Soot particles from the exhaust gases from industry, heating systems and road traffic are considered to be harmful to health and the climate. Measurements are now confirming how widespread these air pollutants are. In the Thuringian Forest, around half of the soot particles detected came from several hundred kilometers away. According to the researchers, it is therefore not enough to reduce soot emissions only locally – they must be reduced across Europe.
Soot consists of tiny, carbon-containing particles that are produced, for example, in traffic, in industry or when burning wood and fossil fuels for heating. As a constituent of fine dust, soot in the air has considerable consequences: if people breathe in, the ultrafine particles can get into the lungs and bloodstream and increase the risk of lung and cardiovascular diseases. In addition, global warming is accelerating because the dark particles absorb light and contribute to the formation of clouds.
Where do the soot particles come from?
But where exactly does the soot in the air over Germany come from? An international team of researchers led by Laurent Poulain from the Leibniz Institute for Tropospheric Research (TROPOS) in Leipzig investigated this question. It was already known that soot particles not only come from local sources, but can also be carried away by the wind. During transport, so-called aging processes change the chemical composition of the particles and also influence their physical properties, such as optics, volatility or size. “In the course of their short life, the soot-containing particles grow,” explains Poulain. “The larger these particles are, the older they are and the longer they must have been in the atmosphere.”
Carbon particles that are smaller than 400 nanometers are therefore considered to be relatively young and mostly come from local sources. Soot particles with a size of more than 400 nanometers are mostly older and come from more distant sources, as the researchers explain. On the basis of these assumptions, they have now analyzed soot that was captured during a major measurement campaign in the Thuringian Forest. “The data analysis made it possible to differentiate local soot emissions, which are dominated by the burning of fossil fuels, from soot that was transported from great distances,” says Poulain.
52 percent do not come from local sources
The result confirms that soot particles can be transported and distributed over great distances. The scientists found that local soot emissions at the measuring station accounted for around 48 percent. Around 35 percent of this came from liquid fuels and around 15 percent from the combustion of biomass. However, the greater part of the captured soot particles had reached the station via long-distance atmospheric transport – 52 percent of the particles came from hundreds of kilometers away. These results confirm earlier studies by the research team, according to which 44 to 62 percent of the fine dust up to ten micrometers in diameter measured at rural locations in Eastern Germany comes from regions of Eastern Europe that are further away. The main sources were combustion emissions, probably from wood and coal heating.
The results thus show that soot particles from oil and wood heating systems and from road traffic, for example, spread over hundreds of kilometers and pollute the air. In order to keep the air over Germany clean, soot emissions must also be reduced in other regions of Europe. “The present results underline the key role that far-reaching transport processes also play for soot mass concentration,” said Poulain and his team. In order to reduce pollution, they therefore recommend setting European limits for carbon black, for example. This should also happen by updating the EU Air Quality Directive by 2022.
Source: Leibniz Institute for Tropospheric Research e. V., Article: Atmospheric Chemistry and Physics, doi: 10.5194 / acp-21-3667-2021