This lecture introduces the ReCLEAN Joint Initiative, focusing on the impact of reactive nitrogen at the Climate, Energy, Agriculture, Water, and Health Nexus. The presentation covers the development of atmospheric modeling systems, observational datasets, and outreach plans within the project framework. It discusses the challenges and strategies related to atmospheric acidity, aerosol distributions, and nitrogen-containing components. The lecture also addresses the importance of ammonia emissions, soil greenhouse gas emissions, and the vulnerability of Swiss ecosystems to nitrogen pollution.