soot

Why is it useful to measure soot?

Soot is part of fine dust. It mainly consists of particles that are created by incomplete combustion of fossil and other fuels. For example, think of diesel, wood or coal. Soot is also known as black carbon and has the scientific abbreviation BC (" black carbon ").
Traffic and households are by far the 2 main sources of soot emissions. Traffic mainly concerns the combustion of diesel and to a lesser extent petrol. Households mainly emit soot by burning wood in stoves and fireplaces. The more traffic you see on the street, the more soot you measure in the air. The consequences of these emissions for your health are significant. In addition, soot retains heat, which has an impact on the climate. That is why it is interesting to determine the soot concentration in your area yourself.
More information about soot can be found on the website of the Flemish Environment Agency .

Measuring method

To measure the soot concentration, use a soot monitor or aetholometer . At home you can get started with the small version of the soot monitors, the microAeth or AE51 .
This unit draws in air while the filter inside retains the soot particles from the drawn-in air. The darker the filter contains the more soot it contains. The monitor measures the number of soot particles in the filter through light absorption : the extent to which the filter allows less light to pass through is a measure of the soot in the air.
The AE51 is a small device (12 x 7 x 4 cm) and also very light (280 g). This makes it very suitable for short and/or mobile measurement campaigns. Thanks to the built-in battery, it lasts up to 24 hours. If you plan longer measuring periods, simply connect the device to the electricity grid. Remember to replace the filter every 2 to 3 days, depending on the amount of soot.
The aethalometer measures the soot concentration permanently, but you cannot read the measurements on a display. If you connect the device to a laptop, you can follow the measurements in real time.
After the measurements, you can read the data via a PC or laptop. You will receive the software for this when you pick up the devices.
At certain institutions, such as the PIH in Antwerp , the PCM in Ghent or VITO in Mol , you can borrow a portable soot monitor for a fee.
More technical information and tips for concrete applications of the AE51 can be found on the Aethlabs website .

How do you measure the soot concentration?

Before you start the experiment

• Check 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 the latest measurements or model maps ( Flanders , the Netherlands ).
• The readings may vary widely over time, due to both the source's emission pattern and the weather. We recommend that you measure for a sufficient time in the same place. It is also best to measure at a reference location where you expect little air pollution. This is how you calculate the local net contribution and track variations in the background concentration.
• It is better not to measure during a rain shower. The concentrations of BC are then lower than when it is dry. In addition, soot monitors are expensive devices that should not get wet, so only measure during dry weather conditions . Attention: the flexible air supply casing must always remain free.
• Set the time resolution of your aethalometer yourself: if you expect large differences in a short time because, for example, you are cycling through the city, it is best to use a short time resolution such as 10 seconds. For measurements at a fixed location, it is better to determine the average over 5 minutes.
• The soot concentration clearly varies in space and time . Weather conditions, location and traffic, among other things, have a major influence:
  • More traffic increases the local soot concentration. Which type of vehicles do you see most: passenger cars, vans or trucks? The soot emissions from diesel cars are also much higher than from petrol cars. The higher the Euro standard of the vehicle, the lower the soot emissions.
  • With mobile measurements where you walk or cycle, it is useful to save your route on a GPS or to note where you are at regular intervals. This helps you to properly interpret the measurements afterwards.
  • On dry, windless days there is usually more soot than on windy days or when it has just rained.
  • Always keep a log in which you write down all this data

To work

• If necessary, perform your measurement several times in the same place. This gives you a more reliable picture of the measurement location and also a view of the variation from day to day.
• Where do you hang your soot monitor? Choose a place where you breathe the air every day.
• Make sure that the air can flow freely around the opening of your measuring device.
• Determine the accuracy of your aethalometer. To do this, compare it with a reference monitor in the nearest VMM or RIVM monitoring station.
• In addition to the real measurements at measuring stations, the Flemish Environment Agency draws up models with the concentrations of BC in places where we do not measure. These model results also give you an idea of what concentrations you can expect. Note, however, that the time resolution used is taken into account.
• Take your measurement for a while with two or three devices at the same time in the same place. Check whether there are differences between the devices. Do they measure the same?

During your experiment

Note the external circumstances in your log : renovations, street works or the weather.

After your experiment

After the measurements, you can read the data via a PC or laptop. You will receive the software for this when you pick up the devices.

• View the data with a critical eye. Are there measurements that give a strange result? Or that strongly deviate from the complete measurement series? Perhaps there was a problem with your test set-up, an electronic problem with your device or there were exceptional circumstances.
• At very high soot concentrations, the filter becomes saturated in a short time and you can no longer measure correctly. This can occur, for example, in the event of a fire in the vicinity or during measurements near a soot source.
• Measurement results with a high time resolution are best viewed over a longer period of time. This way you get more reliable results.

Need more information about how to correctly prepare a test? Read the guidelines for measuring yourself.

Which situations can you measure?

Determine the concentration of black carbon on your cycling route

Take a look at your route in advance on existing model maps on which you outline your route. What is the BC concentration on your route? What is the least harmful route? Then think about your test design.

Soot measurements are very suitable for comparing cycling routes. This kind of research was carried out a few years ago by researchers from the University of Antwerp. More information can be found in this scientific article.

It is useful to know whether your sensor still registers the same after one month as it did at the beginning of the month. Therefore, carry out some measurements again.

Keep track of what time you leave and arrive exactly. During rush hours, the values will be higher than during off-peak hours. It is best to do this several times to get a representative picture. One-off effects (eg a heavy rain shower or traffic jam) then play a much less important role. The following also applies here: it is best to measure as much and for as long as possible to get a correct picture.

For those who want to carry out this type of research on a larger scale, VITO has developed a user-friendly and scientifically substantiated measurement platform with AirQmap . It allows you to map the air quality at street level for a larger area by repeatedly carrying out soot measurements by bicycle. More information can be found on the VITO website .

Measure the difference between the street side and the garden

Comparative measurements provide the most interesting information. You then measure simultaneously in several places so that you eliminate the possible influence of changing weather conditions. Check out this example:

• The figure shows the soot concentration on the street ( BC street ) and in a background location with less traffic ( BC rear) . Both measurements took place on the same day from 8 am to 11 am.
• There was almost always more soot on the street side (BC street) than on the background location (BC rear). On the street side you notice more changes over time due to the differences in local traffic. Have you got a taste for it? Count the traffic in your street (manually or with a Telraam ) to collect even more additional information.