Open Engineering
Environment and Development.

Air Pollution and DIY Measurement

Air pollution contributed to 6.5 million premature deaths worldwide in 2015 – similar to deaths from smoking [1]. 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:

Measuring Air Pollution Yourself

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:

Measuring Particulates (PM2.5, PM10).

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 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.

Measuring NOx.

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.

Air Pollution Overview

To Be Written.