Particles In The Air Are More Dangerous Than Previously Thought

November 3, 2021

Researchers at the Paul Scherrer PSI Institute (Switzerland) have observed for the first time photochemical processes inside the smallest particles in the air. In doing so, they found that additional oxygen radicals are formed in these aerosols that can be harmful to human health in everyday conditions.

It is well known that airborne particles can pose a danger to human health. The particles, with a maximum diameter of ten micrometers, can penetrate deep into the lung tissue and settle there. They contain reactive oxygen species (ROS), also called oxygen radicals, which can damage cells in the lungs. The more particles there are 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 concentrations reach a critical level. The potential of the particles to carry oxygen radicals to the lungs, or to generate them there, has already been investigated in relation to various sources.

It is known from previous research that some ROS are formed in the human body when the particles dissolve in the surface fluid of the airways. The particles often contain chemical components, for example metals such as copper and iron, as well as certain organic compounds. These exchange oxygen atoms with other molecules and create 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, which can then no longer serve as building blocks for cells. Doctors attribute pneumonia, asthma, and other respiratory diseases to these processes. Even cancer could break out

New insights from a unique combination of devices

It has long been known that certain reactive oxygen species are already present in particles in the atmosphere, and that they enter our body as so-called exogenous ROS through the air we breathe, without the need to form there first. Now it turns out that scientists had not yet looked closely enough: “Previous studies have analyzed the particles with mass spectrometers to see what they are made of,” explains Peter Aaron Alpert, first author of the new PSI study. “But that doesn’t give any information about the structure of the individual particles and what happens inside.”

Instead, Alpert used the possibilities offered by the PSI to take a more precise look: “With the brilliant X-ray light from the Swiss Light Source SLS, we were not only able to see these individual particles with a resolution of less than a micrometer, but even looking at the particles while reactions were taking place inside them. ‘ To do this, he also used a new type of cell developed at PSI, in which a wide variety of atmospheric environmental conditions can be simulated. It can precisely regulate temperature, humidity, and gas exposure, and has an ultraviolet LED light source that replaces solar radiation. “In combination with high-resolution X-ray microscopy, this cell only exists in one place in the world,” says Alpert. Therefore, the study would only have been possible at the 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 with particulate matter were conducted, as well as experts working with Hartmut Hermann from the Leibniz Institute for Tropospheric Research. from Leipzig.

How dangerous compounds are formed

The researchers examined particles that contained organic components and iron. Iron comes from natural sources, such as desert dust and volcanic ash, but it is also contained in emissions from industry and traffic. Organic components also come from 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. These, in turn, bind to all available oxygen and thus produce ROS.

Normally, on a humid day, a large proportion of these ROS diffuses from the particles into the air. In that case, it no longer poses an additional danger if we inhale the particles, which contain less ROS. However, on a dry day, these radicals accumulate inside the particles and consume all the oxygen available there in a matter of seconds. And this is due to the viscosity: The particles can be solid like stone or liquid like water, but depending on the temperature and humidity, they can also be semi-fluid like syrup, dry gum or Swiss herb drops for the throat. “This state of the particle, we found, ensures that the radicals remain trapped in the particle,” says Alpert. And no extra oxygen can get in from the outside.

It is especially alarming that the highest concentrations of ROS and radicals are formed through the interaction of iron and organic compounds in everyday weather conditions: with an average lower than 60% and temperatures around 20 degrees C., conditions also typical of interior rooms. “ROS were previously thought to only form in air – if at all – when fine dust particles contained comparatively rare compounds such as quinones,” says Alpert. These are oxidized phenols found, for example, in plant pigments and fungi. It has recently become clear that there are many other sources of ROS in particles. «As we have now determined, these known radical sources can be significantly strengthened under completely normal everyday conditions. ‘ About one in twenty particles is organic and contains iron.

But that’s not all: “It is likely that the same photochemical reactions take place in other fine dust particles as well,” says Research Group Director Markus Ammann. “We even suspect that almost all airborne particles form additional radicals in this way,” adds Alpert. “If this is confirmed in other studies, we will have to urgently adapt our models and critical values ​​with regard to air quality. We may have found an additional factor that helps explain why so many people develop respiratory diseases or cancer without any specific cause. ”

At least ROS have a silver lining – especially during the Covid-19 pandemic – as the study also suggests: They also attack bacteria, viruses and other pathogens present in aerosols and render them harmless. This connection could explain why the SARS-CoV-2 virus has the shortest survival time in air at room temperature and medium humidity.

Dr. Loony Davis5
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Born and raised in Brussels in an English family, I have always lived in a multicultural environment. After several work experiences in marketing and communication, I came to Smart Water Magazine, which I describe as the most exciting challenge of my career.
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