fine dust
Why is it useful to measure particulate matter?
Particulate matter is a mixture of very small particles that float in the air. It is an important form of air pollution and very harmful to health. The scientific abbreviation is PM. Wood burning in stoves and fireplaces is the main local source of particulate matter, followed by traffic and industry.
There are different types of fine dust. Outside, for example, you will find a lot of ' secondary particulate matter ': particles that are created by chemical reactions of ammonia with nitrogen dioxide or sulfur dioxide.
When we measure the concentration of particulate matter, the size of the particles is also important. For example, PM 10 are particles smaller than 10 micrometers, and PM 2.5 particles smaller than 2.5 micrometers. A micrometer is one thousandth of a millimeter. Really tiny, but very harmful to your lungs.
More information can be found on the website of the Flemish Environment Agency.
Measuring method
You can measure fine dust yourself with fine dust sensors. These devices all work in the same way:
- A small fan or a heat resistance draws in air.
- The sucked in air moves through a beam of light from an LED or laser lamp.
- A detector measures how the dust particles in this air deflect the light beam. This phenomenon is called scattering .
The detector actually measures the light pulses, say light flashes, that cause this scattering of the light. Those pulses are a measure of the number and mass of the particles in the air.
By multiplying the value of the light pulses by the average mass density of a dust particle, the sensor calculates the mass concentration (often expressed in micrograms per cubic meter, or µg/m 3 ).
With a well-adjusted sensor you can measure the proportion of PM2.5 particles in a fairly reliable way. The reliability for measuring larger particles is usually much less good.
When the difference between the concentration of PM 10 and PM 2.5 is large, ie when there are relatively many large particles, the PM 10 value of the sensor is rarely reliable.
Even with high humidity you have to be careful with the sensor measurements. From about 80% relative humidity, certain particles grow strongly because they absorb water. This causes them to scatter more light and the sensors overestimate the concentrations.
Even the smallest particles, the so-called ultra-fine dust (UFP) that are smaller than 100 nanometers, are difficult to measure with the cheaper sensors. Because the mass of these particles is usually very small relative to the mass of the larger particles, their presence usually has little or no effect on the PM concentrations shown.
Which sensor do you choose?
In our region, the Nova Fitness SDS011 is the most commonly used sensor. In the LIFE VAQUUMS project , the Flemish Environmental Agency, together with two Dutch partners (TNO and RIVM), conducted research into the reliability of particulate matter sensors. The researchers compared the measurements of the SDS011 and five other sensors over 400 days with official measurements.
The sensors were given a score based on five criteria. The final assessment depends on which criterion you take into account and whether you calibrate the data. Calibration means that you compare the measurements with official standards in order to determine the deviation of the device.
With some sensors calibration was necessary anyway ( Shinyei PPD60PV ) or strongly recommended ( Dylos DC 1700-PM, Plantower PMS7003 ). The frequently used Nova Fitness SDS011, the Honeywell HPMA 115S0 and the Winsen ZH03B already gave fairly reliable results without calibration. However, calibration also improves reliability here.
The calibration comparisons per sensor can be found under ' PM 2.5 comparison with gravimetric reference ' in the various chapters of the VAQUUMS field test report . To be sure, compare your individual device with an official measurement. The Sensiron SPS30 also delivers good results according to certain sources, but this sensor was not part of the VAQUUMS project.
Do you measure with multiple sensors in different places? Have them measure together at the same location for a while beforehand. This way you get an idea of the differences between them.
Which situations can you measure?
What impact do road works in your street have on particulate matter?
Attention! Road works may affect the air quality in your street in two ways.
- Closing off traffic may result in fewer emissions and less non-exhaust dust (such as dust from the wear of tires or brakes and the blown up ground dust).
- In addition, the works themselves often also bring a lot of dust.
Keep in mind that fine dust sensors have difficultymeasuring coarse dust and therefore probably underestimate the dust from construction or road works. Measuring this contribution is thus ' qualitative ' rather than 'quantitative' in nature: it gives a direction when there was extra pollution, but the measurement value measurement itself is probably not very accurate.
