Ozone, a reactive molecule located in Earth’s troposphere, has a complex role in atmospheric chemistry. While it protects life by filtering ultraviolet radiation in the stratosphere, surface-level ozone poses a toxic threat to plants, animals, and humans. Its formation is driven by photochemical reactions involving nitrogen oxides (NOₓ) and volatile organic compounds (VOCs). HONO, often overlooked in standard air quality models, plays a crucial intermediary role by releasing hydroxyl radicals (OH) upon photolysis, which accelerate these reactions, ultimately increasing ozone concentration. The PolyU research team focused their quantitative analysis on the dynamics of soil HONO emissions, seeking to clarify the mechanisms by which these emissions interact with atmospheric chemistry on a global scale.

The study’s lead, Professor Tao Wang, Chair Professor of Atmospheric Environment at PolyU’s Department of Civil and Environmental Engineering, spearheaded a multi-disciplinary team that meticulously compiled an expansive dataset of soil HONO emission measurements from global ecosystems. The data, sourced from 110 laboratory studies and field experiments, were synthesized into a novel parameterisation scheme that encapsulates the interplay of environmental and anthropogenic factors affecting HONO fluxes from soil. This integrated approach accounted for variables such as soil temperature, moisture content, fertiliser types, and application rates. For the complex and less directly measurable factors like microbial activity and soil texture, the team designed probabilistic representations based on geospatial metadata, allowing for refined simulations in diverse land use settings.

Crucially, the model captured the temporal and spatial variability of soil HONO emissions over a 36-year period from 1980 to 2016. The findings reveal a notable increase in global soil HONO emissions, ascending from an estimated 9.4 teragrams of nitrogen (Tg N) annually to 11.5 Tg N. This escalation correlates strongly with intensified agricultural fertilisation practices and variations in climate parameters, including rising soil temperatures and altered moisture regimes due to climate change. The incorporation of these emissions into the Community Atmosphere Model with Chemistry (CAM-Chem), a state-of-the-art chemistry-climate model developed by the U.S. National Center for Atmospheric Research, allowed for an unprecedented simulation of their impacts on atmospheric composition and subsequent ozone formation.

Through these rigorous simulations, the research team discovered that soil HONO emissions contribute to an average global increase of 2.5% per year in surface ozone mixing ratios, with localized spikes reaching as much as 29%. These elevated ozone levels have the potential to inflict widespread ecological damage by impairing photosynthetic activity, reducing plant growth, and destabilizing ecosystems. Particularly, crop production is threatened by chronic ozone overexposure, which disrupts cellular functions in vegetation. The repercussions extend further to climate regulation, as diminished plant health impairs carbon dioxide absorption, thus exacerbating greenhouse gas accumulation and global warming.

The geographical distribution of emissions was found to be uneven, highlighting notable “hotspots” primarily in regions with intensive agricultural activity. Asia emerged as the largest contributor, responsible for approximately 37.2% of total soil HONO emissions, followed by significant contributions from India, eastern China, parts of North America, Europe, African savannahs, and South America. Seasonal fluctuations also emerged as a defining feature, with emissions peaking during summer months when soil temperatures elevate microbial activity and fertiliser application coincides with crop growth phases. This seasonality underscores the intrinsic linkages between human land management, microbial processes, and atmospheric chemistry.

Another revelatory aspect of the study concerns the interplay between anthropogenic emissions and soil HONO’s influence on ozone production. In regions with lower human-induced NOₓ emissions, the surface ozone chemistry is typically NOₓ-limited, meaning that increases in NOₓ concentration can disproportionately drive ozone formation. Therefore, soil HONO emissions exert a more pronounced impact on ozone levels in these cleaner air zones. As global policies aimed at reducing industrial and vehicular nitrogen emissions take effect, more regions are expected to transition into this NOₓ-sensitive regime, inadvertently heightening the relative importance of soil HONO emissions.

