New insights into the formation of artificial organic aerosols suggest an impact on a larger area

Artificial organic aerosols are carbon-containing particles released by humans and are classified as particulate matter. They pose serious health threats and contribute to the deaths of millions of people around the world each year. Incomplete combustion processes from transportation, industry and homes, especially in large cities, produce exhaust gases that form harmful, breathable particles.

In an international study at CERN, the European nuclear research institute in Geneva, researchers led by PSI have gained new insights into the formation of these organic aerosols. Their results show that such contaminants often form only after several oxidation steps. This suggests that contamination by anthropogenic particulate matter has a greater local effect than previously assumed.

This suggests that simply reducing direct emissions from factories, homes and vehicles, for example, using particulate matter filters is not sufficient. Rather, it is also necessary to control the precursor gas that will later form harmful organic aerosols. The findings are published in the journal Nature Geoscience.

Human particulate matter forms more slowly

Researchers previously assumed that organic aerosols would be formed through a single oxidation step. Natural precursor gases such as terpenes and isoprene (water skin released from plants adds oxygen to them, thus forming solid air particles directly.

However, new research reveals that artificial emissions behave differently. Precursor gases such as toluene and benzene in automobile exhaust and in combustion of organic materials are loaded with multiple oxidation steps before forming solid particles.

“The discovery challenges previous assumptions that pollutants form primarily near emission sources,” said Imad El Haddad, project leader for the new research. “Instead, it shows that artificial aerosols will undergo longer formation processes and their impact will expand regionally.”

Unique simulation chamber

The new research was conducted in CERN’s cloud (space leaving outdoor droplets) simulation chamber. More than 70 researchers from Europe and North America worked together to simulate urban air pollution and track the formation of organic aerosols.

Cloud facilities are the cleanest atmospheric simulation chambers in the world, allowing researchers to control parameters such as temperature and pressure with extreme accuracy. Its stainless steel cylinder capacity is approximately 26 cubic meters. The high-precision sensor allows you to observe changes in the cylinder in order to the second sender.

For their experiments, researchers filled the chamber with a gas mixture similar to urban smog and traced the conversion of the exhaust gas into organic aerosols.

Working on the shift, researchers continuously measured simulated urban smogs. They used a technique known as mobility analysis to determine the size distribution of the formed particles and used mass spectrometry to determine the molecular identity of the condensed vapor in real time. They also tracked exactly what precursor gases and their products were condensed into the chamber walls. This should be considered in the calculation of contaminant formation.

“A precise observation gives us a better understanding of how artificial aerosols are formed and grown in the air,” says El Haddad.

More accurate predictions

The bottom row of this study is that a significant proportion of artificial organic aerosols are formed only after an additional oxidation step that can take from 6 hours to 2 days, not after the initial oxidation. The researchers estimate that this multi-step oxidation accounts for more than 70% of the total artificial organic aerosol contamination.

Their results can improve air pollution models by enabling more accurate predictions of particulate matter concentrations and better understanding of local impacts. It also emphasizes the importance of controlling not only the direct release of particulate matter through the particle filter, but also the release of precursor gases that later form solid particles. This will help you fight air pollution more effectively and thus improve public health.