How are particles created

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Particles in exhaust gas - how are they created? Health hazards What is particulate matter?

The combustion produces CO, HC, NOx and soot particles. In a gasoline engine, the soot particles are around a factor of 20 to 200 lower, which is why they do not play a role in the discussion.

Exhaust smoke - Gabi Eder / Pixelio

Diesel particles

  • also PM (Particulate matter)
  • or PAH (polycyclic aromatic hydrocarbons)
  • or PAH (polycyclic aromatic hydrocarbons)

Despite its good environmental performance due to the low consumption alone, the diesel engine continues to be criticized for its particle emissions and diesel smoke.

Particulate health hazards

Particles from the diesel exhaust, i.e. the soot cores and also the deposits (PAH), can cause cancer.

The microscopic soot particles can enter the lungs via the airways. Diesel soot particles that are smaller than 0.0025 mm can be a health hazard, especially for elderly and ailing people.

With the air, the smallest particles penetrate the airways into the alveoli. By then, the larger particles as well as dust, pollen and bacteria are filtered through the mucous membranes in the nose and the cilia in the bronchi and transported outside. Very fine particles (from 0.0001 mm = 100 nm) that have made it into the alveoli are usually removed by the phagocytes.

A larger amount of particles can lead to the formation of cancer or genetic damage in the case of poor health or elderly people due to the rejection of oxygen radicals and nitrogen oxides. Scientists disagree about the amount and size of particles that can lead to cancer. It is assumed that only an overload of the body's defenses causes damage. The public discussion about particles and the legal provisions on exhaust gas limit values ​​has led to German car manufacturers also relying on soot filters in the future.


Latest knowledge(obtained from the GSF Research Center for Environment and Health)

How ultrafine particles from the air damage the heart and blood vessels

Tiny dust particles can throw the heart out of sync. The mechanisms by which the ultrafine particles in particular damage the heart and blood vessels were discovered by Dr. Holger Schulz from the Institute for Inhalation Biology and Dr. Annette Peters from the Institute for Epidemiology, GSF Research Center for Environment and Health in Neuherberg.

Macrophages ingest bacteria and other microorganisms through phagocytosis.
These are then enclosed in vacuoles in the cells and digested by enzymes.
Ultrafine particles are too small to be specifically taken up by the macrophages.
Recording: S. Takenaka, U. Heinzmann, H. Wehnes (GSF).

The scientists discovered three ways in which the carbon particles, which mainly come from exhaust gases from cars and factories, can damage the organism.
In the bloodstream, the airborne dust can activate platelets, which increase the blood's ability to clot. This makes the blood more viscous and increases the likelihood that clots will form. The particles also prevent arteries from increasing their diameter as quickly. The heart is not supplied with sufficient blood in stressful situations. The consequences are cardiac arrhythmias, which can lead to a heart attack.

The pollutants also affect the autonomic control that controls the heartbeat. The pulse is accelerated and the heart beats too regularly under the influence of the dust. At the same time, the muscle can no longer contract as much because the cell's calcium balance is disturbed. The changed ion concentration can also lead to ventricular fibrillation and cardiac arrest.

The particles can also influence the autonomic nervous system via receptors on the surface of the alveoli and activate the sympathetic nervous system, which puts the body on alert. In pre-stressed people, this can lead to the heart beating irregularly and insufficient blood supply.

As a third possibility, the particles can ignite the lung tissue, which releases messenger substances. The blood then coagulates faster and the body mobilizes its defenses. As a result, more fibrinogen is released, the blood becomes thicker and the arteries calcify faster. If such an arteriosclerotic site tears, the blood clots that form on it are larger, the more fibrinogen is present. This greatly increases the risk of a heart attack.

Above all, their small size makes the ultrafine particles, which are less than a hundred nanometers in size, so dangerous: nasal mucosa, membranes and macrophages are more specialized in catching larger particles

More details on the GSF homepage

Particles consist of microscopic carbon spheres with a diameter of approximately 0.05 µ, on which the hydrocarbons from fuel and lubricants accumulate and condense; water and sulphates also form on the surface. The particles measured in the exhaust gas flow have a diameter of around 0.09 µ. This value is independent of engine technology and operating conditions, which only affect the number of particles formed. The particles separated by a filter form clusters with a size of 0.1 to 1 µ.

The particle formation

In the diesel engine, the diesel fuel is burned by self-ignition in a heterogeneous environment made up of air and fuel.

The quality of combustion depends on how the mixture of air and fuel is formed.

In principle, a diesel engine always works with the same amount of air; the desired performance is achieved by the amount of fuel injected. Under certain engine operating conditions (especially when accelerating) the mixture may be too rich in some areas of the combustion chamber. The combustion then remains incomplete because there is not enough oxygen. In this case, particles form.

The diesel cloud contains so-called PAH (polycyclic aromatic hydrocarbons), which may be carcinogenic (see above). The soot is of course still there, even if it is less common today. However, this has led to the exhaust gas legislation becoming gradually stricter and only 0.05g / km diesel particles will be permitted in the EU (Stage 3 type test) from 1.1.2000. The exhaust gas components CO with 0.64g / km - NOx with 0.5g / km - and (HC + NOx) with 0.56g / km are limited.

Measurements have shown that the soot immissions are declining in the annual mean and only slightly exceed the limit values ​​valid since July 1, 1998 at individual, unusually heavily polluted stations.
Our - new - cars are cleaner than ever. Therefore, the more old cars are replaced by new cars, the lower the air pollution. The introduction of EURO 4 (from 2005) will further improve air quality.

As mentioned above, it should not be forgotten that soot is also produced in petrol engines. However, the amount is 20 to 200 times lower than for diesel and is therefore usually not mentioned any further. The term solids is often used here. In the case of gasoline direct injection engines, noticeable soot formation is conceivable under certain operating conditions. However, I am not aware of any values.


What is particulate matter? 

Info from ADAC

Fine dust is invisible to the naked eye; its particles are less than ten micrometers (thousandths of a millimeter) in diameter. It can be of natural origin, but it is also released in industry or private households. In road traffic, fine dust is created by tire abrasion, blown dust and exhaust gases - especially from unfiltered diesel vehicles. Fine dust particles cannot be filtered by the body and penetrate into the alveoli. Possible consequences: respiratory diseases, heart and circulatory diseases.

Seven years ago the EU passed a directive to improve air quality, according to which air pollution with fine dust may only exceed a limit value (50 micrograms per cubic meter of air) on a maximum of 35 days a year. In order to be able to issue driving bans, the federal government passed the "Ordinance on the Marking of Low-Emission Vehicles" in May 2006 (Badge Ordinance). This will come into force on March 1, 2007. It regulates nationwide the labeling of cars, trucks and buses with stickers depending on the pollutant group.

The federal states must draw up air pollution control plans with which local traffic restrictions can also be ordered. On the basis of these plans, the municipalities can then determine exactly which roads or regions can be used and to what extent. Areas with a high level of particulate matter can - temporarily or permanently - be declared as an »environmental zone«, in which driving bans apply to certain cars.


You can read more details about diesel exhaust specifically in my report on diesel exhaust.

see also: | CO | HC | NOx | SO2 | Catalyst | Exhaust gas values ​​| Badge Ordinance | Cabin filter

Sources: Vienna University of Technology, GSF Dipl.Chem. Kester Lausecker, ADAC,

Author: Johannes Wiesinger

edited: 02/26/2021
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