HONO and NOx production from renoxification of nitrate-containing aerosols.

Dr. Fengxia Bao, Postdoctoral researcher, Paul Scherrer Institute – PSI, Switzerland

Abstract: Oxides of nitrogen (NOx = NO + NO2) and nitrous acid (HONO) play crucial roles in forming tropospheric ozone (O3), hydroxyl radicals (·OH), and secondary aerosols. The photochemical reduction of nitrate aerosol is of significant atmospheric interest as it produces HONO and NOx, a process termed renoxification. Organic species, especially light-absorbing brown carbon (BrC), predominantly derived from biomass burning, are suggested to be key players in renoxification. However, evidence of BrC from authentic ambient aerosols is lacking and the mechanism remains unclear. Here, we investigate BrC-associated renoxification upon irradiation of films containing BrC extracts from authentic biomass-burning aerosols and BrC model compounds using the coated wall flow tube (CWFT) technique. We mimic real-world aerosol conditions by adjusting pH, the concentration of nitrate and BrC, and the relative humidity of the CWFT films, ensuring atmospheric relevance. We find that the renoxification rate is enhanced in the presence of BrC and elucidate the role of BrC as a photosensitizer that promotes the reduction of nitrate, challenging the previously proposed mechanism of surface-enhanced photolysis of nitrate. Given the prevalence of the coexistence of nitrates and BrC in ambient aerosols, the BrC-photosensitized renoxification could be a substantial source of HONO and NOx, which should be considered by atmospheric models for atmospheric nitrogen chemistry and air quality.

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Governing Nutrient Pollution Beyond Farmers.

Dr. David R. Kanter, Associate Professor of Environmental Studies, New York University, USA

Abstract: Nutrient pollution is one of the most significant environmental issues of our time, driven by the oversupply of fertilizer and manure to agricultural land. Most policies focus on changing farmer behavior, which is extremely difficult, largely ineffective and a major reason why pollution levels continue to rise. A more creative governance framework that can avoid the pitfalls of farmer-focused policies while spurring reductions in agricultural nutrient pollution is critical. Consequently, the core objective of the Governing Nutrient Pollution Beyond Farmers project is to design a new governance framework to address agricultural nutrient pollution in the US and the EU aimed at agri-food system actors beyond the farm capable of influencing farm-level nutrient management – from fertilizer companies to multinational retailers. Doing so would shift the regulatory burden away from the farmer and transform an intractable non-point source problem into a series of more manageable point source approaches.

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Aspects of measuring atmospheric deposition of nitrogen to forest ecosystems

Dr. Peter Waldner, Forest Soils and Biogeochemistry Research Unit at the Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Switzerland

Abstract: Rising concerns of air pollution effects on forests, potentially accelerated soil acidification or eutrophication triggered a now 40 years joint forest ecosystem monitoring effort covering Europe. Emissions, transmission and deposition are monitored under the UNECE Air convention. In forests, leaves and needles of trees may filter particles, aspire gaseous compounds and exchange solutes over tissues. A feasible approach to continuously sample nitrogen deposition at several hundred sites has been developed. The presentation will mention some challenges and quality assurances measures taken, as well as potential the comparability to other approaches and present spatial and temporal trends as determined in the ICP Forests network across Europe. Further, ways to assess nitrogen deposition to forests, such as the concept of critical loads, as well as some recent findings on the effects of nitrogen deposition to forests will be discussed.

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How does low NO concentration modify secondary particle formation

Prof. Chao Yan, Associate Professor at Nanjing University, China

Abstract: Low atmospheric concentration of nitrogen monoxide (NO) represents common conditions in pristine environments and becomes progressively more frequent in urban settings due to the implementation of strict emission controls. Given the highly nonlinear nature of atmospheric chemical processes, the effects of high NO concentration on secondary particle formation may not apply to low-NO conditions. In this presentation, we will introduce our recent findings regarding the influences of NO at low concentrations on atmospheric chemistry and secondary particle formation in two aspects. Firstly, we will show the pivotal role of NO in the production of highly oxygenated organic molecules (HOM) and subsequently, the new particle formation; Secondly, we will present evidence that low-NO conditions can activate nocturnal nitrogen chemistry, which is responsible for the persistently high particulate nitrate concentration in urban environments.

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Plant elemental ecology: understanding plant nutrient flows in a global change context

Dr. Helena Vallicrosa, Postdoctoral researcher at EPFL and WSL, Switzerland

Abstract:

This seminar tackles three main points:

1. Introduction to the concept of elemental ecology, which studies the interactions between organisms (plant-soil-ecosystem) through elemental composition and elements flow. Elemental ecology is a relevant tool to study the impact of changes in chemical cycles (Carbon, Nitrogen, Phosphorus…) associated to global change on ecosystems.
2. Presentation of the results of a study in preparation: leaf habits and climate drives tree growth sensitivity to N deposition. This study addresses the ReClean goal about better understanding the impacts of N deposition on vegetation at continental scale.
3. An experiment set up to better understand the N flow in grasslands, accounting for soil N, the microbial community, belowground biomass, aboveground biomass, and reproductive tissues.

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Quantifying climate-dependent ammonia emissions – a starting point for understanding N in the environment.

