This lecture explores the challenges posed by reactive nitrogen in the context of climate, energy, agriculture, water, and health, focusing on technological and policy solutions. Dr. Yixin Guo discusses the impacts of agricultural ammonia emissions, food-sector strategies, and the importance of nitrogen management. The presentation delves into the role of nitrogen in air pollution, biodiversity loss, and climate change, emphasizing the need for sustainable food systems and dietary shifts. The lecture also addresses the potential benefits of reducing food loss and waste in improving air quality and biodiversity conservation.