A cruise that almost did not happen
Our paper began not with a scientific result, but with a research cruise that repeatedly seemed as though it might never happen.
The research was funded by the UK Natural Environment Research Council in 2019 through the Shipping Emissions in the Arctic and North Atlantic Atmosphere project, or SEANA. The project was designed to investigate how natural aerosol sources and increasing shipping emissions may shape the future Arctic atmosphere.
A research cruise was central to our plans, but no suitable ship was available in 2020. The voyage was postponed to 2021—and then COVID-19 disrupted international travel and ship-based research worldwide.
By late 2021, research vessels were beginning to operate again. In November, we learned that a ship had become available for a cruise around Greenland the following spring. This was excellent news, but also a considerable logistical challenge. An expedition of this scale would normally take around a year to prepare. We had five months.
The DY151 cruise brought together two research programmes, SEANA and M-Phase. Neither project alone had every instrument or area of expertise needed to answer our questions, so we assembled a much wider collaboration. Scientists and instruments joined the expedition from several UK and international research groups, including the University of Leeds, University of Exeter, British Antarctic Survey, Chinese Academy of Meteorological Sciences, University of York, Plymouth Marine Laboratory, Zhejiang University, Droplet Measurement Technologies and Peking University.
Dr Congbo Song, then a research fellow at the University of Birmingham, did an outstanding job preparing our instruments. Behind every measurement made at sea were months of testing, calibrating, packing, shipping, risk assessment and coordination. We also had to assemble the scientific party, arrange visas and secure diplomatic clearances and research permissions across several jurisdictions in such a short time.
Building a floating atmospheric observatory
In mid-May 2022, we travelled to Reykjavík to meet RRS Discovery. COVID precautions meant arriving early, testing and isolating before boarding. Once aboard, we had only a few days to transform empty laboratories and shipping containers into a working atmospheric observatory.
Royal Research Ship Discovery at Reykjavik, Iceland where the cruise started
Sampling lines were installed, instruments were secured against rough seas and teams worked through the inevitable last-minute technical problems. Even then, departure remained uncertain. Sailing was delayed, and shortly after we eventually left Reykjavík, several crew members tested positive for COVID-19 and had to isolate.
The procedures established by the captain and crew prevented a wider outbreak, allowing the voyage to continue. After years of postponement, we were finally heading towards Greenland.
Our route first took us towards southeastern Greenland and then northwards along its western coast. Near southeastern Greenland, calm weather allowed us to observe the first clear new particle formation event of the cruise. From the deck, we can see melting sea ice and Greenland.
Melting Sea Ice and Greenland at the background
New particle formation begins when gases in the atmosphere cluster together to form particles only a few nanometres across. Most of these molecular clusters disappear. Those that survive may continue growing and eventually become large enough to influence cloud formation. Understanding this process is especially important in the Arctic, where background particle concentrations are low and relatively small changes can significantly affect clouds and climate.
Storms, sea ice and the “magic event”
The calm conditions did not last. As we travelled around Greenland, several days of storms produced rough seas that challenged both the instruments and the scientists operating them.
For me personally, this meant several days of severe seasickness. Conducting atmospheric research while the ship rolled heavily—and while feeling unable to stand, eat or concentrate—was one of the less glamorous aspects of Arctic fieldwork. At times, the movement was so great that it was difficult to see from one end of the deck to the other as the ship rose and fell with the waves.
High productivity brought whales to Greenland fjords
The quieter periods were unforgettable. In Nuuk, Maniitsoq and Sisimiut, we saw Greenland’s mountains, fjords, glaciers and icebergs. We encountered humpback whales and, during a test of one of the rescue boats, some of us were able to circle RRS Discovery and view the ship against the surrounding sea and ice.
These landscapes were not simply a spectacular backdrop. The boundaries between the ocean, melting sea ice and atmosphere are chemically and biologically active environments. Gases released from these interfaces can be transformed in the atmosphere and contribute to particle formation, but the underlying mechanisms remain poorly understood.
The defining scientific moment came near the marginal ice zone.
There, we observed an exceptionally strong new particle formation event—what the team began calling the “magic event”. The number of newly formed particles increased by approximately fifty-fold. Even more importantly, we watched the particles continue to grow towards sizes relevant for cloud condensation nuclei.