The PolyU researchers caution that the rise in soil HONO emissions driven by climate warming and continued fertilisation practices may counterbalance anticipated improvements achieved through reductions in conventional anthropogenic activities. This finding challenges current pollution mitigation frameworks that prioritize emission cuts from factories and traffic while neglecting biogeogenic sources. Professor Wang emphasizes the imperative to integrate soil emissions into air quality management strategies, highlighting that more comprehensive approaches are essential for effective pollution control and environmental sustainability.

To tackle this complex issue, the study deployed a synergistic methodology that fused diverse observational datasets with sophisticated climate and chemical modeling. Measurements from over a century of global soil samples were fed into MERRA2 reanalysis data—a powerful platform that reconstructs past atmospheric conditions—to anchor simulation parameters. CAM-Chem was then utilized to merge these inputs and simulate the resultant atmospheric chemical dynamics over time. This methodological rigor adds robustness and credibility to the conclusions drawn about soil HONO’s role in atmospheric processes.

Looking to the future, the research team plans to extend this pioneering work by enhancing the global observational network dedicated to soil HONO emissions. Improved field measurements, especially in under-represented regions, will refine model accuracy and predictive power. Additionally, the team aims to deepen understanding of the microbiological pathways governing HONO production in soils, illuminating the soil-atmosphere interface mechanisms that modulate emission rates. Such knowledge is critical for identifying intervention points to mitigate emissions effectively.

Furthermore, the study underscores the necessity of investigating agricultural mitigation strategies that balance fertiliser effectiveness with minimised environmental harm. Techniques such as precision deep fertiliser placement and the application of nitrification inhibitors are poised to reduce soil HONO emissions while maintaining or enhancing crop yields. These approaches could serve as practical solutions to simultaneously address food security and air quality objectives, epitomizing the integrated management required for sustainable development.

In summary, this landmark study from PolyU not only revises the understanding of ozone pollution drivers but also spotlights the complex interdependence of climate change, agricultural practices, and atmospheric chemistry. By elucidating the pathways through which soil emissions contribute to ozone formation, the research offers critical insights for policy-makers, environmental scientists, and agricultural managers alike. Addressing soil HONO emissions is now an essential frontier in the global battle against pollution and climate change, demanding coordinated efforts across scientific disciplines and societal sectors.

Subject of Research: Rising soil nitrous acid emissions driven by climate change and fertilisation and their impact on global ozone pollution.

Article Title: Increasing soil nitrous acid emissions driven by climate and fertilization change aggravate global ozone pollution

News Publication Date: 12-Mar-2025

Web References:

• Nature Communications Article
• DOI: 10.17632/6wmrvyp5xb.1

Image Credits:
© 2025 Research and Innovation Office, The Hong Kong Polytechnic University. All Rights Reserved.

Keywords

Climate change, Ozone, Ecosystems, Soils, Soil chemistry, Pollution

The groundbreaking research employed a sophisticated chemistry–climate model, specifically the SOCOL:14C-Ex model, developed by Postdoctoral Researcher Kseniia Golubenko and Professor Ilya Usoskin at the University of Oulu, Finland. This model represents a significant advancement in our ability to assess solar particle storms as it was meticulously crafted to imitate ancient glacial climate conditions. Prior to this achievement, the intensity of solar events, particularly the formidable spike observed in 12350 BC, remained elusive and poorly understood. The new model confirms that this ancient event was approximately 18% stronger than the previously acknowledged record-holder, the AD 775 solar storm, known only through tree-ring archives.

Dr. Golubenko elaborated on these findings, noting that the intensity of the ancient 12350 BC event dwarfs even the most significant solar events recorded in modern times. According to their estimates, the 12350 BC event was over 500 times more intense than the infamous solar particle storm of 2005, which is recognized as the most powerful event documented during the modern satellite era. This stark comparison highlights not only the exceptional strength of the ancient event but also underscores the potential risks that current technologies might face in light of such powerful solar storms.

