Researchers have measured a lot of a little‑known silicone chemical in the air. The chemical is called methylsiloxane. It is used in cosmetics, industrial products, cars and many household items.
The study was led by scientists from Utrecht University and the University of Groningen. Their findings were published in the journal Atmospheric Chemistry and Physics.
Silicone Pollution Hides in the Sky
We already know that chemicals like PFAS and tiny plastic pieces are everywhere. Methylsiloxanes are water‑repelling silicone compounds that act as lubricants. They have not been studied much until now.
For years, experts thought the methylsiloxanes in the air came mainly from vapors that left personal‑care products and factories. New data show that ships and cars also release larger methylsiloxane molecules that do not evaporate easily.
These big molecules were found not only where traffic is heavy, but also in coastal towns, rural villages and even deep forests. This suggests the chemicals travel far in the atmosphere.
"We see far more methylsiloxane in the air than we expected," says Rupert Holzinger, an associate professor at Utrecht University.
The large molecules make up about 2 % to 4.3 % of all organic particles in the air. That makes them some of the most common synthetic chemicals floating around. By comparison, PFAS levels are usually a thousand times lower.
How Engine Oil Sends Methylsiloxanes Up
Methylsiloxanes are added to engine oil to help parts move smoothly. When the engine runs, a tiny amount of oil slips into the combustion chamber. Because the chemicals resist heat, they do not fully burn and escape in the exhaust.
Highest Amounts Seen in Cities
Urban areas showed the strongest signals. In the São Paulo region of Brazil, researchers measured 98 nanograms of the chemical per cubic meter of air. The lowest readings came from a forest in Lithuania, where only 0.9 nanograms were found.
In a small Dutch village called Cabauw, the level was about 2 nanograms per cubic meter. The study covered sites in the Netherlands, Lithuania and Brazil, giving a picture of different climates, hemispheres and economies.
Possible Health and Climate Impacts
Since methylsiloxanes seem to be everywhere in the sky, people are likely breathing them all the time. Scientists do not yet know what long‑term health effects this might cause.
"Our estimates show that daily inhalation of methylsiloxanes could be higher than that of PFAS or tiny plastics," says Holzinger. "We need urgent research on health risks."
The chemicals may also affect the climate. They can change how tiny particles behave, which influences cloud formation and how clouds reflect sunlight.
For example, methylsiloxanes might lower the surface tension of aerosols, making clouds form differently. They could also interfere with the way ice crystals start to grow in clouds.
Vehicles Likely Main Source
More than half of the large methylsiloxane particles seem to come from traffic emissions. The pattern of these particles matches the spread of long‑chain hydrocarbons that are found in engine oil.
Unlike those hydrocarbons, which fade as they travel, methylsiloxanes stay stable and can travel long distances in the air.