Imagine you are lying on a beach in the sun and letting the sand trickle through your fingers. Fine sand has an average grain diameter of 0.5 mm/500 µm. The ratio of a grain of sand to a particle with a size of 0.5 µm/500 nm that is too small to be detected by the naked eye roughly corresponds to that of a rock with a diameter of 5 m to this grain of sand. This gives you an idea of the proportions we have to deal with when measuring particles.
It is necessary to know the mass or size distribution of particles in order to be able to evaluate their behaviour. There are a variety of measurement methods to do this, which depend not least on the properties of the particles. In this white paper, we want to provide you with basic information about the methods of particle measurement which are used at Testo and at the same time present our particle measuring instruments to you. You will find information and application examples here concerning 

• testo 338, the degree of blackening measuring instrument for flue gases from diesel engines
• testo 380, the fine particle measuring instrument for chimney sweeps according to the 1st German Federal Immission Control Ordinance (BImSchV)
• testo DiSCmini, the handheld measuring instrument for measuring the number concentration of nanoparticles
• testo NanoMet3, the PEMS (Portable Emission Measurement System) for measuring nanoparticle emissions on vehicles.

Do you have further suggestions or would you like to see more points added? Just let our Testo project team know about this. We will be happy to take your advice and suggestions into account in the subsequent versions of this white paper.

A variety of reasons can be identified for particle measurement. In addition to controlling particle exposure due to particulate matter in inner cities, particles are also measured to assess the efficiency of combustion processes or to enable statements to be made about material properties. There are several reasons and we have identified the following three for our measuring instruments.

Health aspects
We do almost everything we can nowadays to maintain our health. We are aware of the need to nourish ourselves properly, do sports and avoid activities that affect health. Those are the obvious factors.

However, when we turn to fine particles with their maximum particle size of 10 µm, then it quickly becomes clear that this health risk cannot be established by glancing out of the window every morning. While particles with a size of 10 µm – still five or eight times thinner than a human hair – are already filtered out by the upper respiratory tracts and do not get into the bronchia, smaller particles with a size of 1 µm do get that far. Ultra-fine particulates made up of nanoparticles with a size of less than 0.1 µm are not only deposited in the pulmonary alveoli, but also get into the bloodstream. This means they can be transported to every organ and be deposited there [3]. The surfaces of particles are often wetted with other substances. If these include harmful hydrocarbons, fine particles can present a major risk to health.

Reason enough to curb fine particle emissions and to verify successes through regular measurements of concentrations.

Machine efficiency and process monitoring
We have already identified the heating of our living spaces as a source of fine particles. This reveals a quandary: On the one hand the emission of particles has indeed been reduced by optimizing combustion processes, but on the other hand this has led to more small particles – particles which have an impact on the fine particle balance sheet. In order to be able to design these heating systems to be even more environmentally friendly, the possible emission of particles not only needs to be checked during the new development and optimization of these systems. Compliance with emission limit values must be regularly scrutinized.

This consideration also underlies regular checks of particle emissions from vehicles. In this respect, diesel engines, which are often decried as “dirty polluters”, are often unjustifiably criticized. It is indeed important to regularly check that a particle filter is working properly. However, when a filter is working properly, a modern diesel engine now emits fewer nanoparticles than the amounts found in the ambient air on an averagely busy street. In this area, it is more a case of GDI petrol engines as originators of ultra-fine particles constituting a health risk and in future likewise needing efficient filters for treating exhaust gas, along with regular checks [4].

Material properties
It is not only the quantity of particles that is consistently the reason for particle measurements. There are also measurement methods which are intended to provide information about the qualitative properties of the particles. For example, if you let particles grow in a process (granulation), then speed of growth and achievable particle size have an influence on factors like particle stability or speed of particle decomposition in liquids.

[3] https://pubs.acs.org/doi/abs/10.1021/es0522635
[4] https://www.zeit.de/mobilitaet/2017-02/feinstaub-auto-partikelfilter-abgas-diesel-benziner-eu/seite-2