If you want to measure the effect of a measure, it is best to carry out a measurement beforehand . This way you notice the difference in your measurements. Because the weather usually has a very large effect on particulate matter concentrations, it is best to compare with a reference location where you do not expect the intervention to have an impact.
What is the impact of wood burning?
When burning wood, quite a lot of fine dust is released. This often results in high concentrations, especially at start-up, which can be clearly measured with particulate matter sensors.
Just this:
- Sources of particulate matter may be more or less present in certain seasons. Wood burning, for example, is especially a problem in the winter, although some people like to light a campfire in the summer as well.
- Wood smoke generally produces multiple, sharper peaks lasting a few seconds to minutes. This will give your graph a somewhat erratic course. If you see gradual increases, it is usually a regional phenomenon, often under the influence of the weather.
- Typical profile of a gradual variation of the regional background (see image)
- We already said that particulate matter concentrations vary greatly due to the weather. In windless weather, for example, pollution can accumulate and often a lot of secondary dust is created. You can follow these regional trends via the official measurements and via the general behavior of sensors in your environment . Therefore make a note of the weather in your log .
- You probably spend little time in front of your house. That is why a measurement at the rear of your home is most interesting. Combine this with measurements at home, even in places where you ventilate.
- Check the guidelines to keep in mind before, during and after your trial setup.
Build your own particulate matter meter
Would you like to start measuring yourself with a particulate matter sensor? Good idea! We are happy to help you on your way.
You can opt for a ready-made kit , where you only have to assemble the parts (the correct software is already installed), as shown in the video of the city of Roeselare.
You can also choose to do everything yourself, from ordering parts to installing the software. Then first view the extensive documentation on sensor.community . You might also want to read the frequently asked questions on Influencair.be .
Before you start the experiment
Check out the situation in your area. What information is already available? Has one of your neighbors already taken measurements? You may find the answer to your question in detailed computer models or in the official measurements of Flanders or the Netherlands .
- Make sure that the air can flow freely around the opening of your measuring device. Also avoid the proximity of, for example, the exhaust of a cooker hood.
- Outdoor air: you use the device at a fixed location in the open air. Think carefully about where you want to hang the sensors. On the street side is fine (for example on a windowsill on the 1st floor), but a measurement is also useful on the back wall, on the terrace or in the garden.
- Power supply: The power cord is a thin 5 V micro USB cable. You can usually plug the wire into a power outlet indoors without any problem and connect it to the device outside through a closed window.
- WiFi network: for the standard setup of sensor.community you need a permanent WiFi connection to store the data online and display it on the map.
- If necessary, place 2 or 3 sensors per measuring location. This way you lose less data if a device has technical problems and you can easily test whether one of your devices shows a deviating value.
- Request information from the manufacturer about the accuracy and range of your sensor under certain conditions (temperature, relative humidity).
To work
- Determine the reliability of your sensor by comparing it with a reference device in the nearest measuring station of the Flemish Environment Agency or the RIVM.
- In addition to the real measurements in measuring stations, the Flemish Environment Agency and the RIVM also draw up models with the concentrations of PM 10 and PM 2.5 in places where we do not measure. You can also use these model results for comparison. Keep in mind the time resolution (for example, do not compare a minute value with an annual average). Please note that not all local sources of particulate matter are included in the models.
- Make sure every part of your setup is watertight!
During your experiment
- Record in a log anything that may have an effect on your measurements. For example, think of the weather, renovations at the neighbors, working in your street or periods with smog. It is important to keep a good record of this information so that you can refer to it when interpreting the results.
- Be sure to check out the document ' Guidelines ' for self-measurement. There you will find more information on how to set up the test correctly.
After your experiment
- Download the data from your sensor . How you do this exactly depends on which sensor you use.
- View the data with a critical eye . Are there measurements that give a strange result? Or that strongly deviate from the complete measurement series? Maybe there was a problem with your test setup, an electronic problem with your sensor in exceptional circumstances.
Would you like to give a workshop yourself with more background information about air quality, the different measurement methods or the points for attention during measurements? Be sure to view the presentation below and the document about exactly how your particulate matter sensor works and consult the data on your smartphone