Seeing the event unfold in real time was exhilarating. But observing something extraordinary and understanding it are very different things.
Sunset at Davis Strait. Credit: Dr. Yuqing Dai
From an unexpected event to a chemical mechanism
Interpreting atmospheric measurements from the remote Arctic is exceptionally difficult. Concentrations are often close to instrument detection limits, many chemical and physical processes occur simultaneously, and no single instrument can provide the complete explanation.
The analysis took several years and required repeated examination and discussion across the team. Dr Mao Du and Dr James Brean, the lead authors, played central roles in integrating the measurements and developing the scientific interpretation. Their work pushed the limits of both our instruments and our analytical approaches.
Professor Doug Worsnop provided exceptionally generous support throughout this process, visiting and working with us repeatedly—around ten times—as the story developed. His experience was invaluable in helping us interpret the molecular-cluster measurements and test competing explanations.
One of the most exciting moments came when the team recognised real-world evidence for a recently discovered mechanism in which iodine oxoacids and sulfuric acid work together to promote particle nucleation. Doug, who had contributed to the laboratory study proposing this mechanism, encouraged us to investigate whether the same chemistry could explain our Arctic observations.
Finding evidence that a mechanism identified under carefully controlled laboratory conditions was operating in the real Arctic atmosphere became one of the paper’s most important contributions.
The data contained another surprise. Dr. Mao Du identified a previously unrecognised group of oxygenated organic molecules associated with the formation and growth of the particles. This initiated extensive discussions about where these compounds came from, how they formed and whether they helped newly formed particles survive and grow.
Rather than closing the story, this discovery opened a new research direction. With new NERC funding, we are now investigating how rapidly these molecules form, the chemistry responsible for their production and their importance for Arctic particle growth.
The second expedition: publishing the paper
The publication process became an expedition of its own.
Across several rounds of review, the manuscript was considered by ten reviewers. Our combined responses exceeded 150 pages, and the Supplementary Information grew to more than 80 pages. The final study contains seven main figures and 25 additional figures when the supplementary analyses are included.
The process was demanding, but the scrutiny strengthened the paper. It required us to test alternative explanations, sharpen the proposed mechanisms and demonstrate that our conclusions were supported by several independent measurements.
This was one of the most challenging papers I have led, but also one of the most rewarding. It reflects not only the work of the lead authors, but the contributions of a large international team—from those who prepared and operated instruments at sea to those who provided technical support, specialist measurements, modelling, laboratory evidence and critical interpretation.
Why it matters
The implications extend beyond one cruise or one spectacular particle event.
The Arctic is changing rapidly. Sea ice is retreating, newly exposed waters may become more biologically active, terrestrial inputs are changing and shipping is expected to increase. All these changes could alter the gases and particles present in the Arctic atmosphere.
New particles that survive and grow can contribute to cloud condensation nuclei. Arctic clouds affect both the sunlight reflected back to space and the heat retained near the surface. Changes in particle formation may therefore influence clouds, regional warming and sea-ice loss—potentially creating climate feedbacks that are still poorly represented in models.
Schematic representation of natural nucleation and growth of new particles to CCN in the Arctic marine boundary layer. Volatile gases are emitted from diverse sources including sea ice, open ocean, coastal systems and bird colonies via both biotic and abiotic processes. They then undergo oxidation to produce new particle precursors such as HIO3, HIO2, and H2SO4, driving particle formation, and oxygenated organic matter which are the primary drivers of particle growth.
Major questions remain. How common are the mechanisms we observed? Which natural and anthropogenic sources will dominate in a warmer Arctic? How important are the newly identified organic molecules? And can climate models represent these processes accurately?
Answering these questions will require further field observations, laboratory experiments and model development.
For our team, the journey from an uncertain ship allocation during a global pandemic to a paper in Nature Geoscience demonstrates why ambitious collaborative expeditions remain essential. The most important discoveries were not necessarily those we expected to make. They emerged because we brought together the right people and instruments, persisted through uncertainty and difficult conditions, and remained open to what the Arctic atmosphere was telling us.