exhaust gases and by dust from tyre and brake wear. For certain types of pollutants, low-cost meters are now available, one of which is described on this page.
There is plenty of excellent material available on the web about air pollution, but specifically on air pollution and low cost sensors, see:
The World Air Quality Index project which is a social enterprise project started in 2007. Its mission is to promote Air Pollution awareness and provide a unified Air Quality information for the whole world. The project is proving a transparent Air Quality information for more than 80 countries, covering more than 10,000 stations in 800 major cities, via those two websites: aqicn.org and waqi.info. The base team is located in Beijing, China and composed of several contributors in the domain Environmental Sciences, System Engineering, Data Science and Visualization, Machine Learning as well as Visual Design. The team has been expanding worldwide, and several contributors, located in Singapore, India, Australia and USA are now also supporting the project.
A number of low-cost meters for various types of pollutants are now available via eBay from sellers in China. The specifications provided in the seller's advertisement can be a bit limited. However, typically these devices will be based on a module or sensor provided by a specialist company, and with luck the seller will specify what module/sensor the device uses. You can therefore also search on-line for the specifications of the module/sensor provided by its manufacturer.
What we want to know about a meter is:
Does it actually measure the pollutant of interest, e.g. PM2.5 as opposed to any size of dust?
Is the device and any module/sensor it is based on, sensitive enough to detect the pollutant at the concentrations you are interested in? Remember that pollution levels in Chinese cities are often much higher than in Europe so the device may still be useful there even if it isn't sensitive enough to measure European levels.
Is the device accurate? This is hard to assess unless detailed specifications have been supplied (and the manufacturer appears trustworthy) or you can find on-line some evaluations of the device and/or the module/sensor it uses. Ideally one would test the device by exposing it to known concentrations of the pollutant and confirming that it reads correctly - but such tests require proper laboratory equipment unavailable to a DIYer. You can get some confidence by taking readings with the meter and subsequently comparing them to published data for your town or city, but be aware that pollutant levels can be very variable, especially if you are near a pollution source such as a busy road and one moment a gust of wind wafts a truck exhaust to your meter and the next moment the wind shifts and blows the road pollution away from you. Another possibility is to buy more than one meter and compare readings when they are operated side by side: if they match it gives re-assurance that the meter provides consistent readings, though not proof of accuracy; if they differ substantially then at least one of the two units is clearly inaccurate - you could investigate with different pollution levels to see if the meters at least move in the same direction (i.e. both read higher or both read lower) and if the difference is a constant offset (by a fixed amount or a fixed percentage)!
A number of meters are available on eBay for measuring particulates. I bought a couple of these to try.
The first to arrive has a simple numerical readout that claims to be the PM2.5 concentration in ug/m3 (micrograms per cubic meter). I could get no reading above zero on this except by creating household dust (banging a cushion!) next to it. On opening the meter I could see that it contains an 'Optical Dust Sensor' from a reputable company (Sharp) but on looking up the data sheet for this sensor, there is no indication that it can distinguish dust particles of 2.5 micron size and the concentration levels of PM2.5 that I would like to measure are at the very bottom of its quoted operating range (so it might not detect those levels at all).
The second meter looks much more promising. Its display shows concentration for both PM2.5 and PM10 as well as ambient temperature and humidity. It is based on a laser sensor from the company 'Plantower' (www.plantower.com): it's the small blue metal box visible within the unit. I found some tests that have been carried out on the Plantower sensor by he World Air Quality Index project which look encouraging, they seem to show that multiple sensors located together give reasonably consistent readings with one another: (http://aqicn.org/sensor/pms5003-7003/).
Other evaluations of Plantower sensors include:
This second meter is sold as "Household PM2.5 Detector Module Air Quality Dust Sensor LCD Display Monitor UK" and is available I think from more than one eBay seller (e.g. from (comyur) for about £38.
Particulates Meter: (1) Display; (2) Showing the Plantower module contained within it.
Constructing a Power Supply for the PM2.5 Meter
This meter has no power supply; it gets its power from a micro-usb connector. You can use a standard 'micro-USB to USB' cable and connect it to a powered device such as a laptop. However, as it’s not convenient to carry around a laptop just to power the meter, I use a small module that provides a powered USB connector when connected to a PP3 9v battery. To do this you need:
The module that provides the 5V USB supply: "6V-12V-24V to 5V 3A CAR USB Charger Module DC Buck step down voltage Converter" (available from eBay seller: haiy_95inliao. NOTE: You will need a soldering iron to attach the battery leads to this module - the + and - connections are the two square pads on the right hand corners.
A 9V PP3 (ideally Rechargeable) Battery.
A PP3 Battery Clip Connector with leads (lots of suppliers on eBay).
You may also want to include an ON/OFF switch in the circuit as there is none on the device.
The Meter connected by the 'micro-USB to USB' cable to the completed power supply box. The ON/OFF switch is mounted at one end of the box.
What goes inside the power supply box: (LEFT) the power supply module with the USB cable plugged into it and the battery leads soldered on (all wrapped in black tape); (RIGHT) the 9V PP3 battery.
I measured the power consumption from the 9V PP3 battery when the meter is operating, as 87mA with peaks every 2 seconds or so of 106mA. The rechargeable 9V PP3 battery I'm using is labelled as having a capacity of 250mAh so hopefully it should be possible to run the meter for about two hours if it started fully charged. A non-rechargeable alkaline battery has a capacity of about 550mAh and thus should run the meter for about 5 hours. The reading seems to settle within about a minute of the meter being switched on so maybe to conserve the battery power it is acceptable to only turn it on shortly before making a measurement.
Readings I obtain with the unit out and about in London, seem realistic when compared to published data. For PM2.5 background readings in my quiet London street are typically 4 to 10, readings near a major road nearer 20, walking past a mobile diesel compressor for a pneumatic drill gave 30, standing next to a smoker gave several hundred!
More recently I built the unit into a box. The unit is at the left side of the box which has that end open to the air and lateral ventilation holes, so that the unit's fan can draw in the air to measure. The other side of the box contains exactly the same power module and battery as before. As it can be difficult to read the display in bright sun, a detachable hood can be placed on top (made from a plastic flower pot!).
The unit boxed: (1) The unit's fan is near the open end of the box; (2) The detachable hood.
I have looked for a low-cost NOx meter but haven't been able to find anything suitable - I suspect it's more difficult to measure. I found a sensor which needs to be built into a meter but that looks like it may not be sensitive enough for the levels of NOx of interest.
To Be Written.