Kanakidou recalls that at the beginning of the project, she had merely hoped to refine methods for local emission controls. However, the merged data revealed significantly more than expected. “These results highlighted that atmospheric deposition of nitrogen and other nutrients in marine ecosystems is more closely linked to distant emission sources than previously believed,” says Kanakidou. This is particularly evident in the Mediterranean basin, where the long-range transport of ozone, carbon monoxide, and reactive nitrogen compounds contributes substantially to air pollution and sea eutrophication. About half of these substances originate from far-distant sources rather than local ones. This proportion increases further in summer due in part to emissions from distant wildfires.

International Research Network Expanded

Kanikadou launched her project, “Impacts of emissions and feedbacks to the Earth system” in 2020 as a U Bremen Excellence Chair holder. Excellence Chairs are awarded to outstanding researchers who serve as bridges between the University of Bremen and leading universities around the world. Maria Kanakidou is Director of the Environmental Chemical Processes Laboratory in the Department of Chemistry at the University of Crete. She is internationally recognized for her cutting-edge research on atmospheric chemistry, biogeochemical cycles, and climate science. Her host at the University of Bremen, chemistry professor Mihalis Vrekoussis from the Institute of Environmental Physics (IUP), highlights benefits that extend far beyond the project’s duration. “This partnership has significantly expanded our international research network, facilitated student exchanges between our institutions, enabled joint applications for competitive third-party funding, and established collaborative supervision of PhD students and postdoctoral researchers,” says Vrekoussis, head of the LAMOS (Laboratory for Modelling and Observation of the Earth System) group at IUP. Early in the project, Vrekoussis had nominated Kanakidou for a Humboldt Research Award, which she subsequently received.

Pollution Plumes with Millionfold Impact

Over the course of the six-year project, Kanikadou spent a considerable amount of time in Bremen, fostering close collaboration, rapid knowledge transfer, and strong support for early-career researchers, says Vrekoussis. “We have also gained a better understanding of how pollution plumes originating from the world’s largest cities affect the health of millions. Furthermore, using cutting-edge satellite technology and advanced computer models developed in-house, we have produced more accurate estimates of greenhouse gas emissions, a critical tool for informing climate policy.” Additional work aims to improve the understanding of ozone sources and sinks in polluted regions globally. Another outcome of the project is the forthcoming publication of an open-access atlas of pollutant transport pathways from megacities. The project has also shed new light on global atmospheric ammonia levels and how the levels are changing over time. This finding has important implications for air quality and ecosystem health.

Complex Combination of Diverse Datasets

These results stem from intensive effort. First, the team had to merge very different satellite and ground-based measurement datasets, reports Kanakidou. A precise understanding of data collection methods was fundamental to this process, and with the amount of available satellite data far exceeding that of terrestrial data, this imbalance had to be addressed to ensure realistic results. The project’s findings have been presented in 34 scientific publications and at 77 national and international conferences.

Both Maria Kanakidou and Mihalis Vrekoussis are convinced that these results will shape their research for a long time to come. This is because the findings reveal the complex and multifaceted impacts of air pollution. To better understand these impacts, precise, long-term satellite data on pollutant concentrations are necessary as well as terrestrial and marine measurements, says Kanakidou. “More systematic monitoring of under-researched regions, such as the climate-vulnerable Eastern Mediterranean, the Middle East, and the Global South, is also a priority.”

Impacts for Future Earth System Models

In principle, pollutants should not be considered in isolation, says Kanakidou. “Because there are several interactions between air pollution and the biosphere, terrestrial and marine environments, and human health, understanding these effects requires an integrated view of the Earth system that accounts for complexity and feedbacks.” Future Earth system models will also need to incorporate these dynamics. “They require a better representation of the coupled carbon-nitrogen cycles and their feedback with the climate.”

The findings so far make one point clear, says Kanakidou. Effectively combating air pollution and its consequences cannot rely solely on national measures, because the range of emitted pollutants is too great. Since pollutants do not stop at national borders, political measures should not either, emphasizes the researcher. Instead, what is needed are coordinated, transboundary air-quality agreements. First and foremost, these agreements must address the most far-reaching sources of pollution: megacities.

Further Information

Excellence Chairs