Dr Jize Jiang, ETH Zurich, Switzerland

Abstract:

Ammonia (NH3) is one of the primary forms of reactive nitrogen and can negatively affect the environment and human health. It has adverse impacts on air, water, soil quality and ecosystems. Emissions of NH3 mainly originate from agricultural activities and are found to be strongly dependent on environmental conditions. A dynamic, process-based emission model, AMmonia–CLIMate (AMCLIM) has been developed to quantify agricultural NH3 emissions. AMCLIM simulates important physical, chemical and biological processes that are sensitive to climatic conditions in agricultural systems, focusing on major livestock farming and synthetic fertilizer use.

Global agricultural NH3 emissions estimated by AMCLIM accounted for 22±2 % of agricultural nitrogen input (synthetic fertilizer and livestock excreta). The volatilization of NH3 shows strong spatial and temporal variations. High volatilization tends to occur in hot regions and hot seasons. Water availability is also a critical environmental factor influencing NH3 volatilization, with larger emissions found under dry conditions. Meanwhile, local management practices have significant impacts. Combining a suite of tested improved management can result in NH3 reduction by 40 % globally.

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Past and future changes in atmospheric deposition of nitrogen and its consequences.

Prof. Maria Kanakidou, Department of Chemistry of the University of Crete, Heraklion, Greece and University of Bremen, Germany

Abstract:

Nitrogen is an essential nutrient for the functioning of ecosystems, which are a major source of food for humanity and responsible for the atmospheric oxygen we breathe. Nitrogen inputs to both terrestrial and marine ecosystems have been modified during the Anthropocene period with consequences such as eutrophication and acidification. Atmospheric deposition is one of the pathways through which reactive nitrogen is reaching the ecosystems. Atmospheric acidity is a key factor in the partitioning of reactive nitrogen species between the gaseous and the particulate phases of the atmosphere, which affects the lifetime of reactive nitrogen in the atmosphere and thus the pattern of its global deposition. Satellites allow the observation of atmospheric columns of ammonia and nitrogen dioxide, resulting from nitrogen emissions, transformations and transport in the global atmosphere. We will discuss recent global chemistry-transport modeling studies focusing on the biogeochemical cycle of nitrogen, the role of atmospheric acidity and organic matter, how this cycle has been affected by human activities and the potential consequences for the ecosystems. We will also discuss recent efforts in improving the total global atmospheric deposition data by measurement-model fusion activities.

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Grasping Nitrogen! What science do we need to mobilize a halving of nitrogen waste by 2030?

Prof. Mark A. Sutton, UK Centre for Ecology and Hydrology, UK

Abstract:

Everyone has heard of nitrogen, so why have so few people heard about nitrogen as a global environmental challenge?  This presentation will reflect on the way humans have altered the global nitrogen cycle, leading to multiple environmental impacts, from polluted skies to poison lakes. It will explore how the complexity and diversity of nitrogen impacts has fragmented scientific research and the policy responses, and argue that this fragmentation is at least one of the reasons for insufficient awareness and action to date. The presentation will recount progress through the European Nitrogen Assessment and the UNECE Air Convention leading to engagement with the United Nations Environment Programme, coupling science synthesis, preparation of international guidance and awareness raising that can mobilize change. Key outcomes include the Colombo Declaration and the first ever resolutions on Sustainable Nitrogen Management adopted by the UN Environment Assembly (4/14 and 5/2), which provide an opportunity to distil key scientific conclusions and to mobilize countries to start embracing nitrogen as a new intergovernmental challenge. The presentation will complete with an update on current progress in developing the first ever International Nitrogen Assessment, the Kunming Montreal Global Biodiversity Framework and the emerging challenges which could see nitrogen pollution get worse or better in the years ahead.

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Looking Back and Forward: Advanced Air Quality Modeling Techniques to Address Health and Climate.

Prof. Armistead (Ted) Russell, Georgia Institute of Technology,  US

Abstract:

Despite the great strides made over the last 50 years, air pollution still causes more premature deaths than any other environmental exposure globally and in most countries.  Climate will exacerbate air pollution, and increasing tropospheric ozone will exacerbate climate.  Policies can be designed to address both, simultaneously, providing co-benefits.  Here, advanced air quality modeling techniques, including using both emissions-focused (i.e., forward) and receptor-oriented (the adjoint method) are used to assess how emissions impact air quality and health, and to examine the spatial variation in the health benefits and value of reducing emissions.  The potential air quality benefits are linked to CO2 reductions to also show the added value in terms of reducing CO2 emissions.  Air pollution benefits can be on the same order as the climate benefits of climate strategies.  The development of forward (the decoupled direct method) and adjoint sensitivity approaches in three dimensional air quality models are presented along with their application to air quality, health and climate applications are discussed.

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Mitigating reactive nitrogen and associated environmental challenges: technological and policy opportunities.

Dr Yixin Guo, Postdoctoral Scholar, Peking University, ChinaProf. Mark A. Sutton, UK Centre for Ecology and Hydrology, UK

Abstract:

Accelerated global food and energy production has led to reactive nitrogen (Nr; ammonia (NH3) and nitrogen oxides (NOx)) emissions, which contribute considerably to severe health-damaging PM2.5 and ozone (O3) air pollution, and excess N deposition harmful for terrestrial ecosystem biodiversity. However, Nr abatement still lacks broad policy attention and its potentials for future coordinated environmental governance remain unclear. In this talk, Yixin will present research that examined, for China, potentials of improving agricultural N management practices and changing diets for improving air quality while reducing climate and water impacts, and, for the globe, potentials of addressing food loss and waste along supply chains for improving air quality and ecosystem health. Yixin will also talk about more recent work that examined the evolving role of reactive nitrogen emissions in future air quality.

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