It is well known that airborne particulate matter PM2.5 can pose a health hazard
It is known from previous studies thatFree radicals are formed in the human body when particles dissolve in the surface fluid of the respiratory tract. Particulate matter typically contains chemical constituents such as metals such as copper and iron, as well as certain organic compounds. They exchange oxygen atoms with other molecules to form highly reactive compounds such as hydrogen peroxide (H2O2), hydroxyl (HO) and hydroperoxyl (HO2), which cause so-called oxidative stress. For example, they attack unsaturated fatty acids in the body that can no longer serve as building blocks for cells. Doctors refer to such processes as pneumonia, asthma and other respiratory diseases. Even cancer can be provoked, as free radicals can also damage the DNA of the genetic material.
Thanks to the bright X-ray light fromUsing the Swiss light source SLS, scientists were able to not only view such particles individually with a resolution of less than one micrometer, but even looked inside the particles while reactions took place inside them. To do this, they also used a new type of cell that can simulate a wide range of atmospheric environmental conditions. It can precisely regulate temperature, humidity and gas exposure and has an ultraviolet LED light source that replaces solar radiation.
Researchers have studied particles containingorganic components and iron. Iron comes from natural sources such as desert dust and volcanic ash, but is also found in emissions from industry and transportation. Organic components come from both natural and anthropogenic sources. In the atmosphere, these components combine to form iron complexes, which then react to so-called radicals when exposed to sunlight. They, in turn, bind all available oxygen and thus generate free radicals.
Usually on a wet day, most are loose.radicals diffuses from the particles into the air. In this case, there is no more additional danger if we inhale particles that contain less free radicals. However, on a dry day, these radicals build up inside the particles and consume all available oxygen in seconds. And this is due to viscosity: solids can be solid, like rock, or liquid, like water, but depending on temperature and humidity, they can also be semi-liquid.
What is especially alarming is that the highestFree radical concentrations are formed as a result of the interaction of iron and organic compounds in everyday weather conditions: on average below 60% and temperatures around 20 degrees Celsius, which is also typical for indoor environments.
“It used to be thought that free radicalsare formed in the air, if at all, when small dust particles contain relatively rare compounds such as quinones. These are oxidized phenols that are present, for example, in the pigments of plants and fungi. It has recently become clear that there are many other sources of free radicals in particulate matter. As we have now determined, these known radical sources can be greatly enhanced under completely normal everyday conditions. About one in 20 particles is organic and contains iron.”
Peter Aaron Alpert, PSI researcher at the Paul Scherrer Institute
The same photochemical reactions are likely to haveplace in other small dust particles. Scientists suspect that almost all suspended particles in the air in this way form additional radicals. If this is confirmed by further research, then there is an urgent need for researchers to adapt models and critical values for air quality. This finding could be an additional factor that can help explain why so many people develop respiratory disease or cancer for no specific reason.
Anyway, free radicals have oneOn the positive side, the study also suggests, they attack bacteria, viruses and other pathogens present in aerosols and render them harmless. This link may explain why the SARS-CoV-2 virus has the shortest survival time in air at room temperature and moderate humidity.
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