Volatile organic compounds

Why is it useful to measure VOCs?

Some VOCs, such as benzene, are carcinogenic. The aldehydes and ketones (A/K) such as formaldehyde, for example, should not be forgotten. These are harmful to our health. Other VOCs are harmful to the ozone layer. They are precursors in the formation of ozone .

In the appendix you get an overview of the VOC and A/C that are measured by the VMM with passive samplers. Those analyzed depend on occurrence and severity to effects.

Measuring technique

You can start measuring yourself, on the photo below you can see the system that you can use. Then you measure yourself with a passive VOC or A/K sampler. You are going to attach it to a system provided for this purpose and hang it up that way. The sampler consists of an adsorption tube in a casing, the so-called body. The body is yellow for VOS and blue for A/K. The bodies should be replaced after 5 periods of use, as the pores may clog or enlarge, which will change the rate of absorption. The samplers are always in a housing. Please note that the air flow must not be compromised by the housing. The opening of the housing is directed to the east, northeast to avoid rain ingress.

Passive samplers have the advantage of being small, light and easy to use. No electricity is needed to measure with this technique and shipping by post is possible. This makes this measurement technique suitable for large, widely distributed networks for screening as well as for shorter projects. Please note that both the passive samplers that measure volatile organic compounds and those that measure aldehydes/ketones must be kept cool from sampling to analysis.

Passive samplers can be used for many components, below we discuss the passive sampler technique for the component volatile organic compounds (VOC).

Passive sampler: working principle

The radial type sampler consists of a body into which a metal adsorption tube is inserted. This metal tube was filled in advance by the supplier with different phases of adsorption material on which VOC or A/K are adsorbed. The air can flow through the body and the components to be measured will adsorb to the phases of the sampler. After exposure to air for a certain period of time (typically 14 days), the adsorption tube is analyzed in a laboratory. You cannot do this yourself. For example, the laboratory can use gas chromatography with flame ionization detection for the analysis of VOCs and high performance liquid chromatography with ultraviolet detection for the analysis of A/K.

Which passive sampler do you choose?

The radial type passive sampler has a large diffusion area

Below in the photo an A/K sampler in a glass transport tube. Always be careful when opening and closing these tubes. After sampling, the sampler is also transported in this transport tube.

The VOC sampler is located in a double tube, namely an iron tube in a glass tube. This can be seen in the photo below. The iron tube has a side with a notch and a side without a notch. The sampler is taken in and out of the iron tube via the side without a notch. After you have carefully removed the two white caps, you need a pair of pliers with which you can remove the small metal sealing piece from the iron tube.

Start measuring

Make sure you have contact with a company or laboratory for the delivery of the samplers for VOC or A/K, and also for returning them refrigerated after the sample has been taken. Install a suitable housing in the places where you want to measure. Think of line or point sources that require a different location of the measuring points. Also provide a background measurement point where there are no local emissions of VOCs.

• Investigate your environment, and estimate where the major sources of VOCs are. Think of companies and industry, mainly in storage and transshipment activities of volatile (petro)chemical products, processing companies of train sleepers, but also, for example, road traffic and specific household products;
• Remember not to brush with products containing these substances around the sampler;
• Always use gloves when you hang up or take down the samplers;
• Hang the sampler at a height of one and a half to two meters;
• Work with fixed measurement periods, where you have to estimate the severity of the pollution because the passive samplers can quickly become saturated;
• Keep a logbook, in which you can note the periods with data, the weather conditions such as temperature, wind direction and precipitation and any events that may be important.

Interpret your results

The analysis results come from the laboratory. Compare the analysis results from the lab with the data from your logbook to make correct interpretations. You now have an idea of the VOC and A/K concentration in the ambient air. You cannot yet decide how much VOC and A/C comes from a specific source. You can compare with measurements on the VMM website.