Products are more dangerous than previously thought

Researchers at the Paul Scherrer Institute PSI have for the first time observed photochemical processes within the smallest particles in the air. By doing this, they discovered that excess oxygen radicals that can be harmful to human health are created in these aerosols under daily conditions. They will report their findings today in the magazine Nature Communication.

It is known that airborne substances can be dangerous to human health. The particles, with a diameter of ten micrometres, can penetrate deep into lungs and settle there. They contain reactive oxygen species (ROS), also known as oxygen radicals, which can damage lung cells. The more grains floating in the air, the greater the risk. The particles get into the air from natural sources such as forests or volcanoes. But human activities, for example in factories and traffic, multiply the amount so that densities reach a critical level. The ability of granular substances to absorb or release oxygen radicals into the lungs has already been studied for a number of sources. Now the PSI researchers have gained important new insights.

From previous research it is known that some ROS are formed in the human body when granules disperse in the surface fluid of the respiratory tract. Certain materials usually contain chemical components, for example metals such as copper and iron, as well as certain organic fertilizers. These oxygen atoms exchange with other molecules, and highly reactive fertilizers are formed, such as hydrogen peroxide (H2O2), hydroxyl (HO), and hydroperoxyl (HO2), which cause oxidative stress to the canar. For example, they attack the unsaturated fatty acids in the body, which can then act as building blocks for the cells. Doctors treat asthma, asthma, and various other respiratory diseases on these processes. Even cancer may be induced, as the ROS can also damage the DNA genetic material.

New looks thanks to a unique combination of tools

It has been known for some time that some species of oxygen are already reactive in the atmosphere, and that they enter our body as exogenous ROS called the air we breathe, without to be there first. As it turned out now, scientists had not yet looked closely enough: “Previous studies have analyzed the case with large spectrometers to see what it is,” explained Peter Aaron Alpert, the first author of the new PSI study. “But that doesn’t give you any information about the structure of the individual pieces and what’s going on within them.”

Alpert, by contrast, used the opportunities offered by PSI to take a closer look: “With the brilliant X-ray light from the Swiss Light Source, it was possible for us not only see these grains alone with a resolution of less than one micrometer, but even look into grains while reactions occur within them. ” To do this, he used a new cell type developed at PSI, in which many environmental types can be simulated. It can precisely control temperature, humidity and gas, and has an ultraviolet LED light source that stands up for solar radiation. “In conjunction with a high-resolution X-ray microscope, this cell exists in just one place in the world,” says Alpert. Therefore the study would only be possible at PSI. He worked closely with the head of PSI’s Surface Chemistry Research Group, Markus Ammann. It was also supported by researchers working with atmospheric chemists Ulrich Krieger and Thomas Peter at ETH Zurich, where additional experiments were performed with suspended particles, as well as experts working with Hartmut Hermann of the Leibniz Institute for Research Tropospheric in Leipzig.

How dangerous fertilizers do

The researchers studied particles that contained organic and iron components. The iron comes from natural sources such as desert dust and volcanic ash, but is also present in emissions from industry and traffic. The organic components likewise come from natural and anthropogenic sources. In the atmosphere, these components combine to form iron ratios, which then react with the so-called radicals when exposed to sunlight. These then bind all available oxygen and thus make the ROS.

Normally, on a humid day, a large proportion of these ROS would spread from the grains into the air. In that case it is not an additional risk if we introduce the grains, which contain less ROS. On a dry day, however, these radicals accumulate inside the grains and consume all the oxygen available there within seconds. And this is due to sluggishness: A particular substance can be as hard as stone or liquid as water – but depending on the temperature and humidity, it can also be semi-wet like syrup, dried chewing gum, or herbal neck drops. Switzerland. “This guy’s condition, we found, ensures that the radicals are still locked in the piece,” Alpert said. And extra oxygen can’t get in from the outside.

It is particularly alarming that the highest concentrations of ROS and radicals come through the interaction of iron and organic fertilizers under daily weather: with an average below 60 percent and temperatures around 20 degrees C., also normal conditions for interior rooms. “It used to be thought that ROS only forms in the air – if at all – when the fine dust grains contain relatively rare fertilizers such as quinones,” says Alpert. these are oxidized fences that occur, for example, in plant pigments and fungi. It has recently become apparent that many other sources of ROS are in the case of grains. “As we have proven now, these known radical sources can be substantially fortified under completely normal daily conditions. ”About every twentieth part is organic and contains iron.

But that’s not all: “The same similar photochemical reactions also occur in other fine dust particles,” said research group director Markus Ammann. “We even suspect that almost every grain suspended in the air creates additional radicals in this way,” adds Alpert. “If this is proven in further studies, we need to change models and our required values ​​for air quality. We may have found an additional feature here to help explain why so many people develop respiratory diseases or cancer for no particular reason. “

At least ROS have at least one positive side effect – especially during Covid-19 pandemic – as the study also suggests: They also attack bacteria, viruses, and other pathogens that present in aerosols and making them harmless. This connection 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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Text: Jan Berndorff

In PSI

The Paul Scherrer Institute PSI develops, builds and operates large, complex research facilities and makes them available to the national and international research community. The institute’s own key research priorities are in the areas of subject matter and materials, energy and the environment and human health. PSI is committed to the training of future generations. So about a quarter of our staff are postmasters, postgraduates or apprentices. In total PSI employs 2100 people, making it the largest research institute in Switzerland. The annual budget comes to around CHF 400 million. PSI is part of ETH Domain, with the other members such as the two Swiss Federal Institutes of Technology, ETH Zurich and EPFL Lausanne, as well as Eawag (the Swiss Federal Institute for Aquatic Science and Technology), Empa (Work- the Swiss Federal Reserve for Materials Science and Technology) and WSL (Swiss Federal Institute for Forest, Snow and Landscape Research).

Contact

Prof. Dr. Markus Ammann

Head of Surface Chemistry Research Group

Paul Scherrer Institute, Forschungsstrasse 111, 5232
Villigen PSI, Switzerland

Phone: +41 56 310 40 49;
e-mail: [email protected]
[German, English]

Dr. Peter Aaron Alpert

Surface Chemistry Research Group

Paul Scherrer Institute, Forschungsstrasse 111, 5232
Villigen PSI, Switzerland

Phone: +41 56 310 39 34;
email: [email protected]
[English]

Original publication

Photolytic Radical Stability due to Anoxia in Viscous Aerosol Grains

Peter A. Alpert, Jing Dou, Pablo Corral Arroyo, Frederic Schneider, Jacinta Xto, Beiping Luo, Thomas Peter, Thomas Huthwelker, Camelia N. Borca, Katja D. Henzler, Thomas Schaefer, Hartmut Herrmann, Jörg Raabe, Benjamin Watts, Ulrich K. Krieger, Markus Ammann

Nature Communication, 19.03.2021

DOI: 10.1038 / s41467-021-21913-x