The persistent presence of nitrates in the atmosphere has long been a concern for environmental scientists. Despite efforts to reduce emissions over the past few decades, nitrate levels remain stubbornly high. A recent study published in Nature Communications sheds light on this enigma, revealing that chemical processes within the atmosphere are responsible for the persistence of these pollutants.

The research team led by Hokkaido University’s Professor Yoshinori Iizuka examined nitrate deposition history from 1800 to 2020 in an ice core taken from southeastern Greenland. The results showed a gradual increase in nitrates up to the 1970s, followed by a slower decline after the 1990s. This trend mirrors the changes in emissions of nitrate precursors over the same period.

The study’s findings suggest that factors other than emission reductions are driving the persistence of atmospheric nitrates. The researchers used a global chemical transport model to investigate these factors and discovered that atmospheric acidity is the key culprit. As acidity levels rise, more nitrates become trapped in particulate form, enabling them to persist longer and travel farther.

The implications of this study are significant. Accurate measurements of particulate nitrates in ice cores provide valuable data for refining climate modeling predictions. Moreover, the findings suggest that atmospheric nitrates will soon replace sulfates as the primary aerosol in the Arctic, further amplifying warming in the region.

As Professor Iizuka notes, “Ours is the first study to present accurate information for records of particulate nitrates in ice cores.” The persistence of these pollutants highlights the importance of continued research into atmospheric chemistry and climate modeling. By understanding the complex interactions within our atmosphere, we can better predict and prepare for the challenges that lie ahead.

The article highlights a critical aspect of environmental degradation: the rising soil nitrous acid (HONO) emissions driven by climate change and fertilization, which accelerate global ozone pollution. A team of researchers from The Hong Kong Polytechnic University has examined global soil HONO emissions data from 1980 to 2016 and incorporated them into a chemistry-climate model. Their findings reveal that soil HONO emissions contribute significantly to the increase in the ozone mixing ratio in air, which has negative impacts on vegetation.

The researchers found that soil HONO emissions have increased from 9.4 Tg N in 1980 to 11.5 Tg N in 2016, with a 2.5% average annual rise in the global surface ozone mixing ratio. This increase may lead to overexposure of vegetation to ozone, affecting ecosystem balance and food crop production. Moreover, ozone damage reduces vegetation’s capacity to absorb carbon dioxide, further aggravating greenhouse gas emissions.

The study emphasizes that soil HONO emissions are influenced by nitrogen fertiliser usage and climate factors like soil temperature and water content. Emissions hotspots cluster in agricultural areas worldwide, with Asia being the largest emitter (37.2% of total).

Interestingly, regions with lower pollution levels are more affected by ozone formation due to higher volatile organic compound concentrations and lower nitrogen oxide levels. This implies that as global anthropogenic emissions decrease, the impact of soil HONO emissions on ozone levels may increase.

To mitigate this issue, Prof. Tao Wang recommends considering soil HONO emissions in strategies for reducing global air pollution. The research team developed a robust parameterisation scheme by integrating advanced modelling techniques and diverse datasets, which can facilitate more accurate assessments of ozone production caused by soil HONO emissions and their impact on vegetation.

Future studies should explore mitigation strategies to optimise fertiliser use while maintaining agricultural productivity, such as deep fertiliser placement and the use of nitrification inhibitors.

As scientists continue to push the boundaries of innovation, researchers at Tohoku University have made a groundbreaking discovery in the realm of electrocatalysis. They have successfully demonstrated that applying an external magnetic field can significantly enhance the performance of single-atom catalysts (SACs), leading to a staggering 2,880% improvement in oxygen evolution reaction magnetocurrent.

This revolutionary finding has far-reaching implications for various industries, particularly those involving ammonia production and wastewater treatment. Traditionally, electrocatalysis focused on tweaking the chemical composition and structure of catalysts. However, the introduction of magnetic-induced spin state modulation offers a new dimension for catalyst design and performance improvement.

By regulating the electronic spin state of the catalyst through an external magnetic field, researchers can precisely control the adsorption and desorption processes of reaction intermediates. This, in turn, reduces the activation energy of the reaction, allowing it to proceed more quickly. As explained by Hao Li of Tohoku University’s Advanced Institute for Materials Research (WPI-AIMR), “More efficient production processes can reduce costs, which may translate into lower prices for products such as fertilizers and treated water at the consumer level.”

The study employed advanced characterization techniques to confirm that the magnetic field causes a transition to a high spin state, which improves nitrate adsorption. Theoretical analysis also revealed the specific mechanics behind why this spin state transition enhances electrocatalytic ability.

In an experiment conducted with a Ru-N-C electrocatalyst exposed to an external magnetic field, researchers achieved a remarkable NH3 yield rate (~38 mg L-1 h-1) and a Faradaic efficiency of ~95% for over 200 hours. This represents a significant improvement compared to the same catalyst without the boost from an external magnetic field.

This groundbreaking work enriches our theoretical understanding of electrocatalysis by exploring the relationship between magnetic fields, spin states, and catalytic performance. The experimental results offer valuable insights for future research and development of new catalysts, paving the way for practical applications in electrochemical technologies.