The research team also intends to further investigate other significant solar particle storms that have been recorded through history, such as those occurring around 994 AD, 663 BC, 5259 BC, and 7176 BC. The recent findings build upon a solid foundation of scientific inquiry that seeks to deepen our understanding of solar activities and their terrestrial effects. The validation of the SOCOL:14C-Ex model was achieved using wood samples discovered in the French Alps, reinforcing the model’s reliability when analyzing conditions from 14,300 years ago.

Solar particle storms are infrequent occurrences, yet when they do transpire, they unleash a torrent of high-energy particles toward Earth. To clarify, these storms can lead to increases in the production of cosmogenic isotopes in the atmosphere, especially radiocarbon (14C). This naturally occurring isotope is crucial for modern radiocarbon dating efforts, providing scientists with the capacity to derive accurate age estimates for archaeological and geological samples. Such radiant spikes in cosmogenic isotopes—termed Miyake events—are associated with extreme solar activity and yield pivotal data for researchers focusing on both solar dynamics and ancient Earth systems.

Golubenko emphasized the significance of Miyake events for archaeological chronologies, offering researchers a timeline to accurately date historical events and activities. The applicability of radiocarbon signals from these ancient spikes provides opportunities for precision in dating significant sites, including Viking settlements in Newfoundland and Neolithic cultures in Greece. This revelation propels radiocarbon dating into a new era, allowing scientists to undertake a comprehensive analysis of climatic and geomagnetic shifts over extensive timeframes.

The implications of these findings extend beyond the geological and archaeological realms; they fundamentally revise the scientific understanding of extreme solar physics and space weather phenomena. The research establishes a new benchmark for interpreting the scale and potential consequences of future solar storms amidst rapidly advancing technology. Golubenko warns that comprehending the magnitude of the ancient solar event provides insights critical for assessing the risks that similar phenomena pose to modern infrastructure, including satellites, power grids, and communication systems, which are increasingly susceptible to solar radiation.

The revelations from this pioneering study challenge the existing paradigm that solar storms were only a concern during the Holocene epoch, the past 12,000 years characterized by a relatively stable climate. By extending the analysis through the application of validated models to glacial conditions, scientists can now broaden their investigations into past solar activity, revolutionizing how we understand its relationship with Earth’s climatic transformations.

The collaborative nature of this research was underscored by the involvement of an international team comprising scientists from France, Switzerland, and Finland, operating under the leadership of Professor Edouard Bard from the CEREGE in France. This diverse expertise not only enriched the research findings but also reinforced the significance of cross-border cooperation in tackling the complex phenomena of solar physics and climate science.

In conclusion, the discovery of an extreme solar particle storm dated to 12350 BC heralds a transformative moment in the fields of astrophysics, archaeology, and climate studies. The incorporation of innovative modeling techniques positions scientists to better analyze historical solar activities and their far-reaching effects on climate and life on Earth. This new perspective empowers us to anticipate and mitigate the potential hazards posed by solar storms, ensuring the resilience of modern civilization in the face of cosmic upheaval.

As the research continues to unfold and new insights emerge, it is clear that the intersection of space weather and terrestrial impacts will remain a critical area of inquiry within the scientific community for years to come. The ongoing pursuit of knowledge surrounding our Sun’s behavior and its ramifications on our planet forms a vital part of understanding not just our immediate environment but also our place within the cosmos.

Subject of Research: The impact of extreme solar particle storms on Earth and their implications for radiocarbon dating and space weather.

Article Title: New Findings Uncover Record-Setting Solar Storm, Transforming Our Understanding of Space Weather and Radiocarbon Dating

News Publication Date: April 28, 2025

Web References: https://link.mediaoutreach.meltwater.com

References: Earth and Planetary Science Letters

Image Credits: University of Oulu, Finland

Keywords

Solar particle storms, radiocarbon dating, extreme weather events, climate science, ancient solar activity.