Humans have massively altered flows of nitrogen on our planet, leading to both benefits for food production and multiple threats to the environment. There are few places on Earth more affected than South Asia, with levels of nitrogen pollution rapidly increasing. The result is a web of interlinked problems, as nitrogen losses from agriculture and from fossil fuel combustion cause air and water pollution. This damages human health, threatens biodiversity of forests and rivers, and leads to coastal and marine pollution that exacerbates the effects of climate change, such as by predisposing reefs to coral bleaching. Altogether, it is clear that nitrogen pollution is something we should be taking very seriously. The amazing thing is that so few people have heard of the problem. Everyone knows about climate change and carbon footprints, but how many people are aware that nitrogen pollution is just as significant? One reason for this is that scientists and policy makers have traditionally specialised. Different experts have focused on different parts of the nitrogen story, and few have the expertise to see how all the issues fit together. This challenge is taken up by a major new research hub established under the UK Global Challenge Research Fund. The ""GCRF South Asian Nitrogen Hub"" is a partnership that brings together 32 leading research organisations with project engagement partners from the UK and South Asia. All eight countries of the South Asia Co-operative Environment Programme (SACEP) are included. The hub includes research on how to improve nitrogen management in agriculture, saving money on fertilizers and making better use of manure, urine and natural nitrogen fixation processes. It highlights options for more profitable and cleaner farming for India, Pakistan, Bangladesh, Nepal, Afghanistan, Sri Lanka, Bhutan and the Maldives. At the same time, the hub considers how nitrogen pollution could be turned back to fertilizer, for example by capturing nitrogen oxide gas from factories and converting it into nitrate. The fact that all the SACEP countries are included is really important. It means that lessons can be shared on good experiences as well as on whether there are cultural, economic and environmental differences that prevent better management practices from being adopted. It is also important from the perspective of international diplomacy, and provides an example to demonstrate how working together on a common problem is in everyone's interest. It puts the focus on future cooperation for a healthier planet, rather than on the past. The South Asian case provides for some exciting scientific, social, cultural and economic research challenges. The first is simply to get all the researchers talking together and understanding each other. There are dozens of languages in South Asia, matching the challenge met when different research disciplines come together. This is where developing a shared language around nitrogen can really help. There are lots of nitrogen forms ranging from unreactive atmospheric nitrogen (N2), to the air pollutants ammonia (NH3) and nitrogen dioxide (NO2), to nitrate (NO3-) which contaminates watercourses, and nitrous oxide (N2O) which is a greenhouse gas. The impacts of each of these are being studied to provide a better understanding of how they all fit together. The result is an approach that aims to give a much more coherent picture of the nitrogen cycle in South Asia: What is stopping us from taking action, and what can be done about it. One of the big expectations is that the economic value of nitrogen will help. India alone spends around £6 billion per year subsidising fertilizer supply. It means that South Asian governments are strongly motivated to use nitrogen better. At which point research from the South Asian hub can provide guidance on where they might start.

The overall goal of the GCRF South Asian Nitrogen Hub is to develop an approach that links the many impacts of human alteration of the nitrogen cycle on environment, health, food security and climate resilience. The partnership recognizes that historical specialisation across the nitrogen cycle has led to fragmented policy responses, often associated with little progress. The hub therefore builds interdisciplinary integration as a foundation to overcoming the barriers, which is vital to meet the Sustainable Development Goals (SDGs). The hub will take this forward by developing better understanding of the social, cultural and economic barriers to adopting measures, technologies and lifestyles that reduce N pollution. It then aims to assemble the evidence, developing linked models of the South Asian N cycle. Integration of the models with measurements and social surveys will help to distil future visions that support the emergence of an effective South Asian Nitrogen Policy Arena. By linking scales from field, village and catchment to country and region, the hub will improve understanding of how impacts and solutions interact and how they vary across natural and cultural contexts (e.g. gender, religion, class). Ultimately, the goal is to demonstrate how the N cycle perspective can catalyse transformational change, allowing South Asia to become a world leader in championing a strategic approach to N management, as a step towards the SDGs globally. The hub has four key objectives: OBJECTIVE 1: To establish an approach that integrates the scientific, social, cultural and economic evidence needed for an effective NITROGEN POLICY ARENA. This requires evaluation of the current (inter-) governmental policy landscape, developing future visions and scenarios, considering options for N management, while recognizing the role of environmental diplomacy. Scenarios will link the key drivers (crop-livestock options, food choice, waste reduction, technological 'circular economy' approaches). The hub will develop guidance and e-tools to aid policy makers and practitioners. OBJECTIVE 2: To identify the solutions to producing more food and energy with less pollution, maximizing resilience and co-benefits, while minimizing trade-offs. The hub will focus first on AGRICULTURAL SOLUTIONS, exploring how agronomy, genetics and biotechnology could raise nitrogen use efficiency and reduce nitrogen losses. It will then test solutions with VILLAGE GROUPS across South Asia to provide a deeper understanding of the practical and social challenges. These will be complemented by feasibility testing of ENGINEERING APPROACHES to recapture and recycle N, with a focus on adsorption/desorption of nitrogen oxides (NOx), aiming to open up a multi-billion dollar sector turning air pollution into fertilizer. OBJECTIVE 3: To improve understanding and awareness of KEY NITROGEN THREATS in South Asia, including education through MOOCs. This will give special attention: a) to assess the effects of air pollution from the Indo-Gangetic Plain (highest ambient NH3 in the world) on HIMALAYAN FORESTS. The hub will assess ecosystem services (esp. epiphytes used for perfume manufacture) and deploy an innovative field NH3 micro-dosing system to understand the mechanisms of epiphyte damage; b) to quantify how much eutrophication predisposes reefs to CORAL BLEACHING and prevents recovery, sharing observational capability to improve understanding and inform mitigation strategies. OBJECTIVE 4: To integrate regional nitrogen flows and impacts in South Asia: a) to assess how much rural NH3 and NOx sources contribute to urban AIR POLLUTION; b) to assess the relative contributions of SOIL, FRESHWATER and MARINE N POLLUTION to human and ecosystem health; c) to quantify the two-way interaction between GREENHOUSE GAS emission and CLIMATE RESILIENCE. Integration will be supported by data harmonization, modelling and experimentation to support the Nitrogen Policy Arena.