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 (March 19, 2021) in the journal Nature Communication.
It is known that airborne substances can be dangerous to human health. The particles, with a diameter of ten micrometers, 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 can be induced, as the ROS can also damage the genetic material DNA.
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, scientists had not yet looked closely enough: “Previous studies have analyzed the matter with large spectrometers to see what it is,” explained Peter Aaron Alpert, first author of the new PSI study. “But that doesn’t give you any information about the structure of the individual items and what’s going on within them.”
Markus Ammann at one of the devices used for fine dust tests. Credit: Paul Scherrer / Markus Fischer Institute
In contrast, Alpert used the opportunities offered by PSI to take a closer look: “With the brilliant X-ray light from the Swiss Light Source SLS, we were able to not only see these grains alone with a resolution of less than one micrometer, but even look into grains while reactions were taking place inside 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.
Peter Aaron Alpert analyzes the processes in the best grains in the air. Harmful substances are already formed in the atmosphere, not just in the human body. Credit: Paul Scherrer / Markus Fischer Institute
Normally, on a humid day, a large proportion of these ROS would spread from the grains into the air. In that case, it will not be 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. “We found that the condition of this glass ensures that the radicals remain trapped in the piece,” says Alpert. 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. “ROS used to be thought to form only in the air – if at all – when relatively fine grains such as quinones are present in the fine dust particles,” says Alpert. These are oxidized fences that occur, for example, in plant pigments and fungi. It has recently come to light that many other ROS sources are in case of malignancy. “As we have now proven, these well-known radical sources can be greatly consolidated under normal daily conditions.” About every twentieth part is organic and contains iron.
But that’s not all: “The same photochemical reactions also occur in other fine dust particles,” says 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 our models and values of 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 link may explain why the SARS-CoV-2 the virus has the shortest survival time in air at room temperature and moderate humidity.
Information: 19 March 2021, Nature Communications.
DOI: 10.1038 / s41467-021-21913-x