Friday, March 21, 2025

Pollutants often originate in the air

Paul Scherrer Institute

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Imad El Haddad is head of the Atmospheric Molecular Processes group in the Laboratory for Atmospheric Chemistry at PSI’s Center for Energy and Environmental Sciences. For his new study of the formation of organic aerosols, he led a team of more than 70 researchers from Europe and North America. © Paul Scherrer Insitut/Mahir Dzambegovic
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Credit: © Paul Scherrer Insitut/Mahir Dzambegovic

At CERN, the European Organisation for Nuclear Research in Geneva, an international research team led by the Paul Scherrer Institute PSI has conducted especially precise measurements of atmospheric chemistry. Through this study the researchers were able to show how harmful particulate matter arises from vehicular emissions and biomass combustion. Their findings are helping to make existing models of particle formation more accurate.

Anthropogenic organic aerosols are carbon-containing particles emitted by humans into the air, which are classified as particulate matter. They pose a significant health threat and contribute to millions of deaths worldwide each year. Especially in large cities, incomplete combustion processes from transportation, industry, and households produce exhaust gases that form harmful, respirable particles.

In an international study at CERN, the European Organisation for Nuclear Research in Geneva, researchers led by PSI have gained new insights into the formation of these organic aerosols. Their results show that such pollutants often form only after several oxidation steps. This suggests that pollution with anthropogenic particulate matter has a greater regional impact than previously assumed. This in turn suggests that it is not enough to simply reduce direct emissions from factories, homes, and vehicles, for example, with particulate matter filters. Rather, the precursor gases from which harmful organic aerosols later form must also be controlled. The researchers report their findings in the journal Nature Geoscience.

Human-made particulate matter forms more slowly

Researchers previously assumed that organic aerosols form through a single oxidation step. Natural precursor gases such as terpenes and isoprene – hydrocarbons emitted by plants – quickly add oxygen and thus directly form solid airborne particles.

However, the new study reveals that anthropogenic emissions behave differently. The precursor gases—such as toluene and benzene from automobile exhaust and organic material combustion—undergo multiple oxidation steps before forming solid particles. «This finding challenges the previous assumption that pollutants form primarily near the emission sources,» says Imad El Haddad, project leader of the new study. «It shows instead that anthropogenic aerosols undergo a longer formation process whereby their impacts extend regionally.»

A unique simulation chamber

The new study was conducted at CERN's CLOUD (Cosmics Leaving Outdoor Droplets) simulation chamber. More than 70 researchers from Europe and North America collaborated to simulate urban air pollution and track the formation of organic aerosols. The CLOUD facility is the cleanest atmospheric simulation chamber in the world and enables researchers to control parameters such as temperature and pressure with extreme precision – the temperature to approximately one-tenth of a degree. Its stainless steel cylinder has a capacity of approximately 26 cubic metres. High-precision sensors ensure that changes inside the cylinder can be observed down to the second. For their experiments, the researchers filled the chamber with a gas mixture resembling urban smog to trace the transformation of exhaust gases into organic aerosols.

Working in shifts, the researchers continuously measured the simulated urban smog. They determined the size distribution of the forming particles using a technique known as mobility analysis and determined the molecular identity of the condensing vapours in real time using mass spectrometry. They also precisely tracked what proportions of precursor gases and their products condensed on the chamber walls. This must be taken into account in calculations for pollutant formation. «Thanks to the precise observations, we are now better able to understand how anthropogenic aerosols form and grow in the air,» says El Haddad.

More precise predictions

The bottom line of the study is that a significant proportion of anthropogenic organic aerosols forms not after the initial oxidation, but only after additional oxidation steps that can take between six hours and two days. The research team estimates that this multi-step oxidation accounts for more than 70 percent of the total anthropogenic organic aerosol pollution.

Their results can improve air pollution models by enabling more accurate predictions of particulate matter concentrations, providing a better understanding of regional impacts. They also underscore the importance of controlling not only the direct emission of particulate matter, for example, through particle filters, but also the emission of precursor gases that later form solid particles. This could help to combat air pollution more effectively and thus improve public health.

Text: Jan Berndorff

Contact

Dr. Imad El Haddad
Center for Energy and Environmental Sciences
Paul Scherrer Institute PSI

+41 56 310 29 95
imad.el-haddad@psi.ch
[English]

Journal

Nature Geoscience

DOI

10.1038/s41561-025-01645-z

Method of Research

Experimental study

Article Title

Anthropogenic organic aerosol in Europe produced mainly through second-generation oxidation

Article Publication Date

20-Mar-2025

Microplastic pollution disrupts photosynthesis, threatening global food security

Chinese Academy of Sciences Headquarters

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Global maps of annual production losses for three main food crops
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Credit: DANG Fei

A research group led by Prof. DANG Fei from the Institute of Soil Science of the Chinese Academy of Sciences, in collaboration with Prof. ZHONG Huan from Nanjing University, has uncovered a significant yet often overlooked consequence of microplastic pollution: its detrimental impact on photosynthesis—a critical process underpinning Earth's primary productivity and food security.

The study, recently published in PNAS, provides a comprehensive evaluation of the relationship between microplastic exposure and photosynthesis across terrestrial, marine, and freshwater ecosystems.

Microplastics—defined as plastic debris smaller than 5 mm—contaminate environments from deep-sea sediments to mountain glaciers. Despite growing awareness of this environmental hazard, the effects of microplastics on photosynthesis at the ecosystem level have remained unclear.

Previous studies have produced fragmented or contradictory results due to ecosystem complexities, differences among affected photoautotrophs (e.g., plants and algae), and the diverse nature of microplastics themselves. This knowledge gap poses a significant challenge to global efforts to achieve the United Nations (UN) Sustainable Development Goals (SDGs), particularly the Goals of Zero Hunger (#2), Good Health and Well-being (#3), Responsible Consumption and Production (#12), and Life Below Water (#14).

By analyzing 3,286 records using meta-analysis and machine learning techniques, the researchers quantified the global decline in photosynthesis due to microplastic exposure. Their findings reveal that microplastics decrease photosynthetic efficiency by 7.05–12.12% across terrestrial plants, marine algae, and freshwater algae. These reductions translate to estimated annual global losses of 4.11–13.52% (109.73–360.87 MT·yr-1) for key staple crops such as rice, wheat, and maize.

In aquatic ecosystems, microplastic-induced photosynthesis inhibition is projected to cause net primary productivity (NPP) losses of 0.31–7.24% (147.52–3,415.11 MT C·yr-1), leading to seafood production declines of 1.05–24.33 MT·yr-1. These figures underscore the hidden yet profound threat that microplastic pollution poses to global food security.

Encouragingly, the study suggests a pathway for mitigation. The researchers estimate that a 13% decrease in environmental microplastic levels could reduce photosynthesis losses by approximately 30%, preventing global losses of 22.15–115.73 MT·yr-1 in major crops and 0.32–7.39 MT·yr-1 in seafood production.

The findings highlight the urgent need to address microplastic pollution as a critical factor affecting global primary productivity. The study emphasizes the importance of incorporating plastic pollution mitigation strategies into broader sustainability and food security initiatives. It also calls for greater data collection and publication on the extent and mechanisms of microplastic-induced photosynthesis disruptions in future field studies.

As more high-quality field data and advancements in remote sensing technologies become available, researchers can refine their understanding of this emerging threat. These insights can then inform international plastic treaty negotiations and support efforts to achieve the UN SDGs.

A conceptual framework that allows the continual updating of data input to ameliorate our model’s precision and accuracy

Credit

DANG Fei