Nitrogen Dioxide

Why is it useful to measure nitrogen dioxide?

Nitrogen dioxide is a harmful gas that is released during high temperature combustion. For example, think of fuel in the engine of a car. The gas is also known by the scientific spelling NO ₂ . Especially (older) diesel engines still emit a lot of nitrogen dioxide. Traffic is responsible for more than half of NO ₂ emissions. That is why this gas is an excellent benchmark for measuring air pollution from traffic.

Measuring method

You can easily measure the concentration of nitrogen dioxide yourself with special tubes through which air flows. These tubes are more than 7 centimeters long. Inside is a mesh containing a chemical (TEA) that traps the nitrogen dioxide from the air. When you stop the measurement period, usually after 2 to 4 weeks, you send the sealed tube to the lab where scientists determine the amount of NO ₂ on the gauze. Then they calculate the average concentration of the gas during your measurement.

We also call these tubes ' passive samplers' because they do not actively suck in the air. The most commonly used samplers are the Palmes diffusion tubes and are available from BuroBlauw, among others.

Scientists use the rather expensive official measuring devices to measure nitrogen dioxide. That is why scientists, companies and citizens are fully developing NO ₂ sensors as an alternative. Unfortunately, the current offer is not yet very reliable and we therefore do not recommend it. More information can be found at the VAQUUMS project . We explain below how to get started with a sampler. Most tips are also useful when you work with a sensor.

How do you measure the concentration of nitrogen dioxide?

Before starting the experiment:

Check the situation in your area . What information is already available? Are there already similar measurements known in your area? Take a look at CurieuzeNeuzen , on the website of the Flemish Environment Agency and on the data portal .

Think about how many samplers you need. Keep these tips in mind for this:

1. Where are you going to hang the samplers? Choose a place where you breathe the air every day.
2. Order 2 or 3 measuring tubes per measuring location. This way you can easily check whether a measurement is correct. In addition, you lose less data if a tube has measured poorly. Normally, the difference between tubes in the same location should be less than 20%.
3. Provide some unused/blank samplers for checking . You hang these tubes unopened at your measurement locations.
4. Also choose one or more control places where you expect little air pollution, for example in your garden.
5. Possibly hang one or more samplers close to official measuring stations for checking. The results of the samplers sometimes deviate a bit from the official measurements. Therefore, compare the results of a few control tubes with the official measuring equipment in your area afterwards. This is called 'rescaling' or 'calibration' and it reduces the measurement uncertainty of your result.

To work

• Store the measuring tubes in the refrigerator beforehand.
• Make sure that the air can flow freely around the opening of your sampler. Therefore, fix the sampler to a tube or beam. Or attach the measuring tubes in a special tube for a more reliable measurement. You can usually rent or buy the tube together with the tubes.
• To start the measurements, remove the caps from the samplers. Any unused 'blank' measuring tubes must remain closed.
• Keep the caps well: you will need them afterwards to close the tubes again.
• Note the time at which the measurement starts, so you can calculate the exact duration of your measurement afterwards

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.
• Leave the measuring tubes hanging for 2 to 4 weeks. You don't have to do anything in the meantime. Check every now and then that everything is in order. At the end of the measurements, collect the samplers and close them again with the yellow caps. Note the time when the measurement stops.
• After the measurements, it is best to keep your measuring tubes in the refrigerator until you send them to the BuroBlauw laboratory for analysis. Note that the samplers must also remain cool during shipment.

After your experiment

• The lab will send you measurement results after analysis. 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, the cooling during transport or was there an exceptional weather phenomenon?
• The Flemish Environment Agency annually calculates one calibration function for the samplers of BuroBlauw. These measuring tubes hang in tubes for 2 weeks for sampling.
• Compare the result of the control measuring tubes that you have hung near the official measuring equipment. Look here for official measurement locations and model maps for Flanders and the Netherlands . You can also contact CurieuzeNeuzen or the data portal of the Dutch National Institute for Public Health and the Environment ( RIVM). Do your control results deviate? Then it is necessary to 'rescale' or 'calibrate' all your results.

Attention! Models also have their limitations . In addition, the weather influences the concentrations of NO ₂ in the air. The Flemish Environment Agency annually calculates one calibration function for its own BuroBlauw samplers that are sampled in tubes during 2 weeks. See the guidelinesfor more information on how to convert your result from a month of a NO ₂ sampler to a period of 12 months.

Which situations can you measure?

Discover the NO ₂ concentration in your street

What is the average NO ₂ concentration in your street? Hang up measuring tubes and do your own research! The longer the period in which you collect more data, the better you can estimate the annual average.
Did you know that the World Health Organization (WHO) and the European Union (EU) stipulate that the annual average nitrogen dioxide should not exceed 10 micrograms per cubic meter (10 µg/m³)? What do you think, is your street doing better?

Examine your personal exposure with passive samplers.

Although a passive sampler is usually set up in one fixed location, you can also try to compare the personal exposure of a group of people. You therefore perform a combination of 'stationary' and 'mobile' measurements.

It is best to use a different type of sampler that is designed for shorter exposure periods (from 8 to 48 hours, for example). In any case, with this approach it is best to first perform some test measurements to investigate whether your measurement period is sufficiently long.

With this approach, also take into account possible indoor NO ₂ sources, such as gas stoves, for example. You can also close your samplers in between and only examine certain parts of the day, such as only your time on the road and at work or school. In any case, keep a close eye on how long you measure exactly.

If you want to measure during your route to or from work or school, it is best to take a look at your route in advance on existing model maps. By comparing different routes you get an idea of the least harmful route.

More information about the use of passive samplers for personal exposure can be found in these two scientific publications: Passive dosimeters for nitrogen dioxide in personal/indoor air sampling: A review en Personal exposures to NO2 in the EXPOLIS-study and Relation to residential indoor, outdoor and workplace concentrations in Basel, Helsinki and Prague .