Particulates damage the lungs. With a diameter of up to ten micrometres, fine dust particles are so tiny that they can be breathed into the innermost reaches of the lungs (a human hair, at 90 micrometres thick, is huge by comparison). The particles can even penetrate into the cells of the lungs. And they can also lead to respiratory diseases – including asthma.
What we knew so far
Particulates contain many chemical components, such as metals and certain carbon compounds. Oxygen is exchanged through a reaction with other molecules. This ultimately creates highly reactive compounds. These reactive oxygen compounds (ROS) are also called ‘oxygen radicals’. They include hydrogen peroxide and hydroperoxyl. Larger amounts damage the cells. For example, they attack unsaturated fatty acids in the body, so that a cell can no longer use the unsaturated fatty acid as a building material. It is likely that ROS even changes genetic material.
So far we know that:
- Certain ROS that are already present in airborne particulate matter (as ‘exogenous ROS’) enter the body via the inhaled air.
- In addition, some ROS also occur in the body when the particulates dissolve in the surface fluid of the respiratory tract.
What was the study about?
The researchers studied particulate matter containing carbon components and iron. They produced ROS in the air in several steps.
Normally, a large part of the ROS would be rendered harmless in the air by the sun – the ROS would then disperse into the environment before they were inhaled.
But under certain conditions, the ROS remain trapped inside particulate matter: This happens when the particulates are viscous – like syrup or chewing gum. The study determined at which temperature and humidity this occurs most often.
The highest concentrations of ROS in particulate matter are formed in normal everyday weather conditions: at an average humidity of 50 per cent and temperatures of around 20 degrees. In other words, conditions typical for indoor rooms.
This is due to the interaction of iron and organic compounds – a combination that is found in approximately every twentieth fine dust particle.
A second finding is also troubling: Particulates also contain many other ROS sources. These known ROS sources can also be reinforced under completely normal everyday conditions. “We even suspect that almost all suspended particles in the air form additional radicals in this way”, says Peter Aaron Alpert, the first author of the study.
Why is this important?
If additional studies reveal similar results, particulate matter limits will have to be significantly lowered.
“We urgently need to adapt our models and critical values with regard to air quality. We may have found an additional factor here to help explain why so many people develop respiratory diseases or cancer without any specific cause”, says Alpert.
How did the researchers discover this?
The researchers managed to get a look inside the particulates. Using a special microscope and a specially designed cell:
- The high-resolution X-ray microscope can view individual fine dust particles with a resolution of less that one micrometre and monitor the reactions taking place in them in real time.
- The newly developed cell can be used to simulate how very different environmental conditions affect it. Temperature, humidity and air composition can be adjusted precisely. A UV LED light source mimics the sun’s rays.
“In combination with high-resolution X-ray microscopy, this cell exists just one place in the world”, says Alpert, who conducts research at the Paul Scherrer Institute PSI in Villigen, Switzerland. He collaborated on this study with other colleagues from Switzerland and the Leibniz Institute for Tropospheric Research in Leipzig.